The moon is the celestial body closest to the Earth. Its radius is 1737 km, its mass is 81.3 times less than that of the Earth, and its average density is 3.35 g / cu. cm, i.e. one and a half times less than the density of the Earth. The duration of the lunar days is 29.5 Earth days. The average distance on the Earth-Moon-Earth path is 750 thousand km, the signal attenuation along this path for radio waves of the meter range is about 200 dB, i.e. the signal is attenuated tenfold, to the tenth power, and goes back and forth for 2.5 seconds.

The idea to use the Moon - the Earth's satellite as a passive repeater came a long time ago. The first reflections of radio waves from the lunar surface were obtained back in 1946 by scientists from Hungary and the United States, working in this direction independently of each other. In the experiments, we used 200 kW transmitters operating at a wavelength of about 2 meters and antennas with a gain of 400.

Extensive work in this direction was carried out in 1954-57 at the Gorky University. For the experiments, waves of 10 and 3 cm were used, the directivity of the antennas at a wave of 3 cm reached 120 thousand, i.e. the energy was concentrated in an angle of 0.5 degrees. As a result of these experiments, the coefficient of reflection of radio waves from the Moon was measured, which was approximately 0.25 - and it was found that the reflection occurs from the central part of the visible disk of the Moon. The experiments of the lunar radar gave real ground for the implementation of the idea of ​​using the lunar as a passive repeater.

Radio amateurs also took an interest in this idea. And in July 1960, the first amateur radio communication in the 1296 MHz band was carried out between the American club amateur radio stations W6HB and W1BU. In 1964, the first radio communication in the 144 MHz band was carried out between the OH1NL and W6DNG radio amateurs.

In the Soviet Union, the first amateur radio communication through the Moon was carried out on May 11, 1979 by operators of the collective radio station UK2BAS, in the 432 MHz band. Their partner was K2UYH. Later on January 19, 1981, the first radio communication in the 144 MHz band was carried out by the UT5DL radio amateur. His partner was Maine-based K1WHS, which had the largest antenna at the time (24 booms of 14 elements).

April 20, the same 1981, conducted his first radio contact and the author of this article (ex UB5JIN). And then it went - it went: December 6, 1981, the first intra-union radio communication (UB5JIN and UA3TCF), January 11, 1982 - the first radio communication from the territory of the USSR on SSB - (UB5JIN and K1WHS), August 15, 1982 the first communication with Japan (UB5JIN and JA6DR), October 10 with Venezuela (UB5JIN and YV5ZZ) and so on ...

Today, thousands of radio amateurs of all continents of the globe in the 144, 432, 1296, 5600 MHz bands conduct amateur communications through the Moon. Each of the ranges has its own characteristics, advantages and disadvantages.

Reception on the ground of signals reflected from the Moon encounters great fundamental difficulties:

The moon moves relative to the Earth with a high angular velocity, therefore the reflected signal is subject to the “Doppler” effect, ie. a wave reflected from a moving body has a vibration frequency different from the frequency of the sent wave. This difference for the 144 MHz band reaches 427 Hz.

The Faraday effect also has a great influence on the received signal; rotation of the polarization vector of the transmitted signal, which results in deep fading of the signal. To eliminate this effect, antennas with circular polarization are required, which are difficult to implement in the 144 MHz band for design reasons.

Space noises strongly affect the reception of VHF signals, for example: the minimum noise temperature of the celestial sphere at a frequency of 136 MHz in February 1982 was 210 degrees Kelvin or 2.35 db at minimum points and 2750 degrees or 10.2 db at maximum points.

Many problems are also associated with the transparency of the Earth's troposphere and ionosphere, atmospheric and local electrical interference.

The approximate attenuation on the Earth-Moon-Earth path for different bands can be expressed in the table:

Moon position	Distance (thousand km)	144 MHz (db)	432 MHz (db)	1296 MHz (db)
Perigee	356,334	187,08	196,62	206,15
Apogee	406,610	188,21	197,76	207,21

In order to cover such attenuation, a radio amateur who wants to practice E-M-E radio communications, has to make very serious equipment and antennas. Based on the path attenuation and the known initial data of the receiver and transmitter, it is possible to plot the antenna gain for different radio wave bands:

Graph from 1982 drafts!

At: TX = 700 watts

RX = 1 db

DF = 100 Hz

As you can see from the graph, in order to get an echo of your signal with a level of 1 db above noise in the 144 MHz range, it is necessary that the antennas (transmitting and receiving) have a total of about 43 db, i.e. A good antenna for E-M-E should have a gain of at least 21.5 db. Although radio communications are possible when using antennas with a lower gain, so, to conduct radio communications with a radio amateur K1WHS (antenna 24 x14 and KU equal to 27db), it is quite enough to have an antenna with a gain of 15-16 db!

For successful E-M-E work, you need to clearly know the position of the moon, the time of its rising and setting for you and your partners. The “Astronomical calendar” (yearbook, variable part) and computer programs, for example, “Orbitron”, which can be downloaded from us >> You do not have access to download files from our server

The radio amateur needs to know the periods of perigee and apogee of the moon and the "window" to Europe, Japan, South and North America. It is necessary to know the days when the trajectory of the moon is close to the trajectory of the sun, because conducting radio communications with a difference of less than 30 degrees is impossible, due to the large noise emissions of the Sun.

During the Lunar work, an interesting phenomenon is also observed, called the "soil effect", i.e. at the rising and setting of the moon, there is a noticeable increase in the level of reflected signals by 1-3 db. So, for the square “KN74BX”, a pronounced effect was observed at approach (in this direction, the plain of 40-50 km ends with the Black Sea basin), at sunrise the “ground effect” was not observed (hilly terrain, turning into the ridge of the Crimean mountains).

A very interesting activity when working through the moon is doing echo tests. It is better to do this outside the E-M-E section (144,000-144.015 MHz). A series of dots or dashes is transmitted, the combinations “BK”, “SK” are better perceived. After about 2.5 seconds, an echo is received. It will be sideways in frequency (Doppler effect) no more than 427 Hz. The echo is not always heard and not constantly, it depends on the conditions. If in this moment time, the echo is not heard in your QTH - this does not mean that the signal is not reflected or received, for example, in Africa or America. And vice versa - you can hear your partner well, your echo, but your partner does not hear you at that moment. Experiments have shown that an echo with a level of 1-2 db above the noise, received from time to time, will be quite acceptable for E-M-E work.

Vasily Beketov, UU2JJ

So far, my experience with amateur radio has been limited exclusively to the shortwave bands (3-30 MHz). However, VHF bands of 2 meters are also available to radio amateurs. (she is "two", 144-146 MHz) and 70 centimeters (430-440 MHz). Working in these ranges has some nuances. If you just get a VHF walkie-talkie and yell CQ on the ringing frequency from the balcony, then most likely you will not get the best experience. Here are some of the underwater rakes on VHF and how to avoid them, and further will be discussed.

A bit of theory

A few words about terminology are required as it is a little confusing.

Ultra-short waves (VHF) is a huge frequency range from 30 MHz to 3000 GHz. It includes the ranges of meter waves (MW, wavelength 1-10 meters, or in frequencies from 30 to 300 MHz) and decimeter waves (UHF, wavelength 10-100 cm, frequency from 300 MHz to 3 GHz). MVs are also known as VHF, very high frequency. Similarly, another name for UHF is UHF, ultra high frequency (UHF, ultra high frequency). In English, the terms VHF and UHF are often used. For some reason, the abbreviations VHF and UHF did not take root in the Russian language, and they often say VHF, meaning both ranges. Further in the text under VHF will mean exclusively the radio amateur VHF and UFH bands.

As you may be aware, HFs are refracted in the ionized layers of the atmosphere and returned to Earth. Thanks to this, radio communications for thousands and even tens of thousands of kilometers are possible on HF. VHF doesn't work like that. Tropospheric passage is possible for them, but this phenomenon is relatively rare. Therefore, usually VHF communication is possible on short distances, typically about 100 km. When using "exotic" types of communication (for example, via satellites), it is possible to make QSOs over much longer distances. But these types of communication deserve their own separate articles, so for now let's forget about them.

VHF may not be suitable for long-distance communications, but in terms of stability they have no equal. If there is a connection on VHF, then it is there 24/7, regardless of the passage, and without any fading, lightning discharges, and so on. Besides, on VHF there are no problems with high levels of noise on the air and pile-ups.

The presence of obstacles between the correspondents (high buildings, mountains, and so on) impedes the conduct of radio communications on VHF. However, in urban environments, radio communications are possible by reflecting radio signals from buildings. Let's say your balcony faces east and there is a tall building nearby. This building can act as a reflector, with the help of which it will be possible to contact the correspondent located in the west. Also, obstacles can be bypassed using repeaters, which we will talk about below.

The wavelengths in the VHF bands are significantly shorter than in the HF bands. This makes the VHF antennas more compact. As a result, wearable and car radios are very popular. In addition, VHF can be used to build directional antennas with a high gain of a fairly reasonable size.

To all that has been said, it should be added that VHF is usually operated in FM. This is not very important, but it is another difference from HF, where SSB is used.

Choosing a transceiver

There are quite cheap walkie-talkies for VHF made in China for example from Baofeng. But with such walkie-talkies, a number of inconveniences await you - low quality of the microphone and speaker, cut-down functionality and an interface inconvenient for radio amateur purposes, short battery life, low case strength, and so on. But the worst part is that such radios are often not designed to work with an external antenna installed on the roof or balcony, and the antenna on the radio itself extremely ineffective.

The problem is that Baofeng's are not full-fledged analog transceivers, but are based on the RDA1846 integrated circuit (datasheet). This circuit has a relatively small blocking dynamic range. This means that if you connect an external antenna to the radio, the receiver will most likely be blocked by strong signals from local TV and radio stations. In theory, this can be solved with additional filters. But from a practical point of view, it is much easier to use a walkie-talkie from another manufacturer, for example, Yaesu, ICOM or Kenwood.

Important! There is a good chance that you will not make any radio communications using some Baofeng UV-5R. Tested by personal bitter experience.

When choosing a transceiver, it will not be superfluous to look for reviews on the models you are interested in. Many radio amateurs post these reviews on YouTube. The list of recommended YouTube channels I previously provided in the article Going through the quest to get a callsign and register a RES. If the new transceiver does not fit into your budget, it makes sense to look at the ads for the sale of used transceivers, for example, on the qrz.ru bulletin board.

That's how I got my walkie-talkie, Kenwood TH-D72A (manual):

This is far from new, but a very high quality device. It is especially interesting because it is almost the only real full duplex walkie-talkie. That is, while you are transmitting in the 2m range, the walkie-talkie can continue to receive and play a signal on the second channel in the 70cm range (with the DUP function turned on). This is especially convenient when working with those very "exotic" types of communication.

The radio also has GPS, APRS support and probably some other useful functions that I have not figured out yet. Like most portable radios, Kenwood TH-D72A operates at a maximum of 5W. As we will soon see, this is sufficient for VHF operation.

Fun fact! Although the walkie-talkie is no longer in production, Kenwood continues to release firmware updates for it.

Given the uniqueness of the radio, the fact that the owner sold it together with charger KSC-32, SMC-34, spare battery and case, and extremely attractive price, the purchase was made without any hesitation. The deal went through without any problems - the device arrived quickly and in perfect working order.

Making an antenna

The default antennas of most portable radios are useless. The Kenwood TH-D72A antenna is no exception. Antenna analyzer EU1KY shows the following SWR graphs:

When plotting such graphs, it is necessary to hold onto the body of the antenna analyzer. The fact is that for normal operation, the antenna needs a human body, which acts as a counterweight. If you don't hold on to the case, the graphics will turn out even worse. As you can see, the resonance missed a little on two, only at "some" 15 MHz, and at 70 cm the SWR does not drop below 2.4. In general, the antenna is pretty nasty.

It was decided to make a full-size antenna for a range of 2 meters and place it on the balcony. Firstly, there will be no questions about its effectiveness to such an antenna. Secondly, it will be possible to safely work on a deuce in the winter, being in warmth and comfort. Thirdly, for safety reasons, there should be no people near the antenna during transmission. Now this is not so critical, since I am working on 5 watts. But in the future I can get a more powerful transceiver.

A diagram of a suitable antenna made from RG58 cable was found on the blogs of Australian radio amateurs John, VK2ZOI and Andrew, VK1NAM:

The antenna is an ordinary dipole, only located vertically. Unlike HF, VHF requires monitoring the polarization. Usually radio amateurs use vertical polarization on VHF, therefore a vertical dipole is required. The cable core acts as the upper arm of the antenna, and the outside of the cable shield acts as the lower arm. The choke choke consists of nine cable turns on a 25 mm frame.

Fun fact! Sometimes on VHF they work in telegraph and SSB, while it is customary to use horizontal polarization. However, most modern VHF transceivers only support FM. Telegraph and SSB are mainly supported in transceivers capable of operating on both HF and VHF. Examples of such transceivers include the Yaesu FT-991A and ICOM IC-7100. Digital modes of communication also work, with the difference that they are used for long-distance communications, and therefore polarization is not important.

First, a marching version was made:

The antenna was made slightly longer than indicated in the diagram, and then cut to the minimum SWR on the band:

As you can see, the antenna has a relatively good resonance at 70 cm. In this range it operates at the third harmonic. Is not best antenna for 70 cm, if only for the reason that the cut-off choke is completely not designed for this frequency. In particular, when the antenna is powered through a couple of meters of coaxial cable, the VSWR graph changes significantly. But, if necessary, the antenna allows radio communications in this range (checked!).

After tuning, the antenna was completely placed in a PVC pipe. At both ends, the pipe was covered with pieces of sponge, and the top was covered with a lid. I printed the lid on a 3D printer, but a kefir lid or a piece of fiberglass would work just as well. All holes, except for the bottom one, were sealed with epoxy. I did not glue the bottom hole in case moisture somehow gets into the antenna. In this situation, she will have where to drain.

The antenna was fixed on the balcony in the same way as I previously fixed the OPEK HVT-400B HF antenna:

Unlike HF, the RG58 cable is not like VHF for powering antennas. RG213 or even lower loss cable should be used instead. When using 10 meters RG58 signal attenuation at 144 MHz is 1.82 dB, and at 450 MHz - 3.65 dB. For RG213, it is 0.86 dB and 1.73 dB, respectively. However, if the cable is short, only a couple of meters, then the RG58 will do.

We go on the air

Calling frequency in the range of 2 meters - 145.500 MHz. Just go in and make a general call, like on HF. They don't always answer. But if it is so without much fanaticism to call in the morning before work and in the evening after, then people regularly respond. Provided, of course, that you are using a normal transceiver, an effective antenna, and the correct cables, as described above.

At 70 cm, everything is a little more interesting. The official common calling frequency is 433.500 MHz. However, this frequency falls into the LPD range of 433.05-434.79 MHz and in Moscow there is a strong interference on it. The alternative frequency is 432.500 MHz. But this frequency falls within the range of 430-433 MHz, which is prohibited from using within a radius of 350 km from the center of Moscow. As far as I could find out, there is an agreement among Moscow radio amateurs to use 436.500 MHz as the calling frequency. You can also try the so-called "pharmacy" frequency, 436.600 MHz.

Fun fact! Like on HF, on VHF there are radio hooligans, many of whom behave incorrectly on the air, shall we say. My philosophy in life is that if you meet such a person on the air, don't talk to him about anything and make sure that you are standing as far as possible in frequency :)

Experiments show that in urban conditions, the 2 meter range works noticeably better range 70 cm. Although radio communications can be carried out both there and there. I also do not exclude that the matter is in my antenna, which is not particularly designed to work at 70 cm.

We work through repeaters

Often radio communications on VHF are conducted through repeaters. A repeater is a device that picks up your signal on one frequency and repeats it on another. Usually the repeater antenna is installed somewhere high, where it can receive a signal from many radio amateurs, and the transmission from the repeater is carried out at high power. This is one of the reasons why it was said above that 5 watts is quite enough for working on VHF. The task comes down to getting through to the repeater. And it will already provide you with good power and coverage.

Repeaters often “open up” with a specific tone. A tone is a low frequency signal that is mixed with your voice during transmission. The main tone transmission standards are CTCSS and DCS.

Tone is not a repeater password. It is more of a foolproof protection. Let's say a radio amateur is equidistant between two repeaters using the same frequencies. With the help of a tone, one of the repeaters can understand that the radio amateur is talking to him and receive the signal. A second repeater using a different tone will recognize that the message is not addressed to him and will ignore the signal. Without the tone, the radio amateur would work simultaneously on two repeaters, and, unwillingly, would interfere with the work of colleagues.

The easiest way to find out about active local repeaters is to ask local radio amateurs about them. You can also search through the catalogs of repeaters, at least on the same qrz.ru. But information in catalogs is often either outdated or simply incorrect.

It is clear that to work through a repeater, the walkie-talkie must be properly configured. Let's consider this setting with a specific example. A familiar radio amateur says that in your city there is a repeater with an input at a frequency of 145.050 MHz and a transmission at 145.650 MHz (channel R2), a tone of 88.5 Hz. You are using a Kenwood TH-D72A radio. The question is how to get to the repeater?

Press VFO and set the frequency to 145.650 MHz. Go to MENU → Radio → Repeater → Offset Freq, enter 0.6 MHz here, that is, the difference between the frequency of transmission and reception of the repeater. We press the green button F, and then SHIFT (located on the asterisk symbol, to the left of zero). The plus sign lights up on the screen. It means that during transmission, the previously specified offset frequency will be added to the current frequency. But we want the frequency to be subtracted. Press F again, then SHIFT. The plus sign has changed to a minus sign. You can check that everything is working as expected by quickly pressing and releasing PTT. During transmission, the frequency should automatically change to 145.050.

Adjusting the tone. To do this, press TONE (located at number 8). The letter T lights up. It means that the radio will transmit a CTCSS tone, but will not require it to open the squelch. If you want the radio to check the tone during reception, you can switch it from T to CT by pressing TONE again. In the same way, you can switch to using DCS instead of CTCSS. Then press the F button. Go to the Tone Freq selection. Specify 88.5 Hz, save.

Now, in order not to lose the settings, press F, and then M.IN. We save to a memory cell. You can now switch from VFO mode to MR mode and switch between stored channels. This is much more convenient than manually adjusting frequencies and tones all the time. If desired, the cell can be given a name in MENU → Memory → Name (only works in MR mode). Long press MR to enter continuous scan mode for stored channels.

If everything was done correctly, you should now be heard by the people on the repeater. You can check the connection to the repeater by short pressing PTT. After you release PTT, the repeater will transmit the carrier for some time, which you will hear. If there is no carrier, then either the repeater is not receiving your signal, or the tone has been incorrectly tuned, or the repeater is not working. If there is a carrier, then everything is fine.

Fun fact! With a certain amount of luck, it is possible to reach the repeater with 5 watts of the antenna located inside the house.

It is clear that when using a different radio, the setting will be different. But the principle will be the same, and I think that you can easily figure it out.

Conclusion

So, you are on VHF. Now what? You can stop there and just communicate for life with radio amateurs living nearby. Or you can learn how to use APRS, conduct radio communications via satellites or EchoLink, receive SSTV from the ISS, install your own repeater, experiment with antennas, filters, amplifiers, digital voice modes (D-STAR, C4FM, DMR), transceivers from different manufacturers, or maybe and homemade. You might even want to try EME, which is radio communications by bouncing radio waves off the moon. In general, you have a range of frequencies. What you will do on it is mainly limited by your imagination.

73 and see you on VHF!

Addition: Replacing the standard antenna Kenwood TH-D72A is discussed in the post

A short time ago, mostly home-made equipment was used to work on the 144-145 MHz range. Among radio amateurs, VHF transverters were popular, many of which were comparable in size to the transceiver used with it. Radio amateurs converted decommissioned industrial VHF-type "Palma" radio stations to the amateur VHF band of 145 MHz, receiving a radio station operating on several channels. Then "Viola" became available to radio amateurs, and later "Mayaki" operating on forty channels. These radio stations then looked fantastic in their capabilities!

At present, it is relatively inexpensive to purchase multichannel portable VHF transceivers of world famous companies - "YAESU", "KENWOOD", "ALINCO", which in their parameters and ease of operation significantly surpass both homemade equipment in the 145 MHz range, and converted industrial equipment - "Palms "," Lighthouses "," Viols ".

But to work through a repeater from home, office, while driving when working from a car, an antenna is needed that is more effective than the "rubber band" used in conjunction with a portable radio station. When using a stationary "branded" VHF station, it is often advisable to use a homemade VHF antenna with it, since a decent "branded" outdoor antenna of the 145 MHz range is not cheap.

This material is devoted to the manufacture of simple homemade antennas suitable for use with stationary and portable VHF radio stations.

Features of 145 MHz antennas

Due to the fact that for the manufacture of antennas in the 145 MHz range, a thick wire is usually used - with a diameter of 1 to 10 mm (sometimes thicker vibrators are used, especially in commercial antennas), antennas in the 145 MHz range are broadband. This often makes it possible, when making the antenna exactly according to the specified dimensions, to do without its additional tuning to the 145 MHz range.

To tune antennas in the 145 MHz range, you must have a SWR meter. It can be either a homemade device or an industrial one. On the 145 MHz band, radio amateurs practically do not use bridge antenna resistance meters, due to the apparent complexity of their correct manufacture. Although with careful manufacture of the bridge meter and, therefore, its correct operation in this range, it is possible to accurately determine the input impedance of the VHF antennas. But even using only SWR - a through-type meter, it is quite possible to tune homemade VHF antennas. The power of 0.5 W, which is provided by imported portable radio stations in the "LOW" mode and domestic portable VHF radio stations such as "Dnepr", "Viola", "VEBR", is quite enough for the operation of many types of SWR meters. The "LOW" mode allows tuning antennas without fear of failure of the output stage of the radio station at any input impedance of the antenna.

Before tuning the VHF antenna, it is advisable to make sure that the SWR meter readings are correct. It is a good idea to have two SWR meters rated for 50 and 75 ohm transmission paths. When tuning VHF antennas, it is desirable to have a control antenna, which can be either a "rubber band" from a portable radio station or a homemade quarter-wave pin. When tuning the antenna, the level of the field strength created by the tuned antenna is measured relative to the reference one. This makes it possible to judge the comparative efficiency of the tunable antenna. Of course, if a standard calibrated field strength meter is used in the measurements, an accurate estimate of the antenna performance can be obtained. When using a calibrated field meter, it is easy to remove the antenna directional pattern. But even using home-made field strength meters for measurements and having obtained only a qualitative picture of the distribution of the electromagnetic field strength, it is possible to draw a conclusion about the efficiency of the tuned antenna and approximately estimate its directional pattern. Consider the practical designs of VHF antennas.

Simple antennas

The simplest outdoor VHF antenna (Fig. 1) can be made using an antenna that works in conjunction with a portable radio station. On the window frame from the outside (Fig. 2) or from the inside, on an extension wooden bar, a metal corner is attached, in the center of which there is a socket for connecting this antenna. It is necessary to strive to ensure that the coaxial cable leading to the antenna was the minimum required length. Along the edges of the corner, 4 counterweights, each 50 cm long, are attached. It is necessary to ensure good electrical contact of the counterweights, the antenna connector with the metal corner. The shortened twisted antenna of the radio station has an input impedance in the range of 30-40 ohms, so that a coaxial cable with a characteristic impedance of 50 ohms can be used to power it. With the help of the angle of inclination of the counterweights, it is possible to change the input impedance of the antenna within certain limits, and, therefore, to match the antenna with the coaxial cable. Instead of a proprietary "rubber band", you can temporarily use an antenna made of a copper wire with a diameter of 1-2 mm and a length of 48 cm, which is inserted into the antenna socket with its sharply sharpened end.

Figure 1. Simple outdoor VHF antenna

Figure 2. Construction of a simple outdoor VHF antenna

The VHF antenna, made of a coaxial cable with the outer sheath removed, works reliably. The cable is terminated in the HF-connector similar to the connector of the "proprietary" antenna (Fig. 3). The length of the coaxial cable used for the manufacture of the antenna is 48 cm. This antenna can be used in conjunction with a portable radio station instead of a broken or lost standard antenna.

Figure 3. Simple homemade VHF antenna

For quick production of a remote VHF antenna, you can use a connecting coaxial cable 2-3 meters long, which is terminated with connectors corresponding to the antenna socket of the radio station and the antenna. The antenna can be connected to such a piece of cable using a high-frequency tee (Fig. 4). In this case, a “rubber band” antenna is connected from one end of the tee, and 50 cm counterweights are screwed on the other end of the tee, or another type of radio technical “ground” for the VHF antenna is connected through the connector.

Figure 4. Simple remote VHF antenna

Homemade antennas portable radio station

If you lose or break the standard antenna of a portable radio station, you can make a homemade twisted VHF antenna. For this, a base is used - polyethylene insulation of a coaxial cable with a diameter of 7-12 mm and a length of 10-15 cm, on which initially 50 cm of a copper wire with a diameter of 1-1.5 mm is wound. It is very convenient to use a frequency response meter to tune a twisted antenna, but you can also use an ordinary SWR meter. Initially, the resonant frequency of the assembled antenna is determined, then, by biting off part of the turns, shifting, moving apart the turns of the antenna, the twisted antenna is tuned to resonance at 145 MHz.

This procedure is not very complicated, and by tuning 2-3 twisted antennas, the radio amateur can tune new twisted antennas in literally 5-10 minutes, of course, if the above devices are available. After tuning the antenna, it is necessary to fix the turns either with electrical tape, or with a cambric soaked in acetone, or with a heat-shrinkable tube. After fixing the turns, it is necessary to check the frequency of the antenna again and, if necessary, adjust it using the upper turns.

It should be noted that in "branded" shortened twisted antennas, heat-shrinkable tubes are used to fix the antenna conductor.

Half-wave field antenna

For quarter-wave antennas to work effectively, multiple quarter-wave counterweights must be used. This complicates the design for a field quarter-wave antenna, which must be spaced out in relation to the VHF transceiver. In this case, you can use a VHF antenna with an electrical length of L / 2, which does not require counterweights for its operation, and provides a directional pattern pressed to the ground and ease of installation. For an antenna with an electrical length of L / 2, there is a problem of matching its high input impedance with the low characteristic impedance of the coaxial cable. An antenna with a length L / 2 and a diameter of 1 mm will have an input impedance on the 145 MHz band of about 1000 ohms. Matching using a quarter-wave resonator, which is optimal in this case, is not always convenient in practice, since it requires the selection of points for connecting the coaxial cable to the resonator for its effective operation and precise tuning of the antenna pin to resonance. The dimensions of the resonator for the 145 MHz range are also relatively large. The destabilizing factors on the antenna when it is matched using a resonator will be especially pronounced.

However, at low powers supplied to the antenna, quite satisfactory matching can be achieved with the help of a P - loop, similarly to how it is described in the literature. A diagram of a half-wave antenna and its matching device is shown in Fig. 5. The length of the antenna rod is chosen slightly shorter or longer than the length L / 2. This is necessary so that even with a small difference in the electrical length of the antenna from L / 2, the active resistance of the antenna impedance decreases noticeably, and its reactive part at the initial stage increases insignificantly. As a result, matching with the help of the P-loop of such a shortened antenna is possible with greater efficiency than matching an antenna with a length of exactly L / 2. It is preferable to use an antenna with a length slightly longer than L / 2.

Figure 5. Coordination of the VHF antenna using the P - loop

Air trimming capacitors of the KPVM-1 type were used in the matching device. Coil L1 contains 5 turns of silver-plated wire with a diameter of 1 mm, wound on a mandrel with a diameter of 6 mm and a pitch of 2 mm.

Antenna tuning is not difficult. By including the SWR meter in the cable path of the antenna and at the same time measuring the level of the field strength created by the antenna, by changing the capacitance of variable capacitors C1 and C2, compressing-stretching the turns of the L1 coil, they achieve the minimum readings of the SWR meter and, accordingly, the maximum readings of the field strength meter. If these two maxima do not coincide, it is necessary to slightly change the length of the antenna, and repeat its adjustment again.

The matching device was placed in a case soldered from foil-clad fiberglass with dimensions of 50 * 30 * 20 mm. When working from a stationary workstation of a radio amateur, the antenna can be placed in the window opening. When working in the field, the antenna can be suspended from the upper end from a tree using a fishing line, as shown in fig. 6. A 50-ohm coaxial cable can be used to power the antenna. The use of a 75-ohm coaxial cable will slightly increase the efficiency of the antenna matching device, but at the same time, it will require tuning the output stage of the radio station to operate on a 75-ohm load.

Figure 6. Installing Antenna for Field Operation

Foil Window Antennas

On the basis of the adhesive foil used in security alarm systems, very simple designs of VHF window antennas can be built. This foil can be purchased with an adhesive base. Then, having freed one side of the foil from the protective layer, it is enough just to press it against the glass and the foil is instantly reliably glued. Foil without an adhesive base can be glued to glass with varnish or glue like "Moment". But for this you need to have some skill. The foil can even be secured to the window with adhesive tape.

With proper training, it is quite possible to make a good soldered connection between the center conductor and the braid of the coaxial cable with aluminum foil. Based on personal experience, each type of such foil requires its own flux for soldering. Some types of foil solder well even using rosin alone, some can be soldered with soldering grease, other types of foil require the use of active fluxes. The flux must be tested on the specific type of foil used to make the antenna, in advance of its installation.

Good results are obtained by using a foil-clad fiberglass substrate for soldering and fixing the foil, as shown in Fig. 7. A piece of foil-clad fiberglass is glued to the glass using Moment glue, the antenna foil is soldered to the edges of the foil, the coaxial cable cores are soldered to the copper foil of the fiberglass at a short distance from the foil. After soldering, the connection must be protected with a moisture-resistant varnish or glue. Otherwise, this connection may corrode.

Figure 7. Connecting Antenna Foil to Coaxial Cable

Let us examine the practical designs of foil-based window antennas.

Vertical window dipole antenna

A diagram of a vertical dipole window VHF antenna based on a foil is shown in Fig. eight.

Figure 8. Windowed vertical dipole VHF antenna

The quarter-wave post and counterweight are positioned at 135 degrees to bring the antenna system's input impedance closer to 50 ohms. This makes it possible to use a coaxial cable with a characteristic impedance of 50 Ohm to power the antenna and use the antenna in conjunction with portable radio stations, the output stage of which has such an input impedance. The coaxial cable should run perpendicular to the antenna over the glass for as long as possible.

Foil frame antenna

A frame window VHF antenna shown in Fig. 2 will work more efficiently than a dipole vertical antenna. 9. When the antenna is fed from the lateral angle, the maximum of the radiated polarization is in the vertical plane, when the antenna is fed in the lower angle, the maximum of the radiated polarization is in the horizontal plane. But at any position of the power points, the antenna emits a radio wave, with combined polarization, both with vertical and horizontal. This circumstance is very favorable for communication with portable and mobile radio stations, the position of the antennas of which will change during movement.

Figure 9. Frame VHF window antenna

The input impedance of the windowed loop antenna is 110 ohms. To match this impedance to a coaxial cable with a characteristic impedance of 50 ohms, a quarter-wave section of coaxial cable with a characteristic impedance of 75 ohms is used. The cable should run perpendicular to the antenna axis for as long as possible. The loop antenna has a gain of about 2 dB higher than a dipole window antenna.

When making foil window antennas with a width of 6-20 mm, they do not require tuning and operate in a frequency range much wider than the amateur band of 145 MHz. If the obtained resonant frequency of the antennas is lower than the required one, then the dipole can be tuned by symmetrically cutting off the foil from its ends. The loop antenna can be tuned using a jumper made from the same foil used to make the antenna. The foil closes the antenna web in the corner, opposite the power points. Once configured, contact between the jumper and the antenna can be achieved either by soldering or using adhesive tape. Such adhesive tape should press the jumper firmly against the antenna web in order to ensure reliable electrical contact with it.

Antennas made of foil can be supplied with significant power levels - up to 100 watts or more.

Outdoor vertical antenna

When placing the antenna outside the room, the question always arises about protecting the opening of the coaxial cable from atmospheric influences, about using a high-quality antenna support insulator, moisture-resistant wire for antennas, etc. These problems can be solved by installing a protected outdoor VHF antenna. The design of such an antenna is shown in Fig. ten.

Figure 10. Protected outdoor VHF antenna

A hole is made in the center of a 1 meter long plastic water pipe, into which the coaxial cable can fit tightly. Then the cable is threaded there, protrudes out of the pipe, is exposed at a distance of 48 cm, the cable shield is twisted and soldered at a length of 48 cm. The cable with the antenna is put back into the pipe. Standard plugs are put on the top and bottom of the pipe. It is not difficult to waterproof the hole where the coaxial cable enters. This can be done with automotive silicone or a fast curing automotive epoxy. As a result, we get a beautiful, moisture-insulated protected antenna that can work for many years under the influence of atmospheric influences.

To fix the vibrator and the antenna counterweight inside, you can use 1-2 cardboard or plastic washers tightly put on the antenna vibrators. The antenna tube can be installed on a window frame, on a non-metallic mast, or in any other convenient location.

Simple coaxial collinear antenna

A simple collinear coaxial VHF antenna can be made of coaxial cable. A piece of water pipe can be used to protect this antenna from the weather as described in the previous paragraph. The design of a collinear coaxial VHF antenna is shown in Fig. eleven.

Figure 11. Simple collinear VHF antenna

The antenna provides a theoretical gain of at least 3 dB more than a quarter-wave vertical. It does not need counterweights for its operation (although their presence improves the performance of the antenna) and provides a flattened radiation pattern to the horizon. A description of such an antenna has repeatedly appeared on the pages of domestic and foreign radio amateur literature, but the most successful description was presented in the literature.

Antenna dimensions in fig. 11 are in centimeters for coaxial cable with a shortening factor of 0.66. Most coaxial cables with polyethylene insulation have such a factor of shortening. The dimensions of the matching loop are shown in Fig. 12. Without using this loop, the VSWR of the antenna system can exceed 1.7. If the antenna turned out to be tuned below the 145 MHz range, it is necessary to slightly shorten the upper section, if higher, then lengthen it. Of course, optimal setting possible by proportional shortening-lengthening of all parts of the antenna, but this is difficult to do in an amateur radio environment.

Figure 12. Dimensions of the matching loop

Despite the large size of the plastic pipe required to protect this antenna from atmospheric influences, the use of a collinear antenna of this design is quite reasonable. The antenna can be moved away from the building using wooden battens, as shown in fig. 13. The antenna can withstand significant power input to it up to 100 watts or more and can be used in conjunction with both stationary and portable VHF radio stations. The use of such an antenna in conjunction with low-power portable radio stations will give the greatest effect.

Figure 13. Installing a collinear antenna

Simple collinear antenna

This antenna was assembled by me similarly to the construction of a car remote antenna used in a cellular radiotelephone. To convert it to the amateur band of 145 MHz, I proportionally changed all dimensions of the "telephone" antenna. As a result of this, an antenna was obtained, the diagram of which is shown in Fig. 14. The antenna provides a horizontal radiation pattern and a theoretical gain of at least 2 dB over a simple quarter-wave rod. A coaxial cable with a characteristic impedance of 50 Ohm was used to power the antenna.

Figure 14. Simple collinear antenna

A practical antenna design is shown in Fig. 15. The antenna was made from a single piece of copper wire with a diameter of 1mm. Coil L1 contained 1 meter of this wire, wound on a mandrel with a diameter of 18 mm, the distance between the turns was 3 mm. When making a design exactly to the dimensions, the antenna practically does not require adjustment. It may be necessary to slightly tune the antenna by squeezing-stretching the turns of the coil to achieve a minimum SWR. The antenna was housed in a plastic water pipe. Inside the pipe, the antenna wire was fixed with pieces of foam. Four quarter-wave counterweights were installed at the lower end of the pipe. They were threaded and fastened to a plastic pipe with nuts. Counterweights can be 2-4 mm in diameter depending on the ability to thread them. For their manufacture, you can use copper, brass, or bronze wire.

Figure 15. Construction of a simple collinear antenna

The antenna can be installed on wooden rails on the balcony (as shown in fig. 13). This antenna can withstand significant levels of power input.

This antenna can be thought of as a shortened HF antenna with a center extension coil. Indeed, the antenna resonance measured with a bridge resistance meter in the HF range was found to lie in the frequency region of 27.5 MHz. Obviously, by varying the diameter of the coil and its length, but keeping the length of its winding wire, it is possible to achieve that the antenna works both in the VHF range of 145 MHz, and in one of the HF ranges - 12 or 10 meters. To operate on the HF bands, four L / 4 counterweights for the selected HF band must be connected to the antenna. This dual use of the antenna will make it even more versatile.

Experimental 5/8 wave antenna

When carrying out experiments with radio stations of the 145 MHz range, it is often necessary to connect the antenna under test to its output stage in order to check the operation of the reception path of the radio station or adjust the output stage of the transmitter. For these purposes, I have been using a simple 5/8 - wave VHF antenna for a long time, the description of which was given in the literature.

This antenna consists of a section of copper wire with a diameter of 3 mm, which is connected at one end to an extension coil and the other to a tuning section. At the end of the wire connected to the coil, a thread is cut, and at the other end, a tuning section made of copper wire with a diameter of 1 mm is soldered. The antenna is matched with a coaxial cable with a characteristic impedance of 50 or 75 Ohm by connecting to different turns of the coil, and may be a slight shortening of the tuning section. The antenna diagram is shown in Fig. 16. antenna design is shown in fig. 17.

Figure 16. Scheme of a simple 5/8 - wave VHF antenna

Figure 17. Construction of a simple 5/8 - wave VHF antenna

The coil is made on a plexiglass cylinder with a diameter of 19 mm and a length of 95 mm. At the ends of the cylinder, a thread is made into which the antenna vibrator is screwed on one side, and on the other side it is screwed to a piece of foil-clad fiberglass with dimensions of 20 * 30 cm, which serves as the “ground” of the antenna. On the back side, a magnet from an old speaker was glued to it, as a result of which the antenna can be attached to the windowsill, to the radiator, to other iron objects.

The coil contains 10.5 turns of wire with a diameter of 1 mm. The coil wire is evenly spaced over the frame. The coaxial cable is tapped from the fourth turn from the grounded end. The antenna vibrator is screwed into the coil, a contact lamella is inserted under it, to which the "hot" end of the extension coil is soldered. The lower end of the coil is soldered to the antenna ground foil. The antenna provides a SWR in the cable no worse than 1: 1.3. The antenna is tuned by shortening its upper part with pliers, which is initially slightly longer than necessary.

I have experimented with installing this antenna on a window pane. In this case, a vibrator with an original length of 125 centimeters made of aluminum foil was glued to the center of the window. The extension reel was used the same and was installed on the window frame. The counterweights were made of foil. The ends of the antenna and counterweights were curved slightly to fit on the window pane. Window 5/8 view - wave VHF antenna is shown in Fig. 18. The antenna is easily tuned into resonance by gradually shortening the vibrator foil using a blade, and by gradually switching the coil turns to minimize SWR. The window antenna does not spoil the interior of the room and can be used as a permanent antenna for operating on the 145 MHz band from home or office.

Figure 18. Window 5/8 - wave VHF antenna

Efficient Portable Radio Antenna

In the event that communication using a standard "rubber band" is not possible, a half-wave antenna can be used. It does not require "ground" for its work and when working over long distances it gives a gain in comparison with a standard "rubber band" up to 10 dB. These are quite realistic numbers, given that the physical length of a half-wave antenna is almost 10 times longer than the "rubber band".

The half-wave antenna is supplied with voltage and has a high input impedance, which can reach 1000 ohms. Therefore, this antenna requires a matching device when used with a radio with a 50 ohm output. One of the variants of the P-loop matching device has already been described in this chapter. Therefore, for a change, for this antenna, we will consider the use of another matching device, made on a parallel circuit. In terms of their efficiency, these matching devices are approximately equal. A diagram of a half-wave VHF antenna together with a matching device on a parallel circuit is shown in Fig. 19.

Figure 19. Half-wave VHF antenna with a matching device

The coil of the loop contains 5 turns of copper silver-plated wire with a diameter of 0.8 mm, wound on a mandrel with a diameter of 7 mm along a length of 8 mm. Tuning the matching device consists in tuning the circuit L1C1 to resonance using a variable capacitor C1; using a variable capacitor C2, the connection of the circuit with the transmitter output is regulated. Initially, the capacitor is connected in the third turn of the coil from its grounded end. Variable capacitors C1 and C2 must be air dielectric.

It is advisable to use a telescopic antenna for the antenna vibrator. This will make it possible to carry the half-wave antenna in a compact folded state. It also makes it easier to tune the antenna together with a real transceiver. At initial setup antenna, its length is 100 cm.During the tuning process, this length can be slightly adjusted according to better work antennas. It is advisable to make appropriate marks on the antenna in order to subsequently install the antenna from its folded position to the resonant length immediately. The box where the matching device is located must be made of plastic, in order to reduce the capacity of the coil to "ground", it can be made of foil-coated fiberglass. This depends on the actual operating conditions of the antenna.

The antenna is tuned using a field strength indicator. With the help of a SWR meter, tuning the antenna is advisable only if it works not on the body of the radio station, but when using an extension coaxial cable together with it.

When the antenna is working twice on the radio station body and using an extension coaxial cable, two marks are made on the antenna pin, one corresponding to the maximum field strength level when the antenna is operating on the radio station body, and the other risk corresponds to the minimum SWR when using an extension coaxial cable in conjunction with the antenna. Usually these two marks are slightly different.

Vertical continuous gamma-matched antennas

Vertical antennas made of a whole vibrator are wind-resistant, easy to install, and take up little space. For their implementation, you can use copper tubes, aluminum power electrical wire with a diameter of 6-20 mm. These antennas can be easily matched with a coaxial cable with a characteristic impedance of both 50 and 75 ohms.

An inseparable half-wave VHF antenna, the design of which is shown in Fig. 20. Gamma matching is used to power it through the coaxial cable. The material from which the antenna vibrator is made and the gamma matching must be the same, for example, copper or aluminum. Due to mutual electrochemical corrosion of many pairs of materials, it is unacceptable to use different metals for antenna and gamma matching.

Figure 20. Continuous half-wave VHF antenna

If a bare copper tube is used to make the antenna, then it is advisable to adjust the antenna gamma matching using a closing jumper as shown in Fig. 21. In this case, the surface of the pin and the conductor of the gamma matching is carefully cleaned and using a clamp of bare wire as shown in fig. 21a achieve the minimum VSWR in the coaxial power cable of the antenna. Then, in this place, the gamma matching wire is slightly flattened, drilled and connected with a screw to the antenna sheet, as shown in Fig. 21b. Soldering is also possible.

Figure 21. Setting gamma - matching copper antenna

If an aluminum wire is used for the antenna from a power electrical cable in plastic insulation, then it is advisable to leave this insulation to prevent corrosion of the aluminum wire with acid rain, which is inevitable in urban conditions. In this case, the antenna gamma matching is adjusted using a variable capacitor, as shown in Fig. 22. This variable capacitor must be carefully protected from moisture. If it is not possible to achieve the SWR in the cable less than 1.5, then the length of the gamma matching must be reduced and the setting repeated again.

Figure 22. Adjusting the gamma - matching of the aluminum-copper antenna

With sufficient space and materials, a continuous VHF vertical wave antenna can be installed. The wave antenna works more efficiently than the half-wave antenna shown in Fig. 20. A wave antenna provides a more horizontal radiation pattern than a half-wave antenna. You can match the wave antenna using the methods shown in Fig. 21 and 22. The design of the wave antenna is shown in fig. 23.

Figure 23. Continuous vertical wave VHF antenna

When performing these antennas, it is desirable that the coaxial power cable is at least 2 meters perpendicular to the antenna. The use of a balun together with a continuous antenna will increase the efficiency of its operation. When using a balun, use symmetrical gamma matching. The balun connection is shown in fig. 24.

Figure 24. Connecting the balun to a continuous antenna

Any other known balun can also be used as the antenna balun. When placing the antenna near conductive objects, it may be necessary to slightly reduce the length of the antenna due to the influence of these objects on it.

Round VHF antenna

If the placement in space vertical antennas shown in Fig. 20 and fig. 23 in their traditional vertical position is difficult, then they can be placed by rolling the antenna web in a circle. The position of the half-wave antenna shown in Fig. 20 in the "round" version is shown in fig. 25, and the wave antenna shown in Fig. 23 in Fig. 26. In this position, the antenna provides combined vertical and horizontal polarization, which is favorable for communications with mobile and portable radios. Although, theoretically, the level of vertical polarization will be higher with side feeding of circular VHF antennas, but in practice this difference is not very noticeable, and the side feeding of the antenna complicates its installation. The side power supply of the circular antenna is shown in Fig. 27.

Figure 25. Continuous round vertical half-wave VHF antenna

Figure 26. Continuous round vertical wave VHF antenna

Figure 27. Lateral power supply of circular VHF antennas

The round VHF antenna can be placed indoors, for example, between window frames, or outdoors, on a balcony or on a roof. When placing a circular antenna in the horizontal plane, we get a circular radiation pattern in the horizontal plane and the operation of an antenna with horizontal polarization. This may be necessary in some cases when conducting amateur radio communications.

Passive "amplifier" of the portable station

When testing or working with portable radios, sometimes there is not enough power for reliable communication. I made a passive "amplifier" for portable VHF stations. A passive "amplifier" can add up to 2-3 dB to the signal of a radio station on the air. This is often enough to reliably open the squelch of the correspondent station and ensure reliable operation. The design of the passive "amplifier" is shown in Fig. 28.

Figure 28. Passive "amplifier"

The passive "amplifier" is a large enough tinned coffee can (the bigger the better). A connector is inserted into the bottom of the can, similar to the antenna connector of a radio station, and a connector for connecting to the antenna jack is sealed into the lid of the can. 4 counterweights 48 cm long are soldered to the bank. When working with a radio station, this "amplifier" is switched on between the standard antenna and the radio station. Due to the more effective "ground" and there is an increase in the place of reception of the strength of the emitted signal. Other antennas can be used in conjunction with this "amplifier", for example, a L / 4 pin made of copper wire, simply inserted into the antenna socket.

Broadband survey antenna

Many imported portable radios provide reception not only in the amateur band of 145 MHz, but also in the survey bands of 130-150 MHz or 140-160 MHz. In this case, for successful reception in survey bands, on which a twisted antenna tuned to 145 MHz does not work effectively, you can use a broadband VHF antenna. The antenna diagram is shown in Fig. 29 and dimensions for different ranges of operation are given in table. 1.

Figure 29. Broadband VHF vibrator

Range, MHz	130-150	140-160
Size A, cm	26	24
Size B, cm	54	47

Table 1. Dimensions of broadband VHF antenna

To work with the antenna, you can use a coaxial cable with a characteristic impedance of 50 Ohm. The antenna can be made of foil and glued to the window. You can make the antenna fabric from an aluminum sheet, or by printing on a piece of foil-clad fiberglass of suitable dimensions. This antenna can transmit and receive in the specified frequency ranges with high efficiency.

Zigzag antenna

Some service VHF long-distance radio stations use antenna arrays consisting of zigzag antennas. Radio amateurs can also try to use elements of such an antenna system for their work. The view of an elementary zigzag antenna included in the design of a complex VHF antenna is shown in Fig. thirty.

Figure 30. Elementary zigzag antenna

The zigzag elementary antenna consists of a half-wave dipole antenna that supplies voltage to the half-wave vibrators. In real antennas, up to five such half-wave vibrators are used. Such an antenna has a narrow directional pattern pressed to the horizon. The type of polarization emitted by the antenna is combined - vertical and horizontal. It is advisable to use a balun for antenna operation.

In antennas used in service communication stations, a reflector made of a metal mesh is usually placed behind elementary zigzag antennas. The reflector provides one-way directivity of the antenna. Depending on the number of vibrators included in the antenna and the number of zigzag antennas included together, the required antenna gain can be obtained.

Radio amateurs practically do not use such antennas, although they are easy to perform for the amateur VHF bands of 145 and 430 MHz. For the manufacture of the antenna sheet, you can use an aluminum wire with a diameter of 4-12 mm from a power electrical cable. In the domestic literature, a description of such an antenna, for which a rigid coaxial cable was used, was given in the literature.

Antenna Kharchenko in the range of 145 MHz

Kharchenko's antenna is widely used in Russia for television reception and in service radio communications. But radio amateurs use it to work on the 145 MHz band. This antenna is one of the few that works very efficiently and requires little or no tuning. The diagram of Kharchenko's antenna is shown in Fig. 31.

Figure 31. Kharchenko's antenna

Both 50 and 75 ohm coaxial cables can be used for antenna operation. The antenna is broadband, operates in a frequency band of at least 10 MHz on a range of 145 MHz. To create a one-sided radiation pattern, a metal mesh is used behind the antenna, located at a distance of (0.17-0.22) L.

The Kharchenko antenna provides a width of the beam pattern in the vertical and horizontal planes close to 60 degrees. For further narrowing of the radiation pattern, passive elements in the form of vibrators with a length of 0.45L are used, located at a distance of 0.2L from the diagonal of the square of the frames. To create a narrow radiation pattern and increase the gain of the antenna system, several combined antennas are used.

Directional loop antennas in the range of 145 MHz

One of the most popular directional antennas for operation in the 145 MHz band are loop antennas. The most common two-element loop antennas on the 145 MHz band. In this case, an optimal cost / quality ratio is obtained. The diagram of a two-element loop antenna as well as the dimensions of the perimeter of the reflector and the active element are shown in Fig. 32.

Figure 32. VHF loop antenna

The antenna elements can be made not only in the form of a square, but also in the form of a circle, a delta. To increase the vertical component radiation, the antenna can be powered from the side. The input impedance of the dual element antenna is close to 60 ohms, and both 50 ohm and 75 ohm coaxial cables are suitable for operation. The gain of a two-element VHF loop antenna is at least 5 dB (above the dipole) and the ratio of radiation in the forward and reverse direction can reach 20 dB. When working with this antenna, it is useful to use a balun.

Circularly polarized loop antenna

An interesting design for a circularly polarized loop antenna has been proposed in the literature. Circularly polarized antennas are used for communication via satellites. The dual feed of the 90 degree phase shift loop antenna allows the synthesis of a circularly polarized radio wave. The loop antenna power circuit is shown in Fig. 33. When designing an antenna, it is necessary to take into account that the length L can be any reasonable, and the length L / 4 must correspond to the wavelength in the cable.

Figure 33. Circularly polarized loop antenna

To increase the gain, this antenna can be used in conjunction with a loop reflector and a director. The frame must be powered only through a balun. The simplest balun is shown in Fig. 34.

Figure 34. The simplest balun

Industrial antennas of the range of 145 MHz

Currently, you can find a large selection of branded antennas for the 145 MHz range on sale. If you have the money, of course, you can buy any of these antennas. It should be noted that it is advisable to purchase solid antennas already tuned to the 145 MHz range. The antenna must have a protective coating that protects it from corrosion by acid rain, which can fall in a modern city. Telescopic antennas are unreliable in urban environments and may fail over time.

When assembling antennas, it is necessary to strictly follow all instructions in the assembly instructions, and do not spare silicone grease for waterproofing connectors, telescopic joints and screw connections in matching devices.

Literature

1. I. Grigorov (RK3ZK). Matching devices 144 MHz band // Radio amateur. KV and UKV-1997.-№ 12.-С.29.
2. Barry Bootle. (W9YCW) Hairpin Match for the Collinear - Coaxial Arrau // QST.-1984.-October.-P.39.
3. Doug DeMaw (W1FB) Build Your Own 5/8-Wave Antenna for 146 MHz // QST.-1979.-June.-P.15-16.
4. S. Bunin. Antenna for communication through satellites // Radio. 1985. No. 12. S. twenty.
5. D. S. Robertson, VK5RN The “Quadraquad” - Circular Polarization the Easy Way //QST.-April.-1984.-pages16-18.

American radio amateurs use the following DXpedition calling frequencies (in kHz):

• 1828.5,
• 3505,
• 7005,
• 7065,
• 10110,
• 14025,
• 14195,
• 18075,
• 18145,
• 21025,
• 21295,
• 24895,
• 24945,
• 28025,
• 28495.

Calling frequencies for QRP stations (in kHz):

• 1810,
• 3560,
• 10106,
• 14060,
• 14285,
• 21060,
• 21385,
• 28060,
• 28385.

In Europe and some other countries, it is recommended to use frequencies (kHz) for low power operation (QRP) in SSB mode:

• 3690,
• 7090,
• 14285,
• 21285.

For telegraph (in kHz):

• 1843,
• 3560,
• 7030,
• 10106,
• 14060,
• 18096,
• 21060,
• 24906,
• 28060.

Frequencies for DXpeditions in Europe have not yet been announced.

SSB-QRP round tables are held at 3620 kHz at 18:30 MEZ (MES).

Western radio amateurs supporting the SOTA program use frequencies (kHz):

• 7030,
• 7060,
• 14060,
• 14285,
• 145575 (FM),
• 144285 (SSB),
• 430150,
• 430475 (FM),
• 432200 (SSB).

In Russia, fans of the RDA program (working "through fraction") can usually be found around the frequency of 14180 kHz ± QRM.

Frequencies for mountain expeditions under the RMA program are not precisely specified, therefore mountain radio amateurs use standard frequencies for DXpeditions and QRPs described above.

Frequencies in Moscow and Moscow region

Frequencies of the Ministry of Internal Affairs

148-149 MHz - 25 kHz step (NFM mode).

148.2250 and 148.9500 - channel of the Ministry of Internal Affairs on railway transport.

171-173 MHz - 25 step (NFM mode)

171.7250 and 171.7500 - the duty unit of the Main Internal Affairs Directorate of Moscow.

171.7750 and 172.3250 - the special channel of the Main Internal Affairs Directorate of Moscow.

172.3000 and 172.2750 - the duty unit of the Main Internal Affairs Directorate of Moscow.

205.100 is the frequency of the UGAI GUVD of Moscow.

450-453 MHz - 12.5 step (NFM)

450.3000 450.3750 450.4750 450.5000 450.5705

450.6250 450.6500 450.6750

451.0500 451.1500

451.3000 451.4000

451.5250 and 451.5375 - scrambling.

452.4250 452.5875 452.6200

460-463 MHz - 12.5 step (NFM mode)

460.8000 and 461.4500 - scrambling.

461.0000 - special communication channel of the Ministry of Internal Affairs of the Russian Federation.

Ministry of Defense of the Russian Federation

RF Ministry of Defense frequency ranges:

• 254.000,
• 254.685,
• 380.000,
• 393.100.

FAPSI

• 148-149 (step 1) - the radio frequency band is intended for preferential use by radio communications of the Ministry of Internal Affairs of the Russian Federation.
• 149-149.9 (step 0.9) - the radio frequency band is intended for use by radio electronic means of government communications, security and defense of the Russian Federation.
• 157.875 - FAPSI special purpose channel.
• 162.7625-163.2 (step 0.4375) - the radio frequency band is intended for use by radio electronic means of government communications, security and defense of the Russian Federation.
• 168.5-171.15 (step 2.65) - the radio frequency band is intended for use by radio electronic means of government communications, security and defense of the Russian Federation.
• 169.455 and 169.462 - FAPSI special purpose channels.
• 171.15-173 (step 1.85) - the radio frequency band is intended for preferential use by radio communications of the Ministry of Internal Affairs of the Russian Federation.
• 173-174 (step 1) - the radio frequency band is intended for use by radio electronic means of government communications, security and defense of the Russian Federation.
• 273-300 (step 27) - the radio frequency band is intended for use by radio electronic means of government communications, security and defense of the Russian Federation.
• 300-308 (step 8) - The radio frequency band is dedicated to fixed and mobile services. Separate sections in this band are used by radio-electronic means of government communications, security and defense of the Russian Federation.
• 308-328.6 (step 20.6) - the radio frequency band is intended for preferential use by radio electronic means of government communications, security and defense of the Russian Federation.
• 328.6-335.4 (step 6.8) - the radio frequency band is intended for the aeronautical radio navigation service and is mainly used by radio electronic means of government communications, security and defense of the Russian Federation.
• 335.4-336 (step 0.6) - the radio frequency band is intended for preferential use by radio electronic means of government communications, security and defense of the Russian Federation.
• 336-344 (step 8) - The radio frequency band is dedicated to the fixed and mobile services. Separate sections in this band are used by radio-electronic means of government communications, security and defense of the Russian Federation.
• 344-390 (step 46) - the radio frequency band is intended for preferential use by radio electronic means of government communications, security and defense of the Russian Federation.

Fire brigade

All frequencies of the Moscow fire brigade headquarters:

• 148.050,
• 148.075,
• 148.125,
• 148.200.

Citizen Band

• 26.965-27.855 MHz (Europe),
• 26.960-27.850 MHz (Russia) - step 10 (NFM, AM, USB, LSB mode).
• 144-146 MHz - NFM USB CW DATA (for NFM 25 kHz step).
• 145.025, 145.125, 145.625, 145.725 - frequencies of the repeaters of the Moscow Radio Club.
• 146.100, 146.700 - radio amateur repeaters.
• 430-440 MHz - NFM USB CW DATA (for NFM step 25).

Some of the frequencies are occupied by trunk operators.

1260-1300 MHz (amateur radio 23 cm band). 240-250 GHz (amateur radio 12 cm band). This is the European grid. For the Russian grid, respectively, the last digit is "0".

For example, 27.155MHz - C16E, 27.150MHz - C16R.

From useful channels (as applied to Moscow) - ЗсЕ, 9сЕ, 19сЕ, 21dE.

These are emergency channels, there are dispatchers who report and receive messages about traffic jams and accidents. It is better to transmit information about road accidents and other emergencies in channels ЗсЕ ("Petrovka") or 9сЕ (Rescue Service).

Channel 9сE is dedicated to the transmission of exclusively road accidents and other emergencies. If you register with the Scream service (Petrovka, ZsE) or with the Rescue Service (19sE, 21dE, registration is free, but mandatory), then the dispatcher can be asked to call and send something or use it all as a pager (you can call control room and ask to transfer information to the person you need (of course, if he has a CB station).

The service "Flight-27" (9dE) works in a similar way, only free of charge. And in other cases, just your own connection, to go out of town, the connection between cars, etc. There are channels occupied by some kind of clubs of interest (to some extent this is "Flight-27", since it is organized by Association-27) and certain districts of Moscow.

The allowed channels (40 channels each in grids C and D) are pretty much clogged, and the additional grids are empty (A, B, E, F - if you really want to, then you can work in them, everyone pretends that they do not notice this violation)

VHF

Frequencies of the amateur VHF band:

• 144-146 MHz - NFM USB CW DATA (for NFM step 25).
• 145.025, 145.625 inverse repeater (Dmitrov).
• 145.125, 144.525 repeater.
• 145,600, 145,000 Serpukhov repeater.
• 145.625, 145.025 repeater.
• 145.650, 145.050 suspension repeater at Moscow State University.
• 145.700, 145.100 Shchelkovo repeater.
• 145.725, 145.125 repeater Troitsk.
• 145.750, 145.150 Mitino repeater.
• 430-440 MHz - the same, part of the frequencies were sold to trunk operators.

Note. As a rule, the transmit and receive frequencies of radio amateur repeaters (repeaters) have a discrepancy with respect to each other by 600 kHz. This parameter is also programmed by the manufacturer in the Kenwood TH-F7 transceiver.

Moreover, if the receiving frequency of the repeater is 145.750, then the frequency of its transmission will be -600 kHz, that is, 145.150 MHz .. In inverse repeaters, everything is exactly the opposite.

The Kenwood TH-F7 transceiver allows you to work with inverted repeaters, for this the transceiver is reprogrammed from the keyboard so that the R indicator is lit on the display (see section 3.12).

Radio amateur satellite communications

Frequencies of radio amateur satellite communication:

• 7000-7100 (step 100) - The radio frequency band is intended for amateur and amateur-satellite services.
• 14000-142 50 (step 250) - The radio frequency band is intended for amateur and amateur-satellite services.
• 21000-21450 (step 450) - The radio frequency band is intended for amateur and amateur-satellite services.
• 28-29.7 MHz (step 1.7) - The radio frequency band is intended for the amateur and amateur-satellite services.
• 1240.000 - the beginning of the radio amateur 25-centimeter range (up to 1300.000).
• 1300.000 - the end of the radio amateur 25-centimeter range (from 1240.000).
• 2310.000 - the beginning of the amateur radio 12-centimeter range (up to 2450.000).
• 2450.000 - the end of the amateur radio 12-centimeter range (from 2310.000).

Kv

HF Amateur Band Frequencies:

• 1.83-1.93 MHz (160 m).
• 3.5-3.8 MHz (80 m).
• 7-7.1 MHz (40 m).
• 10.1-10.15 MHz (30m CW only).
• 14-14.35 MHz (20 m).
• 18.068-18.168 MHz (16 m).
• 21-21.45 MHz (15 m).
• 24.89-24.99 MHz (12 m).
• 28-29.7 MHz (10m).

When working with voice at frequencies below 10 MHz, LSB is used, above 10 MHz - USB. AM stations operate on 160 and 10 meters. Mainly CW, SSB and digital communications (Packet Radio, SSTV, RTTY) are used. FM stations are rarely heard on only 10 meters.

LOW BAND radio stations

LOW BAND radios are used by radio amateurs, security guards and various "outside" services.

• 30-36 MHz;
• 39-50 MHz;
• 36-42 MHz;
• 42-50 MHz;
• 136-162 MHz;
• 136-174 MHz;
• 146-174 MHz;
• 300-345 MHz;
• 403-433 MHz;
• 403-470 MHz;
• 438-470 MHz;
• 465-495 MHz;
• 490-520 MHz.

Some frequencies dedicated to radiotelephones

For example, Panasonic radiotelephones operate at frequencies of 31-40 MHz.

All frequencies are known (the author of the book has a complete list) on which all modern radiotelephones operate. To tune the receiver of the transceiver to the frequency of the base or handset of the telephone set, it is necessary to know the model of the radiotelephone used.

Air Frequencies

Paging companies

In Moscow, paging companies operate + in the range of 146—168 and 450-475 MHz in NFM mode.

Closed paging systems can work:

1. on subcarriers of radio stations and television;
2. in regular paging companies, but messages are encrypted in transit;
3. at frequencies not typical for paging communications;
4. using transmission methods other than Pocsag.

Frequencies not owned by any of the well-known companies: 160.5500, 164.3500, 474.5000.

Cellular network Beeline (AMPS, DAMPS)

• 825-845 MHz -. mobile objects.
• 870-890 MHz - repeaters in NFM mode, step 30 (for AMPS, for D-AMPS - multiple channels per carrier).

MTS cellular network (Moscow cellular communication, NMT-450)

• 453-457.5 MHz - mobile objects.
• 463-467.5 MHz - repeaters.

MTS cellular network (Mobile Telesystems, GSM-900)

NFM mode, step 25. Frequencies:

• 890-915 MHz - mobile objects.
• 935-965 MHz - repeaters.

Digital communications, multiple channels per carrier

Cellular network GSM-1800 (Beeline).

Frequencies: 1.8-1.9 GHz digital communication, multiple channels per carrier.

Cellular CDMA network (no data).

Trunking networks

In Moscow, there are a lot, mainly from 140 to 470 MHz (with exceptions) NFM mode, step 12.5 kHz.

Examples of frequencies (MHz):

• 150 (150.450)
• 373-375
• 435-452
• 433-434 (433.45, 433.475, etc.)
• 477-478 (477.60, 477.61, 477.625, 477.65, 477.675, 477.70, etc.)
• 484 (484.86)
• 864-870 possibly MTK trunk.

RusAltai Network (ASVT)

• 337-343 MHz - mobile objects.
• 368-388 MHz - repeaters.

NFM mode, step 25.

AMT network

NFM mode, step 12.5 or 25. Duplex and half duplex. Frequencies:

transmission / reception

• 300-308 MHz / 336-344 MHz,
• 336-340 MHz / 346-350 MHz.

Satellite network INMARSAT

• 1626.5-1646.5 upstream beam from terminal stations.
• 1530-1545 downward beam to terminal stations.

Other frequencies that are active on the air

• 30-50 MHz (Low band);
• 34.150 Moslift;
• 34.200 Mosvodoprovod;
• 34.875 Fireworks;
• 36.050 Regional water supply;
• 36.075 Control and measuring devices;
• 36.325 Sewerage;
• 36.925 Moslift;
• 38.750, 39.800, 42.870, 44.350, 44.600 Military;
• 40.100, 44.800 Regional firefighters;
• 41.700 Autobeeper;
• 41.800 Oblast doctors 41.900 DEZ;
• 41.950 Depot;
• 42.150 Moscow sewerage;
• 42.250 Forestry;
• 43.125, 43.825 Reserve channels in case of war;
• 43.200 Mosenergo;
• 43.800, 44.750 Taxi;
• 46.200, 43.975, 44.500 armored personnel carriers;
• 45.950 Mosga.

Frequencies of some service radio stations in St. Petersburg, and not only

List of frequencies permanently banned on the territory of Russia

495-505 kHz(step 10) - 500 kHz radio frequency is international distress and calling frequency for radiotelegraphy morse.

Any radiation that may cause harmful interference to communications in case of distress, accident, urgency or safety is prohibited on the following frequencies:

• 500 kHz,
• 2174.5 kHz,
• 2182 kHz,
• 2187.5 kHz,
• 4125 kHz,
• 4177.5 kHz,
• 4207.5 kHz,
• 6215 kHz,
• 6268 kHz,
• 6312 kHz,
• 8291 kHz,
• 8376.5 kHz,
• 8414.5 kHz,
• 12290 kHz,
• 12520 kHz,
• 12577 kHz,
• 16420 kHz,
• 16695 kHz,
• 16804.5 kHz,
• 121.5 MHz,
• 156.525 MHz,
• 156.8 MHz
• and in the frequency bands 406-406.1 MHz, 1544-1545 MHz and 1645.5-1646.5 MHz.

Any radiation on any other discrete frequency causing harmful interference to communications in the event of distress and to ensure safety is also prohibited.

2173.5-2190.5 (step 17) - radio frequency 2182 kHz (carrier) is also a call for radiotelephony.

This radio frequency can be used for search and rescue purposes for manned spacecraft. Radio frequency 2174.5 kHz, 4177.5 kHz, 6268 kHz, 8376.5 kHz, 12520 kHz and 16695 kHz are international frequencies exclusively for the exchange of information in the event of distress and for safety at sea using narrow-band telegraphy (direct-printing) equipment.

Radio frequency 2187.5 kHz, 4207.5 kHz, 6312 kHz, 8114.5 kHz, 12577 kHz and 16804.5 kHz are international frequencies intended solely for distress calling and for the safety of navigation using digital selective calling equipment. Other transmissions in the specified frequency band are prohibited.

117.975-137 (step 19.025) - the radio frequency band is intended for preferential use aeronautical mobile service... Sections in this radio frequency band may be used by the aeronautical mobile-satellite (P) service.

Airborne emergency radio frequency 121.5 MHz used by stations in the aeronautical mobile service operating in the frequency band 117.975-137 MHz for radiotelephone distress and safety communications.

121.5 MHz can also be used for these purposes by stations life-saving appliances and emergency radio beacons-indicators places of distress, for the purposes of search and rescue of manned spacecraft. 121.45-121.55 MHz may be used by the mobile-satellite service to receive on-board satellite signals from emergency beacons transmitting signals on the 121.5 MHz radio frequency.

123.1 MHz is the auxiliary frequency for air emergency frequency 121.5 MG c and is intended for use by stations of the aeronautical mobile service, as well as other mobile and land stations participating in joint search and rescue operations.

Mobile stations in the maritime mobile service may communicate on these frequencies with stations in the aeronautical mobile service for distress and safety purposes.

136-137 MHz can be used space exploitation service(Space-to-Earth), space research service (Space-to-Earth) and meteorological satellite (Space-to-Earth) service on a secondary basis.

156.8 MHz is an international distress frequency, safety and calling in the maritime mobile service for radiotelephony. This radio frequency can be used for search and rescue of manned spacecraft.

406-406.1 (step 0.1) - the radio frequency band is intended exclusively for satellite emergency beacons- indicators of the place of disaster (Earth-Space).

List of prohibited frequencies for radio traffic

• 500 kHz 40,000
• 1.544-1.545 MHz (hereinafter MHz) 40.100
• 1,645-1,646 40,200
• 2,040 40,500
• 2125-2135 41,800
• 2,145 42,000
• 2,147-2,153 42,450
• 2,173-2,190 42,750
• 2,380 43,150
• 2,498-2,502 43,750
• 2,850-3,155 44,300
• 3,400-3,500 44,400
• 3.900-3,950 44,600
• 4,125 44,700 4,175 44,800 4,177 44,900 4,188 45,100 4,207 45,125 4,210 45,200 4,430 45,300 4,650-4,750 45,350
• 4.995-5,005 45,400 5,410 45,600 5,480-5,730 45,700 6,215 45,800 6,268 46,425 6,282 46,475 6,312 46,550 6,314 46,600 6,525-6,765 46,650 8,195-8,416 46,700 8,815-9,040 46,775
• 9.995-10,100 46,825
• 11,175-11,400 46,875 12,230-12,575 46,956 13,200-13,360 47,075 14,957-14,967 47,125
• 14.990-15,900 47,375 16,360-16,800 47,575
• 17.900-18,030 47,825 18,055-18,065 47,975 18,780-18,900 48,075 19,680 74,600-75,400
• 19.990-20,010 121,500
• 21,850-21,870 121,716-121,784 21,924-22,000 130,133-130,201 22,376 139,174-139,242
• 24.990-25,010 156,525
• 26,100 156,800 33,825 243,000 36,650 300,20.

Literature: Kashkarov A.P. Electronic devices for coziness and comfort.

The conditions for the use of allocated radio frequency bands by categories of radio amateur stations can be viewed

The main activities of radio amateurs are: telegraph (CW), single-sideband (SSB) telephone, frequency modulation telephone (VHF ranges) and radio amateur teletype (RTTY).

Radio amateurs are allocated 10 sections of the DV, SV, HF bands:

2,200m (135.7-137.8 kHz)
160-meter (1.81 - 2 MHz),
80m (3.5 - 3.8 MHz),
40-meter (7 - 7.2 MHz),
30-meter (10.1 - 10.15 MHz),
20-meter (14 - 14.35 MHz),
16-meter (18.068 - 18.168 MHz),
15-meter (21 - 21.45 MHz),
12-meter (24.89 - 24.99 MHz),
10m (28 - 29.7 MHz).

The frequency distribution over VHF bands is as follows:

2 meters - 144-146 MHz
144000-144500 CW
144150-144500 SSB
144625-144675 Digital communication modes
144500-145800 FM
145800-146000 SSB
145800-146000 CW
70 cm - 430-440 MHz
430000-432500 CW
432150-432500 SSB
433625-433725 Digital communication modes
432500-435000 FM
438000-440000 FM
438025-438175 Digital communication modes
435000-438000 SSB
435000-438000 CW
23 cm - 1296-1300 MHz
1296000-1297000 CW
1296000-1297000 SSB
1297000-1298000 FM
1297000-1300000 FM
1296150-1297000 SSB
1296000-1297000 CW

Frequencies above 1.3 GHz
2400-2450 MHz
5650-5670 MHz
10.0-10.5 GHz
24.0-24.25 GHz
47.0-47.2 GHz
75.5-81.0 GHz
119.98-120.02 GHz
142-149 GHz
241-250 GHz

The radio amateur broadcast is never empty. Amateur radio stations can be heard at any time of the day. However, at different amateur bands the passage of radio waves has its own characteristics. Consider the conditions for the propagation of radio waves in each amateur band.

HF transmission largely depends on the ability of radio waves to be reflected from the ionosphere layer. The reflection from the ionosphere of radio waves of different frequencies at the same time is different. Low-frequency waves are reflected more strongly, high-frequency waves are weaker. Therefore, with weak ionization (for example, on a winter night), long-range propagation in low-frequency ranges is possible. In this case, high-frequency waves pass through the ionosphere and do not return to the Earth. With strong ionization (for example, during the day "" in the spring), there are conditions for long-range propagation in high-frequency ranges.

Range 1.8 MHz Most difficult range for long distance communications. Until recently, completely mistakenly in Russia, it was left to the mercy of beginners. Long-distance communication (over 1500-2000 km) is possible only under special circumstances and for a limited time (half an hour or an hour), mainly at dawn and dusk. And communications up to 1500 km are possible with the onset of darkness. At dawn, the range freezes. In some countries, the site is limited to only a few khz. In Japan, for example, radio amateurs are allowed to operate in the 1815-1825 KHz range.

3.5 MHz band is a pronounced night range. In the daytime, communication on it is possible only with the nearest correspondents. With the onset of darkness, long-distance stations begin to appear. So, in the European part of Russia, after sunset, stations of the Ukraine, the Volga region, and the Urals appear. Then the stations of Eastern Europe are heard, and by 23-24 hours Moscow time (according to the radio amateur code 23-24 MSK) - and Western Europe. A little earlier, it is possible (especially in the winter months) the appearance of DX signals from Asia (most often Japan), less often - Africa, very rarely - Oceania. By 3-4 MSK, signals from stations in Canada, the USA and South America may appear, which, with good transmission, can be heard even for some time after dawn. An hour or two after sunrise, the range becomes empty.

7 MHz band usually "lives" around the clock. During the day, you can hear the stations of the nearby regions (in summer - at a distance of 500-600 km, in winter - 1000-1500 km). DX signals appear in the evening and night hours. Japanese, American and Brazilian amateurs work quite a lot in this range, whose radio signals pass especially well (in the European part of Russia) on winter nights at 1-5 MSK. Of the European shortwave, the Yugoslavs, Romanians, Finns, and Swedes are especially willing to use the 7 MHz band. US radio amateurs are allowed to work in the 7.100-7.300 MHz section (in Europe, these frequencies are used by broadcast stations), and therefore SSB with Americans can only be operated at split frequencies.

14 MHz band- the range in which the majority of radio amateurs work. Passage on it (with the exception of winter nights) is available almost round the clock. Particularly good passage is observed in April-May. In the morning hours (4-6 MSK), signals from stations in America and Oceania pass well in the European part of Russia. In the daytime, European stations are mainly heard, - by evening, signals from Asian and African stations appear.

21 MHz band also, widely used by shortwave. The passage on it is mainly observed during the daytime. It is less stable than at 14 MHz, I can change dramatically. There are especially many Japanese amateur radio stations operating on SSB here: it is worth giving a general call during a good passage to Japan, as soon as several calling radio stations appear on this frequency. Sometimes they create significant interference, interfering with the reception of other distant stations. Early in the morning (or, conversely, in the evening, depending on the characteristics of the passage), loud signals of American stations can be heard at 21 MHz. In the afternoon and in the evening, African stations are usually well heard - TR8, ZS, 9J2. Less often, VK and ZL pass at the same time.

28 MHz band lies on the "edge" of short waves. This is the most "capricious" short-wave range: a day - two excellent transits can suddenly be replaced by a week of its complete absence. Radio signals can be heard here only during the day, more precisely - during daylight hours, with the exception of some rare cases of anomalous radio wave propagation, therefore, communications are possible only between correspondents who are in the sunlit zone of the Earth. Most often, at 28 MHz, you can hear the signals of African stations, Asia, less often - Oceania. Sometimes in the evening in the European part signals of shortwave radio stations of the USA pass well. The most active European stations are F, G, I, DL / DJ / DK. Signals from the Eastern European station are relatively rare. The 28 MHz band is free from interference and is most interesting for observations due to the sharp changes in transmission. Its uniqueness lies in the fact that if there is a passage, then even with the lowest power, you can manage communication for 10-12 thousand km. If there is no passage, then the presence of a powerful transmitter will not help either.

As for the remaining bands 10.1 MHz, 18.1 MHz and 24.9 MHz (they are also called WARC bands, thanks to the world radio amateur conference, at which they were assigned to radio amateurs), then the passage on them is something between the ranges described above ... One of the differences on the 10.1 MHz band is the use of only telegraph and teleprinter. And the passage is very similar to 7 MHz, with the difference that in the daytime communications are possible at a distance of up to 2000-3000 km. And the distant stations pass at nightfall.