When designing and operating your “antenna field,” you have to constantly maneuver on a tiny patch of roof between elevator boxes, ventilation shafts, all kinds of television, satellite and other antennas, various cable communications, open radio broadcasting wiring... In addition, one should take into account the very detrimental all-season “ harvesting season" 🙂 and dangerous natural phenomena - wind storms, thunderstorm activity. And what is the cost of, say, icing... By the way, in the winter of 2011, many radio amateurs in central Russia encountered this. One more or less continuous rain at minus temperatures is enough - even without wind - and immediately your beautiful antenna, the object of your former pride, right before your eyes turns into a shapeless icy lump of twisted scrap metal, fragments of fiberglass and wire scraps!
Probably, the elements should also include raids by representatives of the native municipal services, as well as other “bodies in power.” First of all, naturally, this applies to short-wavelength workers living in standard multi-story buildings.
The number of happy owners of capital and reliable superantennas is growing steadily, but not yet as high as we would like. First of all, capital is usually spent on purchasing a “bourgeois apparatus”, and there is no longer enough money to buy a branded antenna...
What then remains to be done by the average domestic radio amateur, who often has practically no free access to the roof of his house? But I want to work on the world airwaves, and preferably not just any way, but with the highest possible efficiency.
So various cheap alternatives are invented (“the need for invention is cunning!”) various cheap alternatives: window and balcony mini-structures, antennas “for emergency work”, 🙂 “invisible”, “backup”, “disposable” - almost made of thin copper wiring, “on buttons”, as in the era of “fifth category spy”...
Selecting the optimal antenna based on the wide variety of shapes and parameters, as well as specific local conditions, is not always quite simple. Everyone knows that “a good antenna is the best amplifier.” Alas, not everyone can afford to have more than one antenna, and several for each band is generally a dream... Some are forced to refuse to work, say, on the 80 m band adjacent to 7 MHz only because it “Inverted” has too high SWR there. However, unfortunately, it also happens that almost no attention is paid to matching the transceiver with the antenna. Personally, I know a rather curious case when one short-wave operator, having replaced an old homemade “Lapovka” with an imported device, “attached” it to the usual “rope”, naively believing that “there is also protection for the output transistors...”.
“The poor radio amateur’s antennas” have been repeatedly described in the literature, but all of them are far from the simplest and not at all the cheapest designs. Unfortunately, sometimes, due to an oversight by the authors of the descriptions, certain important details are overlooked - for example, the length of a two-wire line or the material of the mast, which is sometimes unacceptable to be made of metal. This makes it difficult for inexperienced colleagues to replicate the design.
Beginners (and, to be honest, also some “finishers” 🙂) radio amateurs use mainly the simplest antennas - “Delta Loop” of the 80m range (moreover, they often have an unfortunate location and are powered as it was more convenient locally), the “notorious” Inverted V and quarter-wave Ground Plane... To work on other bands (and preferably on all!) one or another matching device can be used. The results of antenna operation in this case, depending on optimization on a particular band, vary from very good to very bad. Some of the shortwave operators even select the cable length to “improve” the SWR...
However, we should not forget about the essence, that no matching device, no matter how sophisticated, is able to reduce the SWR in the antenna feeder. With its help, we can achieve perfect coordination only between our radio station and the matching device itself, located on the same desktop in the shack. The main effect achieved here is different - the transmitter, as they say, “was deceived”, and the output stage will produce all possible power. But power losses directly in the feeder itself have not disappeared.
As has been noted more than once, a conventional dipole with an SWR of about 1, intended for the 80m range, at a frequency of 7 MHz (where it is already a wave vibrator with an input impedance of about 4 kOhm) will have a SWR of about 53, and in the 20 m range we get SWR = 57. Let's assume that with the help of a certain matching device (tuner) it was possible to obtain the SWR between the transceiver and the control system and also equal to 1 on these ranges. But the feeder is still mismatched with the load (emitter). Having used a two-wire line that has relatively low losses, one could turn a blind eye to this and still work on the air with varying success, but here another problem immediately arises - how to constructively connect that same open two-wire line to the operator’s desk? You won’t be running out onto the balcony every now and then to the matching device installed there! If it is possible to run conductors through a window, that's great. And if not? And is it worth having certain HF radiation near your workplace? In addition, a matching device for a symmetrical feeder is incomparably more complex in design and configuration than a matching device for an asymmetrical load.
The proposed version of the antenna system based on the development of Oleg Safiullin, UA4PA, solves most of the issues raised. Such an antenna is by no means intended to replace other, much more efficient designs, but may be of interest to those radio amateurs who do not have sufficient resources, free space and suitable supports for hanging the antenna fabric.
Many beginner shortwave operators are often put off by the basic description of the UA4PA antenna by the need to install a vertical pole 11.2 m high on the roof and the problem of placing counterweights of the same length in a limited space underneath it. Meanwhile, in the magazine “Radio”, in previous years almost the only source of information necessary for a radio amateur, the idea of applying this matching method to a dipole with almost any arm size was proposed long ago. It was noted that due to the increase in the effective radiating part, such an antenna works even better than a relatively short vertical one in low-frequency ranges, and the dipole itself can also be successfully positioned in the form of an Inverted Vee. On my personal radio station (call sign in Soviet times - UB5LEW) for almost 20 years, a simple inclined beam 35.5 m long with power from the end, but connected to a matching device using an appropriate piece of cable, was successfully used as a reliable backup.
O. Safiullin’s idea itself was actively discussed in amateur radio circles and on relevant forums on the Internet. The main disadvantage of such an antenna, its zealous opponents (however, mostly “theoreticians” who did not even set themselves the task of practical testing of the design) called the operation of a coaxial cable in a standing wave mode - they say that well-known computer programs simply “are horrified” when analyzing losses. 🙂
Yes, apparently, for QRO supporters, those who like to “pump up a kilowatt”, this antenna is really not suitable - the cable can simply melt and burn out... However, for many shortwave operators who are content with the standard oscillating power of an imported device of 100 W, losses in a cable that functions in 100% standing wave mode (in this case it’s not a feeder at all, but part of the antenna fabric itself, only almost non-emitting!), are by no means as scary as they are painted to be!
Naturally, there are losses in any real feeder, but they can be reduced to some extent by using, for example, a cable with a higher characteristic impedance or of better quality.
Previously, I used a 100-ohm cable RK-100-4-31 with a diameter of about 8 mm with double braiding and a copper-plated steel core, and currently I use RK-75-7-11. In order for it, which is quite thick and elastic, not to crawl around on the desktop with the miniature and light box of the matching device, the short part of the line near the matching device - up to about half a meter in length - is generally made of thin RG-58.
The undeniable advantage of the matching method proposed by Oleg Safiullin is the configuration of the entire antenna system to operate on any range directly on the shortwave operator’s desktop. In this case, between the transceiver and the matching device (and then the antenna itself begins!), SWR = 1 is easily achieved, i.e. the output stage will deliver 100% of the assigned power “on the mountain”, and a single control unit allows, if necessary, to instantly adjust the antenna more precisely and at the edges of the ranges.
The disadvantages of such a matching device include only the need to select taps in the coil of the oscillating circuit, as well as limited use - exclusively with one given antenna in its specific design and location. Any attempts to use a ready-made matching device with any other antenna will necessarily lead to a certain mismatch, and a complete reconfiguration of the entire device will inevitably be required.
Individual radio amateurs, having installed a vertical emitter 11.2 m high and connected it through a coaxial cable of arbitrary length and a T-type matching device (for example, from MFJ), have achieved excellent results. Well, that's great! Just don’t say that in this case the “UA4PA antenna” is supposedly used, without noticing that nothing remains from the very idea of matching “according to Safiullin”, except the length of the pin...
The control system diagram is shown below (for simplicity, taps for only one range are shown) and does not have any special features - a regular parallel oscillatory circuit (as in the original UA4PA antenna) with an indicator of the current flowing in the antenna.
Comparing the proposed matching device with the widely used T-shaped, L-shaped and U-shaped matchers, it is easy to notice the gain in ergonomics (one range switch and only one smooth adjustment knob) and in size. However, as they say, options are possible here too, including the use of roller variometers.
The antenna itself is a well-known G5RV design with a two-wire overhead line “dropped down” at one end.
The dimensions of the vibrator (material - bimetal copper/steel with a diameter of 2 mm) - a total length of about 31 m - were chosen based on the available placement possibilities on the ground. The upper part of the directly active canvas is a kind of vertical (unfortunately, its upper end is to some extent close to the wall of a nine-story panel building - where can you go?), and the second half is, accordingly, a counterweight. A two-wire line going to the balcony, and then, without any tricks, the cable itself (naturally, taking into account the shortening factor) completes the length of the entire system to the required 42.5 m.
The dimensions of the line are the length of each conductor is 10.4 m, the material is copper wire with a diameter of 1.8 mm, insulating spacers installed every 30 cm are made of fluoroplastic sheets 3 mm thick. The distance between the conductors is not critical, and for a characteristic impedance of 200 - 400 Ohms it is in the range of 50 - 150 mm (in my antenna - 50 mm).
At the same time: a) there are no additional losses in the “balcony - center of the canvas” section due to the replacement of the coaxial cable with an overhead line, and b) there is a fairly comfortable continuation of the antenna-feeder device directly throughout the apartment (in my case, into the room next to the balcony) with a coaxial cable.
The only critical parameter is the required length of the cable section from the two-wire line to the matching device, which is calculated by the formula: 
The excess can be rolled into a bay in any convenient place. O. Safiullin himself pointed out the desirability of using a cable with a higher characteristic impedance (to reduce losses), as well as the possibility of substituting logically multiples of 85 or 21.3 m into the formula instead of the value of 42.5 (in the latter case, the antenna will work only in the ranges from 40 to 10 m).
Design of the matching device
The dimensions of the matching device housing I used are small - only 190x125x70mm, and it looks very harmonious when combined with the Yaesu FT-897 transceiver. To achieve the desired small size of the device, I deliberately departed from the classically accepted canons, reducing the distance between the coils and the walls of the case to the detriment of some efficiency.
Design of the matching device:
Switch SA1 (according to the diagram above) is a regular PGK, 11P4N (11 positions, 4 directions). KPE C1 - with a maximum capacity of about 150 pF. You can use a KPI with a higher maximum capacity, or even completely abandon additional capacitors and SA1.4 biscuits, but you should keep in mind that the circuit tuning will become much “sharper”.
By the way, even with a small excitation power, the voltage on the oscillatory circuit can reach a significant value. Additionally, “clip-on” capacitors with an input power of about 100 W (an imported transceiver or UW3DI with an output stage on a GU-29 lamp, etc.) must have an operating voltage of at least 2 kV (ordinary KSO-3 with a voltage of up to 500 V “stitches” "). The remaining details are indicated on the circuit diagram or visible in the photo of the matching device and do not require additional explanation.
Each radio amateur can freely select coils for the control system from any available with similar parameters - they are absolutely not critical, the total number of turns can be “estimated by eye”, based on the lowest frequency required range, and the taps will be selected during the setup process. In approaching the selection of coil products, one should be guided by one thing - it is desirable to achieve the highest possible quality factor of the coil. If possible, it is advisable to make the coils from silver-plated wire (at least L1).
Inductor data: L1 is wound on a ceramic ribbed frame (or without it) with a diameter of 32 mm and contains 8 turns of silver-plated wire 02.2 mm, wound in increments of 5 mm; L2 is wound on a 060 mm ceramic frame and contains 23 turns of PEV-2 wire with a diameter of 1.2 mm, wound in increments of 1.8 mm.
The taps from the coils, switchable by range, counting from the top (according to the diagram) terminal (their approximate position is indicated), as well as the capacitances of additional capacitors connected in the low-frequency ranges are shown in the table.
Settings
After sealing the connectors, armed with patience, tweezers and a soldering iron, you can begin setting up the matching device. At the initial stage, using elementary measuring instruments - GSS and a lamp voltmeter, or GIR - it is advisable to select circuit taps according to ranges with the KPI rotor in the middle position and the transmitter disconnected from the matching device. Then, by monitoring the SWR using the SWR meter connected between the transceiver and the matching device, or by looking at the LCD hidden in the “bourgeois” device, the matching of the 50-ohm output of the transmitter with the circuit is selected, i.e. the tap is made at the point where the input resistance is about 50 ohms. It should be taken into account that, most likely, it may be necessary to select the connection point to the antenna cable circuit on each individual band.
Specifically, setting up a matching device is not particularly difficult and is quite accessible even to a beginner shortwave operator (in this case, for simplicity and gaining initial experience, you can limit yourself to one range - 80 or 40m). And as a result, the radio amateur receives a simple, cheap, inconspicuous and difficult-to-access short-wave antenna for strangers, which allows him to work well on the air on all amateur HF bands even in cramped urban conditions!
By the way, in the 160m range I do not use a parallel circuit of the matching device, because The vibrator, with its existing length of 42.5 m, is half-wave only for 3.5 MHz. Approximately equal in length to a quarter wave at 1.8 MHz, it is matched using a small additional coil connected in series (frame - 25 mm in diameter, PEV-2 wire - 1.5 mm in diameter, 18 turns, winding - turn to turn). For greater efficiency, you should also set the control system circuit itself to 160 m, and either include a special extension inductance between the circuit and the cable connector, or use the original figure of 85 m in the formula for calculating the cable length. In this case, the technique for setting the matching device to 1. 8 MHz will be similar to other bands.
results
In conclusion, a few words about the efficiency of the antenna. Due to the inclined position of the vibrator, which to some extent approaches the vertical, a significant component of the radiation in the radiation pattern falls on the lobe pressed to the ground, which is favorable for long-distance radio communications. When installing an antenna, any practically feasible variations are possible both with the spatial arrangement and length of the elements in any particular location, and with the dimensions of the matching line - the main thing is that the overall dimensions fit into the formula.
Fans of computer calculations can simulate the expected radiation patterns, as well as calculate the efficiency of the antenna and “unacceptable losses” in the cable :)
In the process of setting up the matching device on the FT-897 transceiver with an output power of 100 W in the 1.8 MHz range, radio communications were carried out with OH3XR, UA9KAA, LA3XI; in the 3.5 MHz range - with UA0WB, RKOUT, E7/DK9TN; in the 7 MHz range - with 4S7AB, P40L, VQ9JC; in the 10 MHz range - with 9M6XRO/P, TS7TI, OY6FRA; in the 14 MHz range - with KN6MV, 9Q500N, WH0DX (from the first call!), in the 18 MHz range - with KH0/KT3Q, ZS6X, 9M2TO, in the 21 MHz range - with BD6JJX; BD1ISI, HS0ZEE; in the 24 MHz range -CVQ9LA, 5Р5Х, EX8MLE; in the 28 MHz range - with 4J9M, OG20YL, IK2SND.
To be fair, I note that all radio communications are telegraphic, since of all other types of radiation I prefer this one.
In daily practical work on all amateur bands, the antenna fully met the expected performance characteristics and allows reliable radio communications with all continents and various expeditions, without experiencing any special need for an additional power amplifier. However, by eliminating the relatively low-current toggle switch from the circuit (here it is used deliberately, for the convenience of switching the grounding of the antenna) and increasing the electrical strength of the KPI and coils, it is quite possible to increase the oscillatory power of the transmitter to 300 - 500 W. A similar version of the design was used by the author for a long time together with various amplifiers using GU-50 lamps (from 2 to 4 pcs.), and no noticeable, let alone significant heating of the cable, or interference with television was observed at all.
With appropriate settings, this matching device can be successfully used with another antenna (for example, Delta Loop) to increase the efficiency of its matching when operating on all amateur bands.
It’s impossible to even imagine how many antennas are growing around us: mobile phone, TV, computer, wireless router, radios. There are even antenna devices for psychics. What is a HF antenna? Most non-radio people will answer that it is a long wire or a telescopic pole. The longer it is, the better the reception of radio waves. There is some truth in this, but it is very little. So what size should the antenna be?
Important! The dimensions of all antennas must be commensurate with the length of the radio wave. The minimum resonant length of the antenna is half the wavelength.
The word resonance means that such an antenna can operate effectively only in a narrow frequency band. Most antennas are resonant. There are also broadband antennas: for a wide band you have to pay for efficiency, namely gain.
Why does the stereotype work that the longer the HF antennas, the more effective they are? In fact, this is true, but to certain limits, since this is typical only for medium and long waves. And as the frequency increases, the antenna sizes can be reduced. At short waves (lengths from approximately 160 to 10 m), antenna sizes can already be optimized for efficient operation.
Dipoles
The simplest and most effective antennas are half-wave vibrators, also called dipoles. They are powered in the center: a signal from the generator is supplied to the dipole gap. Amateur radio portable antennas can operate as both transmitters and receivers. True, transmitting antennas are distinguished by thick cables and large insulators - these features allow them to withstand the power of transmitters.
The most dangerous place for a dipole is its ends, where voltage antinodes are created. The maximum current of the dipole is in the middle. But this is not scary, because the current antinodes are grounded, thereby protecting receivers and transmitters from lightning discharges and static electricity.
Note! When working with powerful radio transmitters, you may receive shock from high-frequency currents. But the sensations will not be the same as from a blow from a socket. The blow will feel like a burn, without shaking in the muscles. This is due to the fact that the high-frequency current flows over the surface of the skin and does not penetrate deep into the body. That is, the antenna can burn the outside, but the inside will remain untouched.
Multiband antenna
Quite often it is necessary to install more than one antenna, but this is not possible. And in addition to a radio antenna for one band, antennas for other bands are also needed. The solution to the problem is to use a multi-band HF antenna.
Possessing fairly decent characteristics, multi-band vertical antennas can solve the antenna problem for many shortwave operators. They are becoming very popular for a number of reasons: lack of space in cramped urban environments, the growth in the number of amateur radio bands, the so-called “bird license” life when renting an apartment.
Multi-band vertical antennas do not require much space for installation. Portable structures can be placed on the balcony or you can go with this antenna somewhere to a nearby park and work there in the field. The simplest HF antennas are a single wire with asymmetrical feeding.
Someone will say that a shortened antenna is not that. The wave loves its size, so the HF antenna must be large and efficient. We can agree with this, but most often there is no opportunity to purchase such a device.
Having studied the Internet and looked at the designs of finished products from different companies, you come to the conclusion: there are a lot of them, and they are very expensive. All these designs contain is a wire for HF antennas and one and a half meters of pin. Therefore, it will be interesting, especially for a beginner, to find a fast, simple and cheap option for making homemade effective HF antennas.
Vertical Antenna (Ground Plane)
The Ground Plane is a vertical ham radio antenna with a long quarter wavelength pole. But why a quarter and not a half? Here the missing half of the dipole is a mirror reflection of the vertical pin from the surface of the earth.
But since the earth conducts electricity very poorly, either sheets of metal or just a few wires spread like a chamomile are used as it. Their length is also chosen equal to a quarter of the wavelength. This is the Ground Plane antenna, which means earthen platform.
Most car antennas for radios are made according to the same principle. The wavelength of the VHF radio broadcast is about three meters. Accordingly, a quarter of a half-wave will be 75 cm. The second beam of the dipole is reflected in the car body. That is, such structures must, in principle, be mounted on a metal surface.
Antenna gain is the ratio of the field strength received from the antenna to the field strength at the same point, but received from the reference emitter. This ratio is expressed in decibels.
Magnetic loop antenna
In cases where the simplest antenna cannot cope with the task, a vertical magnetic loop antenna can be used. It can be made from a duralumin hoop. If in horizontal loop antennas their technical performance is not affected by the geometric shape and method of power supply, then this does affect vertical antennas.
This antenna operates on three bands: ten, twelve and fifteen meters. It is rebuilt using a capacitor, which must be reliably protected from atmospheric moisture. Power is supplied by any 50-75 Ohm cable, because the matching device ensures the transformation of the transmitter output impedance into the antenna impedance.
Short dipole antenna
There are shortened 7 MHz antennas, the arms of which are only about three meters long. The antenna design includes:
- two shoulders about three meters;
- edge insulators;
- ropes for guy ropes;
- extension coil;
- small cord;
- central node.
The coil winding length is 85 millimeters and 140 turns wound closely. Accuracy isn't that important here. That is, if there are more turns, this can be compensated by the length of the antenna arm. You can also shorten the length of the winding, but this is more difficult; you will have to solder the ends of the fastening.
The length from the edge of the coil winding to the central unit is about 40 centimeters. In any case, after manufacturing, the antenna will have to be adjusted by selecting the length.
DIY vertical HF antenna
How to make it yourself? Take an unnecessary (or buy) inexpensive carbon fishing rod, 20-40-80. Glue a paper strip with dot markings onto it on one side. Insert clips into the marked places to connect jumpers and bypass the unnecessary coil. Thus, the antenna will switch from band to band. The shaded areas will contain the shortening coil and the indicated number of turns. A pin is inserted into the “fishing rod” itself.
You will also need materials:
- copper winding wire is used with a diameter of 0.75 mm;
- wire for counterweight with a diameter of 1.5 mm.
A whip antenna must work with a counterweight, otherwise it will not be effective. So, if you have all these materials, all that remains is to wind the wire bandage on the rod so that you first get a large reel, then smaller and even smaller. The process of switching antenna bands: from 80 m to 2 m.
Selecting the first HF transceiver
When choosing a shortwave transceiver for a novice radio amateur, first of all, you need to pay attention to how to buy it, so as not to make a mistake. What are the features here? There are unusual, highly specialized radios - this is not suitable for the first transceiver. There is no need to choose handheld radios designed for on-the-go operation with a whip antenna.
This radio station is not convenient for:
- use it as a conventional amateur radio device,
- start making connections;
- learn to navigate the amateur radio airwaves.
There are also radio stations that are programmed exclusively from a computer.
The simplest homemade antennas
For radio communications in the fields, it is sometimes necessary to communicate not only over distances of hundreds of kilometers, but also over short distances from small portable radio stations. Stable communication is not always possible even over short distances, since terrain and large buildings can interfere with signal propagation. In such cases, raising the antenna to a small height can help.
A height of even 5-6 meters can give a significant increase in the signal. And if audibility from the ground was very poor, then by raising the antenna a few meters the situation can improve significantly. Of course, by installing a ten-meter mast and a multi-element antenna, long-distance communications will definitely improve. But masts and antennas are not always available. In such cases, homemade antennas raised to a height, for example, on a tree branch, come to the rescue.
A few words about shortwaves
Shortwave operators are specialists with knowledge in the field of electrical engineering, radio engineering, and radio communications. In addition, they are qualified radio operators, capable of conducting radio communications even in conditions in which professional radio operators do not always agree to work, and, if necessary, they are able to quickly find and fix a malfunction in their radio station.
The work of shortwave operators is based on shortwave amateurism - the establishment of two-way radio communications on short waves. The youngest representatives of shortwave frequencies are schoolchildren.
Mobile phone antennas
A dozen years ago, small beads stuck out of mobile phones. Today nothing like this is observed. Why? Since there were few base stations at that time, it was possible to increase the communication range only by increasing the efficiency of the antennas. In general, the presence of a full-size antenna for a mobile phone in those days increased its operating range.
Today, when base stations are stuck every hundred meters, there is no such need. In addition, with the growth of generations of mobile communications, there is a tendency to increase frequency. HF mobile communication bands have expanded to 2500 MHz. This is already a wavelength of only 12 cm. And not a shortened antenna, but a multi-element one can be inserted into the antenna body.
You can’t live without antennas in modern life. Their variety is so huge that I could talk about them for a very long time. For example, there are horn, parabolic, log-periodic, directional antennas.
Video
In one of his books in the late 80s of the twentieth century, W6SAI, Bill Orr proposed a simple antenna - 1 element square, which was installed vertically on one mast. The W6SAI antenna was made with the addition of an RF choke. The square is made for a range of 20 meters (Fig. 1) and is installed vertically on one mast. In continuation of the last bend of the 10-meter army telescope, a fifty centimeter piece of texto-textolite is inserted, in shape no different from the upper bend of the telescope, with a hole at the top, which is the upper insulator. The result is a square with a corner at the top, a corner at the bottom and two corners on guy wires on the sides. From an efficiency point of view, this is the most advantageous option for locating the antenna, which is located low above the ground. The watering point turned out to be about 2 meters from the underlying surface. The cable connection unit is a piece of thick fiberglass 100x100 mm, which is attached to the mast and serves as an insulator. The perimeter of the square is equal to 1 wavelength and is calculated by the formula: Lm = 306.3\F MHz. For a frequency of 14.178 MHz. (Lm=306.3\14.178) the perimeter will be equal to 21.6 m, i.e. side of the square = 5.4 m. Power supply from the bottom corner with a 75 ohm cable 3.49 meters long, i.e. 0.25 wavelength. This piece of cable is a quarter-wave transformer, transforming Rin. antennas are about 120 Ohms, depending on the objects surrounding the antenna, into a resistance close to 50 Ohms. (46.87 ohms). Most of the 75 Ohm cable is located strictly vertically along the mast. Next, through the RF connector there is a main transmission line of a 50 Ohm cable with a length equal to an integer number of half-waves. In my case, this is a segment of 27.93 m, which is a half-wave repeater. This power supply method is well suited for 50 ohm equipment, which today in most cases corresponds to R out. Silo transceivers and the nominal output impedance of power amplifiers (transceivers) with a P-circuit at the output. When calculating the cable length, you should remember the shortening factor of 0.66-0.68, depending on the type of plastic insulation of the cable. With the same 50 ohm cable, next to the mentioned RF connector, an RF choke is wound. His data: 8-10 turns on a 150mm mandrel. Winding turn to turn. For antennas for low frequency ranges - 10 turns on a 250 mm mandrel. The RF choke eliminates the curvature of the antenna radiation pattern and is a shut-off choke for RF currents moving along the cable braid in the direction of the transmitter. The antenna bandwidth is about 350-400 kHz. with SWR close to unity. Outside the bandwidth, the SWR increases greatly. The antenna polarization is horizontal. The guy wires are made of wire with a diameter of 1.8 mm. broken by insulators at least every 1-2 meters. If you change the feeding point of the square, feeding it from the side, the result will be vertical polarization, more preferable for DX. Use the same cable as for horizontal polarization, i.e. a quarter-wave section of 75 Ohm cable goes to the frame (the central core of the cable is connected to the upper half of the square, and the braid to the bottom), and then a 50 Ohm cable, a multiple of half-wave. The resonant frequency of the frame when changing the power point will go up by about 200 kHz. (at 14.4 MHz), so the frame will have to be lengthened somewhat. An extension wire, a cable of approximately 0.6-0.8 meters, can be inserted into the lower corner of the frame (at the former antenna power point). To do this, you need to use a section of a two-wire line about 30-40 cm. Characteristic impedance does not play a big role here. A jumper is soldered on the cable to minimize the SWR. The radiation angle will be 18 degrees, not 42, as with horizontal polarization. It is very advisable to ground the mast at the base.
Antenna horizontal frame
The design of this antenna was told to me over the air about 10...15 years ago by radio amateur V. Voliy (UA6DL), for which I am very grateful to him. The antenna still works, and I am, in principle, satisfied with its performance as a backup antenna. The measured SWR values for a frequency of 1.9 MHz are 1.9; for 3.6 MHz - 1.3; for 7.05 MHz-1.2; for 14.1 MHz -1.4; for 21.2 MHz -1.7; for 28.6 MHz - 1.6. The antenna design is shown in Fig. 1. The antenna is an ordinary dipole with a beam length of 20.5 m. The antenna is powered by a coaxial cable with a characteristic impedance of 50...75 Ohms. For matching, a broadband matching device on a ferrite ring and a two-wire line with a characteristic impedance of 300 Ohms are used. The two-wire line is made of a 17.7 m long CATV television cable, open at the end. The broadband transformer is made on a ferrite ring of grade 30...50 HF with an outer diameter of 24...32 mm - depending on the transmitted power (1 cm of the cross-section of the ring core is capable of transmitting about 500 W without damage). If one ring is not enough, take two or three rings folded together. The ring(s) are pre-wrapped with fluoroplastic tape. At maximum power, the ring can heat up to 70°C. The transformation ratio of the broadband transformer is 1:4. To make a transformer, a PEV 00.8...1.0 wire folded in parallel or a stranded wire in vinyl or fluoroplastic insulation (not afraid of heating) is wound around the ring. The number of turns is 9...10. After winding, the end of one wire is connected to the beginning of the other, forming a midpoint. The broadband transformer is mounted at a distance of 5.9 m from the point where the dipole is connected to the two-wire line. The transformer is protected from moisture by wrapping it with insulating material and varnishing it. The antenna fabric is made of galvanized wire dia. 2 mm, and, apparently, that’s the only reason it stood for such a long time in the acid rain conditions of Donbass.
Rice. 1
In principle, the antenna arms can be made from 5...8 twisted copper wires of PEV grade 0.8 mm. Tested - good strength. Horizontal wire wave channel. As amateur radio wisdom says, the best high-frequency amplifier in a transceiver (receiver) is an antenna. And this is 100% true! Having a good antenna, you can even work with a home-made transceiver with DX, and vice versa, you cannot “pull out” the same high-frequency correspondents with “weak” correspondents with an expensive imported transceiver and a bad antenna. Directional antennas are widely used for these purposes, since they make it possible to concentrate most of the emitted electromagnetic energy in a certain direction, thereby increasing the field strength at the receiving location and reducing interference in other directions, as well as receiving a higher signal level when receiving from this direction. Of course, the best option is to install a rotating directional antenna, but not all shortwave operators can afford to purchase and install such an antenna.
Fig.2
I propose the design of a compromise version of a single-band two-element “Wave Channel” antenna (Fig. 2) with a fixed radiation pattern. The antenna is located in a horizontal plane and has clearly defined directional properties. The design of the antenna is clear from the figure. In this antenna, one active vibrator is a half-wave dipole, the second passive vibrator is a director. The current in a passive vibrator is created due to electromagnetic induction by the field of the active vibrator. By changing the length of the passive vibrator and its distance from the active vibrator, you can change the relative phase of the current in it. This is the basis of the principle of concentration of electromagnetic energy in a certain direction. If the phase of the current in a passive vibrator is such that the resulting field in the direction of this vibrator increases, and in the opposite direction it decreases, the passive vibrator works as a director. Such an antenna provides a power gain of about 5 dB. The weakening of interference from radio stations located perpendicularly and behind the direction towards the correspondent is also significant, which for this antenna is approximately 15 dB. An antenna made according to the given dimensions, as a rule, does not need to adjust the length of the elements and the distance between them. The antenna fabric is made of copper rope, copper, galvanized or bimmetallic wire, dia. 2 mm. If such wire is not available, you can make a homemade copper rope from 6...8 PEV-I or PEV-II 0.7...0.8 mm wires twisted in increments of 2-3 turns per 1 cm. The ends of the rope should be well soldered. This homemade wire rope is quite durable. Naturally, before installing this antenna, the radio amateur must determine for himself the most interesting direction of radiation (reception). The design dimensions of the antenna for each range are given in Table 1.
The antenna fabric itself is attached to stationary supports using a nylon (synthetic) cord, which can be buildings, residential buildings, tall trees, etc. Porcelain nut insulators are used as insulators. However, if such insulators cannot be purchased, they can be successfully replaced by homemade insulators made from textolite or getinax. To make them, take an insulating block (parallelepiped made of textolite, getinax, etc.) of suitable dimensions, and two holes are drilled in it along the diameter of the wire at an angle of 90°. Homemade insulators must work in compression. Insulation strips made of bamboo (pine, getinax or textolite) serve as distance clamps (spacers) between the director and the active element. All cord connections are made only with viscous knots. To protect against moisture, insulators and spacers are coated with insulating varnish. The design of these insulators is shown in Fig. 3.
Rice. 3
Simple, effective G3XAP antenna for 160 and 80 m.
Long-distance communication on short waves is carried out due to the so-called spatial wave, which is reflected by the ionosphere and can have both vertical and horizontal polarization. When operating on the 160 and 80 m bands, shortwave radio amateurs use both ground waves and sky waves. That is why it is desirable for this range to have an antenna with vertical radiation. Since a vertical quarter-wave vibrator for the 160 m range is difficult to imagine even in the imagination (its height should be about 40 m!), the antenna for low-frequency ranges has to be made as a compromise. Its emitter consists of horizontal and vertical conductors (Fig. 4), or the emitter is placed at an angle to the horizon.
Rice. 4
Naturally, the greater the height of the vertical part of the antenna, the higher its efficiency. In addition, the efficiency of a vertical U4 antenna largely depends on the quality of the grounding. It is best to use special grounding - a pin driven into damp ground, a buried sheet of galvanized iron, etc. As a last resort, you can use metal structures fixed in the ground. It is unacceptable to use water supply and heating pipes as such grounding, because In addition to the poor quality of such grounding, severe interference with radio and television reception is possible, as well as burns from high-frequency currents for people who touch the pipelines. The proposed antenna was repeated by Yuri in the late 80s, US31VZ, ex RB41VZ. Actively operating SSB on the 160m band, in one year he received QSL from 150 regions of the former USSR. US3IVZ uses this antenna without counterweights. For more efficient operation, it must have counterweights. A 2-inch diameter steel pipe is mounted on a small support insulator, which can be used as porcelain insulator used in electrical installations, or simply by placing a sheet of insulating material under the vertical pipe. To tune the antenna, use a variable capacitor C^^=500 pF, which has a gap between the plates of at least 1...2 mm (depending on the PA power). The quality of matching is judged by the readings of the SWR meter. The input impedance of such an antenna is approximately 60 Ohms (depending on the quality of the ground), so it is advisable to power it with a coaxial cable with a characteristic impedance of 50 Ohms. With careful tuning of the antenna, we can achieve SWR = 1.1...1.2. The antenna dimensions are given in Table 2.
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Range, m |
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V. BASHKATOV, USOIZ, Gorlovka, Donetsk region.
Literature
1. S.G.Bunin, L.P.Yaylenko. Shortwave Radio Amateur's Handbook. - Kyiv, "Technology", 1984.
The frequency range 1-30 MHz is traditionally called shortwave. On short waves you can receive radio stations located thousands of kilometers away.
Which antenna to choose for shortwave reception
No matter which antenna you choose, it is best for it to be external(outdoor), highest positioned and away from power lines and metal roofs (to reduce interference).
Why is the outdoor one better than the indoor one? In a modern apartment and apartment building there are many sources of electromagnetic fields, which are such a strong source of interference that the receiver often receives only interference. Naturally, the external one (even on the balcony) will be less susceptible to these interferences. In addition, reinforced concrete buildings shield radio waves, and therefore the useful signal indoors will be weaker.
Always use coaxial cable to connect the antenna to the receiver, this will also reduce the level of interference.
Receiving antenna type
In fact, on the HF band the type of receiving antenna is not so critical. Usually a 10-30 meter long wire is sufficient, and a coaxial cable can be connected at any convenient location on the antenna, although to ensure greater broadband (multi-band), it is better to connect the cable closer to the middle of the wire (you will get a T-antenna with shielded reduction). In this case, the braid of the coaxial cable is not connected to the antenna.
Wire antennas
Although more long antennas can receive more signals, they will also receive more interference. This somewhat equalizes them with short antennas. In addition, long antennas overload ("phantom" signals appear throughout the entire range, the so-called intermodulation) household and portable radios with strong signals from radio stations, because they are small compared to amateur or professional radios. In this case, you need to turn on the attenuator in the radio receiver (set the switch to the LOCAL position).
If you are using a long wire and connecting to the end of the antenna, it would be better to use a 9:1 matching transformer (balun) to connect the coaxial cable, because The “long wire” has a high active resistance (about 500 Ohms) and such matching reduces losses on the reflected signal.
Matching transformer WR LWA-0130, ratio 9:1
Active antenna
If you do not have the opportunity to hang an external antenna, then you can use an active antenna. Active antenna- this is, as a rule, a device that combines a loop antenna (either ferrite or telescopic), a broadband low-noise high-frequency amplifier and a preselector (a good active HF antenna costs over 5,000 rubles, although for household radios there is no point in purchasing an expensive one, something will do just fine like Degen DE31MS). To reduce interference from the network, it is better to choose an active antenna that runs on batteries.
The point of an active antenna is to suppress interference as much as possible and amplify the desired signal at the RF (radio frequency) level without resorting to conversion.
In addition to the active antenna, you can use any indoor antenna that you can make (wire, frame or ferrite). In reinforced concrete houses, the indoor antenna should be located away from the electrical wiring, closer to the window (preferably on the balcony).
Magnetic antenna
Magnetic antennas (loop or ferrite), to one degree or another, under favorable circumstances, can reduce the level of “urban noise” (or rather, increase the “signal-to-noise” ratio) due to their directional properties. Moreover, the magnetic antenna does not receive the electrical component of the electromagnetic field, which also reduces the level of interference.
By the way, EXPERIMENT is the basis of amateur radio. External conditions play a significant role in the propagation of radio waves. What works well for one radio amateur may not work at all for another. The most visual experiment of radio wave propagation can be carried out with a decimeter television antenna. By rotating it around the vertical axis, you can notice that the highest quality image does not always correspond to the direction towards the television center. This is due to the fact that radio waves, when propagating, are reflected and “mixed with others” (interference occurs) and the highest quality signal comes from the reflected wave, and not from the direct one.
Grounding
Don't forget about grounding(through the heating pipe). Do not ground to the protective conductor (PE) in the socket. Old tube radios especially “love” grounding.
Jokes
Anti-radio interference
In addition to this, to combat interference and overloads, you can use preselector(antenna tuner). Using this device can suppress out-of-band interference and strong signals to a certain extent.
Unfortunately, in the city all these tricks may not give the desired result. When you turn on the radio, you can only hear noise (as a rule, the noise is stronger in the low frequency ranges). Sometimes novice radio observers even suspect their radios of malfunction or unworthy performance. It's easy to check the receiver. Disconnect the antenna (fold the telescopic antenna or switch to an external one, but do not attach it) and read the S-meter reading. After this, extend the telescopic antenna or connect an external one. If the S-meter readings increase significantly, then everything is in order with the radio receiver, and you are out of luck with the receiving location. If the interference level is close to 9 points or higher, normal reception will not be possible.
Finding and identifying the source of interference
Alas, the city is full of “broadband” interference. Many sources generate broad spectrum electromagnetic waves, like a spark discharge. Typical representatives: switching power supplies, brushed electric motors, cars, electric lighting networks, cable television and Internet networks, Wi-Fi routers, ADSL modems, industrial equipment and much more.
The easiest way to “search” for the source of interference is to examine the room using a pocket radio (no matter what range, DV-SV or HF, just not the FM range). Walking around the room, you can easily notice that in some places the receiver is noisier - this is the “localization location” of the interference source. Almost everything connected to the network (computers, energy-saving lamps, network cables, chargers, etc.), as well as the electrical wiring itself, will make noise.
It is in order to somehow reduce the harmful effects of urban interference that “super-duper” sophisticated radios and transceivers have become popular. A city radio amateur simply cannot work comfortably on household equipment that performs well “in the wild.” Greater selectivity and dynamics are required, and digital signal processing (DSP) can “work wonders” (for example, suppressing tonal interference) that analog methods cannot.
Of course, the best HF antenna is directional (wave channel, QUARD, traveling wave antennas, etc.). But let's be realistic. Building a directional antenna, even a simple one, is quite difficult and expensive.
