shortwave antennas. construction notebook

End-fed antennas, and in particular multi-band long wire antennas, are often fed with tuned lines (Figure 2-24).

The zeppelin antenna is a simple half-wave vibrator powered by a tuned two-wire line transmission 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 lines must be λ/4 or be a multiple of λ/4. If the length of the transmission lines is 2λ/4; 4λ/4; 6λ / 4, etc., i.e., equal to an even number of quarters of the wave, then the distribution of currents and voltages is the same at the input and output of the transmission line. If the length of the transmission line is equal to an odd number of quarters of the wave, 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 by a line with a length of 2λ/4, then there is also a voltage antinode at its lower end, and one speaks of a voltage connection with the line. 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 connecting the transmission line to the transmitter at the 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-range antenna with some restrictions, since on a wave of 40 m this antenna works like a wave antenna "zeppelin", and on 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 length of the transmission line is approximately 40 m, i.e. 2λ / 4 for 80 m, then on all ranges there is a connection with the voltage transmission line. 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 connection, and on the remaining ranges - by voltage.

Tuning charts for various kinds connections are given in fig. 2-25.

The procedure for setting up such antenna communication devices will be described in detail in Chap. thirteen.

Multiband Zeppelin Antenna

An antenna constructed on the basis of the above considerations is shown in Fig. 2-26.

This antenna for the ranges of 80, 40, 20 and 15 m has a current connection, and in the range of 10 m it has a voltage connection and can also be made with a vibrator length of 20, 42 m, but at the same time in the range of 80 m 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 via a P-loop, then in this case such an antenna can be used on a wave of 80 m as the simplest L-shaped antenna.

If the end-fed antenna is intended for use in only one band, then it makes sense to connect a closed quarter-wave segment of a two-wire line to the end of the vibrator and power it in traveling wave mode, as shown in Fig. 2-27.

A piece of ribbon cable of any length or a self-made two-wire line can be used as a transmission line operating in the traveling wave mode.

Dual zeppelin antenna

As already mentioned, the center-fed dipole has the simplest polar pattern. One such center-fed antenna used on all shortwave bands is known as the dual zeppelin antenna (Figure 2-28).

To tune the transmission line and its coordination with the terminal stage of the transmitter, the circuits shown in Fig. 2-25. However, the most commonly used, as well as for an ordinary Zeppelin antenna, is the connection of the transmission line with the final stage of the transmitter using a symmetrical P-loop (Fig. 2-28).

In the case of using a balanced 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 a traveling wave mode. It should be borne in mind that if the total length of the vibrator is at least 1λ or an integer λ (voltage antinode at the feedpoint), then a closed quarter-wave stub is applied, 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 provided that they are easily feasible constructively.

When describing an L-shaped antenna as multiband antenna it was found that a vibrator operating on all ranges, in practice, can be finely tuned to resonance for only one range. In all other ranges, more or less deviation from the resonant length of the vibrator should be taken into account.

The above is true not only for an 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 the 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.

As a rule, a novice radio amateur, starting to manufacture an antenna, is lost in front of a choice in a variety of different antenna designs. It is probably necessary to 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, antenna "Wind" ("American"),
• Y-antenna, shelf vibrator,
• vibrator with cable power line,
• all-wave antenna W3DZZ, Zeppelin antenna.

All these antennas in relation to the gain are completely equivalent 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, consequently, with an increase in the length of the conductor, the direction of the main radiation approaches the direction of the wire tension more and more.

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 frame directional 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 vertical plane one above the other.

Approximately the same gain in the direction of the main radiation have rotating directional antennas. 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 terms of design and at the same time the most efficient rotating directional antenna is the antenna " double square". Having only two elements, it is not inferior in its parameters to the four-element "wave channel" antenna.

Finally, we mention vertical radiators, 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 best-known and most effective design of such antennas is the Ground Plane (GP) antenna, which, when properly installed, despite the fact that it has a circular radiation pattern, still gives a small gain and a shallow angle of vertical radiation.

Which shortwave antenna to choose?

A novice radio amateur can be recommended to design the following antennas, 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.

An emitter with a circular pattern and a minimum usable area for the ranges of 10, 15, 20 meters is a Ground Plane type antenna.

An all-wave antenna with a small gain in the high-frequency short-wave bands and a weakly pronounced directional action - the all-wave antenna W3DZZ.

Directional radiator with a very large footprint and high gain for all bands - V-shaped antenna.

Rotating directional radiator with a very high gain for the ranges of 20, 15 and 10 meters - antenna "double square".

The winged amateur radio expression reads: best amplifier power is the antenna.

Here we will consider simple to manufacture, but quite effective types of antennas.

half wave dipole

The radiation pattern in the horizontal plane looks like a figure of eight, the maximum radiation (reception) falls on the plane of the antenna web.

From the ends, the radiation is minimal.

In the vertical plane, the form of the radiation diagram depends on the height of the dipole suspension above the ground. The higher the antenna is suspended, the more efficiently it works on long-distance routes.

The input impedance of the dipole is about 75 ohms and changes slightly when the suspension height is H greater than λ / 2. If the suspension height is less than a quarter of the wavelength, the input impedance decreases.

The length of a 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 cord or bimetal is best suited for this.

Multi-band antenna W3DZZ

One way to use a dipole with multiple ranges is to turn off part of it using resonant circuits.

The multi-band antenna with a matched cable transmission line, designed by the radio amateur W3DZZ, deserves special attention. For radio amateurs who want to have an all-band antenna, this design is by far the most simple and practical.

The space required for the antenna is small, and on the bands where most long-haul links travel, significant gain can be obtained. If the specified dimensions are observed, additional amendments are usually not required. Antenna power supply coaxial cable in the traveling wave mode, it also eliminates radio interference (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 (PEV-2 wire 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 a resonance is obtained at a frequency of 7050 kHz. Capacitors C1 and C2 - 60 pF, must be rated for voltage up to 3000 V and reactive power up to 10 kVA. Given that the antenna circuits should not be detuned when the ambient temperature changes, the capacitors must be with a negative TKE.

Vertical Antenna (GP)

Vertical antenna - a quarter-wave pin with counterweights. Counterweights act as an artificial earth. Research 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 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 form of a clover leaf.

The optimal vertical radiation angle, equal to 6 - 7 °, is achieved, according to the HB9OP radio amateur, with an antenna suspension height of 6 meters. The number of radial conductors at a given angle of inclination of 45° affects the input impedance of the antenna and for the specified antenna it ranges from 50 to 53 ohms.

Viewed: 437

By the name "Levy" we mean all antennas with center feed and two-wire line with any length of beams and line wires.

Consider first an antenna of the LW type (Fig. 1). The beam length must be at least a quarter of the wavelength of the lowest frequency band used. The matching device will help you tune it to any frequency. LW can be thought of as half of a Levy antenna.

But this option is inconvenient, since the RF currents flowing through the beam and the matching device require good grounding of the entire system. It is necessary not to place television antennas in this huge "capacitor" (beam-to-ground), which causes obvious difficulties.

Antenna "Levy" (Double Zeppelin Antenna) is shown in fig. 2.

So far it has been said that the radiating wires of vibrators must have resonant lengths of 41.40 m or 20.40 m. In reality, this condition is not so necessary. A quarter wave is the minimum length if you want to keep the efficiency of the antenna, but enough nice results can be obtained using shorter beams.

The properties of a two-wire line allow it to be taken away from the antenna web not perpendicularly downwards, as is desirable for a coaxial cable. And in this case, the RF currents are compensated in the matching device (the RF potential is always zero with respect to the ground).

This ground symmetry makes the Levy unaffected by TV reception. The length of the two-wire line is chosen as short as possible.

You can give the antenna an inverted V shape. The lower ends of the antenna must be at least 3 m high, which is dictated by safety considerations, because. voltage antinode at the ends of the antenna.

The radiating part of Levy is not defined by rays. Its matching device, two-wire line, beams are inseparable elements.

The line is in standing wave mode and it would be erroneous to call this line a "feeder". The real feeder in Levy is a piece of coaxial cable connecting the output of the transceiver to the antenna matching device and the SWR meter. It operates in the traveling wave mode with SWR-1, which is provided by a matching device. The matching device compensates for the reactance of the line and radiating wires, and also transforms the line impedance into 50 ohms.

The Levy antenna is excited by an odd number of half-waves, which is determined by the total length of the wired part and the reactances of the coils and capacitors of the matching device.

Matching devices for Levy antennas

All non-aperiodic antennas tune well with an oscillating circuit, but a vibratory load can resonate at many frequencies, while an oscillatory circuit consisting of a coil and a capacitor can only resonate at one frequency.

Most stations have matching devices that compensate for reactance and transform resistances. Consider several schemes of matching devices. In the device shown in Fig. 1, Balun at the input having 50 ohms is constantly matched with a ratio of 1:1, it feeds the double L with 50 ohms symmetrically. Capacitors C1 and C2 are the same and rotate with the same knob.

The design (Fig. 2) does not require the use of a Balun, but it is necessary to have a dual PDA.

Since there is a double circuit, it is very selective, because has a strong resonance. This allows you to tune the antenna when receiving. Levy is considered to have better performance than KB antennas with shortening coils, with the same linear dimensions. However, the quality factor that allows you to get these results is paid by the need to adjust the matching at QSY per kHz!

Depending on the specific range, it is necessary to feed the two-wire line in the current or voltage node and switch from the series oscillatory circuit to the parallel circuit using clamps.

There are a lot of circuits - the most easily feasible design is with an autotransformer connection, but it introduces some asymmetry. The simplest one (Figure 3) is published by F3LG. The autotransformer version (Fig. 4) is represented by F9HJ.

Another option, where the output impedance is determined by capacitors, is shown in Fig. 5

On all KB bands, Levy is undeniably the best antenna: it is simple and works in the right sections of short waves, the radiating canvas is the same for all bands. Due to its symmetry and two-wire power line, it does not give TVI.

SOMETHING ABOUT ANTENNAS

I bring to your attention interesting, in my opinion, information about antennas and antenna amplifiers, obtained from various sources and as a result of experiments.

So, did you know that:

The most multi-element “wave channel” described in amateur radio literature is a 34-element antenna for the 1296 MHz range proposed by G8AZM, and the traverse length is not so long - 2m

The first place in terms of the length of the traverse (16 meters!) Is occupied by a 24-element antenna (at 144 MHz) of the DJ40B design, which is also the “softest” of the “wave channels”, since it can be rolled up during transportation;

A traverse length of about 10 meters has a 22-element version of the Spindler antenna at 144 MHz. This design does not roll up!

In "wave channel" antennas with simple reflectors, the dependence of the protective action coefficient Kzd (i.e., the radiation ratio "forward / backward") on the number of directors has an oscillating character with extrema of about -10 dB and -20 dB. Antennas with 2.5, 8, etc. have the largest Kzd. directors;

When adjusting the “wave channels”, two options are possible: when the antenna is tuned to the maximum gain, the Kzd can decrease by 10 dB or more, and when adjusted to the maximum Kzd, the gain will decrease within 0.5 ... 1 dB;

In antennas with the so-called. the "absorbing" element, located behind the main reflector at a distance of 0.18 ... 0.25 wavelengths, manages to obtain very large values ​​of Kzd (over 70 dB!), However, in a rather narrow radiation sector;

One of the reasons for the deterioration of the RP of both HF and VHF antennas can be resonant phenomena in the supporting structure. You can eliminate them different ways: by isolating the main element from the traverse, by putting ferrite rings on the traverse near the active element, or, most simply, by painting the traverse (but not the elements!) with paint with the addition of graphite powder;

With a long feeder, it is possible to improve the balancing of the antenna and reduce local interference using two ferrite rings. One is installed on the feeder near the antenna feed points, and the other - near the antenna input / output of the device. In some complex cases, it may be necessary to additionally place several ferrite rings along the entire feeder and select the distance between them experimentally;

Applying as antenna amplifier(AU) differential stage, it is possible not only to provide broadband antenna balancing, but also to significantly reduce local interference, incl. and from cars. As a differential TV AU for MB, the m / s K174PS1 works well.

Using some digital ESL m / s of the K500 (K100) series in linear mode, it is possible to manufacture a differential AU with a bandwidth of up to 160 ... 180 MHz. The gain (inversely proportional to the bandwidth) of such an AU reaches 40 (!) dB.

Over the past month, the radio craze 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 pulled.

There will be separate posts about the first two, because T2FD is still lying in the corridor and waiting for the key to the cherished 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") - it will be discussed.

It is noteworthy that the antenna was invented by Windom already in 1936 and still has not lost its relevance, like many other things in the radio. In its standard form, it should be exactly 41 meters long and cover almost all HF amateur radio bands, except for 160m.

Turning the encoder once again in the evening, I realized that I needed to expand my horizons, and until T2FD was installed on the roof, pull a long beam.

Looking out the window, he quickly chose the lowest point of suspension - an old wooden power pole. Not the best solution, of course, given that I have a yard-box of 10 floors, 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. Clamps duplex M2 - 6 pcs - 72 rubles.
3. Cable d2 - 2 m - 16 rubles.
4. Retro insulator - 2 pcs. -24 rub.
5. Dowel with a ring 10 * 60 - 12 rubles.
6. Eye screw - 12 rubles.
Total, 436 rubles)

Mounting the antenna took about 5 hours, along with all the little things and winding the transformer.
The balun 1:9 is made on a PC40 ring with a diameter of 38 mm. according to the scheme known throughout the Internet.

The length of the canvas turned out to be something around 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 definitely accumulate static, a separate ground wire was laid from the balcony railing (which are connected to the fittings and the house circuit). Atmospheric stress is a serious thing:

Immediately, together with the feeder, I extended the core to the kitchen, where I have a radio box. In the future, I will put an antenna switch with the position of all antennas "on the ground".

So far, just in case, I stick a vein in the radio - it's calmer. Reception is not affected, 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 didn’t want currents to run through the receiver. In any case, the May thunderstorms are long gone, 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 give a slight sag to the web to relieve physical stress on the wire. It is necessary to take into account both possible icing and hurricane-force winds, which a thin vole may not withstand.

As a result:
- the 80-meter range was opened: I hear amateurs from all zones in Russia, but no more.
- the railway frequency of 2130 kHz was opened. Nothing interesting
- medium and long waves - now thunder with a bang. It's a pleasure to listen.
- broadcast stations in the range of 70, 60 meters are now heard loudly, and most importantly - there are a lot of them!).
Africa, 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!..

Radio amateurs are constantly on the lookout for antennas that are ideal for specific conditions. Of course, knowledge of the theory in this process is necessary, but no theory can replace personal experience. In other words, there is nothing left but to try different antennas again and again, weighing their strengths and weaknesses, and then draw conclusions. What are we going to do today. This time we will experiment with several antennas made from a two-wire line.

A bit of 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, of which the most important are (1) impedance, (2) velocity factor, and (3) loss 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 feeding antennas on VHF. Instead, use RG213 or even lower loss cable. 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 little loss. 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, a two-wire line must be located from the ground and metal objects at a distance of at least ten distances between its wires. Unlike a two-wire line, coaxial cable can be laid anywhere - along walls, along the ground, or even underground.

How to measure the wave impedance and KU of the line?

Genuine ham radio two-wire lines are available from specialist online retailers as well as on eBay for queries like "450 Ohm Ladder Line" and "MFJ-18H250". But the prices for such lines fluctuate around $1.5-3 per meter, which is a bit expensive. Therefore, two-wire lines are often made independently from available wires and spacers, or lines designed for slightly different purposes are used as them. As examples of available two-wire lines, one can cite the P-274M wire (“vole”, about $ 0.17 per meter) and TRP 2x0.4 (“telephone noodles”, about $ 0.06 per meter). On eBay you can also find many offers for "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 KU. The question is, how can they be measured?

Characteristic impedance can be measured in at least two ways. The first way is this. A few meters of the line and an RLC meter are taken. The device is applied to one of the ends of the line and the capacitance C is measured. Then the wires of the line are connected at its second end and the inductance L is measured. The impedance is determined by the formula Z = sqrt(L / C) .

fun fact! The linear capacity mentioned earlier 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 segment of the measured line is connected to the second. A potentiometer is connected to 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 shows 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. It remains only to take a multimeter and measure the resulting resistance of the potentiometer. The process is illustrated in video by Alan Wolke, W2AEW.

However, it should be noted that both methods are far from ideal. Practice shows that the measurement error is at least 5%.

Using the same technique with an oscilloscope, the line gain can be determined. 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 twice along the line (round trip time). The length of the line is known, which makes it possible to measure the propagation speed of the signal. Dividing this speed by the speed of light, we get the KU.

If you do not have an oscilloscope, then KU can be measured using an SWR meter and a dummy load of 50 ohms. A line segment 5 meters long is taken. One end is connected to an SWR meter, the other end is connected to a dummy load. Further, in the interval of 15-30 MHz, a minimum SWR is sought. As a result, you should find the frequency where the SWR is 1 or very close to this value. At this frequency, the line acts as a half-wave repeater and the device sees a 50 ohm load. The line length is known, half the wavelength too. The ratio of the first to the second is CU.

Simple camping antenna from a two-wire line

The theory described above is necessary to understand and manufacture 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 wave resistance of 100-600 ohms, nothing good will come of it. But above, we found out that a line with a length of λ / 2 works like a half-wave repeater. It remains to find a suitable line, measure its KU, cut the line to the appropriate length, and we get a very light and compact dipole. Since the dipole is powered by a two-wire line, no common-mode currents occur in the line, which means that such an antenna does not need a balun. You can use a thin rod as a mast, and not be afraid that it will break under the weight of the balun.

For the entourage, it was decided to purchase 100 feet (30 meters) of the same speaker wire with a thickness of 20 AWG and make a dipole out of it for a range of 20 meters. The measured AC 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, which is exactly the length of light and inexpensive rods.

To attach the rod, instead of braces, as last time, it was decided to use a chiseled pike:

A turned pike is a piece of aluminum profile, cut to half a meter and sharpened with a dremel. The peak is driven into the ground about half the length. The rod is attached to it with Velcro straps, like those used to attach batteries to quadrocopters. Contrary to intuition, this design is quite reliable, and in terms of weight and space 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 is plugged into the SO-239 connector. They fit perfectly in diameter. Crocodile is the easiest way to grab the ground terminal of the transceiver.

The exact dimensions of the antenna I got the following. The length of the line is 758 cm. The length of one arm is 490 cm. The antenna SWR graph 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, SWR at 20 meters can be driven into one. By a happy coincidence, the antenna turned out to be fairly well matched at 15 meters. The SWR in this range is from 1.7 to 2. We managed to make radio communications in each of the ranges. In terms of noise level and received reports, 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 taller mast (for example, 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-range option

A multi-band version of such an antenna is also possible (the illustration is again borrowed from The ARRL Antenna Book):

This antenna is known by the names double zepp, double zepp, center-fed zepp, and also, when using certain sizes and line types, as the G5RV antenna. The antenna does not have a very clear input impedance. However, with a good 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 tunes perfectly to any amateur radio band from 80 to 10 meters with an SWR of 1-1.2. Test QSOs were made on 20, 40 and 80 meters as the most popular bands. Good reports were received on 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 dipoles, or verticals, or even loop antennas (however, the latter is installed close to home). For example, at the same 40 meters I typically see 6-7 noise points. What this is connected with is not very clear, but working on the air is much more pleasant.

Conclusion

The described variants of antennas are inexpensive, easy to manufacture, weigh little and take up little space in a backpack. Unlike classical dipoles, they do not require a heavy balun. Therefore, in the field, using a fishing rod, such antennas can be installed on b O higher height. Unlike verticals, they do not need counterweights that someone always stumbles over. The 20 meter antenna does not require a tuner and when mounted on a 10 meter mast (you will need a balun, but at the bottom of the antenna) this is quite a decent antenna for long distance communications. The multi-band version of the antenna requires a tuner. But it gives access to all HF bands at once and has a low noise level.

Overall, my experience with 2-wire antennas has been overwhelmingly positive. I'm going to invest more time in studying related antennas.

Addition: For the continuation of the topic, see articles