HF antennas for amateur directional bands. Balcony HF antennas for beginners
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We can say that the 80-meter band is one of the most popular. However, many plots of land are too small to install a full-size antenna on this band, which is what the American shortwave Joe Everhart, N2CX, faced. Trying to choose the optimal type of small-sized antenna, he analyzed many options. At the same time, classic wire antennas were not forgotten, which work quite efficiently with a length of more than L/4. Unfortunately, such end-fed antennas require a good grounding system. Of course, high-quality grounding is not required when using a half-wave antenna, but its length is the same as that of a full-size dipole fed centrally.
Without exaggeration, we can say that the 80-meter band is one of the most popular. However, many plots of land are too small to install a full-size antenna on this band, which is what the American shortwave Joe Everhart, N2CX, faced. Trying to choose the optimal type of small-sized antenna, he analyzed many options. At the same time, classic wire antennas were not forgotten, which work quite efficiently with a length of more than L/4. Unfortunately, such end-fed antennas require a good grounding system. Of course, high-quality grounding is not required when using a half-wave antenna, but its length is the same as that of a full-size dipole fed centrally.
Thus, Joe decided that the simplest antenna with good parameters was a horizontal dipole excited at the center. Unfortunately, as already indicated, the length of the 80-meter half-wave dipole is often a hindering factor in its installation. However, the length can be reduced to approximately L/4 without fatally degrading performance. And if we raise the center of the dipole and bring the ends of the vibrators closer to the ground, we get the classic Inverted V design, which will further save space during installation. Therefore, we can consider the proposed design as an Inverted V 40 meter band, which is used on 80 meters (see figure above). The antenna sheet is formed by two 10.36 m vibrators, symmetrically descending from the feeding point at an angle of 90° to each other. During installation, the lower ends of the vibrators must be located at a height of at least 2 m above the ground, for which the suspension height of the central part must be at least 9 m. The low suspension height ensures effective radiation at large angles, which is ideal for connections at distances of up to 250 km. The most important advantage of this design is the fact that its projection does not exceed 15.5 m.
As you know, the advantage of a center-fed half-wave dipole is good matching with a 50 or 75 ohm coaxial cable without the use of special matching devices. The described antenna in the 80 m range has a length of L/4 and, therefore, is not resonant. The active component of the input impedance is small, and the reactive component is large. This means that when such an antenna is paired with a coaxial cable, the SWR will be too high and the level of losses will be significant. The problem can be solved simply - you need to use a line with low losses and use an antenna tuner to match it with 50-ohm equipment. A 300-ohm television flat ribbon cable was used as the antenna feeder. A two-wire overhead line provides lower losses, but it is more difficult to install into a room. In addition, the feeder length may need to be adjusted to fall within the tuning range of the antenna tuner.
In the original design, the end and central insulators were made from scraps of fiberglass laminate 1.6 mm thick, and an insulated mounting wire with a diameter of 0.8 mm was used for the antenna fabric. Small diameter wires have been successfully operated on the N2CX radio station for several years. Of course, more durable mounting wires with a diameter of 1.6...2.1 mm will last much longer.
The conductors of a flat television cable are not strong enough and usually break at the points of connection to the antenna tuner, so an adapter made of foil fiberglass provides the necessary mechanical strength and ease of connecting the line to the tuner.
The tuner circuit is very simple, and is a series resonant circuit that provides matching with a coaxial cable.
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Here's another option:
Short vertical on 80m range
At the end of 2009, Waldek, SP7GXP, designed a shortened vertical antenna for the 80 m band. The design consists of a vertical whip radiator mounted on a support insulator and separated at the top by a second insulator. A delta-shaped frame is connected to the emitter, and a half-wave dipole is located below the support insulator as a counterweight.
The dimensions of the listed antenna design elements are:
- length of the emitter from the support insulator to the top insulator - 8 m;
- length of the emitter installed on the upper insulator - 3 m;
- frame length for fp = 3.8 MHz - about 7.7 m (for fp = 3.5 MHz - about 9.35 m);
- length of one arm of the dipole (counterweight) for fp = 3.8 MHz - minimum 18.7 m (for fp = 3.5 MHz - minimum 20.35 m);
- the height of the dipole above the ground (roof) is at least 2 m.
The frame should be moved away from the vertical emitter. In addition, it serves as two guy wires for the upper part of the emitter. The length of the RG-58U coaxial cable is at least 26.5 m.
Steps for setting up an antenna using a transceiver and an SWR meter:
- install the emitter with a frame;
- stretch the half-wave dipole at a height of at least 2 meters above the surface, but do not connect it to the base of the antenna;
- connect the power cable to a half-wave dipole;
- turn on the transceiver in carrier transmission mode and select the dipole length so as to obtain a minimum SWR at a frequency of 3.780 MHz (or other preferred frequency);
- disconnect the power cable from the dipole, connect the ends of the dipole, as well as the screen (braid) of the power cable at one point, below the base insulator (to the roof, ground, etc.);
- connect the cable core to the emitter;
- turn the transceiver back into transmit mode and, selecting the length of the frame, tune the antenna system to the required frequency (for example, 3.780 MHz).
In order for the antenna to cover the entire range (CW and SSB sections from 3.5 to 3.8 MHz), 3 coils with switches can be used to obtain the corresponding resonant frequencies of the antenna. The coils are installed at the support insulator and the arms of the dipole (counterweight) are connected to two of them, and the vertical emitter is connected to the third. We select the number of coil turns experimentally, depending on the range section.
When installing the antenna, the following rules should be followed. If the roof or surface on which the antenna is installed does not allow the full-size dipole to be stretched in a straight line, you can try to bend its ends (“twist”), being sure to adhere to the requirement of maintaining the required installation height (at least 2 m).
To comply with the rules for safe operation of the antenna, the ends of the dipole ending in insulators should be removed from metal objects (for example, a fence, metal wall, etc.). Do not use any “ground” counterweights or those lying on the ground! When installing the antenna on the ground, the lower part, below the support insulator, must have contact with the ground, and when installing on the roof, it is necessary to connect this part of the antenna (below the insulator) to a lightning rod.
Dipole. The simplest antenna.
Lately, I’ve been hearing more and more often from my novice colleagues about difficulties that arise in the construction of this or that antenna. They aim at antennas that are difficult to build for entry-level knowledge.
I myself was in their “shoes” and thought and acted in approximately the same way, but still returned to the “Half-wave dipole” antenna, which is the easiest to manufacture and configure. In this article I will describe the simplest and most inexpensive way to build a half-wave dipole antenna and configure it. And so, rather than get bogged down in formulas, let’s use online calculation. Below are the dimensions for the 40m range.
And so we take a copper antenna rope or an electrical wire (for example, with a cross-section of 2 squares) and cut the arms into 10 m sections. I will not go into debate here about which material is better for making an antenna. Probably the best material is the one you have on hand or got for free (just kidding). It should be noted that the electrical length of the antenna is slightly different from the physical length calculated.
Below is an example of how you can easily make a dipole
After the elements are cut, a central insulator and an insulator for the ends of the blades are made. You can hang a dipole in space. The recommended suspension height is not lower than 1/4 long wavelength for the selected range. It’s better, of course, as high as possible, but if the height of the suspension is below 1/4, it’s also not a big deal, the antenna will just not work as efficiently. Because a reactive component will be introduced. But more on that later.
The dipole is manufactured, suspended, connected to the transceiver. Can everyone work?
I guess, yes. But we do not know the value of the SWR and whether the antenna resonance lies in the required frequency range. Therefore, working with such an antenna will be ineffective.
So we need to set up the antenna. To do this, you can use an SWR meter or an antenna analyzer. The SWR meter shows us the degree of coordination between the antenna and the transceiver. The value of a well-tuned antenna should tend to 1, but it is quite acceptable to conduct communications on antennas with SWR up to 3. The antenna analyzer shows us slightly larger parameters - these are SWR, active and reactance of the antenna. All these indicators are of great importance, but at the initial stage they are not so important.
This is what the SWR meter looks like (well, at least one of a million options)
Well, the Antenna Analyzer
Unfortunately, not every radio amateur can afford to buy an antenna analyzer, but an SWR meter is quite affordable.
Let's start setting up the antenna. Let's connect the SWR meter between the transceiver and the antenna. And we will measure the SWR value at the beginning, middle and end of the required range. Ideally, the value should be 1 in the entire area, but this is ideal. But in reality, the dipole has a wave impedance of 75 ohms, so we get a value of at least 1.5. But this should not be scary because... Let me remind you that you can work with SWR up to 3. Further, a good SWR level will most likely lie lower in frequency, because remember I said that the physical and electrical lengths of the antenna differ. Therefore, it is necessary to either shorten or lengthen the antenna. The main thing to remember is a few rules when setting up an antenna:
- Shortening should be done not by cutting off an excess piece, but by bending it towards the main arm (true for wire antennas)
- If the gap often with a good SWR lies lower in frequency, then the antenna must be shortened; if higher, then lengthen
- And the most important thing. Best the enemy of the good. Although there is no limit to perfection.
And so, after several measurements, we come to the conclusion that the physical length of the antenna is somewhat longer, because The frequency band with good SWR is in the range 6900-7000 MHz. You can, of course, immediately shorten the antenna strips, but to do this you need to know the shortening factor of the wire (the material from which the antenna strips are made). Therefore, it is necessary to shorten the arms of the dipole several times (at least 2) by the same small distance in order to determine by how many kHz the frequency is shifted. And only then, taking into account this dependence, shorten the arms of the dipole to the required length.
That's all. The easiest way to make and configure an antenna is a half-wave dipole. Of course, I did not take into account the reactive component when setting up the antenna, but I considered the simplest method. You can start working on air.
Good luck to everyone and traditional 73.
Our favorite HF Antennas. Shortwave antennas on amateur bands, is and remains one of the hot topics in amateur radio. The beginner looks at which antenna to use, and the broadcast aces from time to time look at what’s new.
There is no need to stand still, but to constantly improve your results, so we are following this path of understanding and improving our antennas. You can even separate some radio amateurs into a separate group - Antenna operators.
Recently, antennas have become more accessible in finished form. But even having purchased such an antenna along with the installation, the owner, in our case the radio amateur, should have an idea.
In my opinion, everything starts with the place where our antennas will be placed, then the antennas themselves. Of course, not everyone is given the choice of place, but here we can win big, and how to choose, not everyone is given such an instinct, but there are such radio amateurs.
HF Antennas come first
Technically, comparing a location on HF is problematic (on VHF it’s easy and measurements show a difference of four decibels). Let those who have to choose such a place be lucky. For the HF bands we have a larger selection of antennas and the dimensions are tolerable, but for the LF bands the choice of ready-made antennas is smaller. And it’s clear that not everyone can afford five yagi elements for the 80-meter range. This is where the field of work can be large, if a radio amateur has such a field for placing antennas in the low frequency ranges
There is a book with a lot of information on antennas for low frequency bands
Amateur antennas of short and ultrashort waves
An antenna is a device involved in the process of transmitting electromagnetic energy from a power line to free space, and vice versa. Each antenna has an active element, such as a vibrator, and may also contain one or more passive elements. The active element of the antenna is, as a rule, a vibrator. directly connected to the power line. The appearance of alternating voltage on the vibrator is associated both with the propagation of the wave in the power line and with the emergence of an electromagnetic field around the vibrator.
Ideal antenna for amateur radio communications on HF
What antennas do we, radio amateurs, use? Which ones do we need? Do we need an ideal antenna for meter bands? Say that there are no such people, and that nothing is perfect at all. Then close to ideal. What for? You ask. Anyone who wants to achieve results and move forward will sooner or later come to this question. Let's look at how to understand an ideal antenna on the meter amateur bands.
Why exactly on amateur meter, and because our correspondents are at different distances in different directions of the world. Let's add here the local conditions where the antenna is located, and the conditions for the passage of radio waves at a given time at these frequencies. There will be a lot of unknowns. What angle of radiation, what polarization will be maximum in a specific period of time with a specific correspondent (territory).
Yes, some may get lucky. With location, choice of antennas, height of suspension. So what should you do? To always be lucky. We need an antenna that at any given time will have the best parameters for a given passage of radio waves with any territory. More details = We scan (rotate) the antenna in azimuth, this is good. This is the first condition. Second condition = we need to scan along the radiation angle in the vertical plane.
If anyone doesn’t know, depending on the transmission conditions, the signal can arrive at different angles from the same correspondent. The third condition = is polarization. Scanning or changing polarization from horizontal to vertical polarization and back, smoothly or stepwise. By creating and obtaining these three conditions in one antenna, we get ideal antenna for amateur radio communications on short waves.
Ideal antenna
Ideal antenna, so what is it. If we consider, for example, satellite dishes, then perhaps it becomes clearer and easier to understand. Here we take the size (diameter of the plate), this is a direct dependence on the gain. One satellite – we took a 60cm antenna as an example. diameter The signal level at the receiver input will be low, and sometimes we will not see the picture. Let's take an antenna with a diameter of 130 cm. The level is normal, the picture is stable.
Now let's take an antenna with a diameter of 4 meters and what can we observe. Sometimes the picture disappears. Yes, there could be two reasons. It was the wind that shook our 4-meter antenna and the signal disappeared. This satellite in orbit does not maintain its coordinates stably. So, on the one hand, it turns out that the 4-meter antenna is the best in terms of gain, but on the other hand, it is not optimal, which means it is not ideal. In this case, the optimal antenna is 130 cm. In this case, why can’t it be called ideal?
So it is on the meter amateur radio bands. Five yagi elements at a height of 40 meters for the 80-meter range will not always be optimal. So, not ideal. You can even give some examples from practice. In my laboratory work I made 3 elements for the 10-meter range. Passive elements are curved inward of the active one. Then a three-band version of such an antenna will come into fashion under the well-known name.
I listened, twirled it, and of course made connections to this antenna, the first impression was wonderful. Then the weekend came, another contest. But when I turned on 10 with this antenna, there was silence, so I think, yesterday the range thundered, but today there is no passage.
From time to time I turned on this range to listen in case a passage suddenly began. During the next approach to 10, numerous amateur radio stations deafened me - it began. And then I immediately discover that the wrong antenna is connected. Instead of 3-elements there was a pyramid for the 80-meter range. I switch to 3 elements - silence, signals are blaring on the pyramid. I went outside, examined 3 elements, maybe something happened, no, everything is fine.
Well, then I worked on 28 megahertz, made a lot of connections to the pyramid for the 80-meter range. On Monday and Tuesday the same picture was observed, and only on Wednesday things seemed to fall into place. There is silence on the pyramid, but on the 3-element there is noise. What is the difference? Difference in radiation angle.
In my pyramid the radiation is at 28 MHz. at an angle of 90 degrees, that is, at the zenith, and in a 3-element one below 20 degrees. This practical example gives us something to think about. Another example was when I was in the zero area. I hear a call on the 20 for the zero region, I know that this friend has an antenna for several thousand dollars, that it is at a good height and the power amplifier there is no less than a kilowatt. I call him, but he doesn’t hear, or rather, he hears, but he can’t even make out the call sign.
He twisted his expensive antenna, to no avail, and he said out loud that there was no way through today. Here on this frequency I hear - and you receive me. Yes, I accept. It turned out that his neighbor had only five watts and the antenna was such that I had already forgotten (perhaps like a triangle at 80). We made radio contact, and he was pleasantly surprised, knowing what antenna and power his neighbor had. I don’t know how many meters or kilometers there are between them, but in that case the cool antenna was powerless.
Antennas for low frequency ranges
There were such laboratory works on both the 40 and 80 meter bands. All this is in search of which antenna is better. And there is a point where radio amateurs still have the opportunity to work on such an antenna so that it is optimal at any time, and therefore ideal. In part, radio amateurs use some points that should be included in an ideal antenna.
The simplest thing is to set it in azimuth. The second in terms of radiation angle is to place identical antennas on different masts, at different heights or on the same one, while switching them into stacks. We get different radiation angles. And also different antennas with different polarization, some have. But this is partly, not overall.
And some will say, why such an antenna? Ten kilowatts and first place in your pocket. Yes, it's your choice. At the same time, you are deceiving not only everyone, but first of all yourself. Or who has been using such an antenna for a long time on HF (there is one on VHF), where the properties of an ideal antenna are inherent.
Our antennas
What is your antenna? 84 meters 27 centimeters and 28 meters of cable. Wow, I’m 32 centimeters, I should try to shorten it like yours. This is our talk about antennas on the air. Here’s a slightly different answer: I have a cable about three meters long, I’m sitting right next to the window, and there’s an antenna right outside the window. Three is bad, you do 28, you know how great the antenna will work. But just yesterday I heard it, and the conversation was between two experienced radio amateurs. And the conversation was about some kind of secret antenna, about secret dimensions.
kv antennas
For many radio amateurs, this topic was, is and will be one of the most popular. Which antenna to choose, which one to buy. In both cases, we need to mount it, install it, configure it, here we need some knowledge on antenna topics, magazines and books on antenna topics will help here. So that, in the end, we understand something.
A radio amateur's antenna should be one of the first lines. SWR is not an indicator and there is no need to chase after it in the first place. That an antenna with SWR=2 can work much better than with SWR=1. And efficiency decreases with increasing elements and much more.
kv antennas
Log-periodic wire antenna for the 40 meter range. Everything is simple and effective. Several variants of “sloper” antennas for low-frequency bands of 40,80,160 meters. Scanning antenna RA6AA, setup, parts used. In the magazine Radio Amateur 1 1991. Read in full.
Practice tuning and installing antennas. Raising the mast. Options for attaching antenna panels to wood. Tuning using GSS and a tube voltmeter in the magazine Radio Amateur 2 1991. Read.
In the seventh issue for 91 years of Radio Amateur magazine RA6AEG talks about its M antenna.
All this information is primarily for those who already have the call sign of an amateur radio station. Also for everyone else who has not yet come to HF.
When designing and operating your “antenna field,” you have to constantly maneuver on a tiny patch of roof between elevator boxes, ventilation shafts, all kinds of television, satellite and other antennas, various cable communications, open radio broadcasting wiring... In addition, you should take into account the very detrimental all-season “ harvesting season" 🙂 and dangerous natural phenomena - wind storms, thunderstorm activity. And what is the cost of, say, icing... By the way, in the winter of 2011, many radio amateurs in central Russia encountered this. One more or less continuous rain at minus temperatures is enough - even without wind - and immediately your beautiful antenna, the object of your former pride, right before your eyes turns into a shapeless icy lump of twisted scrap metal, fragments of fiberglass and wire scraps!
Probably, the elements should also include raids by representatives of the native municipal services, as well as other “bodies in power.” First of all, naturally, this applies to short-wavelength workers living in standard multi-story buildings.
The number of happy owners of capital and reliable superantennas is growing steadily, but not yet as high as we would like. First of all, capital is usually spent on purchasing a “bourgeois apparatus”, and there is no longer enough money to buy a branded antenna...
What then remains to be done by the average domestic radio amateur, who often has practically no free access to the roof of his house? But I want to work on the world airwaves, and preferably not just any way, but with the highest possible efficiency.
So various cheap alternatives are invented (“the need for invention is cunning!”) various cheap alternatives: window and balcony mini-structures, antennas “for emergency work”, 🙂 “invisible”, “backup”, “disposable” - almost made of thin copper wiring, “on buttons”, as in the era of “fifth category spy”...
Selecting the optimal antenna based on the wide variety of shapes and parameters, as well as specific local conditions, is not always quite simple. Everyone knows that “a good antenna is the best amplifier.” Alas, not everyone can afford to have more than one antenna, and several for each band is generally a dream... Some are forced to refuse to work, say, on the 80 m band adjacent to 7 MHz only because it “Inverted” has too high SWR there. However, unfortunately, it also happens that almost no attention is paid to matching the transceiver with the antenna. Personally, I know a rather curious case when one short-wave operator, having replaced an old homemade “Lapovka” with an imported device, “attached” it to the usual “rope”, naively believing that “there is also protection for the output transistors...”.
“The poor radio amateur’s antennas” have been repeatedly described in the literature, but all of them are far from the simplest and not at all the cheapest designs. Unfortunately, sometimes, due to an oversight by the authors of the descriptions, certain important details are overlooked - for example, the length of a two-wire line or the material of the mast, which is sometimes unacceptable to be made of metal. This makes it difficult for inexperienced colleagues to replicate the design.
Beginners (and, to be honest, also some “finishers” 🙂) radio amateurs use mainly the simplest antennas - “Delta Loop” of the 80m range (moreover, they often have an unfortunate location and are powered as it was more convenient locally), the “notorious” Inverted V and quarter-wave Ground Plane... To work on other bands (and preferably on all!) one or another matching device can be used. The results of antenna operation in this case, depending on optimization on a particular band, vary from very good to very bad. Some of the shortwave operators even select the cable length to “improve” the SWR...
However, we should not forget about the essence, that no matching device, no matter how sophisticated, is able to reduce the SWR in the antenna feeder. With its help, we can achieve perfect coordination only between our radio station and the matching device itself, located on the same desktop in the shack. The main effect achieved here is different - the transmitter, as they say, “was deceived”, and the output stage will produce all possible power. But power losses directly in the feeder itself have not disappeared.
As has been noted more than once, an ordinary dipole with an SWR of about 1, intended for the 80m range, at a frequency of 7 MHz (where it is already a wave vibrator with an input impedance of about 4 kOhm) will have a SWR of the order of 53, and in the 20 m range we get SWR = 57. Let's assume that with the help of a certain matching device (tuner) it was possible to obtain the SWR between the transceiver and the control system and also equal to 1 on these ranges. But the feeder is still mismatched with the load (emitter). Having used a two-wire line that has relatively low losses, one could turn a blind eye to this and still work on the air with varying success, but here another problem immediately arises - how to constructively connect that same open two-wire line to the operator’s desk? You won’t be running out onto the balcony every now and then to the matching device installed there! If it is possible to run conductors through a window, that's great. And if not? And is it worth having certain HF radiation near your workplace? In addition, a matching device for a symmetrical feeder is incomparably more complex in design and configuration than a matching device for an asymmetrical load.
The proposed version of the antenna system based on the development of Oleg Safiullin, UA4PA, solves most of the issues raised. Such an antenna is by no means intended to replace other, much more efficient designs, but may be of interest to those radio amateurs who do not have sufficient resources, free space and suitable supports for hanging the antenna fabric.
Many beginner shortwave operators are often put off by the basic description of the UA4PA antenna by the need to install a vertical pole 11.2 m high on the roof and the problem of placing counterweights of the same length in a limited space underneath it. Meanwhile, in the magazine “Radio”, in previous years almost the only source of information necessary for a radio amateur, the idea of applying this matching method to a dipole with almost any arm size was proposed long ago. It was noted that due to the increase in the effective radiating part, such an antenna works even better than a relatively short vertical one in low-frequency ranges, and the dipole itself can also be successfully positioned in the form of an Inverted Vee. On my personal radio station (call sign in Soviet times - UB5LEW) for almost 20 years, a simple inclined beam 35.5 m long with power from the end, but connected to a matching device using an appropriate piece of cable, was successfully used as a reliable backup.
O. Safiullin’s idea itself was actively discussed in amateur radio circles and on relevant forums on the Internet. The main disadvantage of such an antenna, its zealous opponents (however, mostly “theoreticians” who did not even set themselves the task of practical testing of the design) called the operation of a coaxial cable in a standing wave mode - they say that well-known computer programs simply “are horrified” when analyzing losses. 🙂
Yes, apparently, for QRO supporters, those who like to “pump up a kilowatt”, this antenna is really not suitable - the cable can simply melt and burn out... However, for many shortwave operators who are content with the standard oscillating power of an imported device of 100 W, losses in a cable that functions in 100% standing wave mode (in this case it’s not a feeder at all, but part of the antenna fabric itself, only almost non-emitting!), are by no means as scary as they are painted to be!
Naturally, there are losses in any real feeder, but they can be reduced to some extent by using, for example, a cable with a higher characteristic impedance or of better quality.
Previously, I used a 100-ohm cable RK-100-4-31 with a diameter of about 8 mm with double braiding and a copper-plated steel core, and currently I use RK-75-7-11. In order for it, which is quite thick and elastic, not to crawl around on the desktop with the miniature and light box of the matching device, the short part of the line near the matching device - up to about half a meter in length - is generally made of thin RG-58.
The undeniable advantage of the matching method proposed by Oleg Safiullin is the configuration of the entire antenna system to operate on any range directly on the shortwave operator’s desktop. In this case, between the transceiver and the matching device (and then the antenna itself begins!), SWR = 1 is easily achieved, i.e. the output stage will deliver 100% of the assigned power “on the mountain”, and a single control unit allows, if necessary, to instantly adjust the antenna more precisely and at the edges of the ranges.
The disadvantages of such a matching device include only the need to select taps in the coil of the oscillating circuit, as well as limited use - exclusively with one given antenna in its specific design and location. Any attempts to use a ready-made matching device with any other antenna will necessarily lead to a certain mismatch, and a complete reconfiguration of the entire device will inevitably be required.
Individual radio amateurs, having installed a vertical emitter 11.2 m high and connected it through a coaxial cable of arbitrary length and a T-type matching device (for example, from MFJ), have achieved excellent results. Well, that's great! Just don’t say that in this case the “UA4PA antenna” is supposedly used, without noticing that nothing remains from the very idea of matching “according to Safiullin”, except the length of the pin...
The control system diagram is shown below (for simplicity, taps for only one range are shown) and does not have any special features - a regular parallel oscillatory circuit (as in the original UA4PA antenna) with an indicator of the current flowing in the antenna.
Comparing the proposed matching device with the widely used T-shaped, L-shaped and U-shaped matchers, it is easy to notice the gain in ergonomics (one range switch and only one smooth adjustment knob) and in size. However, as they say, options are possible here too, including the use of roller variometers.
The antenna itself is a well-known G5RV design with a two-wire overhead line “dropped down” at one end.
The dimensions of the vibrator (material - bimetal copper/steel with a diameter of 2 mm) - a total length of about 31 m - were chosen based on the available placement possibilities on the ground. The upper part of the directly active canvas is a kind of vertical (unfortunately, its upper end is to some extent close to the wall of a nine-story panel building - where can you go?), and the second half is, accordingly, a counterweight. A two-wire line going to the balcony, and then, without any tricks, the cable itself (naturally, taking into account the shortening factor) completes the length of the entire system to the required 42.5 m.
The dimensions of the line are the length of each conductor is 10.4 m, the material is copper wire with a diameter of 1.8 mm, insulating spacers installed every 30 cm are made of fluoroplastic sheets 3 mm thick. The distance between the conductors is not critical, and for a characteristic impedance of 200 - 400 Ohms it is in the range of 50 - 150 mm (in my antenna - 50 mm).
At the same time: a) there are no additional losses in the “balcony - center of the canvas” section due to the replacement of the coaxial cable with an overhead line, and b) there is a fairly comfortable continuation of the antenna-feeder device directly throughout the apartment (in my case, into the room next to the balcony) with a coaxial cable.
The only critical parameter is the required length of the cable section from the two-wire line to the matching device, which is calculated by the formula: 
The excess can be rolled into a bay in any convenient place. O. Safiullin himself pointed out the desirability of using a cable with a higher characteristic impedance (to reduce losses), as well as the possibility of substituting logically multiples of 85 or 21.3 m into the formula instead of the value of 42.5 (in the latter case, the antenna will work only in the ranges from 40 to 10 m).
Design of the matching device
The dimensions of the matching device housing I used are small - only 190x125x70mm, and it looks very harmonious when combined with the Yaesu FT-897 transceiver. To achieve the desired small size of the device, I deliberately departed from the classically accepted canons, reducing the distance between the coils and the walls of the case at the expense of some efficiency.
Design of the matching device:
Switch SA1 (according to the diagram above) is a regular PGK, 11P4N (11 positions, 4 directions). KPE C1 - with a maximum capacity of about 150 pF. You can use a KPI with a higher maximum capacity, or even completely abandon additional capacitors and SA1.4 biscuits, but you should keep in mind that the circuit tuning will become much “sharper”.
By the way, even with a small excitation power, the voltage on the oscillatory circuit can reach a significant value. Additionally, “clip-on” capacitors with an input power of about 100 W (an imported transceiver or UW3DI with an output stage on a GU-29 lamp, etc.) must have an operating voltage of at least 2 kV (ordinary KSO-3 with a voltage of up to 500 V “stitches” "). The remaining details are indicated on the circuit diagram or visible in the photo of the matching device and do not require additional explanation.
Each radio amateur can freely select coils for the control system from any available with similar parameters - they are absolutely not critical, the total number of turns can be “estimated by eye”, based on the lowest frequency required range, and the taps will be selected during the setup process. In approaching the selection of coil products, one should be guided by one thing - it is desirable to achieve the highest possible quality factor of the coil. If possible, it is advisable to make the coils from silver-plated wire (at least L1).
Inductor data: L1 is wound on a ceramic ribbed frame (or without it) with a diameter of 32 mm and contains 8 turns of silver-plated wire 02.2 mm, wound in increments of 5 mm; L2 is wound on a 060 mm ceramic frame and contains 23 turns of PEV-2 wire with a diameter of 1.2 mm, wound in increments of 1.8 mm.
The taps from the coils, switchable by range, counting from the top (according to the diagram) terminal (their approximate position is indicated), as well as the capacitances of additional capacitors connected in the low-frequency ranges are shown in the table.
Settings
After sealing the connectors, armed with patience, tweezers and a soldering iron, you can begin setting up the matching device. At the initial stage, using elementary measuring instruments - GSS and a lamp voltmeter, or GIR - it is advisable to select circuit taps according to ranges with the KPI rotor in the middle position and the transmitter disconnected from the matching device. Then, by monitoring the SWR using the SWR meter connected between the transceiver and the matching device, or by looking at the LCD hidden in the “bourgeois” device, the matching of the 50-ohm output of the transmitter with the circuit is selected, i.e. the tap is made at the point where the input resistance is about 50 ohms. It should be taken into account that, most likely, it may be necessary to select the connection point to the antenna cable circuit on each individual band.
Specifically, setting up a matching device is not particularly difficult and is quite accessible even to a beginner shortwave operator (in this case, for simplicity and gaining initial experience, you can limit yourself to one range - 80 or 40m). And as a result, the radio amateur receives a simple, cheap, inconspicuous and difficult-to-access short-wave antenna for strangers, which allows him to work well on the air on all amateur HF bands even in cramped urban conditions!
By the way, in the 160m range I do not use a parallel circuit of the matching device, because The vibrator, with its existing length of 42.5 m, is half-wave only for 3.5 MHz. Approximately equal in length to a quarter wave at 1.8 MHz, it is matched using a small additional coil connected in series (frame - 25 mm in diameter, PEV-2 wire - 1.5 mm in diameter, 18 turns, winding - turn to turn). For greater efficiency, you should also set the control system circuit itself to 160 m, and either include a special extension inductance between the circuit and the cable connector, or use the original figure of 85 m in the formula for calculating the cable length. In this case, the technique for setting the matching device to 1. 8 MHz will be similar to other bands.
results
In conclusion, a few words about the efficiency of the antenna. Due to the inclined position of the vibrator, which to some extent approaches the vertical, a significant component of the radiation in the radiation pattern falls on the lobe pressed to the ground, which is favorable for long-distance radio communications. When installing an antenna, any practically feasible variations are possible both with the spatial arrangement and length of the elements in any particular location, and with the dimensions of the matching line - the main thing is that the overall dimensions fit into the formula.
Fans of computer calculations can simulate the expected radiation patterns, as well as calculate the efficiency of the antenna and “unacceptable losses” in the cable :)
In the process of setting up the matching device on the FT-897 transceiver with an output power of 100 W in the 1.8 MHz range, radio communications were carried out with OH3XR, UA9KAA, LA3XI; in the 3.5 MHz range - with UA0WB, RKOUT, E7/DK9TN; in the 7 MHz range - with 4S7AB, P40L, VQ9JC; in the 10 MHz range - with 9M6XRO/P, TS7TI, OY6FRA; in the 14 MHz range - with KN6MV, 9Q500N, WH0DX (from the first call!), in the 18 MHz range - with KH0/KT3Q, ZS6X, 9M2TO, in the 21 MHz range - with BD6JJX; BD1ISI, HS0ZEE; in the 24 MHz range -CVQ9LA, 5Р5Х, EX8MLE; in the 28 MHz range - with 4J9M, OG20YL, IK2SND.
To be fair, I note that all radio communications are telegraphic, since of all other types of radiation I prefer this one.
In daily practical work on all amateur bands, the antenna fully met the expected performance characteristics and allows reliable radio communications with all continents and various expeditions, without experiencing any special need for an additional power amplifier. However, by eliminating the relatively low-current toggle switch from the circuit (here it is used deliberately, for the convenience of switching the grounding of the antenna) and increasing the electrical strength of the KPI and coils, it is quite possible to increase the oscillatory power of the transmitter to 300 - 500 W. A similar version of the design was used by the author for a long time together with various amplifiers using GU-50 lamps (from 2 to 4 pcs.), and no noticeable, let alone significant heating of the cable, or interference with television was observed at all.
With appropriate settings, this matching device can be successfully used with another antenna (for example, Delta Loop) to increase the efficiency of its matching when operating on all amateur bands.
Today, when most of the old housing stock has been privatized, and the new one is certainly private property, it is becoming increasingly difficult for a radio amateur to install full-size antennas on the roof of his house. The roof of a residential building is part of the property of every resident of the house where they live, and they will never allow you to walk on it again, much less install some kind of antenna and spoil the facade of the building. However, today there are cases where a radio amateur enters into an agreement with the housing department to rent part of the roof with his antenna, but this requires additional financial resources and this is a completely different topic. Therefore, many beginning radio amateurs can only afford antennas that can be installed on a balcony or loggia, risking receiving a reprimand from the building manager for damaging the building’s façade with an absurd protruding structure.
Pray to God that some “know-it-all activist” doesn’t mention harmful antenna radiation, like from cellular antennas. Unfortunately, we must admit that a new era has come for radio amateurs to keep their hobby and their HF antennas secret, despite the paradox of their legality in the legal sense of this issue. That is, the state allows broadcasting on the basis of the “Law on Communications of the Russian Federation”, and the levels of permitted power comply with the standards for HF radiation SanPiN 2.2.4/2.1.8.055-96, but they have to be invisible in order to avoid pointless evidence of the legality of their activities.
The proposed material will help the radio amateur understand antennas with a large shortening, which can be placed on the space of a balcony, loggia, on the wall of a residential building or on a limited antenna field. The material “Balcony HF Antennas for Beginners” provides an overview of antenna options from different authors, previously published both in paper and electronic form, and selected for the conditions of their installation in a limited space.
Explanatory comments will help a beginner understand how the antenna works. The presented materials are aimed at beginning radio amateurs to gain skills in constructing and selecting mini-antennas.
- Hertz dipole.
- Shortened Hertzian dipole.
- Spiral antennas.
- Magnetic antennas.
- Capacitive antennas.
1. Hertz dipole
The most classic type of antenna is undeniably the Hertzian dipole. This is a long wire, most often with an antenna blade size of half a wavelength. The antenna wire has its own capacitance and inductance, which are distributed throughout the antenna surface; they are called distributed antenna parameters. The antenna capacitance creates the electric component of the field (E), and the inductive component of the antenna creates the magnetic field (H).
The classical Hertz dipole by its nature has impressive dimensions and constitutes half a long wavelength. Judge for yourself, at a frequency of 7 MHz the wavelength is 300/7 = 42.86 meters, and half a wave will be 21.43 meters! Important parameters of any antenna are its characteristics from the spatial side, this is its aperture, radiation resistance, effective antenna height, radiation pattern, etc., as well as from the supply feeder side, this is the input impedance, the presence of reactive components and the interaction of the feeder with the emitted wave. A half-wave dipole is a linear, widespread emitter in antenna technology practice. However, any antenna has its advantages and disadvantages.
Let us immediately note that for good operation of any antenna, at least two conditions are required: the presence of an optimal bias current and effective formation of an electromagnetic wave. HF antennas can be either vertical or horizontal. By installing a half-wave dipole vertically, and reducing its height by turning the fourth part into counterweights, we obtain the so-called quarter-wave vertical. Vertical quarter-wave antennas, for their effective operation, require a good “radio ground”, because The soil of planet Earth has poor conductivity. The radio ground is replaced by connecting counterweights. Practice shows that the minimum required number of counterweights should be about 12, but it is better if their number exceeds 20... 30, and ideally you need to have 100-120 counterweights.
We should never forget that an ideal vertical antenna with one hundred counterweights has an efficiency of 47%, and the efficiency of an antenna with three counterweights is less than 5%, which is clearly reflected in the graph. The power supplied to an antenna with a small number of counterweights is absorbed by the earth's surface and surrounding objects, heating them. Exactly the same low efficiency awaits a low-mounted horizontal vibrator. Simply put, the earth reflects poorly and absorbs emitted radio waves well, especially when the wave has not yet formed in the near zone from the antenna, like a clouded mirror. The surface of the sea reflects better and the sandy desert does not reflect at all. According to the theory of reciprocity, the parameters and characteristics of the antenna are the same for both reception and transmission. This means that in the receiving mode, near a vertical with a small number of counterweights, large losses of the useful signal occur and, as a consequence, an increase in the noise component of the received signal.
Classic vertical counterweights must be no less than the length of the main pin, i.e. The displacement currents flowing between the pin and the counterweights occupy a certain volume of space, which participates not only in the formation of the directional pattern, but also in the formation of the field strength. To a greater approximation, we can say that each point on the pin corresponds to its own mirror point on the counterweight, between which bias currents flow. The fact is that displacement currents, like all ordinary currents, flow along the path of least resistance, which in this case is concentrated in a volume limited by the radius of the pin. The generated radiation pattern will be a superposition (superposition) of these currents. Returning to what was said above, this means that the efficiency of a classical antenna depends on the number of counterweights, i.e. the more counterweights, the greater the bias current, the more efficient the antenna, THIS IS THE FIRST CONDITION for good operation of the antenna.
The ideal case is a half-wave vibrator located in open space in the absence of absorbing soil, or a vertical vibrator located on a solid metal surface with a radius of 2-3 wavelengths. This is necessary so that the soil of the earth or objects surrounding the antenna do not interfere with the effective formation of the electromagnetic wave. The fact is that the formation of a wave and the phase coincidence of the magnetic (H) and electric (E) components of the electromagnetic field does not occur in the near zone of the Hertz dipole, but in the middle and far zone at a distance of 2-3 wavelengths, THIS IS THE SECOND CONDITION for good operation antennas. This is the main disadvantage of the classical Hertz dipole.
The formed electromagnetic wave in the far zone is less susceptible to the influence of the earth's surface, bends around it, is reflected and propagates in the environment. All of the very brief concepts outlined above are needed in order to understand the further essence of constructing amateur balcony antennas - to look for an antenna design in which the wave is formed inside the antenna itself.
It is now clear that the placement of full-size antennas, a quarter-wave rod with counterweights or a half-wave Hertz HF dipole is almost impossible to place within a balcony or loggia. And if a radio amateur managed to find an accessible antenna mounting point on the building opposite the balcony or window, then today this is considered great luck.
2. Shortened Hertzian dipole.
With limited space at his disposal, the radio amateur has to make a compromise and reduce the size of the antennas. Antennas whose dimensions do not exceed 10...20% of the wavelength λ are considered electrically small. In such cases, a shortened dipole is often used. When the antenna is shortened, its distributed capacitance and inductance decrease, and accordingly its resonance changes towards higher frequencies. To compensate for this deficiency, additional inductors L and capacitive loads C are introduced into the antenna as lumped elements (Fig. 1).
The maximum antenna efficiency is achievable by placing extension coils at the ends of the dipole, because the current at the ends of the dipole is maximum and distributed more evenly, which ensures the maximum effective antenna height hd = h. Turning on the inductor coils closer to the center of the dipole will reduce its own inductance, in this case the current towards the ends of the dipole drops, the effective height decreases, and subsequently the efficiency of the antenna.
Why is a capacitive load needed in a shortened dipole? The fact is that with a large shortening, the quality factor of the antenna greatly increases, and the antenna bandwidth becomes narrower than the amateur radio range. The introduction of capacitive loads increases the antenna capacity, reduces the quality factor of the formed LC circuit and expands its bandwidth to an acceptable level. A shortened dipole is tuned to the operating frequency in resonance either by inductors or by the length of conductors and capacitive loads. This ensures compensation of their reactance at the resonant frequency, which is necessary under the conditions of coordination with the power feeder.
Note: Thus, we compensate for the necessary characteristics of a shortened antenna to match it with the feeder and space, but reducing its geometric dimensions ALWAYS leads to a decrease in its efficiency (efficiency).
One of the examples of calculating an extension inductor was clearly described in the Radio Magazine, issue 5, 1999, where the calculation is carried out from an existing emitter. The inductors L1 and L2 are located here at the feed point of the quarter-wave dipole A and the counterweight D (Fig. 2.). This is a single band antenna.
You can also calculate the inductance of a shortened dipole on the website of the radio amateur RN6LLV - it provides a link to download a calculator that can help in calculating the extension inductance.
There are also proprietary shortened antennas (Diamond HFV5), which have a multi-band version, see Fig. 3, its electrical diagram is also there.
The operation of the antenna is based on the parallel connection of resonant elements tuned to different frequencies. When moving from one range to another, they practically do not affect each other. Inductors L1-L5 are extension coils, each designed for its own frequency range, just like capacitive loads (an extension of the antenna). The latter have a telescopic design, and by changing their length they can adjust the antenna in a small frequency range. The antenna is very narrowband.
* Mini antenna for 27 MHz band, authored by S. Zaugolny. Let's take a closer look at her work. The author’s antenna is located on the 4th floor of a 9-story panel building in a window opening and is essentially an indoor antenna, although this version of the antenna will work better outside the perimeter of a window (balcony, loggia). As can be seen from the figure, the antenna consists of an oscillatory circuit L1C1, tuned in resonance to the frequency of the communication channel, and the communication coil L2 acts as a matching element with the feeder, Fig. 4.a. The main emitter here is capacitive loads in the form of wire frames with dimensions of 300 * 300 mm and a shortened symmetrical dipole consisting of two pieces of wire 750 mm each. Considering that a vertically located half-wave dipole would occupy a height of 5.5 m, then an antenna with a height of only 1.5 m is a very convenient option for placement in a window opening.
If we exclude the resonant circuit from the circuit and connect the coaxial cable directly to the dipole, then the resonant frequency will be in the range of 55-60 MHz. Based on this diagram, it is clear that the frequency-setting element in this design is an oscillatory circuit, and the antenna being shortened by 3.7 times does not greatly reduce its efficiency. If in this design you use an oscillating circuit tuned to other lower frequencies in the HF range, of course the antenna will work, but with much lower efficiency. For example, if such an antenna is tuned to the 7 MHz amateur band, then the antenna shortening factor from half a wave of this range will be 14.3, and the antenna efficiency will drop even more (by the square root of 14), i.e. more than 200 times. But there’s nothing you can do about it; you have to choose an antenna design that would be as efficient as possible. This design clearly shows that the radiating elements here are capacitive loads in the form of wire squares, and they would perform their functions better if they were all-metal. The weak link here is the oscillatory circuit L1C1, which must have a high quality factor-Q, and part of the useful energy in this design is wasted inside the plates of capacitor C1. Therefore, although increasing the capacitance of the capacitor reduces the resonance frequency, it also reduces the overall efficiency of this design. When designing this antenna for lower frequencies of the HF range, attention should be paid to ensuring that at the resonant frequency L1 is maximum and C1 is minimum, not forgetting that capacitive emitters are part of the resonant system as a whole. It is advisable to design the maximum frequency overlap to be no more than 2, and the emitters should be located as far as possible from the walls of the building. The balcony version of this antenna with camouflage from prying eyes is shown in Fig. 4.b. It was this antenna that was used for some time in the mid-20th century on military vehicles in the HF range with a tuning frequency of 2-12 MHz.
* Single-band version of the “Undying Fuchs Antenna”(21 MHz) is shown in Fig. 5.a. The 6.3 meter long pin (almost half a wave) is fed from the end by a parallel oscillating circuit with an equally high resistance. Mr. Fuchs decided that this is how the parallel oscillatory circuit L1C1 and the half-wave dipole are consistent with each other, and so it is... As you know, the half-wave dipole is self-sufficient and works for itself, it does not need counterweights like a quarter-wave vibrator. The emitter (copper wire) can be placed in a plastic fishing rod. While working on air, such a fishing rod can be moved beyond the balcony railing and put back, but in winter this creates a number of inconveniences. A piece of wire of only 0.8 m is used as a “ground” for the oscillating circuit, which is very convenient when placing such an antenna on a balcony. At the same time, this is an exceptional case when a flower pot can be used as grounding (just kidding). The inductance of the resonant coil L2 is 1.4 μH, it is made on a frame with a diameter of 48 mm and contains 5 turns of 2.4 mm wire with a pitch of 2.4 mm. The circuit uses two pieces of RG-6 coaxial cable as a resonant capacitor with a capacity of 40 pF. The segment (C2 according to the diagram) is an unchanged part of the resonant capacitor with a length of no more than 55-60 cm, and a shorter segment (C1 according to the diagram) is used for fine tuning to resonance (15-20 cm). The L1 communication coil in the form of one turn on top of the L2 coil is made of an RG-6 cable with a 2-3 cm gap in its braid, and the SWR adjustment is carried out by moving this turn from the middle towards the counterweight.
Note: The Fuchs antenna works well only in the half-wave version of the emitter, which can also be shortened like a spiral antenna (read below).
* Multi-band balcony antenna option shown in Fig. 5 B. It was tested back in the 50s of the last century. Here the inductance plays the role of an extension coil in autotransformer mode. And capacitor C1 at 14 MHz tunes the antenna to resonance. Such a pin requires good grounding, which is difficult to find on the balcony, although for this option you can use an extensive network of heating pipes in your apartment, but it is not recommended to supply more than 50 W of power. Inductor L1 has 34 turns of copper tube with a diameter of 6 mm, wound on a frame with a diameter of 70 mm. Bends from 2,3 and 4 turns. In the 21 MHz range, switch P1 is closed, P2 is open, in the 14 MHz range, P1 and P2 are closed. At 7 MHz the position of the switches is the same as at 21 MHz. In the 3.5 MHz range, P1 and P2 are open. Switch P3 determines the coordination with the feeder. In both cases, it is possible to use a rod of about 5m, then the rest of the emitter will hang down to the ground. It is clear that the use of such antenna options should be above the 2nd floor of the building.
This section does not present all examples of shortening dipole antennas; other examples of shortening a linear dipole will be presented below.
3. Spiral antennas.
Continuing the discussion of the topic of shortened antennas for balcony purposes, we cannot ignore helical antennas of the HF range. And of course, it is necessary to recall their properties, which have almost all the properties of a Hertz dipole.
Any shortened antenna, the dimensions of which do not exceed 10-20% of the wavelength, is classified as an electrically small antenna.
Features of small antennas:
- The smaller the antenna, the less ohmic losses it should have. Small antennas assembled from thin wires cannot work effectively, since they experience increased currents, and the skin effect requires low surface resistances. This is especially true for antennas with emitter sizes significantly less than a quarter of the wavelength.
- Since the field strength is inversely proportional to the size of the antenna, a decrease in the size of the antenna leads to an increase in very high field strengths near it, and with an increase in the supplied power it leads to the appearance of the “St. Elmo’s Fire” effect.
- The electric field lines of shortened antennas have a certain effective volume in which this field is concentrated. It has a shape close to an ellipsoid of revolution. Essentially, this is the volume of the near-field quasi-static field of the antenna.
- A small antenna with dimensions λ/10 or less has a quality factor of about 40-50 and a relative bandwidth of no more than 2%. Therefore, it is necessary to introduce a tuning element into such antennas within one amateur band. This example is easy to observe with magnetic antennas with small dimensions. Increasing the bandwidth reduces the efficiency of the antenna; therefore, one should always strive to increase the efficiency of ultra-small antennas in different ways.
* Reducing the size of a symmetrical half-wave dipole led first to the appearance of extension inductors (Fig. 6.a), and a decrease in its interturn capacitance and a maximum increase in efficiency led to the appearance of an inductor for the design of helical antennas with transverse radiation. A spiral antenna (Fig. 6.b.) is a shortened classic half-wave (quarter-wave) dipole rolled into a spiral with distributed inductances and capacitances along the entire length. The quality factor of such a dipole has increased, and the bandwidth has become narrower.
To expand the bandwidth, a shortened spiral dipole, like a shortened linear dipole, is sometimes equipped with a capacitive load, Fig. 6.b.
Since when calculating single-shot antennas, the concept of effective antenna area (A eff.) is practiced quite widely, we will consider the possibilities of increasing the efficiency of helical antennas using end disks (capacitive load) and turn to a graphic example of current distribution in Fig. 7. Due to the fact that in a classic helical antenna the inductor coil (folded antenna sheet) is distributed along the entire length, the current distribution along the antenna is linear, and the current area increases slightly. Where, Iap is the antinode current of the helical antenna, Fig. 7.a. And the effective antenna area is Aeff. determines that part of the plane wave front area from which the antenna removes energy.
To expand the bandwidth and increase the effective radiation area, it is practiced to install end disks, which increases the efficiency of the antenna as a whole, Fig. 7.b.
When it comes to single-ended (quarter-wave) helical antennas, you should always remember that Aeff. depends largely on the quality of the land. Therefore, you should know that the same efficiency of a quarter-wave vertical is provided by four counterweights with a length of λ/4, six counterweights with a length of λ/8 and eight counterweights with a length of λ/16. Moreover, twenty counterweights with a length of λ /16 provide the same efficiency as eight counterweights with a length of λ /4. It becomes clear why balcony radio amateurs came to the half-wave dipole. It works for itself (see Fig. 7.c.), the power lines are closed to their elements and the “ground”, as in the structures in Fig. 7.a;b. he doesn't need it. In addition, helical antennas can also be equipped with concentrated elements of lengthening-L (or shortening-C) of the electrical length of the helical emitter, and their helix length may differ from the full-size helix. An example of this is a variable capacitor (discussed below), which can be considered not only as an element for tuning a series oscillatory circuit, but also as a shortening element. Also a helical antenna for portable stations in the 27 MHz range (Fig. 8). There is an extension inductor for the short helix.
* Compromise solution can be seen in the design of Valery Prodanov (UR5WCA), - a 40-20m balcony spiral antenna with a shortening coefficient K = 14, is quite worthy of the attention of radio amateurs without a roof, see Fig. 9.
Firstly, it is multi-band (7/10/14 MHz), and secondly, to increase its efficiency, the author doubled the number of helical antennas and connected them in phase. The absence of capacitive loads in this antenna is due to the fact that the expansion of the bandwidth and Aeff. antenna is achieved by in-phase connection of two identical radiation elements in parallel. Each antenna is wound with copper wire on a PVC pipe with a diameter of 5 cm, the length of the wire of each antenna is half a wavelength for the 7 MHz range. Unlike the Fuchs antenna, this antenna is matched to the feeder through a broadband transformer. The output of transformer 1 and 2 has common mode voltage. The vibrators in the author’s version are located at a distance of only 1 m from each other, this is the width of the balcony. As this distance expands within the balcony, the gain will increase slightly, but the antenna bandwidth will expand significantly.
* Radio amateur Harry Elington(WA0WHE, source "QST", 1972, January. Fig. 8.) built a spiral antenna for 80m with a shortening coefficient of about K = 6.7, which in his garden can be disguised as a support for a night lamp or flagpole. As can be seen from his comments, foreign radio amateurs also care about their relative peace of mind, although the antenna is installed in a private yard. According to the author, a helical antenna with a capacitive load on a pipe with a diameter of 102 mm, a height of about 6 meters and a counterweight of four wires, easily achieves an SWR of 1.2-1.3, and at SWR = 2 it operates in a bandwidth up to 100 kHz. The electrical length of the wire in the spiral was also half a wave. The half-wave antenna is powered from the end of the antenna via a coaxial cable with a characteristic impedance of 50 Ohms through a -150pF KPI, which turned the antenna into a series oscillating circuit (L1C1) with a radiating inductance of the helix.
Of course, the vertical helix is inferior in transmission efficiency to the classic dipole, but according to the author, this antenna is much better at reception.
* Antennas rolled up into a ball
To reduce the size of a linear half-wave dipole, it is not necessary to twist it into a spiral.
In principle, the spiral can be replaced by other forms of folding of a half-wave dipole, for example, according to Minkowski, Fig. 11. On a substrate with dimensions of 175mm x 175mm, you can place a dipole with a fixed frequency of 28.5 MHz. But fractal antennas are very narrow-band, and for radio amateurs they are only of educational interest in transforming their designs.
Using another method of shortening the size of antennas, the half-wave vibrator, or vertical, can be shortened by compressing it into a meander shape, Fig. 12. At the same time, the parameters of an antenna such as vertical or dipole change slightly when they are compressed by no more than half. If the horizontal and vertical parts of the meander are equal, the gain of the meander antenna decreases by approximately 1 dB, and the input impedance is close to 50 Ohms, which allows such an antenna to be fed directly with a 50 Ohm cable. Further reduction in size (NOT wire length) leads to a decrease in antenna gain and input impedance. However, the performance of a square wave antenna for the short wave range is characterized by increased radiation resistance relative to linear antennas with the same wire shortening. Experimental studies have shown that with a meander height of 44 cm and with 21 elements at a resonant frequency of 21.1 MHz, the antenna impedance was 22 Ohms, while a linear vertical of the same length has an impedance 10-15 times less. Due to the presence of horizontal and vertical sections of the meander, the antenna receives and emits electromagnetic waves of both horizontal and vertical polarization.
By compressing or stretching it, you can achieve resonance of the antenna at the required frequency. The meander step can be 0.015λ, but this parameter is not critical. Instead of a meander, you can use a conductor with triangular bends or a spiral. The required length of vibrators can be determined experimentally. As a starting point, we can assume that the length of the “straightened” conductor should be about a quarter of the wavelength for each arm of the split vibrator.
* “Tesla Spiral” in the balcony antenna. Following the cherished goal of reducing the size of the balcony antenna and minimizing losses in Aeff, instead of end disks, radio amateurs began to use a flat “Tesla spiral”, which is more technologically advanced than the meander, using it as an extending inductance of a shortened dipole and an end capacitance at the same time (Fig. 6. A.). The distribution of magnetic and electric fields in a flat Tesla inductor is shown in Fig. 13. This corresponds to the theory of radio wave propagation, where the E-field and the H-field are mutually perpendicular.
There is also nothing supernatural in antennas with two flat Tesla spirals, and therefore the rules for constructing a Tesla spiral antenna remain classic:
- The electrical length of the helix can be an antenna with asymmetrical feeding, either a quarter-wave vertical or a folded half-wave dipole.
- The larger the winding pitch and the larger its diameter, the higher its efficiency and vice versa.
- The greater the distance between the ends of a coiled half-wave vibrator, the higher its efficiency and vice versa.
In a word, we got a folded half-wave dipole in the form of flat inductors at its ends, see Fig. 14. To what extent to reduce or enlarge this or that structure is decided by the radio amateur after going out onto his balcony with a tape measure (after agreement with the final authority, with his mother or wife).
Using a flat inductor with large gaps between the turns at the ends of the dipole solves two problems at once. This is compensation for the electrical length of a shortened vibrator with distributed inductance and capacitance, as well as an increase in the effective area of the shortened antenna Aeff, expanding its bandwidth at the same time, as in Fig. 7.b.v. This solution simplifies the design of the shortened antenna and allows all dispersed LC elements of the antenna to work with maximum efficiency. There are no non-working antenna elements, for example, such as capacitance in magnetic M.L.-antennas, and inductance in EH-antennas. It should be remembered that the skin effect of the latter requires thick and highly conductive surfaces, but considering an antenna with a Tesla inductor, we see that the folded antenna repeats the electrical parameters of a conventional half-wave vibrator. In this case, the distribution of currents and voltages along the entire length of the antenna fabric is subject to the laws of a linear dipole and remains unchanged with some exceptions. Therefore, the need to thicken the antenna elements (Tesla spiral) completely disappears. In addition, no power is wasted on heating the antenna elements. The facts listed above make us think about the high budget of this design. And the simplicity of its manufacture is suitable for anyone who has at least once in his life held a hammer in his hands and bandaged his finger.
Such an antenna, with some interference, can be called an inductive-capacitive antenna, which contains LC radiation elements, or a “Tesla spiral” antenna. In addition, taking into account the near field (quasi-static) can theoretically give even greater strength values, which is confirmed by field tests of this design. The EH field is created in the body of the antenna and, accordingly, this antenna is less dependent on the quality of the ground and surrounding objects, which is essentially a godsend for the family of balcony antennas. It is no secret that such antennas have existed among radio amateurs for a long time, and this publication provides material on the transformation of a linear dipole into a spiral antenna with transverse radiation, then into a shortened antenna with the code name “Tesla spiral”. A flat spiral can be wound with a wire of 1.0-1.5 mm, because At the end of the antenna there is a high voltage, and the current is minimal. A wire with a diameter of 2-3mm will not significantly improve the efficiency of the antenna, but will significantly drain your wallet.
Note: The design and manufacture of shortened antennas of the “spiral” and “Tesla spiral” type with an electrical length of λ/2 compares favorably with a spiral with an electrical length of λ/4 due to the lack of a good “ground” on the balcony.
Antenna power supply.
We consider an antenna with Tesla spirals as a symmetrical half-wave dipole, coiled into two parallel spirals at its ends. Their planes are parallel to each other, although they may be in the same plane, Fig. 14. Its input impedance differs only slightly from the classic version, so the classic matching options are applicable here.
Windom linear antenna, see Fig. 15. refers to vibrators with asymmetrical power supply, it is distinguished by its “unpretentiousness” in terms of coordination with the transceiver. The uniqueness of the Windom antenna lies in its use on several bands and ease of manufacture. Transforming this antenna into a “Tesla spiral”, in space a symmetrical antenna will look like in Fig. 16.a, - with Gamma matching, and an asymmetrical Windom dipole, Fig. 16.b.
It is better to decide which antenna option to choose to implement your plans to turn your balcony into an “antenna field” by reading this article to the end. The design of balcony antennas compares favorably with full-size ones in that their parameters and other combinations can be made without going onto the roof of your house and without further injuring the building manager. In addition, this antenna is a practical guide for beginning radio amateurs, when you can practically learn on your knees all the basics of building elementary antennas.
Antenna assembly
Based on practice, it is better to take the length of the wire that makes up the antenna fabric with a small margin, slightly larger by 5-10% of its calculated length; it should be an insulated single-core copper wire for electrical installation with a diameter of 1.0-1.5 mm. The supporting structure of the future antenna is assembled (by soldering) from PVC heating pipes. Of course, under no circumstances should pipes with reinforced aluminum pipes be used. Dry wooden sticks are also suitable for carrying out the experiment, see Fig. 17.
There is no need for a Russian radio amateur to tell you the step-by-step assembly of the supporting structure; he just needs to look at the original product from afar. However, when assembling a Windom antenna or a symmetrical dipole, it is worth first marking the calculated feed point on the canvas of the future antenna and fixing it in the middle of the traverse, where the antenna will be powered. Naturally, the length of the traverse is included in the overall electrical size of the future antenna, and the longer it is, the higher the efficiency of the antenna.
Transformer
The impedance of the symmetrical dipole antenna will be slightly less than 50 Ohms, so see Fig. 18.a for the connection diagram. can be arranged by simply turning on a magnetic latch or using gamma matching.
The resistance of the rolled-up Windom antenna is slightly less than 300 Ohms, so you can use the data in Table 1, which impresses with its versatility using just one magnetic latch.
The ferrite core (latch) must be tested before installation on the antenna. To do this, the secondary winding L2 is connected to the transmitter, and the primary winding L1 is connected to the antenna equivalent. They check the SWR, core heating, as well as power losses in the transformer. If the core heats up at a given power, then the number of ferrite latches must be doubled. If there are unacceptable power losses, then it is necessary to select ferrite. For the ratio of power losses to dB, see Table 2.
No matter how convenient ferrite is, I still believe that for the emitted radio wave of any mini-antenna, where a huge EH field is concentrated, it is a “black hole”. The close location of the ferrite reduces the efficiency of the mini-antenna by µ/100 times, and all attempts to make the antenna as efficient as possible become in vain. Therefore, in mini-antennas, the greatest preference is given to air-core transformers, Fig. 18.b. Such a transformer, operating in the range of 160-10m, is wound with a double 1.5mm wire on a frame with a diameter of 25 and a length of 140mm, 16 turns with a winding length of 100mm.
It is also worth remembering that the feeder of such an antenna experiences a high intensity of the radiated field on its braid and creates a voltage in it that negatively affects the operation of the transceiver in transmission mode. It is better to eliminate the antenna effect by using a blocking feeder choke without using ferrite rings, see Fig. 19. These are 5-20 turns of coaxial cable wound on a frame with a diameter of 10 - 20 centimeters.
Such feeder chokes can be installed in close proximity to the antenna surface (body), but it is better to go beyond the limit of high field concentration and install it at a distance of about 1.5-2 m from the antenna surface. A second such throttle, installed at a distance of λ/4 from the first, would not hurt.
Antenna setup
Tuning the antenna brings great pleasure and, moreover, such a design is recommended to be used for conducting laboratory work in specialized colleges and universities, without leaving the laboratory, on the topic “Antennas”.
You can start tuning by finding the resonance frequency and adjusting the SWR of the antenna. It consists of moving the antenna feed point in one direction or another. To clarify the power point, there is no need to move the transformer or power cable along the crossarm and mercilessly cut the wires. Everything is close and simple here.
It is enough to make sliders in the form of “crocodiles” on the inner ends of the flat spirals on one side and the other, as shown in Fig. 20. Having previously planned to slightly increase the length of the spiral taking into account the settings, we move the sliders on different sides of the dipole to the same length, but in opposite directions, thereby moving the power point. The result of the adjustment will be the expected SWR of no more than 1.1-1.2 at the found frequency. Reactive components should be minimal. Of course, like any antenna, it must be located in a place as close as possible to the conditions of the installation site.
The second stage will be to tune the antenna exactly to resonance; this is achieved by shortening or lengthening the vibrators on both sides to equal pieces of wire using the same sliders. That is, you can increase the tuning frequency by shortening both turns of the spiral by the same size, and decrease the frequency, on the contrary, by lengthening it. After completing the setup at the future installation location, all antenna elements must be securely connected, insulated and secured.
Antenna gain, bandwidth and beam angle
According to practicing radio amateurs, this antenna has a lower radiation angle of about 15 degrees than a full-size dipole and is more suitable for DX communications. The Tesla spiral dipole has an attenuation of -2.5 dB relative to a full-size dipole installed at the same height from the ground (λ/4). The antenna bandwidth at the -3dB level is 120-150 kHz! When placed horizontally, the described antenna has a figure-of-eight radiation pattern similar to that of a full-size half-wave dipole, and the minimums of the radiation pattern provide attenuation of up to -25 dB. The efficiency of the antenna can be improved, as in the classic version, by increasing the height of the installation. But when the antennas are placed under the same conditions at heights λ/8 and below, the Tesla spiral antenna will be more effective than a half-wave dipole.
Note: All these “Tesla spiral” antennas look ideal, but even if such an antenna arrangement is worse than a dipole by 6 dB, i.e. by one point on the S-meter scale, then this is already remarkable.
Other antenna designs.
With a dipole for a range of 40 meters and with other dipole designs up to a range of 10m, everything is now clear, but let’s return to the spiral vertical for a range of 80m (Fig. 10.). Here, preference is given to a half-wave helical antenna, and therefore the “ground” is needed here only nominally.
Such antennas can be powered as in Fig. 9 via a summing transformer or in Fig. 10. variable capacitor. Of course, in the second case, the antenna’s bandwidth will be significantly narrower, but the antenna has the ability to adjust its range and yet, according to the author’s information, at least some kind of grounding is necessary. Our task is to get rid of it while on the balcony. Since the antenna is powered from the end (at the voltage “antinode”), the input resistance of a shortened half-wave helical antenna can be about 800-1000 Ohms. This value depends on the height of the vertical part of the antenna, on the diameter of the “Tesla spiral” and on the location of the antenna relative to surrounding objects. To match the high input impedance of the antenna with the low resistance of the feeder (50 Ohm), you can use a high-frequency autotransformer in the form of an inductor with a tap (Fig. 21.a), which is widely practiced in half-wave, vertically located linear antennas at 27 MHz by SIRIO, ENERGY, etc.
Data of the matching autotransformer for the half-wave CB antenna of the 10-11m range:
D = 30mm; L1=2 turns; L2 = 5 turns; d=1.0mm; h=12-13 mm. Distance between L1 and L2 = 5mm. The coils are wound on one plastic frame turn to turn. The cable is connected by the central conductor to the 2nd turn tap. The blade (end) of the half-wave vibrator is connected to the “hot” terminal of the L2 coil. The power for which the autotransformer is designed is up to 100 W. It is possible to select the coil outlet.
Data of the matching autotransformer for a half-wave helix antenna of the 40m range:
D = 32mm; L1=4.6 µH; h=20 mm; d=1.5mm; n=12 turns. L2=7.5 µH; ; h=27 mm; d=1.5mm; n=17 turns. The reel is wound on one plastic frame. The cable is connected by the central conductor to the outlet. The antenna blade (the end of the spiral) is connected to the “hot” terminal of the L2 coil. The power for which the autotransformer is designed is 150 -200 W. It is possible to select the coil outlet.
Dimensions of the Tesla spiral antenna for the 40m range:the total length of the wire is 21 m, the crossbar is 0.9-1.5 m high with a diameter of 31 mm, on radially mounted spokes of 0.45 m each. The outer diameter of the spiral will be 0.9 m
Data of the matching autotransformer for a spiral antenna of the 80m range: D = 32mm; L1=10.8 µH; h=37 mm; d=1.5mm; n=22 turns. L2=17.6 µH; ; h=58 mm; d=1.5mm; n=34 turns. The reel is wound on one plastic frame. The cable is connected by the central conductor to the outlet. The antenna blade (the end of the spiral) is connected to the “hot” terminal of the L2 coil. It is possible to select the coil outlet.
Dimensions of the Tesla spiral antenna for the 80m range:the total length of the wire is 43 m, the crossbar is 1.3-1.5 m high with a diameter of 31 mm, on radially mounted spokes of 0.6 m each. The outer diameter of the spiral will be 1.2 m
Coordination with a half-wave spiral dipole, when fed from the end, can be carried out not only through an autotransformer, but also according to Fuchs, a parallel oscillatory circuit, see Fig. 5.a.
Note:
- When feeding a half-wave antenna from one end, tuning into resonance can be done from either end of the antenna.
- In the absence of at least some kind of grounding, a locking feeder choke must be installed on the feeder.
Vertical directional antenna option
Having a pair of Tesla spiral antennas and some area to place them, you can create a directional antenna. Let me remind you that all operations with this antenna are completely identical with antennas of linear sizes, and the need to minimize them is not due to the fashion for mini-antennas, but to the lack of locations for linear antennas. The use of two-element directional antennas with a distance between them of 0.09-0.1λ allows you to design and build a directional Tesla spiral antenna.
This idea was taken from “KB MAGAZINE” No. 6, 1998. This antenna is perfectly described by Vladimir Polyakov (RA3AAE), which can be found on the Internet. The essence of the antenna is that two vertical antennas located at a distance of 0.09λ are fed in antiphase by one feeder (one by braid, the other by central conductor). The power supply is similar to the same Windom antenna, only with single-wire power supply, Fig. 22. The phase shift between opposite antennas is created by tuning them lower and higher in frequency, as in classic directional Yagi antennas. And coordination with the feeder is carried out by simply moving the feed point along the web of both antennas, moving away from the zero feed point (the middle of the vibrator). By moving the feed point from the middle to a certain distance X, you can achieve a resistance from 0 to 600 Ohms, as in the Windom antenna. We will only need a resistance of about 25 ohms, so the displacement of the power point from the middle of the vibrators will be very small.
The electrical circuit of the proposed antenna with approximate dimensions given in wavelengths is shown in Fig. 22. And practical adjustment of the Tesla spiral antenna to the required load resistance is quite feasible using the technology in Fig. 20. The antenna is powered at the XX points directly by a feeder with a characteristic impedance of 50 Ohms, and its braiding must be insulated with a locking feeder choke, see Fig. 19.
Vertical directional helix antenna option for 30m according to RA3AAE
If for some reason a radio amateur is not satisfied with the “Tesla spiral” antenna option, then the antenna option with spiral emitters is quite feasible, Fig. 23. Let's give its calculation.
We use a half-wavelength spiral wire length:
λ=300/MHz =З00/10.1; λ /2 -29.7/2=14.85. Let's take 15m
Let's calculate the pitch per coil on a pipe with a diameter of 7.5 cm, spiral winding length = 135 cm:
Circumference L=D*π = -7.5cm*3.14=23.55cm.=0.2355m;
number of turns of a half-wave dipole -15m/ 0.2355=63.69= 64 turns;
winding pitch on a ruble length of 135 cm. - 135cm/64=2.1cm..
Answer: on a pipe with a diameter of 75 mm we wind 15 meters of copper wire with a diameter of 1-1.5 mm in the amount of 64 turns with a winding pitch of 2 cm.
The distance between identical vibrators will be 30*0.1=3m.
Note: antenna calculations were carried out with rounding to account for the possibility of shortening the winding wire during setup.
To increase the bias current and ease of adjustment, small adjustable capacitive loads must be placed at the ends of the vibrators, and a locking feeder choke must be placed on the feeder at the connection point. The displaced power points correspond to the dimensions in Fig. 22. It should be remembered that unidirectionality in this design is achieved by a phase shift between opposite spirals by tuning them with a difference of 5-8% in frequency, as in classic Uda-Yagi directional antennas.
Rolled up Bazooka
As you know, the noise situation in any city leaves much to be desired. This also applies to the radio frequency spectrum due to the widespread use of switching power converters for household appliances. Therefore, I made an attempt to use the “Bazooka” type antenna, which has proven itself in this regard, in the “Tesla spiral” antenna. In principle, this is the same half-wave vibrator with a closed circuit system, like all loop antennas. Placing it on the traverse presented above was not difficult. The experiment was carried out at a frequency of 10.1 MHz. A television cable with a diameter of 7 mm was used as the antenna fabric. (Fig. 24). The main thing is that the cable braid is not aluminum like its shell, but copper.
Even experienced radio amateurs get confused by this, mistaking the gray cable braid for tinned copper when purchasing. Since we are talking about a QRP antenna for a balcony, and the input power is up to 100 W, such a cable will be quite suitable. The shortening coefficient of such a cable with foamed polyethylene is about 0.82. Therefore, the length of L1 (Fig. 25.) for a frequency of 10.1 MHz. It was 7.42 cm each, and the length of the L2 extension conductors with this antenna layout was 1.83 cm each. The input impedance of the rolled up Bazooka after installation in an open area was about 22-25 Ohms and is not adjustable in any way. Therefore, a 1:2 transformer was required here. In the trial version, it was made on a ferrite latch using simple wires from audio speakers with the turns ratio according to Table 1. Another version of the 1:2 transformer is shown in Fig. 26.
Aperiodic broadband antenna "Bazooka"
Not a single radio amateur who even has at his disposal an antenna field on the roof of his house or in the courtyard of a cottage will refuse a broadband survey antenna based on a feeder coiled into a Tesla spiral. The classic version of an aperiodic antenna with a load resistor is known to many; here the “Bazooka” antenna acts as a broadband vibrator, and its bandwidth, as in the classical versions, has a large overlap towards higher frequencies.
The antenna diagram is shown in Fig. 27, and the power of the resistor is about 30% of the power supplied to the antenna. If the antenna is used only as a receiving antenna, a resistor power of 0.125 W is sufficient. It is worth noting that the Tesla spiral antenna, installed horizontally, has a figure-of-eight radiation pattern and is capable of spatial selection of radio signals. Installed vertically, it has a circular radiation pattern.
4.Magnetic antennas.
The second, no less popular type of antenna is an inductive radiator with shortened dimensions, this is a magnetic frame. The magnetic frame was discovered in 1916 by K. Brown and was used until 1942 as a receiving element in radio receivers and direction finders. This is also an open oscillatory circuit with a frame perimeter of less than ≤ 0.25 wavelength, it is called a “magnetic loop” (magnetic loop), and the abbreviated name has acquired the abbreviation - ML. The active element of the magnetic loop is inductance. In 1942, a radio amateur with the call sign W9LZX first used such an antenna at the missionary broadcast station HCJB, located in the mountains of Ecuador. Thanks to this, the magnetic antenna immediately conquered the amateur radio world and has since been widely used in amateur and professional communications. Magnetic loop antennas are one of the most interesting types of small-sized antennas, which are convenient to place both on balconies and on window sills.
It takes the form of a loop of conductor, which is connected to a variable capacitor to achieve resonance, where the loop is the radiating inductance of an oscillating LC circuit. The emitter here is only inductance in the form of a loop. The dimensions of such an antenna are very small, and the perimeter of the frame is usually 0.03-0.25 λ. The maximum efficiency of the magnetic loop can reach 90% relative to the Hertz dipole, see Fig. 29.a. Capacitance C in this antenna does not participate in the radiation process and has a purely resonant character, as in any oscillatory circuit, Fig. 29.b..
The efficiency of the antenna strongly depends on the active resistance of the antenna web, on its size, on its placement in space, but to a greater extent on the materials used to construct the antenna. The loop antenna bandwidth is usually from units to tens of kilohertz, which is associated with the high quality factor of the formed LC circuit. Therefore, the efficiency of an ML antenna greatly depends on its quality factor; the higher the quality factor, the higher its efficiency. This antenna is also used as a transmitting antenna. With small frame sizes, the amplitude and phase of the current flowing in the frame are practically constant along the entire perimeter. The maximum radiation intensity corresponds to the plane of the frame. In the perpendicular plane of the frame, the radiation pattern has a sharp minimum, and the overall diagram of the loop antenna has a figure-of-eight shape.
Electric field strength E electromagnetic wave (V/m) at a distance d from transmitting loop antenna, calculated by the formula:
EMF E induced in reception loop antenna, calculated by the formula:
The figure-of-eight radiation pattern of the frame allows you to use its minimums in the diagram in order to detune it in space from nearby interference or unwanted radiation in a certain direction in near zones up to 100 km.
When manufacturing an antenna, it is required to maintain the ratio of the diameters of the radiating ring and the coupling loop D/d as 5/1. The coupling coil is made of coaxial cable, is located in close proximity to the radiating ring on the opposite side of the capacitor, and looks like in Fig. 30.
Since a large current flows in the radiating frame, reaching tens of amperes, the frame in the frequency range 1.8-30 MHz is made of a copper tube with a diameter of about 40-20 mm, and the resonance tuning capacitor should not have rubbing contacts. Its breakdown voltage must be at least 10 kV with an input power of up to 100 W. The diameter of the radiating element depends on the range of frequencies used and is calculated from the wavelength of the high-frequency part of the range, where the frame perimeter P = 0.25λ, counting from the upper frequency.
Perhaps one of the first after W9LZX, German shortwave DP9IV with the ML antenna installed on the window, with a transmitter power of only 5 W, I made QSOs in the 14 MHz range with many European countries, and with a power of 50 W - with other continents. It was this antenna that became the starting point for experiments by Russian radio amateurs, see Fig. 31.
The desire to create an experimental compact indoor antenna, which can also be safely called an EH antenna, in close collaboration with Alexander Grachev ( UA6AGW), Sergey Tetyukhin (R3PIN) designed the following masterpiece, see Fig.32.
It is precisely this low-budget design of an indoor version of an EH antenna that can please a new-comer or summer resident radio amateur. The antenna circuit includes both a magnetic emitter L1;L2 and a capacitive emitter in the form of telescopic “whiskers”.
Particular attention in this design (R3PIN) deserves the resonant system for matching the feeder with the Lsv antenna; C1, which once again increases the quality factor of the entire antenna system and allows you to slightly increase the gain of the antenna as a whole. The braided cable of the antenna web acts here as the primary circuit, together with the “whiskers” as in Yakov Moiseevich’s design. The length of these “whiskers” and their position in space make it easy to achieve resonance and the most efficient operation of the antenna as a whole based on the current indicator in the frame. And providing the antenna with an indicator device allows us to consider this version of the antenna as a completely complete design. But whatever the design of magnetic antennas, you always want to increase its efficiency.
Double loop magnetic antennas in the form of a figure eight relatively recently began to appear among radio amateurs, see Fig. 33. Its aperture is twice as large as the classic one. Capacitor C1 can change the resonance of the antenna with a frequency overlap of 2-3 times, and the total circumference of the two loops is ≤ 0.5λ. This is comparable to a half-wave antenna, and its small radiation aperture is compensated by an increased quality factor. It is better to coordinate the feeder with such an antenna through inductive coupling.
Theoretical retreat: The double loop can be considered as a mixed LL and LC oscillatory system. Here, for normal operation, both arms are loaded onto the radiation medium synchronously and in phase. If a positive half-wave is applied to the left shoulder, then exactly the same is applied to the right shoulder. The self-induction emf generated in each arm will, according to Lenz’s rule, be opposite to the induction emf, but since the induction emf of each arm is opposite in direction, the self-induction emf will always coincide with the direction of induction of the opposite arm. Then the induction in coil L1 will be summed with the self-induction from coil L2, and the induction of coil L2 will be summed with the self-induction of L1. Just as in the LC circuit, the total radiation power can be several times greater than the input power. Energy can be supplied to any of the inductors and in any way.
The double frame is shown in Fig. 33.a.
The design of a two-loop antenna, where L1 and L2 are connected to each other in the form of a figure eight. This is how two-frame ML appeared. Let's call it ML-8.
ML-8, unlike ML, has its own peculiarity - it can have two resonances, the oscillatory circuit L1; C1 has its own resonant frequency, and L2; C1 has its own. The designer’s task is to achieve unity of resonances and, accordingly, maximum efficiency of the antenna, therefore, the dimensions of the loops L1; L2 and their inductances must be the same. In practice, an instrumental error of a couple of centimeters changes one or the other inductance, the resonance tuning frequencies diverge somewhat, and the antenna receives a certain frequency delta. In addition, doubling the inclusion of identical antennas expands the bandwidth of the antenna as a whole. Sometimes designers do this intentionally. In practice, ML-8 is actively used by radio amateurs with radio call signs RV3YE; US0KF; LZ1AQ; K8NDS and others, clearly stating that such an antenna works much better than a single-frame antenna, and changing its position in space can be easily controlled by spatial selection. Preliminary calculations show that for the ML-8, for a range of 40 meters, the diameter of each loop at maximum efficiency will be slightly less than 3 meters. It is clear that such an antenna can only be installed outdoors. And we dream of an effective ML-8 antenna for a balcony or even a windowsill. Of course, you can reduce the diameter of each loop to 1 meter and adjust the resonance of the antenna with capacitor C1 to the required frequency, but the efficiency of such an antenna will drop by more than 5 times. You can go the other way, maintaining the calculated inductance of each loop, using not one, but two turns in it, leaving the resonant capacitor with the same rating, and, accordingly, the quality factor of the antenna as a whole. There is no doubt that the antenna aperture will decrease, but the number of turns “N” will partially compensate for this loss, according to the formula below:
From the above formula it is clear that the number of turns N is one of the factors of the numerator and is on a par with both the area of the turn-S and its quality factor-Q.
For example, a radio amateur OK2ER(see Fig. 34.) considered it possible to use a 4-turn ML with a diameter of only 0.8 m in the range of 160-40 m.
The author of the antenna reports that at 160 meters the antenna works nominally and is mainly used by him for radio surveillance. In the 40m range. It is enough to use a jumper, which reduces the working number of turns by half. Let's pay attention to the materials used - the copper pipe of the loop is taken from water heating, the clips connecting them into a common monolith are used for installing plastic water pipes, and the sealed plastic box was purchased at an electrical store. The matching of the antenna with the feeder is capacitive, and is carried out according to any of the presented schemes, see Fig. 35.
In addition to the above, we need to understand that the following antenna elements have a negative effect on the quality factor-Q of the antenna as a whole:
From the above formula, we see that the active inductance resistance Rk and the capacitance of the oscillatory system C, which are in the denominator, should be minimal. It is for this reason that all MLs are made from a copper pipe of as large a diameter as possible, but there are cases when the loop blade is made from aluminum. The quality factor of such an antenna and its efficiency drops by 1.1-1.4 times. As for the capacitance of the oscillatory system, everything is more complicated. With a constant loop size L, for example at a resonant frequency of 14 MHz, capacitance C will be only 28 pF, and efficiency = 79%. At a frequency of 7 MHz, efficiency = 25%. Whereas at a frequency of 3.5 MHz with a capacitance of 610 pF, its efficiency = 3%. For this reason, ML is most often used for two ranges, and the third (lowest) is considered overview. Therefore, calculations must be made based on the highest range with the minimum capacity C1.
Double magnetic antenna for 20m range.
The parameters of each loop will be as follows: With a blade (copper pipe) diameter of 22 mm, a double loop diameter of 0.7 m, a distance between turns of 0.21 m, the loop inductance will be 4.01 μH. The necessary design parameters of the antenna for other frequencies are summarized in Table 3.
Table 3.
|
Tuning Frequency (MHz) |
Capacitance of capacitor C1 (pF) |
Bandwidth (kHz) |
|
The height of such an antenna will be only 1.50-1.60 m. Which is quite acceptable for an antenna of the ML-8 type for a balcony version and even for an antenna hung outside the window of a residential multi-storey building. And its wiring diagram will look like in Fig. 36.a.
Antenna power can be capacitively or inductively coupled. The capacitive coupling options shown in Fig. 35 can be selected at the request of the radio amateur.
The most budget option is inductive coupling, but its diameter will be different.
Calculation of diameter (d) of communication loop ML-8 is made from the calculated diameter of two loops.
The circumference of the two loops after recalculation is 4.4 * 2 = 8.8 meters.
Let's calculate the imaginary diameter of two loops D = 8.8 m / 3.14 = 2.8 meters.
Let's calculate the diameter of the communication loop - d = D/5. = 2.8/5 = 0.56 meters.
Since in this design we use a two-turn system, the communication loop must also have two loops. We twist it in half and get a two-turn communication loop with a diameter of about 28 cm. The selection of communication with the antenna is carried out at the time of clarifying the SWR in the priority frequency range. The communication loop can have a galvanic connection with the zero voltage point (Fig. 36.a.) and be located closer to it.
Electric emitter, this is another additional element of radiation. If the magnetic antenna emits an electromagnetic wave with the priority of the magnetic field, then the electric emitter will serve as an additional electric field emitter-E. In fact, it must replace the initial capacitance C1, and the drain current, which previously passed uselessly between the closed plates of capacitor C1, now works for additional radiation. In this case, a portion of the supplied power will additionally be emitted by electric emitters, Fig. 36.b. The bandwidth will increase to the limits of the amateur radio band as in EH antennas. The capacity of such emitters is low (12-16 pF, no more than 20), and therefore their efficiency in low frequency ranges will be low. You can get acquainted with the work of EH antennas using the following links:
To tune a magnetic antenna into resonance, it is best to use vacuum capacitors with a high breakdown voltage and high quality factor. Moreover, using a gearbox and an electric drive, the antenna can be adjusted remotely.
We are designing a budget balcony antenna that you can approach at any time, change its position in space, rearrange or switch to another frequency. If at points “a” and “b” (see Fig. 36.a.), instead of a scarce and expensive variable capacitor with large gaps, you connect a capacitance made from sections of RG-213 cable with a linear capacitance of 100 pF/m, then you can instantly change the frequency settings, and use tuning capacitor C1 to clarify the tuning resonance. The “capacitor cable” can be rolled into a roll and sealed in any of the following ways. Such a set of containers can be had for each range separately, and connected to the circuit through a regular electrical outlet (points a and b) paired with an electrical plug. Approximate capacities C1 by range are shown in Table 1.
Indication of antenna tuning to resonance It’s better to do it directly on the antenna itself (it’s more visual). To do this, it is enough to tightly wind 25-30 turns of MGTF wire not far from the communication coil on the L1 canvas (zero voltage point), and seal the setting indicator with all its elements from precipitation. The simplest diagram is shown in Fig. 37. The maximum readings of the P device will indicate successful antenna tuning.
To the detriment of the efficiency of the antenna. Cheaper materials can be used as the material for loops L1; L2, for example, a PVC pipe with an aluminum layer inside for laying a water pipe with a diameter of 10-12 mm.
Antenna DDRR
Despite the fact that the classic DDRR antenna is inferior in efficiency to a quarter-wave vibrator by 2.5 dB, its geometry turned out to be so attractive that the DDRR was patented by Northrop and put into mass production.
As with the Groundplane, the main factor for decent efficiency of a DDRR antenna is a good counterweight. It is a flat metal disk with high surface conductivity. Its diameter must be at least 25% greater than the diameter of the ring conductor. The elevation angle of the main beam is smaller, the higher the ratio of the diameters of the counterweight disk, and increases if as many radial counterweights with a length of 0.25λ are fastened around the circumference of the disk, ensuring their reliable contact with the counterweight disk.
The DDRR antenna discussed here (Fig. 38) uses two identical rings (hence the name "double-ring-circular"). At the bottom, instead of a metal surface, a closed ring with dimensions similar to the top one is used. All grounding points are connected to it according to the classical scheme. Despite a slight decrease in the efficiency of the antenna, this design is very attractive for placing it on a balcony; in addition, with this solution, it is also of interest to connoisseurs of the 40-meter range. Using square structures instead of rings, the antenna on the balcony resembles a clothes dryer and does not raise unnecessary questions from neighbors.
All its dimensions and capacitor ratings are presented in Table 4. In the budget version, an expensive vacuum capacitor can be replaced with segments of feeders according to the range, and fine tuning can be done with a 1-15pF trimmer with an air dielectric, remembering that the linear capacitance of the cable is RG213 = (97pF / m).
Table 4.
|
Amateur bands, (m) |
||||||||
|
Frame perimeter (m) |
||||||||
Practical experience with a double ring DDRR antenna was described by DJ2RE. The 10-meter antenna under test was made of a copper tube with an outer diameter of 7 mm. To fine-tune the antenna, two copper rotating plates measuring 60x60 mm were used between the upper “hot” end of the conductor and the lower ring.
The comparison antenna was a rotating three-element Yagi located 12 m from the ground. The DDRR antenna was located at a height of 9 m. Its lower ring was grounded only through the shield of the coaxial cable. During the test reception, the qualities of the DDRR antenna as a circular emitter immediately emerged. According to the author of the tests, the received signal turned out to be two points lower on the S-meter of the Yagi signal with a gain of about 8 dB. When transmitting with a power of up to 150 W, 125 communication sessions were performed.
Note: According to the author of the tests, it turns out that the DDRR antenna at the time of testing had a gain of about 6 dB. This phenomenon is often misleading due to the proximity of different antennas of the same range, and the properties of their re-emission of electromagnetic waves lose the purity of the experiment.
5. Capacitive antennas.
Before starting this topic, I would like to remember the history. In the 60s of the 19th century, while formulating a system of equations to describe electromagnetic phenomena, J. C. Maxwell was faced with the fact that the equation for a direct current magnetic field and the equation for the conservation of electric charges in alternating fields (continuity equation) are incompatible. To eliminate the contradiction, Maxwell, without any experimental data, postulated that the magnetic field is generated not only by the movement of charges, but also by a change in the electric field, just as the electric field is generated not only by charges, but also by a change in the magnetic field. The quantity where is the electrical induction, which he added to the conduction current density, Maxwell called displacement current. Electromagnetic induction now has a magnetoelectric analogue, and the field equations acquire remarkable symmetry. Thus, one of the most fundamental laws of nature was discovered speculatively, the consequence of which is the existence of electromagnetic waves. Subsequently, G. Hertz, relying on this theory, proved that the electromagnetic field emitted by an electric vibrator is equal to the field emitted by a capacitive emitter!
If so, let us see once again what happens when a closed oscillatory circuit turns into an open one and how can the electric field E be detected? To do this, next to the oscillatory circuit we will place an electric field indicator, this is a vibrator, in the gap of which an incandescent lamp is connected, it is not lit yet, see Fig. 39.a. We gradually open the circuit, and we observe that the electric field indicator lamp lights up, Fig. 39.b. The electric field is no longer concentrated between the plates of the capacitor; its lines of force go from one plate to another through open space. Thus, we have experimental confirmation of J. C. Maxwell's statement that a capacitive emitter generates an electromagnetic wave. In this experiment, a strong high-frequency electric field is formed around the plates, the change of which in time induces eddy displacement currents in the surrounding space (Eikhenwald A.A. Electricity, fifth ed., M.-L.: State Publishing House, 1928, Maxwell’s first equation), forming a high-frequency electromagnetic field!
Nikola Tesla drew attention to this fact that with the help of very small emitters in the HF range, it is possible to create a fairly effective device for emitting an electromagnetic wave. This is how N. Tesla's resonant transformer was born.
* Design of the EH antenna by T. Hard and transformer (dipole) by N. Tesla.
Is it worth stating once again that the EH antenna designed by T. Hard (W5QJR), see Fig. 40, is a copy of the original Tesla antenna, see Fig. 1. The antennas differ only in size, where Nikola Tesla used frequencies calculated in kilohertz, and T. Hard created a design for operation in the HF range.
The same resonant circuit, the same capacitive emitter with an inductor and a coupling coil. Ted Hard's antenna is the closest analogue to Nikola Tesla's antenna and was patented as "Coaxial inductor and dipole EH antenna" (US Patent US 6956535 B2 dated 10/18/2005) for operation in the HF range.
Ted Hard's capacitive HF antenna is inductively coupled to the feeder, although a number of capacitive, direct coupled and transformer coupled capacitive antennas have long existed.
The basis of the supporting structure of engineer and radio amateur T. Hard is an inexpensive plastic pipe with good insulating characteristics. Foil in the form of cylinders fits tightly around it, thereby forming antenna emitters with a small capacity. Inductance L1 of the formed series oscillatory circuit is located behind the emitter aperture. Inductor L2, located in the center of the emitter, compensates for the antiphase radiation of coil L1. The antenna power connector (from the generator) W1 is located at the bottom, this is convenient for connecting the power feeder going down.
In this design, the antenna is tuned by two elements, L1 and L3. By selecting the turns of coil L1, the antenna is tuned to the sequential resonance mode at maximum radiation, where the antenna acquires a capacitive character. The tap from the inductor determines the input impedance of the antenna and whether the radio amateur has a feeder with a characteristic impedance of 50 or 75 Ohms. By selecting a tap from coil L1, you can achieve SWR = 1.1-1.2. Inductor L3 achieves capacitive compensation, and the antenna takes on an active nature, with an input impedance close to SWR = 1.0-1.1.
Note: Coils L1 and L2 are wound in opposite directions, and coils L1 and L3 are perpendicular to each other to reduce mutual influence.
This antenna design undoubtedly deserves the attention of radio amateurs who only have a balcony or loggia at their disposal.
Meanwhile, developments do not stand still and radio amateurs, appreciating the invention of N. Tesla and the design of Ted Hart, began to offer other options for capacitive antennas.
* "Isotron" antenna family is a simple example of flat curved capacitive emitters, it is produced by industry for use by radio amateurs, see Fig. 42. The Isotron antenna has no fundamental difference with the T. Horda antenna. The same series oscillatory circuit, the same capacitive emitters.
Namely, the radiation element here is a radiating capacitance (Sizl.) in the form of two plates bent at an angle of about 90-100 degrees, the resonance is adjusted by decreasing or increasing the bend angle, i.e. their capacities. According to one version, communication with the antenna is carried out by directly connecting the feeder and the series oscillating circuit, in this case the SWR determines the L/C ratio of the formed circuit. According to another version, which began to be used by radio amateurs, communication is carried out according to the classical scheme, through the communication coil Lst. The SWR in this case is adjusted by changing the connection between the series resonance coil L1 and the coupling coil Lst. The antenna is operational and to some extent effective, but it has a main drawback: the inductor, when located in the factory version, is located in the center of the capacitive emitter and works in antiphase with it, which reduces the efficiency of the antenna by approximately 5-8 dB. It is enough to rotate the plane of this coil 90 degrees and the efficiency of the antenna will increase significantly.
The optimal antenna dimensions are summarized in Table 5.
*Multi-band option.
All Isotron antennas are single-band, which causes a number of inconveniences when moving from band to band and their placement. When two (three, four) such antennas are connected in parallel, mounted on a common bus, operating at frequencies f1; f2 and fn, their interaction is excluded due to the high resistance of the series oscillatory circuit of the antenna not participating in resonance. When manufacturing two single-resonant antennas connected in parallel on a common bus, the efficiency (efficiency) and bandwidth of such an antenna will be higher. Using the last option for in-phase connection of two single-band antennas, you need to remember that the total input impedance of the antennas will be half as low and it is necessary to take appropriate measures by referring to (Table 1). A modification of the antenna on a common substrate is shown in Fig. 42 (bottom). There is no need to remind you that the locking feeder choke is an integral part of any mini antenna.
Studying the simplest “Isotron”, we came to the conclusion that the gain of this antenna is insufficient due to the placement of a resonant inductor between the radiating plates. As a result, this design was improved by radio amateurs in France, and the inductor was moved outside the working environment of the capacitive emitter, see Fig. 43. The antenna circuit has a direct connection to the feeder, which simplifies the design, but still complicates full coordination with it.
As can be seen from the presented drawings and photos, this antenna is quite simple in design, especially in tuning it to resonance, where it is enough to slightly change the distance between the emitters. If the plates are swapped, the top one is made “hot” and the bottom one is connected to the feeder braid, and a common bus is made for a number of other similar antennas, then you can get a multi-band antenna system, or a number of in-phase connected identical antennas that can increase the overall gain.
Radio amateur with radio signal call sign F1RFM, kindly provided for general viewing his antenna design with calculations for 4 amateur radio bands, the diagram of which is shown in Fig. 44.
* Antenna "Biplane"
The “Biplane” antenna is named for its similarity to the placement of the twin wings of early 20th century “Biplane” aircraft, and its invention belongs to a group of radio amateurs (Fig. 45). The “Biplane” antenna consists of two serial oscillating circuits L1;C1 and L2;C2, connected back-to-back. Power supply of emitters, symmetrical with direct connection. The planes of capacitors C1 and C2 are used as radiating elements. Each emitter is made of two duralumin plates and is located on both sides of the inductors.
To eliminate mutual influence, the inductors are wound counter-winding or positioned perpendicular to each other. The area of each plate, according to the authors, will be for a range of 20 meters 64.5 cm2, for 40 meters - 129 cm2, for 80 meters - 258 cm2, and for a 160 meter range, respectively, 516 cm2.
The adjustment is carried out in two stages and can be carried out by elements C1 and C2 by changing the distance between the plates. The minimum SWR is achieved by changing capacitors C1 and C2, tuning the transmitter to the frequency. The antenna is very difficult to set up and requires a complex sealing design from the influence of external precipitation. It has no development prospects and is unprofitable.
On the topic of capacitive antennas, it is worth noting that they have occupied a special niche among radio amateurs who do not have the opportunity to install full-fledged antennas and who only have a balcony or loggia at their disposal. Radio amateurs who have the opportunity to install a low mast on a small antenna field also use such antennas. All shortened antennas have the common name QRP antennas. In addition, radio amateurs have a number of mistakes when installing and operating shortened antennas, such as the absence of a locking “feeder choke” or the latter’s location on a ferrite base being very close to the shortened antenna surface. In the first case, the antenna feeder begins to radiate, and in the second, the ferrite of such a choke is a “black hole” and reduces its efficiency.
* EH antenna of the USSR SA troops of the 40s - 50s of the last century.
The antenna was welded from duralumin pipes with a diameter of 10 and 20 mm. A flat, broadband symmetrical split dipole about 2 meters long and 0.75 m wide. Operating frequency range 2-12 MHz. Why not a balcony antenna? It was mounted on the roof of the mobile radio room in a horizontal position at a height of about 1 m.
The author of this article reproduced this design on the second floor balcony back in the 90s, and the emitters were made under a clothes dryer on wooden blocks outside the balcony. Instead of ropes, insulated copper wires were stretched, see Fig. 46.a. The antenna was tuned using the oscillating circuit L1C1, the coupling capacitor C2 with the antenna and the coupling coil Lsv. with transceiver, see Fig. 46.b. All air-insulated capacitors with a capacity of 2 * 12-495 pF were used from tube radios of the 60s.
Inductor L1 diameter 50 mm; 20 turns; wire 1.2 mm; pitch 3.5 mm. A plastic pipe (50mm) sawn lengthwise was tightly placed on top of this coil. A communication coil Lst was wound on top of it. - 5 turns with bends from 3, 4 and 5 turns of 2.2 mm wire. All capacitors used only stator contacts, and the axes (rotors) on capacitors C2 and C3 were connected by an insulating jumper to synchronize rotation. The two-wire line should be no more than 2.0-2.5 meters, this is exactly the distance from the antenna (dryer) to the matching device standing on the windowsill. The antenna was built in the range of 1.8-14.5 MHz, but by changing the resonant circuit to other parameters, such an antenna could operate up to 30 MHz. In the original, in series with the transmission line in this design, current indicators were provided, which were adjusted to the maximum readings, but in a simplified version, between the two wires of a two-wire line, a fluorescent lamp hung perpendicular to it, which, at the minimum output power, glowed only in the middle, and at maximum power ( at resonance) the glow reached the edges of the lamp. Coordination with the radio station was carried out by switch P1 and monitored using the SWR meter. The bandwidth of such an antenna was more than sufficient to operate on each of the amateur bands. With an input power of 40-50W. The antenna did not cause any interference to neighbors' television. Moreover, now that everyone has switched to digital and cable television, it is possible to supply up to 100W.
This type of antenna is capacitive and differs from EH antennas only in the circuit for connecting the emitters. It differs in its shape and size, but at the same time, it has the ability to be tuned to the HF range and used for its intended purpose - drying clothes...
* Combination of E-emitter and H-emitter.
Using a capacitive emitter outside the balcony (loggia), this construct can be combined with a magnetic antenna, as Alexander Vasilievich Grachev did ( UA6AGW), combining a magnetic frame with a half-wave shortened dipole. It is quite well known in the amateur radio world and is practiced by the author at his summer cottage. The electrical circuit of the antenna is quite simple and is shown in Fig. 47.
Capacitor C1 is adjustable within the range, and the required range can be set by connecting an additional capacitor to the contacts of K1. The matching of the antenna and feeder is subject to the same laws, i.e. communication loop at the zero voltage point, see Fig.30. Fig.31. This modification has the advantages that its installation can be made truly invisible to prying eyes and, moreover, it will work quite effectively in two or three amateur frequency bands.
A shortened dipole in the form of a spiral on a plastic base fit perfectly inside a loggia with wooden frames, but the owner of this antenna did not dare to place it outside the loggia. I don’t think that the owner of this apartment is delighted with this beauty.
Balcony antenna - dipole 14/21/28 MHz fits well outside the balcony. It is inconspicuous and does not attract attention to itself. You can build such an antenna by following the link
Afterword:
In conclusion of the material about HF balcony antennas, I would like to say to those who do not have and do not have access to the roof of their house - it is better to have a bad antenna than none at all. Everyone can work with a three-element Uda-Yagi antenna or a double square, but not everyone can choose the best option, develop and build a balcony antenna, and work on the air at the same level. Don’t change your hobby; it will always be useful to you to relax your soul and train your brain, during your vacation or in retirement. Communication over the air gives much more benefits than communication over the Internet. Men who do not have a hobby, who do not have a goal in life, live less.
73! Sushko S.A. (ex. UA9LBG)