Antenna extended double zeppelin sq. Levy All-Wave Antenna
Radio amateurs are constantly looking for antennas that are ideal for specific conditions. Of course, knowledge of theory in this process is necessary, but no theory replaces personal experience. In other words, there is nothing to do but try different antennas again and again, weighing their strengths and weaknesses, and then drawing conclusions. That's what we'll do today. This time we will experiment with several antennas made from a two-wire line.
A little theory
A two-wire line is two wires running in parallel. Like any line, a two-wire line is characterized by a number of properties, the most important of which are (1) characteristic impedance, (2) shortening factor and (3) losses per unit length for a given frequency. Of course, there are other properties, such as linear capacity, as well as cost, weight and others.
Unlike HF, the RG58 cable is not suitable for VHF to power antennas. RG213 or even lower loss cable should be used instead. When using 10 meters of RG58, the signal attenuation at 144 MHz is 1.82 dB, and at 450 MHz it is 3.65 dB. For RG213 it is 0.86 dB and 1.73 dB, respectively. However, if the cable is short, just a couple of meters, then RG58 will do.
On HF, two-wire lines have small losses. With a line length of about 10 meters, you don’t have to worry about losses in it.
Finally, let me remind you that two-wire lines are sensitive to precipitation. Also, the two-wire line must be located at least ten distances between its wires from the ground and metal objects. Unlike a two-wire line, coaxial cable can be laid in any way you like - along walls, along the ground, or even underground.
How to measure the characteristic impedance and gain of a line?
Real ham radio two-wire lines are available both from specialty online stores and on eBay for searches like "450 Ohm Ladder Line" and "MFJ-18H250." But prices for such lines fluctuate around $1.5-3 per meter, which is a little expensive. Therefore, two-wire lines are often made independently from available wires and spacers, or they are used as lines intended for slightly different purposes. As examples of available two-wire lines, we can cite the example of wires P-274M (“vole”, about $0.17 per meter) and TRP 2x0.4 (“telephone noodles,” about $0.06 per meter). You can also find many offers on eBay for the query “speaker wire” (about $0.75 per meter, depending on the thickness of the wire).
The disadvantage of such lines is the unknown wave impedance and gain. The question is, how can they be measured?
Characteristic impedance can be measured in at least two ways. The first way is this. Take a few meters of line and an RLC meter. The device is applied to one end of the line and the capacitance C is measured. Then the wires of the line are connected at the other end and the inductance L is measured. The characteristic impedance is determined by the formula Z = sqrt(L/C) .
Fun fact! The previously mentioned linear capacitance is no more than C per unit line length. For example, one meter of RG58 coaxial cable has a capacitance of about 100 pF. Previously, we used this fact in the manufacture of ladders for the dipole.
For the second method we need an oscilloscope, a signal generator and a multimeter. A T-shaped BNC connector is connected to the oscilloscope. A generator is connected to one of the connector inputs, and a section of the measured line is connected to the second. A potentiometer is connected at the second end of the line. A square wave is generated by the signal generator, and the potentiometer knob is set to a position in which the oscilloscope displays the signal without any distortion. When such a position is found, it means that there are no reflections in the line. This is only possible if the potentiometer has a resistance equal to the characteristic impedance of the line. All that remains is to take a multimeter and measure the resulting resistance of the potentiometer. The process is clearly shown in video, filmed by Alan Wolke, W2AEW.
It is worth noting, however, that both methods are far from ideal. Practice shows that the measurement error is at least 5%.
Using the same technique with an oscilloscope, you can determine the line gain. If we disconnect the potentiometer, the signal will be completely reflected from the end of the line. Using an oscilloscope, we can measure the time it takes for a signal to travel along the line twice (round trip time). The length of the line is known, which allows the speed of signal propagation to be measured. Dividing this speed by the speed of light, we get KU.
If you do not have an oscilloscope, then the gain can be measured using an SWR meter and an equivalent load of 50 Ohms. Take a line segment 5 meters long. One end is connected to the SWR meter, the other end to the load equivalent. Next, in the range of 15-30 MHz, the minimum SWR is sought. As a result, we must find the frequency where the SWR is equal to 1 or very close to this value. At this frequency the line operates as a half-wave repeater, and the device sees a 50 Ohm load. The line length is known, and so is half the wavelength. The relation of the first to the second is KU.
A simple camping antenna made from a two-wire line
The theory described above is necessary to understand and construct the following antenna (illustration taken from The ARRL Antenna Book):
The antenna is an ordinary dipole, powered by a two-wire line. Among English-speaking radio amateurs, the antenna is known as a speaker wire antenna, since it is often made from the same speaker wire. It would seem that if you power a dipole with an input impedance of 50-73 Ohms using a two-wire line with a characteristic impedance of 100-600 Ohms, nothing good will come of it. But we found out above that a line of length λ/2 works as a half-wave repeater. All that remains is to find a suitable line, measure its CV, cut the line to the appropriate length, and we get a very light and compact dipole. Since the dipole is fed by a two-wire line, no common-mode currents arise in the line, which means that such an antenna does not need a balun. You can use a thin fishing rod as a mast, and not be afraid that it will break under the weight of the balun.
For the surroundings, it was decided to purchase 100 feet (30 meters) of the same speaker wire with a thickness of 20 AWG and make a dipole from it for a range of 20 meters. The measured COE of the line turned out to be ~0.75. This is very convenient, because the length of the λ/2 line will be 7.5 meters, and this is exactly the length of light and inexpensive rods.
To attach the rod, instead of guys, like last time, it was decided to use a chiseled pike:
A turned lance is a piece of aluminum profile, cut to half a meter and sharpened using a Dremel. The lance is driven into the ground approximately half its length. The rod is attached to it using Velcro straps, like those used to attach batteries to quadcopters. Contrary to intuition, this design is quite reliable, and in terms of weight and space taken up it significantly outperforms three screwdrivers with ropes.
To connect the antenna to the transceiver, it is convenient to use a crocodile and a banana plug with a diameter of 4 mm:
The plug plugs into the SO-239 connector. In terms of diameter, they fit each other just perfectly. The easiest way to grab a crocodile is to grab the ground terminal of the transceiver.
The exact dimensions of the antenna I got are as follows. Line length - 758 cm. Length of one arm - 490 cm. The SWR graph of the antenna varies slightly depending on the height of the antenna to the ground and the angle between the arms, but on average it looks like this:
If desired, by playing with the shape and height of the antenna, the SWR at 20 meters can be driven to unity. By a happy coincidence, the antenna turned out to be quite tolerably matched at 15 meters. The SWR in this range ranges from 1.7 to 2. Radio communications were carried out in each of the ranges. In terms of noise level and reports received, I did not notice any difference with the classic dipole.
Fun fact! Since the antenna is very compact when folded, it makes sense to always have it with you as a spare.
If you want to place the transceiver further away from the antenna and/or use a higher mast (for example, the optimal 10 meters for this band), the two-wire line can be connected through a 1:1 balun to a coaxial cable of any length.
Multi-band option
A multi-band version of such an antenna is also possible (illustration again borrowed from The ARRL Antenna Book):
This antenna is known as the double zeppelin, double zepp, center-fed zepp, and also, when using certain sizes and line types, as the G5RV antenna. The antenna has not very clear what the input impedance is. However, with a successful choice of line length and shoulders, it can be tuned to any HF band using a tuner.
Important! Contrary to what the legends say, the G5RV antenna does not magically tune itself to all bands. The antenna requires a tuner for all bands except 14 MHz.
This time the antenna was made from a “vole” with the following dimensions. The length of the line is 1340 cm. The length of one arm is 1305 cm. To match the antenna, it was decided to use the mAT-30 autotuner.
The antenna is perfectly tuned to any amateur radio range from 80 to 10 meters with an SWR of 1-1.2. Test radio communications were carried out in the ranges of 20, 40 and 80 meters, as the most popular. Good reports were received in all bands.
At the same time, the antenna turned out to be surprisingly quiet. The noise level was 1-2 points at 20 meters, 2-3 points at 40 meters and 5-6 points at 80 meters. In my QTH, I have never seen such a low noise level before, either with dipoles, or with verticals, or even with loop antennas (however, the latter is installed close to the house). For example, at the same 40 meters I typically observe 6-7 noise levels. What this is connected with is not very clear, but working on air is much more pleasant.
Conclusion
The described antenna options are inexpensive, easy to manufacture, weigh little and take up little space in a backpack. Unlike classic dipoles, they do not require a heavy balun. Therefore, in the field, using a fishing rod, such antennas can be installed on a b O higher altitude. Unlike verticals, they do not need counterweights, which always cause someone to trip. The antenna for the 20 meter range does not require a tuner and when installed on a 10 meter mast (you will need a balun, but at the bottom of the antenna) it is quite a decent antenna for long-distance communications. The multi-band antenna option requires a tuner. But it provides access to all HF bands at once and has a low noise level.
Overall, my experience with two-wire antennas has been extremely positive. I'm going to invest more time into learning about related antennas.
Addition: Continuing the topic, see the article
As a rule, a novice radio amateur starting to make an antenna is at a loss when faced with the choice of a variety of different antenna designs. You should probably pay attention, first of all, to the family of half-wave vibrators.
They have an electrical length equal to λ/2 and radiate in a direction perpendicular to the plane in which they are suspended.
Such simple half-wave antennas are:
- antenna with intermediate circuit, "Windom" antenna ("American"),
- Y-antenna, shelf vibrator,
- vibrator with cable power line,
- all-wave antenna W3DZZ, Zeppelin antenna.
All these antennas are completely equivalent in terms of gain and differ only in the type of power supply.
The next group of antennas are antennas in the form of a long wire. They are emitters, along the length of which several half-waves of the operating frequency fit. In this case, individual half-wave segments are excited in antiphase and, therefore, with increasing length of the conductor, the direction of the main radiation increasingly approaches the direction of tension of the wire.
Long wire antennas include:
- antenna in the form of a long wire, all-wave antenna DL7AB,
- V-shaped antenna,
- rhombic antenna.
The next group consists of directional loop antennas, which have a sharp radiation pattern in the direction perpendicular to the plane in which their elements are located. In this case we are talking about in-phase excited half-wave vibrators located in a vertical plane one above the other.
Rotating directional antennas have approximately the same gain in the direction of the main radiation. They have the advantage that they can be used to establish connections in all directions. They take up little space, but their mechanical design is much more complex. The most economical in design and at the same time the most effective rotating directional antenna is the “double square” antenna. Having only two elements, its parameters are not inferior to a four-element “wave channel” antenna.
Finally, let's mention vertical emitters, which are the simplest vertical antennas in the form of pins. They differ in that they require very little space and have a circular radiation pattern. The most famous and most effective design of such antennas is the Ground Plane (GP) antenna, which, when installed correctly, despite the fact that it has a circular radiation pattern, still gives a small gain and a flat angle of vertical radiation.
Which shortwave antenna should I choose?
A novice radio amateur can be recommended to construct the antennas below, since they are intended for the purposes described, which has been verified by long-term practice of their use, and the ratio between labor costs and materials for their manufacture and the results obtained is very good.
A radiator with a circular radiation pattern and a minimum usable area for the ranges of 10, 15, 20 meters is a Ground Plane antenna.
An all-wave antenna with a small gain in the high-frequency short-wave ranges and a weakly expressed directional effect - the W3DZZ all-wave antenna.
A directional emitter with a very large footprint and high gain for all bands - V-shaped antenna.
A rotating directional emitter with a very high gain for the ranges of 20, 15 and 10 meters - a “double square” antenna.
A popular amateur radio expression says: the best power amplifier is an antenna.
Here we will consider simple to manufacture, but quite effective types of antennas.
Half-wave dipole
The radiation pattern in the horizontal plane has the shape of a figure eight, the maximum radiation (reception) falls on the plane of the antenna fabric.
The radiation from the ends is minimal.
In the vertical plane, the type of radiation diagram depends on the height of the dipole suspension above the ground. The higher the antenna is suspended, the more efficiently it works over long distances.
The input impedance of the dipole is about 75 Ohms and changes slightly with the height of the suspension - H is greater than λ / 2. If the height of the suspension is less than a quarter of the wavelength, the input resistance decreases.
The length of the half-wave dipole is calculated by the formula:
where L is in meters, f is in kHz.
The thicker the wire from which the antenna is made, the wider its bandwidth. In practice, an antenna wire diameter of at least 4 mm is quite sufficient and an antenna cable or bimetal is best suited for this.
Multi-band antenna W3DZZ
One way to use a dipole multi-band is to turn off part of it using resonant circuits.
The multi-band antenna with a matched cable transmission line, designed by radio amateur W3DZZ, deserves special attention. For radio amateurs who want to have a full-band antenna, this design is by far the simplest and most practical.
The space required to place the antenna is small, and significant gain can be obtained in the ranges in which most long-distance communications occur. If the specified dimensions are observed, additional adjustments are usually not required. Powering the antenna via a coaxial cable in traveling wave mode also eliminates interference to radio broadcasting (the cable must be at a distance of 6 m perpendicular to the antenna).
The inductors L1 and L2 are the same. They can be wound on a frame with a diameter of 50 mm (wire PEV-2 1.5, the winding pitch is about 2.5 mm, the number of turns is 20). Before connecting the circuit to the antenna, it is checked by the GIR and the length or number of winding turns L1 and L2 is adjusted until resonance is obtained at a frequency of 7050 kHz. Capacitors C1 and C2 - 60 pF, must be designed for voltages up to 3000 V and reactive power up to 10 kVA. Considering that the antenna circuits should not be detuned when the ambient temperature changes, the capacitors must be with negative TKE.
Vertical antenna (GP)
The vertical antenna is a quarter-wave rod with counterweights. Counterweights act as artificial ground. Research carried out by the Swiss radio amateur HB9OP has shown that with the GP antenna it is possible to achieve directional radiation in the horizontal plane when three radial conductors are used, stretched at an angle of 120° to each other in the horizontal plane and inclined at an angle of 45°.
This antenna radiates predominantly in the directions of the bisectors of the angles between the horizontal conductors and has a vertical radiation angle of the order of 6 - 7°. The radiation pattern of this antenna in the horizontal plane has the shape of a clover leaf.
The optimal vertical radiation angle of 6 - 7° is achieved, according to radio amateur HB9OP, with an antenna height of 6 meters. The number of radial conductors at a given tilt angle of 45° affects the input impedance of the antenna and for the specified antenna it ranges from 50 to 53 Ohms.
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End-fed antennas, and in particular long-wire antennas designed for multi-band operation, are often fed using tuned lines (Figure 2-24).
A Zeppelin antenna is a simple half-wave vibrator powered by a tuned two-wire transmission line connected to its end.
One wire of the transmission line is connected to the vibrator, and the other is isolated from it. The length of the transmission line must be λ/4 or a multiple of λ/4. If the transmission line length is 2λ/4; 4λ/4; 6λ/4, etc., i.e. equal to an even number of quarter waves, then the distribution of currents and voltages at the input and output of the transmission line is the same. If the length of the transmission line is equal to an odd number of quarter waves, i.e. 1λ/4; 3λ/4; 5λ/4, then the distribution of currents and voltages at the input of the line is opposite to the distribution at the output.
At the end of any vibrator there is a voltage antinode. If the vibrator is powered through a line of length 2λ/4, then at its lower end there is also a voltage antinode, and they speak of a connection with the line by voltage. If the transmission line has a length equal to 1/4λ (3/4λ, 5/4λ, etc.), then the ratio changes and, although there is still an antinode at the end of the vibrator, there is a voltage node at the lower end of the line (current antinode). When a transmission line is connected to a transmitter at points of maximum current, they speak of current coupling.
A half-wave Zeppelin antenna, designed for a wave of 80 m, can simultaneously serve as a wide-band antenna with some restrictions, since at a wave of 40 m this antenna operates as a wave Zeppelin antenna, and at waves of 20, 15 and 10 m - like 2λ , 3λ or 4λ antenna in the form of a long wire with power at the end. If the transmission line length is approximately 40 m, i.e. 2λ/4 for 80 m, then there is coupling to the voltage transmission line on all bands. If the transmission line has a length of 20 m, which corresponds to λ/4 for 80 m, then at a frequency of 3.5 MHz there is a current coupling, and in the remaining ranges - a voltage coupling.
Setting diagrams for various types of communication are shown in Fig. 2-25.
The procedure for setting up such antenna communication devices will be described in detail in Chapter. 13.
Multi-band Zeppelin antenna
An antenna designed based on the above considerations is shown in Fig. 2-26.
This antenna for the ranges of 80, 40, 20 and 15 m has a current coupling, and in the 10 m range - a voltage coupling and can also be made with a vibrator length of 20, 42 m, but in the 80 m range the antenna is powered , shown in Fig. 2-26, does not work. Only if the end of the transmission line connected to the transmitter is short-circuited and communication with the final stage is through a P-circuit, then in this case such an antenna can be used on a wave of 80 m as the simplest L-shaped antenna.
If the antenna fed from the end is intended for use in only one band, then it makes sense to connect a closed quarter-wave section of a two-wire line to the end of the vibrator and feed it in traveling wave mode, as shown in Fig. 2-27.
A piece of ribbon cable of any length or a homemade two-wire line can be used as a transmission line operating in traveling wave mode.
Dual zeppelin antenna
As already mentioned, a centrally fed symmetrical vibrator has the simplest polar pattern. One such center-fed antenna, used on all shortwave bands, is known as a dual zeppelin antenna (Figure 2-28).
| Total length of vibrator, m | Length of configured transmission line, m | Range, m | Type of connection between the line and the transmitter |
|---|---|---|---|
| 80 | by voltage | ||
| 40 | -"- | ||
| 41,15 | 12,80 | 20 | -"- |
| 15 | -"- | ||
| 10 | by current | ||
| 80 | by voltage | ||
| 40 | -"- | ||
| 41,15 | 23,60 | 20 | -"- |
| 15 | -"- | ||
| 10 | -"- | ||
| 80 | by current | ||
| 40 | by voltage | ||
| 20,42 | 12,95 | 20 | -"- |
| 15 | -"- | ||
| 10 | -"- | ||
| 80 | by voltage | ||
| 40 | by current | ||
| 20,42 | 19,95 | 20 | by voltage |
| 15 | by current | ||
| 10 | by voltage |
To configure the transmission line and match it with the final stage of the transmitter, the circuits shown in Fig. 2-25. However, the most often used, just like for an ordinary Zeppelin antenna, is the connection of the transmission line with the final stage of the transmitter using a symmetrical P-circuit (Fig. 2-28).
In the case of using a symmetrical vibrator exclusively as a single-band antenna, the power line is matched using a quarter-wave matching loop. The matched transmission line can be of any length, since it operates in traveling wave mode. It should be borne in mind that if the total length of the vibrator is equal to at least 1λ or an integer λ (voltage antinode at the feed point), then a closed quarter-wave stub is used, and if the length of the vibrator is equal to λ/2 or an odd number λ/2, then use an open quarter-wave loop.
It goes without saying that any type of matching devices can be used for matching, provided that they are easily feasible structurally.
When describing the L-shaped antenna as a multi-band antenna, it was found that a vibrator operating on all bands can practically be precisely tuned to resonance for only one band. In all other ranges, greater or lesser deviation from the resonant length of the vibrator should be taken into account.
The above is true not only for the L-shaped antenna, but also for all possible all-wave antennas. The antenna shortening factor largely depends on the capacitive edge effect that occurs at the ends of the antenna. As can be seen from Fig. 2-29, if a conductor is excited at the higher harmonics of its resonant wave, i.e., several half-waves fit along its length, then the capacitive edge effect appears only at its ends.
Since the capacitive edge effect lengthens the electrical length of the antenna, the length of the antenna must be reduced. From Fig. 2-29 it is clear that a vibrator, along the length of which several half-waves fit, should be relatively less shortened than a half-wave vibrator, since the capacitive effect in this case occurs only at the ends of the vibrator.
The antenna at points A-A (see Fig. 5.13) has a high input resistance (about 600 Ohms), depending on the electrical thickness of the wire and the end capacitance. Such an antenna can be excited by a symmetrical line with a characteristic impedance of about 600 Ohms (line length R/4 or ZA,/4). The quarter-wave segment acts as a transformer, reducing the resistance at points B-B.
K-x/2 U/IU p-l/2
Ts15m(2aA2m)
Ts15m(gO,42m)
12.80m or 23.60m (12.95 m or 19.95m)
Transmitter coupling coil
Rice. 5 13 Anteia Zeppelin:
a - antenna design; b - main dimensions of a five-band antenna; c - double Zeppelin antenna
At these points a coaxial line with characteristic impedance Zo=50...75 Ohm can be connected.
A strong electromagnetic field is created in the space near the antenna (from the power line side), which is, in fact,
mirror image of a real antenna. Therefore, this space should be free of all objects. Otherwise, significant deformation of the radiation characteristics is observed, which leads to an increase in the level of interference. Note that this antenna, like the previously considered /.-type antenna, does not have filtering properties and radiates all harmonics of the transmitter into space. True, it is possible to somewhat reduce the level of their radiation, which is achieved by connecting baluns between the transmitter output and the input of the V-V power line.
Note that if the length of the feed line is a multiple of the wavelength, then the antenna in question becomes similar to an L-type antenna. In this case, the power line becomes a source of radiation. To prevent this phenomenon, the length of the power line is chosen in the range from 12.8 to 13.75 m. Instead of a two-wire overhead line with Zo=600 Ohm, you can use a two-wire line in dielectric insulation with Zo=240...300 Ohm; in this case, you should remember the influence of the shortening factor and reduce the line length to 11.9 m. If the antenna is used in only one band, then to improve the matching you should use tuning loops (see Fig. 2.46).
Double Zeppelin antenna. By connecting two single antennas together as shown in Fig. 5.1 Sv, we get a double Zeppelin antenna, which can operate in five amateur radio bands.
B table. 5.4 shows the most appropriate lengths of supply lines and the corresponding power supply methods.
TABLE 5.4
The lengths of the power lines and the corresponding methods of powering the double Zeppelin antenna
Total length of vibrator, m | Power line length, m | Power supply method in frequency ranges, MHz |
||||
/-current supply; U - voltage supply.
Voltage supply requires the use of a parallel circuit, and current supply requires a series circuit (for more information, see § 3.2).
Band antenna with changing the length of the supply line. The reasons for the change in Z\=Ra+\Xa with a change in the range of frequencies used were clarified. The input impedance when the antenna is resonant has only an active component.
This condition can only be implemented in one range. If we excite the antenna using a line having Zo=/?4, then in narrow ranges Za>Ra we get a large degree of mismatch
connection of the antenna with the power line. Instead of using various tuning systems, in this case, you can use another matching method, namely, change the location of the antenna power connection, which in practice does not cause much difficulty.
The possibility of using this matching method is clarified by considering Fig. 5.14, which shows the distributions of resistance Da along the line for various frequencies of the amateur radio bands. The change scale is built on a logarithmic scale and takes into account changes in Ra from 65 Ohm to 3000 Ohm. In addition, in these graphs, the curvilinear segments of the change in Ra are replaced by straight ones, and the shortening coefficient K is equal to 1.
Despite the simplifications taken in the construction, the graphs of changes in Ra are quite accurate for practical purposes. More accurate Ra values can be obtained using the formula
R = - Az + Ro, (5.5)
where Rai and Ra2 are input resistances corresponding to the current and voltage nodes, respectively; Ro - wave impedance of the dipole; b is the distance from the power connection point to the point corresponding to the maximum current in the aitein; I am the wavelength.
From the graphs shown in Fig. 5.14, it is clear that most of the intersections of the lines of change in Ra for different ranges and for different lengths of the power line occur within the bounding-chain values of 200 and 300 Ohms.
Example. With a power line length of 14.1 m, the graphs of changes in Ra for four ranges (3.5, 6, 14 and 28 MHz) intersect at almost one point, corresponding to /?a = 240 Ohm, and for the 21 MHz range the selected power line length corresponds to maximum value of Ra- With a power line length of 7 m, the same Ra values (about 240 Ohms) are observed for three ranges (7, 14 and 28 MHz).
If now the characteristic impedance of the power line, the length of which is selected based on the coincidence of Ra for several ranges, is taken equal to Zo = a = 240 Ohms, then such a system (antenna - power line) will be operational in several frequency ranges simultaneously.
It must be borne in mind that it will be quite difficult to achieve complete coincidence of resistances, since in our reasoning the real value of the shortening coefficient was not taken into account, but K = 1 was taken. Nevertheless, by practical selection of the length of the power line, which has a characteristic impedance Zo- = 240... 300 Ohms, it is possible to achieve very good matching performance in several frequency ranges.
Extended and shortened Zeppeli-n antennas. In Fig. Figure 5.15a shows a diagram of the antenna, called the extended double Zeppelin antenna. This antenna differs from the antenna shown on the RNS. 5.13v, vibrator arm length. The length of the vibrator arm is 27 m. The input impedance of the antenna ranges lengths of 10; 20; 40; 80 m/?а=240 ... 300 Ohm (the exact value of the input impedance depends on the height of the antenna suspension), which allows the use of a two-wire line in a strip dielectric to power the antenna.
Note that the directional coefficient of such an antenna is slightly greater than that of a conventional double antenna. In addition, it should be borne in mind that the input impedance of the extended
Over the past month, the radio hobby has advanced a little: I became the owner of the legendary Icom IC-R75, the T2FD antenna was built, and the simplest but most interesting antenna was strung.
There will be separate posts about the first two, because T2FD is still lying in the corridor and waiting for the key to the treasured door to the attic, and the new receiver simply required something more than a wire on the balcony.
So, LW (long beam, Windom or “American”) - this is what we will talk about.
It is noteworthy that the antenna was invented by Windom back in 1936 and has not lost its relevance to this day, like many other things in radio. In its standard form, it should be exactly 41 meters long and cover almost all HF amateur radio bands, except 160m.
Having turned the valcoder once again in the evening, I realized that I needed to expand my horizons, and while the T2FD was not installed on the roof, stretch a long beam.
Looking out the window, I quickly chose the lowest point of suspension - an old wooden power pole. Not the best solution, of course, given that I have a box yard of 10-story buildings, but given the labor costs, it’s better not to come up with a temporary solution.
The next morning I went to the construction market, where I purchased:
1. Vole P-274 40 meters (untangled and spliced) - 300 rubles.
2. Duplex clamps M2 - 6 pcs - 72 rub.
3. Cable d2 - 2 m - 16 rubles.
4. Retro insulator - 2 pcs. -24 rub.
5. Dowel with ring 10*60 - 12 rub.
6. Eye screw - 12 rubles.
Total, 436 rubles)
Installing the antenna took about 5 hours, including all the little things and winding the transformer.
The 1:9 balun is made on a PC40 ring with a diameter of 38 mm. according to a scheme known throughout the Internet.
The length of the canvas turned out to be about 70 meters. From the pillar to the balcony on the 6th floor in the middle:
The height of the suspension on the pole is about 5 meters.
Since such a long canvas will necessarily accumulate static, a separate grounding wire was installed from the balcony railing (which is connected to the fittings and circuit of the house). Atmospheric tension is a serious thing:
Immediately, together with the feeder, I pulled the wire into the kitchen, where I have a radio box. In the future, I will install an antenna switch with all antennas positioned “on the ground”.
For now, just in case, I stick a wire into the radio - it’s calmer. It does not affect reception, because the antenna already has a “dump” of RF currents through the transformer.
I decided to power the antenna through a transformer only because of this output to the ground; I did not want currents to flow through the receiver. In any case, the May thunderstorms are long behind us, so there is still time to think about the best solution.
Mounting the upper end of the antenna:
General form:
When tensioning, it is also important to allow a slight sag in the fabric to relieve physical stress on the wire. It is necessary to take into account possible icing and hurricane winds, which a thin vole may not be able to withstand.
As a result:
- the 80-meter range has opened: I can hear amateurs from all zones in Russia, but no more.
- the railway frequency of 2130 kHz opened. Nothing interesting
- medium and long waves are now booming with a bang. It's a pleasure to listen to.
- broadcasting stations in the range of 70, 60 meters are now heard loudly, and most importantly - there are a lot of them!).
Africa and Southeast Asia are also well heard.
Today, for example, in the evening, I listened to Radio Australia as if it were a nearby station.
But. America's stations are still a mystery to me. Either Chinaradio is interrupting, or they are waiting for T2FD on the roof!..