How to convert a delta antenna to a digital one. About vibrator antennas

Useful tips

V. DAVYDOV (UW9WR), UfaThe disadvantage of the previously described electronic switches antennas is a significant attenuation in the receiving mode, reaching 45-50% (especially in the ranges of 21 and 28 MHz). Switch, scheme which is shown in the figure, provides an attenuation of no more than 10%. When manufacturing the switch, it is necessary to isolate the body of the output capacitor of the P-circuit (in the diagram - C4) from the chassis with a fluoroplastic or polystyrene gasket 5 mm thick. The antenna is connected to the Gn1 socket, the receiver input - to nest GN2.RADIO No. 7, 1975 p.15...

For the scheme "MINIATURE DIRECTIONAL ANTENNA FOR 144-146 MHz RANGE"

For the "ALL METAL DELTA ANTENNA" circuit

For the diagram "Double square antenna design"

For the "DUAL BAND UHF ANTENNA" circuit

For the "144 MHz VERTICAL ANTENNA" circuit

For the circuit "Antenna amplifier for a radio transmitter"

RF power amplifiersAntenna amplifier for radio transmitter Scheme antenna amplifier does not require any special explanation. The amplifier is mounted in a casing made of galvanized metal 1 mm thick, dimensions 120x60x30 mm. An aluminum plate of the same size, 10 mm thick, is screwed to the bottom of the body. Design printed circuit board the same as in [Z]. The drawing is not shown here, because The board configuration is highly dependent on the type of parts used. It is only important that all connections are as short as possible and reliable thermal contact of transistor VT1 with the heatsink plate is ensured. Details. Relay K1, K2 - RES-15(002). Connectors XW1, XW2 - SR-50-73F. Resistors - MLT. Capacitors - CT, KM; S16.S17-KPK-MP. Inductors: LI - inductor DPMZ-3 10 μH; L2 - 14 turns on a resistor MLT-0.5 150 Ohm PEV-2 0.35 turn to turn. L9, L11 -DPM1-0.1 56 µH. The remaining coils are frameless, wound with PEV-2 0.8 wire on a 5.5 mm mandrel. The number of turns depending on the range is given in the table. The same table shows the capacitances SZ...S15 (pF). RangeL3L4L516L718L1C3С4С5С7С8С9С10С11С12С14С1527. ..29 MHz346999856047011068470200...27027027011Q682750 Hz23577763302706839270120...150150150683915The configuration of the antenna unit is contained in the configuration using C16, C17 of the input circuit of the antenna amplifier for the maximum sensitivity of the receiver radio stations. By connecting an HF generator to input A5...

Once upon a time good TV antenna was in short supply, purchased ones did not differ in quality and durability, to put it mildly. Make an antenna for a “box” or “coffin” (old tube TV) with your own hands was considered an indicator of skill. Interest in homemade antennas continues to this day. There is nothing strange here: the conditions for TV reception have changed dramatically, and manufacturers, believing that there is and will not be anything significantly new in the theory of antennas, most often adapt electronics to long-known designs, without thinking about the fact that The main thing for any antenna is its interaction with the signal on the air.

What has changed on air?

Firstly, almost the entire volume of TV broadcasting is currently carried out in the UHF range. First of all, for economic reasons, it greatly simplifies and reduces the cost of the antenna-feeder system of transmitting stations, and, more importantly, the need for its regular maintenance by highly qualified specialists engaged in hard, harmful and dangerous work.

Second - TV transmitters now cover almost all more or less populated areas with their signal, and a developed communication network ensures the delivery of programs to the most remote corners. There, broadcasting in the habitable zone is provided by low-power, unattended transmitters.

Third, the conditions for the propagation of radio waves in cities have changed. On the UHF, industrial interference penetrates weakly, but reinforced concrete high-rise buildings are good mirrors for them, repeatedly reflecting the signal until it is completely attenuated in the zone, it would seem confident reception.

Fourth - There are a lot of TV programs on air now, dozens and hundreds. How diverse and meaningful this set is is another question, but counting on receiving 1-2-3 channels is now pointless.

Finally, developed digital broadcasting . The DVB T2 signal is a special thing. Where it still exceeds the noise even just a little, by 1.5-2 dB, the reception is excellent, as if nothing had happened. But a little further or to the side - no, it’s cut off. Digital is almost insensitive to interference, but if there is a mismatch with the cable or phase distortion anywhere in the path, from the camera to the tuner, the picture can crumble into squares even with a strong clean signal.

Antenna requirements

In accordance with the new reception conditions, the basic requirements for TV antennas have also changed:

Its parameters such as the directivity coefficient (DAC) and the protective action coefficient (PAC) are now of no decisive importance: modern air is very dirty, and along the tiny side lobe of the directional pattern (DP), at least some interference will get through, and You need to fight it using electronic means.
In return, the antenna's own gain (GA) becomes especially important. An antenna that catches the air well, rather than looking at it through a small hole, will provide a power reserve received signal, allowing the electronics to clear it of noise and interference.
A modern television antenna, with rare exceptions, must be a range antenna, i.e. her electrical parameters should be preserved in a natural way, at the level of theory, and not squeezed into an acceptable framework through engineering tricks.
The TV antenna must be coordinated with the cable over its entire operating frequency range without additional devices coordination and balancing (USS).
The amplitude-frequency response of the antenna (AFC) should be as smooth as possible. Sharp surges and dips are certainly accompanied by phase distortions.

The last 3 points are due to admission requirements digital signals. Customized, i.e. Working theoretically at the same frequency, antennas can be “stretched” in frequency, for example. antennas of the “wave channel” type on the UHF with an acceptable signal-to-noise ratio capture channels 21-40. But their coordination with the feeder requires the use of USSs, which either strongly absorb the signal (ferrite) or spoil the phase response at the edges of the range (tuned). And such an antenna, which works perfectly on analogue, will receive “digital” poorly.

In this regard, from all the great variety of antennas, this article will consider TV antennas, available for self-production, of the following types:

Frequency independent (all-wave)– does not have high parameters, but is very simple and cheap, it can be done in literally an hour. Outside the city, where the airwaves are cleaner, it will be able to receive digital or a fairly powerful analogue not a short distance from the television center.
Range log-periodic. Figuratively speaking, it can be likened to a fishing trawl, which sorts the prey during fishing. It is also quite simple, fits perfectly with the feeder throughout its entire range, and does not change its parameters at all. The technical parameters are average, so it is more suitable for a summer residence, and in the city as a room.
Several modifications of the zigzag antenna, or Z-antennas. In the MV range, this is a very solid design that requires considerable skill and time. But on the UHF, due to the principle of geometric similarity (see below), it is so simplified and shrunk that it can well be used as a highly efficient indoor antenna under almost any reception conditions.

Note: The Z-antenna, to use the previous analogy, is a frequent flyer that scoops up everything in the water. As the air became littered, it fell out of use, but with the development of digital TV, it was once again on the high horse - throughout its entire range, it is just as perfectly coordinated and keeps the parameters as a “speech therapist.”

Precise matching and balancing of almost all antennas described below is achieved by laying the cable through the so-called. zero potential point. They are presented to her special requirements, which will be discussed in more detail below.

About vibrator antennas

In the frequency band of one analog channel, up to several dozen digital ones can be transmitted. And, as already said, the digital works with an insignificant signal-to-noise ratio. Therefore, in places very remote from the television center, where the signal of one or two channels barely reaches, the good old wave channel (AVK, wave channel antenna), from the class of vibrator antennas, can be used for receiving digital TV, so at the end we will devote a few lines and to her.

About satellite reception

Do it yourself satellite dish there's no point. You still need to buy a head and a tuner, and behind the external simplicity of the mirror lies a parabolic surface of oblique incidence, which not every industrial enterprise can produce with the required accuracy. The only thing homemade people can do is set up a satellite dish, about that.

About antenna parameters

Accurate determination of the antenna parameters mentioned above requires knowledge of higher mathematics and electrodynamics, but it is necessary to understand their meaning when starting to manufacture an antenna. Therefore, we will give somewhat rough, but still clarifying definitions (see figure on the right):

KU is the ratio of the signal power received by the antenna on the main (main) lobe of its DP to its same power received in the same place and at the same frequency by an omnidirectional, circular, DP antenna.
KND is the ratio of the solid angle of the entire sphere to the solid angle of the opening of the main lobe of the DN, assuming that its cross section is a circle. If the main petal has different sizes in different planes, you need to compare the area of the sphere and the cross-sectional area of the main lobe.
SCR is the ratio of the signal power received at the main lobe to the sum of the interference powers at the same frequency received by all secondary (back and side) lobes.

Notes:

If the antenna is a band antenna, the powers are calculated at the frequency of the useful signal.

Since there are no completely omnidirectional antennas, a half-wave linear dipole oriented in the direction of the electric field vector (according to its polarization) is taken as such. Its QU is considered equal to 1. TV programs are transmitted with horizontal polarization.

It should be remembered that CG and KNI are not necessarily interrelated. There are antennas (for example, “spy” - single-wire traveling wave antenna, ABC) with high directivity, but single or lower gain. These look into the distance as if through a diopter sight. On the other hand, there are antennas, e.g. Z-antenna, which combines low directivity with significant gain.

About the intricacies of manufacturing

All antenna elements through which useful signal currents flow (specifically, in the descriptions of individual antennas) must be connected to each other by soldering or welding. In any prefabricated area outdoors electrical contact will soon be disrupted, and the parameters of the antenna will deteriorate sharply, until it is completely unusable.

This is especially true for points of zero potential. In them, as experts say, there is a voltage node and a current antinode, i.e. his highest value. Current at zero voltage? Nothing surprising. Electrodynamics has moved away from Ohm's law by DC as far as a T-50 from a kite.

Places with zero potential points for digital antennas are best made bent from solid metal. A small “creeping” current in welding when receiving the analogue in the picture will most likely not affect it. But, if a digital signal is received at the noise level, then the tuner may not see the signal due to the “creep”. Which, with pure current at the antinode, would give stable reception.

About cable soldering

The braid (and often the central core) of modern coaxial cables is made not of copper, but of corrosion-resistant and inexpensive alloys. They solder poorly and if you heat them for a long time, you can burn out the cable. Therefore, you need to solder the cables with a 40-W soldering iron, low-melting solder and with flux paste instead of rosin or alcohol rosin. There is no need to spare the paste; the solder immediately spreads along the veins of the braid only under a layer of boiling flux.

Types of antennas

All-wave

An all-wave (more precisely, frequency-independent, FNA) antenna is shown in Fig. It consists of two triangular metal plates, two wooden slats, and a lot of enameled copper wires. The diameter of the wire does not matter, and the distance between the ends of the wires on the slats is 20-30 mm. The gap between the plates to which the other ends of the wires are soldered is 10 mm.

Note: Instead of two metal plates, it is better to take a square of one-sided foil fiberglass with triangles cut out of copper.

The width of the antenna is equal to its height, the opening angle of the blades is 90 degrees. The cable routing diagram is shown there in Fig. The point marked in yellow is the point of quasi-zero potential. There is no need to solder the cable braid to the fabric in it; just tie it tightly, and the capacity between the braid and the fabric will be enough for matching.

The CHNA, stretched in a window 1.5 m wide, receives all meter and DCM channels from almost all directions, except for a dip of about 15 degrees in the plane of the canvas. This is its advantage in places where it is possible to receive signals from different television centers; it does not need to be rotated. Disadvantages - single gain and zero gain, therefore, in the interference zone and outside the zone of reliable reception, the CNA is not suitable.

Note : There are other types of CNA, for example. in the form of a two-turn logarithmic spiral. It is more compact than the CNA made of triangular sheets in the same frequency range, therefore it is sometimes used in technology. But in everyday life this does not give any advantages; it is more difficult to make a spiral CHNA, with coaxial cable it is more difficult to agree on, so we do not consider it.

Based on the CHNA, the once very popular fan vibrator (horns, flyer, slingshot) was created, see fig. Its directivity factor and coefficient of performance are something around 1.4 with a fairly smooth frequency response and linear phase response, so it would be suitable for digital use even now. But - it works only on HF (channels 1-12), and digital broadcasting is on UHF. However, in the countryside, with an elevation of 10-12 m, it may be suitable for receiving an analogue. Mast 2 can be made of any material, but fastening strips 1 are made of a good non-wetting dielectric: fiberglass or fluoroplastic with a thickness of at least 10 mm.

Beer all-wave

The all-wave antenna made from beer cans is clearly not the fruit of the hangover hallucinations of a drunken radio amateur. It's really very good antenna for all cases of reception, you just need to do it correctly. And it’s extremely simple.

Its design is based on the following phenomenon: if you increase the diameter of the arms of a conventional linear vibrator, then its operating frequency band expands, but other parameters remain unchanged. In long-distance radio communications, since the 20s, the so-called Nadenenko's dipole based on this principle. And beer cans are just the right size to serve as the arms of a vibrator on the UHF. In essence, the CHNA is a dipole, the arms of which expand indefinitely to infinity.

The simplest beer vibrator made of two cans is suitable for indoor analogue reception in the city, even without coordination with the cable, if its length is no more than 2 m, on the left in Fig. And if you assemble a vertical in-phase array from beer dipoles with a step of half a wave (on the right in the figure), match it and balance it using an amplifier from a Polish antenna (we will talk about it later), then thanks to the vertical compression of the main lobe of the pattern, such an antenna will give good CU.

The gain of the “tavern” can be further increased by adding a CPD at the same time, if a mesh screen is placed behind it at a distance equal to half the grid pitch. The beer grill is mounted on a dielectric mast; The mechanical connections between the screen and the mast are also dielectric. The rest is clear from the following. rice.

Note: the optimal number of lattice floors is 3-4. With 2, the gain in gain will be small, and more is difficult to coordinate with the cable.

Video: making simplest antenna from beer cans

"Speech therapist"

A log-periodic antenna (LPA) is a collecting line to which halves of linear dipoles (i.e., pieces of conductor a quarter of the operating wavelength) are alternately connected, the length and distance between which vary in geometric progression with an index less than 1, in the center in Fig. The line can be either configured (with a short circuit at the end opposite to the cable connection) or free. An LPA on a free (unconfigured) line is preferable for digital reception: it comes out longer, but its frequency response and phase response are smooth, and the matching with the cable does not depend on frequency, so we will focus on it.

The LPA can be manufactured for any predetermined frequency range, up to 1-2 GHz. When it changes operating frequency its active region of 1-5 dipoles moves back and forth across the canvas. Therefore, the closer the progression indicator is to 1, and accordingly the smaller the antenna opening angle, the greater the gain it will give, but at the same time its length increases. At UHF, you can achieve 26 dB from an outdoor LPA, and 12 dB from a room LPA.

LPA can be said to be an ideal digital antenna based on its totality of qualities, so let’s look at its calculation in a little more detail. The main thing you need to know is that an increase in the progression indicator (tau in the figure) gives an increase in gain, and a decrease in the LPA opening angle (alpha) increases the directivity. A screen is not needed for the LPA; it has almost no effect on its parameters.

Calculation of digital LPA has the following features:

They start it, for the sake of frequency reserve, with the second longest vibrator.
Then, taking the reciprocal of the progression index, the longest dipole is calculated.
After the shortest dipole based on the given frequency range, another one is added.

Let's explain with an example. Let's say our digital programs lie in the range of 21-31 TVK, i.e. at 470-558 MHz in frequency; wavelengths, respectively, are 638-537 mm. Let’s also assume that we need to receive a weak noisy signal far from the station, so we take the maximum (0.9) progression rate and the minimum (30 degrees) opening angle. For the calculation, you will need half the opening angle, i.e. 15 degrees in our case. The opening can be further reduced, but the length of the antenna will increase exorbitantly, in cotangent terms.

We consider B2 in Fig: 638/2 = 319 mm, and the arms of the dipole will be 160 mm each, you can round up to 1 mm. The calculation will need to be carried out until you get Bn = 537/2 = 269 mm, and then calculate another dipole.

Now we consider A2 as B2/tg15 = 319/0.26795 = 1190 mm. Then, through the progression indicator, A1 and B1: A1 = A2/0.9 = 1322 mm; B1 = 319/0.9 = 354.5 = 355 mm. Next, sequentially, starting with B2 and A2, we multiply by the indicator until we reach 269 mm:

B3 = B2*0.9 = 287 mm; A3 = A2*0.9 = 1071 mm.
B4 = 258 mm; A4 = 964 mm.

Stop, we are already less than 269 mm. We check whether we can meet the gain requirements, although it is clear that we can’t: to get 12 dB or more, the distances between the dipoles should not exceed 0.1-0.12 wavelengths. IN in this case for B1 we have A1-A2 = 1322 – 1190 = 132 mm, which is 132/638 = 0.21 wavelengths of B1. We need to “pull up” the indicator to 1, to 0.93-0.97, so we try different ones until the first difference A1-A2 is reduced by half or more. For a maximum of 26 dB, you need a distance between dipoles of 0.03-0.05 wavelengths, but not less than 2 dipole diameters, 3-10 mm at UHF.

Note: cut off the rest of the line behind the shortest dipole; it is needed only for calculations. Therefore, the actual length of the finished antenna will be only about 400 mm. If our LPA is external, this is very good: we can reduce the opening, obtaining greater directionality and protection from interference.

Video: antenna for digital TV DVB T2

About the line and the mast

The diameter of the tubes of the LPA line on the UHF is 8-15 mm; the distance between their axes is 3-4 diameters. Let’s also take into account that thin “lace” cables give such attenuation per meter on the UHF that all antenna-amplification tricks will come to naught. Coax for outdoor antenna you need to take a good one, with a shell diameter of 6-8 mm. That is, the tubes for the line must be thin-walled, seamless. You cannot tie the cable to the line from the outside; the quality of the LPA will drop sharply.

It is necessary, of course, to attach the outer propulsion boat to the mast by the center of gravity, otherwise the small windage of the propulsion boat will turn into a huge and shaking one. But it is also impossible to connect a metal mast directly to the line: you need to provide a dielectric insert of at least 1.5 m in length. The quality of the dielectric does not play a big role here; oiled and painted wood will do.

About the Delta antenna

If the UHF LPA is consistent with the cable amplifier (see below, about Polish antennas), then the arms of a meter dipole, linear or fan-shaped, like a “slingshot”, can be attached to the line. Then we will get a universal VHF-UHF antenna of excellent quality. This solution is used in the popular Delta antenna, see fig.

Delta antenna

Zigzag on air

A Z-antenna with a reflector gives the same gain and gain as the LPA, but its main lobe is more than twice as wide horizontally. This may be important in rural areas when there is TV reception from different directions. A decimeter Z-antenna It has small dimensions, which is essential for indoor reception. But its operating range is theoretically not unlimited; frequency overlap while maintaining parameters acceptable for the digital range is up to 2.7.

The design of the MV Z-antenna is shown in Fig; The cable route is highlighted in red. There in the lower left there is a more compact ring version, colloquially known as a “spider”. It clearly shows that the Z-antenna was born as a combination of a CNA with a range vibrator; There is also something of a rhombic antenna in it, which does not fit into the theme. Yes, the “spider” ring does not have to be wooden, it can be a metal hoop. "Spider" receives 1-12 MV channels; The pattern without a reflector is almost circular.

The classic zigzag works either on 1-5 or 6-12 channels, but for its manufacture you only need wooden slats, enameled copper wire with d = 0.6-1.2 mm and several scraps of foil fiberglass, so we give the dimensions in fraction for 1-5/6-12 channels: A = 3400/950 mm, B, C = 1700/450 mm, b = 100/28 mm, B = 300/100 mm. At point E there is zero potential; here you need to solder the braid to a metallized support plate. Reflector dimensions, also 1-5/6-12: A = 620/175 mm, B = 300/130 mm, D = 3200/900 mm.

The range Z-antenna with a reflector gives a gain of 12 dB, tuned to one channel - 26 dB. To build a single-channel one based on a band zigzag, you need to take the side of the square of the canvas in the middle of its width at a quarter of the wavelength and recalculate all other dimensions proportionally.

Folk Zigzag

As you can see, the MV Z-antenna is a rather complex structure. But its principle shows itself in all its glory on the UHF. The UHF Z-antenna with capacitive inserts, combining the advantages of the “classics” and the “spider”, is so easy to make that even in the USSR it earned the title of folk antenna, see fig.

Material – copper tube or aluminum sheet with a thickness of 6 mm. The side squares are solid metal or covered with mesh, or covered with a tin. In the last two cases, they need to be soldered along the circuit. The coax cannot be bent sharply, so we guide it so that it reaches the side corner, and then does not go beyond the capacitive insert (side square). At point A (zero potential point), we electrically connect the cable braid to the fabric.

Note: aluminum cannot be soldered with conventional solders and fluxes, so aluminum “folk” is suitable for outdoor installation only after sealing electrical connections silicone, because everything in it is screwed.

Video: example of a double triangle antenna

Wave channel

The wave channel antenna (AWC), or Udo-Yagi antenna, available for self-production, is capable of giving the highest gain, directivity factor and efficiency factor. But it can only receive digital signals on UHF on 1 or 2-3 adjacent channels, because belongs to the class of highly tuned antennas. Its parameters deteriorate sharply beyond the tuning frequency. AVK is recommended to be used with very bad conditions reception, and make a separate one for each TVC. Fortunately, this is not very difficult - AVK is simple and cheap.

The basis of the work of the AVK is “raking” electromagnetic field(EMF) signal to the active vibrator. Externally small, lightweight, with minimal windage, the AVK can have an effective aperture of dozens of wavelengths of the operating frequency. Shortened and therefore having a capacitive impedance ( impedance) directors (directors) direct the EMF to the active vibrator, and the reflector (reflector), elongated, with inductive impedance, throws back to it what has slipped past. Only 1 reflector is needed in an AVK, but there can be from 1 to 20 or more directors. The more there are, the higher the gain of the AVC, but the narrower its frequency band.

From interaction with the reflector and directors, the wave impedance of the active (from which the signal is taken) vibrator drops the more, the closer the antenna is tuned to the maximum gain, and coordination with the cable is lost. Therefore, the active dipole AVK is made into a loop, its initial wave impedance is not 73 Ohms, like a linear one, but 300 Ohms. At the cost of reducing it to 75 Ohms, an AVK with three directors (five-element, see the figure on the right) can be adjusted to almost a maximum gain of 26 dB. A characteristic pattern for AVK in the horizontal plane is shown in Fig. at the beginning of the article.

AVK elements are connected to the boom at points of zero potential, so the mast and boom can be anything. Propylene pipes work very well.

Calculation and adjustment of AVK for analog and digital are somewhat different. For analogue, the wave channel must be calculated at the carrier frequency of the image Fi, and for digital – at the middle of the TVC spectrum Fc. Why this is so - unfortunately, there is no room to explain here. For the 21st TVC Fi = 471.25 MHz; Fс = 474 MHz. UHF TVKs are located close to each other at 8 MHz, so their tuning frequencies for AVCs are calculated simply: Fn = Fi/Fс(21 TVKs) + 8(N – 21), where N is the number desired channel. Eg. for 39 TVCs Fi = 615.25 MHz, and Fc = 610 MHz.

In order not to write down a lot of numbers, it is convenient to express the dimensions of the AVK in fractions of the operating wavelength (it is calculated as A = 300/F, MHz). The wavelength is usually denoted by the small Greek letter lambda, but since there is no default Greek alphabet on the Internet, we will conventionally denote it by the large Russian L.

The dimensions of the digitally optimized AVK, according to the figure, are as follows:

P = 0.52L.
B = 0.49L.
D1 = 0.46L.
D2 = 0.44L.
D3 = 0.43l.
a = 0.18L.
b = 0.12L.
c = d = 0.1L.

If you don’t need a lot of gain, but reducing the size of the AVK is more important, then D2 and D3 can be removed. All vibrators are made of a tube or rod with a diameter of 30-40 mm for 1-5 TVKs, 16-20 mm for 6-12 TVKs and 10-12 mm for UHF.

AVK requires precise coordination with the cable. It is the careless implementation of the matching and balancing device (CMD) that explains most of the failures of amateurs. The simplest USS for AVK is a U-loop made from the same coaxial cable. Its design is clear from Fig. on right. The distance between signal terminals 1-1 is 140 mm for 1-5 TVKs, 90 mm for 6-12 TVKs and 60 mm for UHF.

Theoretically, the length of the knee l should be half the length of the working wave, and this is what is indicated in most publications on the Internet. But the EMF in the U-loop is concentrated inside the cable filled with insulation, so it is necessary (for numbers - especially mandatory) to take into account its shortening factor. For 75-ohm coaxials it ranges from 1.41-1.51, i.e. l you need to take from 0.355 to 0.330 wavelengths, and take exactly so that the AVK is an AVK, and not a set of pieces of iron. The exact value of the shortening factor is always in the cable certificate.

IN Lately domestic industry has begun to produce reconfigurable digital digital videoconferencing systems, see fig. The idea, I must say, is excellent: by moving the elements along the boom, you can fine-tune the antenna to local conditions reception. It is better, of course, for a specialist to do this - the element-by-element adjustment of the AVC is interdependent, and an amateur will certainly get confused.

About “Poles” and amplifiers

For many users Polish antennas, who previously took the analogue decently, refuse to take the digital one - it breaks, or even disappears completely. The reason, I beg your pardon, is the obscene commercial approach to electrodynamics. Sometimes I feel ashamed for my colleagues who have concocted such a “miracle”: the frequency response and phase response resemble either a psoriasis hedgehog or a horse’s comb with broken teeth.

The only good thing about the Poles is their antenna amplifiers. Actually, they do not allow these products to die ingloriously. Belt amplifiers are, firstly, low-noise, broadband. And, more importantly, with a high-impedance input. This allows, at the same strength of the EMF signal on the air, to supply several times more power to the tuner input, which makes it possible for the electronics to “rip out” a number from very ugly noise. In addition, due to the high input impedance, the Polish amplifier is an ideal USS for any antennas: whatever you attach to the input, the output is exactly 75 Ohms without reflection or creep.

However, with a very poor signal, outside the zone of reliable reception, the Polish amplifier no longer works. Power is supplied to it via a cable, and power decoupling takes away 2-3 dB of the signal-to-noise ratio, which may not be enough for the digital signal to go right into the outback. Needed here good amplifier TV signal with separate power supply. It will most likely be located near the tuner, and the control system for the antenna, if required, will have to be made separately.

The circuit of such an amplifier, which has shown almost 100% repeatability even when implemented by novice radio amateurs, is shown in Fig. Gain adjustment – potentiometer P1. The decoupling chokes L3 and L4 are standard purchased ones. Coils L1 and L2 are made according to the dimensions in the wiring diagram on the right. They are part of signal bandpass filters, so small deviations in their inductance are not critical.

Among radio amateurs, the loop antenna with a perimeter of 84M is very popular. It is mainly tuned to the 80M band and with a little compromise it can be used on all amateur radio bands. This compromise can be accepted if we are working with a tube power amplifier, but if we have a more modern transceiver, things will no longer work there. We need a matching device that sets the SWR on each band, corresponding normal operation transceiver. HA5AG told me about a simple matching device and sent me a short description of it (see picture). The device is designed for loop antennas of almost any shape (delta, square, trapezoid, etc.)

Matching device HA5AG
To enlarge, click on the diagram

Short description:
The author tested the matching device on an antenna, the shape of which is almost square, installed at a height of 13M in horizontal position. The input impedance of this QUAD antenna on the 80M band is 85 Ohms, and on harmonics it is 150 - 180 Ohms. The characteristic impedance of the supply cable is 50 Ohm. The task was to match this cable with the input impedance of the antenna 85 - 180 Ohm. For matching, transformer Tr1 and coil L1 were used.

In the 80M range, using relay P1, we short-circuit coil n3. In the cable circuit, coil n2 remains switched on, which, with its inductance, sets the input impedance of the antenna to 50 Ohms. On other bands P1 is disabled. The cable circuit includes coils n2+n3 (6 turns) and the antenna matches 180 Ohm to 50 Ohm.

L1 – extension coil. It will find its application on the 30M band. The fact is that the third harmonic of the 80M band does not coincide with the permitted frequency range of the 30M band. (3 x 3600KHz = 10800KHz). Transformer T1 matches the antenna at 10500 KHz, but this is not enough, you also need to turn on the L1 coil and with this connection the antenna will already resonate at a frequency of 10100 KHz. To do this, using K1, we turn on relay P2, which at the same time opens its normally closed contacts. L1 can also serve in the 80M range, when we want to work in the telegraph section. On the 80M band, the antenna resonance band is about 120 KHz. To shift the resonance frequency, you can turn on L1. The included coil L1 significantly reduces the SWR at the 24 MHz frequency, as well as at the 10 M range.

The matching device performs three functions:
1. Provides symmetrical power to the antenna, since the antenna web is isolated at HF from the ground through transformer coils Tr1 and L1.

2. Matches the impedance described higher way.

3. Using coils n2 and n3 of transformer Tr1, the antenna resonance is placed in the corresponding, permitted frequency bands by range. A little more about this: If the antenna is initially tuned to a frequency of 3600 kHz (without turning on the matching device), then on the 40M ohm band it will resonate at 7200 KHz, on the 20M ohm band at 14400 KHz, and on the 10M ohm band it will resonate at 28800 KHz. This means that the antenna needs to be extended in each range, and at the same time higher frequency range, the more extension it requires. Just such a coincidence is used to match the antenna. Transformer coils n2 and n3, T1 with a certain inductance, the more the antenna extends, the higher the frequency of the range. In this way, on the 40M band the coils are extended to a very small extent, but on the 10M band they are extended to a significant extent. A correctly tuned antenna is placed in resonance by the matching device on each band in the region of the first 100 kHz frequency.
The positions of switches K1 and K2 by range are indicated in the table:

If the input impedance of the antenna on the 80M band is set not within 80 - 90 Ohms but within 100 - 120 Ohms, then the number of turns of coil n2 of transformer T1 must be increased by 3, and if the resistance is even higher, then by 4. The parameters of the remaining coils remain unchanged .

Photo: HA5AG matching device
Click on the photo to enlarge

73! de HA5AG

Translation: UT1DA
source - (http://ut1da.narod.ru)
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Delta antennas have long been used by radio amateurs. It is convenient to place it in any way and vertically if there is sufficient height and when there is no space on the roof, but it happens that it is not possible to place the antenna even at an angle of 45 degrees. Therefore it is proposed different variants implementation of the "Delta" antenna and its placement and fastening.

Figure 1 shows the classic placement of the antenna with a sufficient suspension height.

You cannot position the antenna at an angle to the ground; you can position it horizontally relative to the surface of the earth (Fig.2). To match the input impedance of the antenna and the supply feeder, a transformer is used, which is made of RK 75 cable, 13.94 m long.

If you have enough space to position the Delta at an angle of 45 degrees and get the maximum benefit from this antenna, then Fig. 3 shows the antenna placement diagram indicating the dimensions. Coordinating the antenna with the RK 75 power cable does not cause any particular difficulties. Setting up the antenna is reduced by setting it to the middle frequency of the range by changing the perimeter of the “Delta” frame, and by adjusting the SWR by changing the angle of inclination relative to the ground.

If the height of the suspension is insufficient, an option is proposed with the location of the "Delta" antenna in the horizontal and vertical planes in Fig. 4, while the radiation of the antenna will be directed towards the open arms of the antenna.

If there is a good height difference, if you live in a 9 or 12 storey building, in the yard or nearby there are 4 or 5 storey buildings, you can make a directional antenna from 2 Delta antennas, its diagram is shown in Fig. 5. This antenna has all the properties of a directional antenna and has a gain in the radiation direction of up to 8 dB. The antenna is structurally located on guy wires broken by insulators. Powered by coaxial cable RK 75.

If there are nearby buildings of the same height, you can make an antenna from 3 Delta antennas (Fig. 6). The gain of this antenna up to 9.5 dB is also powered without any matching devices since the input impedance of this antenna is 75 ohms. The perimeter of "Delta" is R = 85.8 meters, Z = 83.3 meters, D = 80.8 meters. The distance between R and Z = 25 meters, and between D and Z = 25 meters. Structurally, the antenna is stretched with guys made of nylon cable with a diameter of 8 - 10 mm with turnbuckles.

The antenna shown in Fig.7 is one of a series of compromises: - low antenna height of 11 meters and the desire to use it in a wide frequency band. To match the input impedance of the antenna, an open line with a resistance of 300 ohms is used, so you can work through such an antenna only through a tuner, this will not only allow you to match correctly, but also makes it possible to use it in a multi-band version.

Tuning all antennas comes down to installing them in the middle of the range or in the area in which you want to work by changing the perimeter of the antenna frame. Minimum SWR by changing the angle of your antenna does not cause any particular difficulties. The guy wires for attaching the antenna should be broken with insulators, preferably made of radio porcelain, but other materials (textolite, fluoroplastic) are also suitable; it is important that the mechanical tensile strength of the insulator is sufficient.

Seal

The topic of this article is inspired by the Delta N311-01A antenna (active with amplifier) that came in for repair. The design of the antenna is such that if the vibrators for receiving the meter range are removed (which will significantly reduce its dimensions), then it can only be used as an antenna for the decimeter range.

Delta N311-01A is a version of the Delta 311-01 antenna without an amplifier. An all-wave television antenna with a broadband amplifier is used in conditions of unsatisfactory reception in the VHF and UHF ranges. Receives analog and digital television broadcasting, in the frequency range 48.5-890 MHz and consisting of decimeter antenna and a meter range vibrator. The antenna has uniform gain over the entire frequency range.

The design of the antenna is quite simple and therefore it is quite accessible for repetition. The main elements that make up the antenna are: decimeter part; vibrator MV; matching board and signal amplifier. Complex elements include: a matching board and an amplifier, but you can do without them by installing an SWA type amplifier.

The decimeter part is log periodic antenna with 20 vibrators.

A log-periodic antenna (LPA) consists of two pipes located one above the other, to which the vibrator arms are attached alternately.

The cable is connected to the LPA without a special matching device as follows. A cable with a characteristic impedance of 75 Ohms is inserted into the down tube at one end and exits at the other. The cable braid is soldered to the end of the lower pipe, and the central core is soldered to the end of the upper pipe.

Depending on the wavelength of the received signal, several vibrators are excited in the antenna structure, the dimensions of which are closest to half the wavelength of the signal. At a given signal wavelength, only one trio of vibrators is excited, while the rest are detuned and do not affect the operation of the antenna. The antenna gain drops somewhat, but the bandwidth is much wider.

It is useful to know that the smoother the surface of the conductors from which the antenna is made, the higher its quality indicators (higher the quality factor).

The MV antenna is designed extremely simply - these are two vibrators 110 cm long, attached to protective housing amplifier

The matching board and amplifier are hidden in a sealed housing.

The balancing device is used to match meter and decimeter range antennas with an amplifier.

Dimensions

For those who want to make a copy, I provide the dimensions UHF antennas and MV.

All antenna dimensions are given in millimeters. The diameter of the tubes is 12 mm, the diameter of the vibrators is 4 mm, the gap between the tubes is 6 mm. At the beginning of the antenna, the tubes are secured with plastic; at the point of attachment to the mast, the tubes are soldered.

The antenna gain can be increased somewhat further by adding a reflector behind the antenna mounting device.