Very good all-wave receiver. You press the key, and immediately the multilingual dialect of the planet bursts into the room. You are aware of all the events of the day.

But this receiver has one drawback. Atmospheric and industrial noise sometimes distorts musical broadcasts so much that it is better to turn off the radio. We propose a way out of this situation. Build a VHF receiver and your room will be filled with the purest music, never interrupted by interference.

Schematic diagrams of the high-frequency components of the receiver are shown in Figures 1 and 3.

Figure 1 shows a diagram of a VHF unit and broadband input circuits: a coupling coil with an antenna L1 and an oscillatory circuit formed by a coil L2 and capacitors C1-C2. The received high-frequency radio signal from the circuit is fed to a high-frequency amplifier (UHF) assembled on a triode T1. The transistor is connected according to a common base circuit and ensures stable operation of the cascade at VHF frequencies of 65.8-73.0 MHz).

The selective oscillatory circuit L4-C4-C5-C6 is included in the collector circuit of the triode T1. The restructuring of the circuit within the operating range is carried out smoothly, using a variable capacitor C4.

From the UHF circuit, the signal is fed to the emitter of transistor T2. It acts as a high frequency converter.

The local oscillator is assembled according to the scheme with inductive-capacitive coupling. Just like the UHF cascade, it contains a tunable circuit L4-C13-C14-C16, which is smoothly tuned using a variable capacitor. The intermediate frequency is 10.7 MHz.

The mixing part of the converter is made according to the standard scheme. The signals of the local oscillator and the received radio station are fed to the emitter of the transistor T2.

A load is included in its collector circuit - a bandpass filter L5-C15, tuned to an intermediate frequency.

The desired modes of transistors T1 and T2 for direct current are provided by the base bias voltage. It is selected by resistors R3 and R6 included in the divider circuit.

Figure 3 is a schematic diagram of a three-stage intermediate frequency amplifier and a frequency detector, made on triodes T3, T4, T5 and diodes D1 and D2. Separate cascades of the IF are loaded on the filters L7-C20; L9-C24; L11-C36, which are tuned to an intermediate frequency of 10.7 MHz (capacitance C20 and C24 are 160 each, C29-150, and Cz0 -300 pf). The connection between the cascades is carried out using coils L8, L10, L12, inductively coupled with the loop ones.

The necessary modes of the transistors of the intermediate frequency amplifier for direct current are determined by the resistors R9, R15, R21 included in the voltage dividers.

The IF through the L6 coil is connected to the high-frequency part of the receiver circuit.

There are few homemade parts - these are contour coils and boards. Any resistors and capacitors are suitable for the receiver. True, before acquiring them, it is necessary to clarify what the receiver will be like. If desktop, then you can use ordinary parts, if portable, then small-sized: resistors such as ULM, VS-0.125, capacitors such as KT-1a, KLS, K10-7V, EM, K-50-6, etc.

A dual block of variable capacitors C4-C13 with a maximum capacitance of 20-30 pF can be selected either ready-made or converted from some block for transistor receivers by removing the required number of rotor and stator plates.

If only one VHF radio station is received in your area, the unit can be replaced with separate trimming ceramic capacitors of the KPK-M type, and the receiver setting can be made fixed. Frames for contour coils are made of plexiglass or polystyrene. Of course, you can also pick up ready-made, factory-made ones (see Fig. 2).

Coil L1 of the input circuit contains 5 turns, and L2 - 6 turns of PEL or PEV wire 0.15-0.18. The coil L3 of the UHF circuit contains 11 turns of copper wire without insulation 0.4-0.51 mm. Winding L1 and L2 turn to turn, and L3 in 1 mm increments.

Wind the coil of the high-frequency choke Dr in a row on the ceramic base of a resistor of the type VS-0.125. The winding consists of 25 turns of PEL or PEV 0.12-0.15 wire. The coil leads are soldered directly to the resistor leads. The heterodyne coil L4 is wound in 1 mm increments with the same wire as L3. It should contain 8 turns with a tap from the 3rd turn, counting from the side of the output connected to the positive bus. High frequency coils with carbonyl iron tuning cores. You will find such trimmers in armor cores of the SB-1a or SB-12a type. They have an M4 thread and a height of 10 mm.

The contour coils of the intermediate frequency filters L5, L7, L9, L11 are wound tightly in a row with PELSHO-0.15 wire, 18 turns each. The communication coils are wound in the same way as the previous ones, with a PEL or PEV-0.1 wire. Coil L6 contains 2, L8 and L10 - 3 each, and L11 - b turns. Coil L12 contains 2x15 turns. It is wound in two wires at once. The individual parts of the coil are connected in series - the end of one with the beginning of the other.

The intermediate frequency filter coils are supplied with 100NN brand ferrite cores pressed into threaded plastic plugs. Such cores are commercially available and are used in short-wave coils of industrial radio receivers "Meridian", "Russia", etc. The coils are enclosed in metal screens used in the intermediate frequency circuits of the same receivers.

To provide inductive coupling between coils L4, L13 and L12, make 5x5 mm holes in the bottom of their shields.

It is desirable to place the high-frequency part on a separate board made of foil getinax or textolite and, after assembly, enclose it in a common rectangular screen, which will facilitate tuning.

The low frequency amplifier can be assembled according to a transformerless circuit. It connects to the IF board at the 4th and "-" points.

After installation, proceed with the configuration. It can also be carried out without a standard signal generator. First, using a DC milliammeter or voltmeter, set the operating modes of the transistors. Collector currents should be within 0.9-1.0 mA. After that, connect an external television antenna to the receiver input, set the tuning cores of the contour coils to the middle position and, rotating the axis of the capacitor unit, try to tune in to the station. If this fails, then the setting should be repeated, only with the help of a tuning core of the local oscillator circuit. Having achieved reception, tune all circuits to the maximum signal, not forgetting the sound quality of the transmission. The accuracy of setting the contour of the frequency detector has a particularly strong effect here.

A bit of history.

In the journal "Radio" No. 9 for 1965 The radio designer "Youth" was described. It was one of the first Soviet kits for assembling a pocket radio receiver - a "transistor", as they were then called. He is dear to me as a memory. This is what my parents gave me in 1973. We bought it in the central department store in Melitopol, where we were visiting my aunt. The case was a pleasant "sea wave" color - as in the photograph on the website "Domestic Radio Engineering of the 20th Century".

I assembled it then, but my English teacher, Valery Nikolaevich, who himself was an avid radio amateur, helped me to set it up. Later, in the case from this radio designer, I assembled the receiver according to a scheme that was very popular at the time. And then he got lost somewhere in space-time...

With the help of colleagues from site "Domestic radio engineering of the twentieth century" I managed to find a case from this designer. Almost the same color, but completely empty. Later, we managed to find two "half-corpses" of a later modification of this constructor - "Youth KP-101". Its case, of course, is no longer so beautiful, but the dimensions of the boards and the installation accessories are the same for both sets. It was then that the idea arose to assemble a receiver in the building of the first "Youth". Very few stations are now broadcasting in the MW or LW bands, but, for example, in the "upper" VHF band in St. Petersburg, there are now about 30 of them. So the choice was obvious - VHF receiver for receiving stations in the range of 87.5 ... 108.0 MHz.

Receiver circuit.

The next stage is the development of a schematic diagram. A fully transistorized version was not even considered, since it is very difficult to set up. I also did not consider ICs with a low IF (KR174XA34, TDA7021 and others) - I already had experience in designing receivers on them and I did not like these devices. Therefore, one solution suggested itself - a superheterodyne on a "single-chip" receiver IC. There are a great many microcircuits of this class, the parameters for all of them are approximately the same. Therefore, when choosing, I was guided by its availability, price, “strapping” and ease of setup. In all these respects, I liked TEA5710. Moreover, there was already a positive experience in manufacturing receivers on it (Fig. 2, 3).

Fig.2 Fig.3

In the binding of this IC, two band-pass filters and a detector on a piezoceramic discriminator are used. This allows you to get a fully tuned node "HF - detector" ... without any configuration at all. And this makes it very, very easy to set up the receiver as a whole. In fact, it remains only to stack the range and adjust the gain uniformity throughout the range. In principle, this can be done even without instruments, “by ear”.

The TEA5710 switching circuit is standard, from the datasheet. Some moments "peeped" in the book B.Yu. Semyonov "Modern tuner with your own hands". In particular, a buffer stage node for connecting a digital scale. He helped me a lot when I did the first setup of the finished receiver - I specified the parameters of the coils and capacitors of the local oscillator and the preselector. In principle, this node can not be assembled - just leave empty spaces on the board. If you make coils according to the recommendations given, and the KPI overlap does not differ much from that indicated in the diagram, then, with a high degree of probability, you will “fall” into the desired range.

The second half of the receiver is ULF. At first I wanted to assemble it on some low-power ULF IC. I rummaged through a lot of literature and reference books, but, to my surprise, I didn’t find anything suitable ... Either stereo (but you need mono), then the power is high, then the supply voltage is not suitable, then the current consumption is large, then the case is “planar” ( but I wanted DIP), then you can’t find it in stores in principle ... In general, in the end I decided to make ULF on discrete elements. At first there was an idea to make a transformer, as in the original Youth. But he quickly abandoned it, because finding transformers in our time is not easy. Then there was an idea to make on modern transistors. And then I accidentally stumbled upon a circuit on old MP-scales with very good parameters. I assembled a layout of this amplifier, drove it in different modes, “listened” with an oscilloscope and how it plays music - I liked it. And the issue with ULF was resolved in favor of this amplifier.

As a result, such a receiver circuit was “born” (Fig. 4) .

Actually, it makes no sense to describe her work. The receiving part is comprehensively described in the datasheet on the TEA5710 IC (and in the mentioned book by Semyonov). ULF is described in detail in the mentioned article by Polyakov (all this is in the archive - link above). I will note only a few points.

The TEA5710 IC is powered from +5 V, for which a voltage regulator is assembled on the board on the IC 78L05 (elements C13 C14 DA2 C15 C16). The buffer stage for the digital scale is also powered from it (elements C12 R2 R3 VT1 R4). As already noted, if the scale is not planned to be connected, then these elements can simply not be installed on the board. No jumpers or alterations need to be done.

The receiver IC itself is "hard" switched to the "FM" mode (the 14th leg is connected to the "ground"). The TEA5710 also has an AM path, but in this case it is not used. LED HL1 is an indicator of fine tuning. It is better to use a red LED with a diameter of 3 mm. I managed to “squeeze” it between the tuning and volume knobs.

Printed circuit board.

Based on this scheme, a printed circuit board was developed, the dimensions are exactly the same as the "original" Yunosti board - 86 x 53 mm (Fig. 5).

It is quite difficult to develop a board for which the dimensions, holes for mounting in the case and for the speaker, as well as the location of the controls (volume control and KPI settings) have already been determined ... For a very long time I "suffered" with the placement of the IC. Sometimes, there was a great desire to “break” it ... J Well, it didn’t “fit in” in any way ... And the requirements for wiring are rather contradictory. On the one hand, you need to spread the preselector and local oscillator coils as much as possible, on the other hand, place them closer to the KPI and the IC, which doesn’t fit anyway ... And also the wiring of the “common” wire ... But everything turned out more or less fine when I realized to turn the case The IC is literally a few degrees clockwise. There were few jumpers, only 3 pieces, but they are there ...

The drawing of the board is made in the format of the Sprint Layout - 5 program. in the File Directory.

In addition, in the same there is a lot of reference and other material designed to help in the work on creating a receiver.

The board is made of one-sided foil fiberglass 1.5 mm thick using the LUT method. All holes must be drilled before cutting boards "in size", since the mounting holes are located on the very edge of the board and with inaccurate drilling, you can simply break it. Next, the board must be cleaned with a fine sandpaper (1000 ... 2000), tinned and washed with alcohol (acetone).

KPI - from the Chinese receiver. It has 2 sections for AM (which are not used), 2 sections for VHF with a maximum capacitance of approximately 20 pF and 4 trims with a maximum capacitance of 8 pF. The KPI leads are the main fastening element, since the KPI itself is attached to the board "in reverse".

Piezoceramic filters (Fig. 7) can use any bandpass ( non-rejection- pay attention to this!) At 10.7 MHz. Also present in many Chinese receivers. Sometimes found in regular and online stores. Like a piezoceramic discriminator. Here it, perhaps, may turn out to be the most scarce part in this receiver. I also note that this NOT QUARTZ!

Coils. There are only three of them (Fig. 8).

L1 - frameless, contains 2.5 turns of PEL or PEV wire with a diameter of 0.4 ... 0.6 mm. The coil is wound on a mandrel with a diameter of 6 mm (for example, a drill shank). Does not require settings. After installation on the board, you can fix it with a few drops of paraffin (drop from a burning candle).

L2 - contains 3 turns of PEL or PEV wire with a diameter of 0.4 ... 0.6 mm

L3 - contains 2 turns of PEL or PEV wire with a diameter of 0.4 ... 0.6 mm

L2 and L3 are wound on polystyrene frames with a diameter of 5 mm with a tuning core made of copper or brass, M3 or M4. If you can find frames with a groove, that's even better. After winding, before installing on the board, it is desirable to fix the turns with paraffin.

Transistors in the ULF (Fig. 9) can use any of the series P10 - P16, MP37 - MP42 of the corresponding conductivity. It is necessary to match in pairs with close odds. amplification VT3-VT4 and VT5-VT6. For their installation, it is desirable to use plastic stands.

Resistors - any output power of 0.125 ... 0.25 W.

Variable resistor - domestic or imported ("wheel") with a switch, resistance 4.7 - 47 kOhm.

Capacitors (non-polar) - small-sized ceramic. As C17, it is desirable to use film. Electrolytes - any high-quality (usually imported).

Loudspeaker - domestic (0.1 GD-6, 0.2GD-1, etc.) or imported (I used an 8-ohm speaker from an old PC system unit) with a resistance of 6 - 8 ohms and suitable dimensions.

Antenna - telescopic, 400 - 600 mm - whatever you find, suitable in size and design.

Assembly and setup.

It is desirable to assemble and configure in approximately the following sequence.

First, solder three jumpers (Fig. 13). Then we install all the fixed resistors and capacitors, IF filters, wind and solder all the circuits. In a word, all passive components. We install a stabilizer on the IC board and check the output voltage - it should be. + 5 V. Before switching on for the first time, it is advisable to wash the board from the soldering side with alcohol. After that, we install ULF transistors (VT2 ... VT6), matched in pairs. We check everything again. Instead of R7, we temporarily turn on a 1.0 MΩ constant resistor plus a 470 KΩ trimmer in series with it.

We connect the speaker, we short-circuit the "minus" C18 to the ground, we connect the "Krona". Next, we connect a milliammeter at the limit of "20 mA" instead of a power switch and check the current consumption of the amplifier. He d.b. about 5 mA. Next, instead of the power switch, we temporarily put a jumper and control the voltage at the "minus" C19. It should be half the supply voltage. We achieve this by selecting R7 (changing the resistance of the tuning resistor). Then we measure the total resistance and solder a constant resistor. I got about 1.3 MΩ.

After that, you can “listen” to it with a generator and an oscilloscope, or simply send a signal from any source, for example, the same PC. Naturally, minus C18 before this must be torn off the ground. The amplifier should sound loud and clear, without overtones and audible distortion (and it “screams” very strongly!).

Next, install the KPI and the variable resistor. This is perhaps the most difficult stage in the installation of the receiver. KPIs come in different heights. Therefore, it is better to do so. We determine where he has the conclusions of the FM sections. The easiest way is to use a capacitance meter. If it is not there, then, with a high degree of probability, they are on the side where the conclusion was made in the upper part of the KPI (circled in red in the photo) (Fig. 14).

The tuning dial from "Youth" has exactly the same seat as on the imported KPI, but in the "native" KPI it is fixed with an M3 countersunk screw, and in the imported one - with an M2.5 screw. I put a washer made of soft material under the screw (for example, it can be made of cambric) and the limb turned out to be well fixed (circled in red in Fig. 6).

Next, we install the KPI on the board without soldering, and install the board in the case and be sure to fix it with fixing screws. We set the desired position of the KPI and determine how much it needs to be raised above the board. In my case, it turned out to be 3 mm. Next, I cut out 4 small corners from 3 mm thick plastic and glued them to the KPE with dichloroethane (Fig. 15).

We set the trimmers to the middle position, again install the KPI on the board and fix it in the case. If everything has risen as it should, we solder the KPI right in place. You can additionally "grab" it to the board with a few drops of hot glue from a gun.

Similar "torments" are coming with a variable resistor. The conclusions must first be lengthened with wires. Also, its installation must be carried out "in place" (Fig. 16).

Only after that you can install the TEA 5710 IC. You can simply solder it into the board, or you can install it on the socket. I did not come across 24-foot panels with a pitch of 1.778 mm and a raster of 10 mm, but you can easily find a 30-foot one. Removing the "extra" 6 contacts, we get what we need.

Fig.17 Fig.18

Once again, we very carefully wash the board from the flux residues and “in the light” we look through all the solderings in the IC area. We solder the power block, loudspeaker and antenna - a piece of wire half a meter long - a meter (Fig. 17). After making sure that there are no random jumpers between the tracks, turn on the receiver. Immediately we should hear a characteristic "hiss". We need to try to tune in to any station and decide which part of the range we "hit". This is where a digital scale can help very well, which can be connected to a buffer stage on a field-effect transistor. In the absence of a digital scale or frequency meter, you can try to tune the receiver using an industrial receiver.

We turn the KPI adjustment dial counterclockwise until it stops and by adjusting local oscillator coils L3 tune in to the most lower"band station (87.5 MHz, in St. Petersburg this is" Road Radio "). Then we turn the KPI clockwise until it stops and using trimmer C9 tune in to the station top"station (in St. Petersburg it is "Russian Radio", 107.8 MHz). Such adjustments must be repeated several times, since they are interdependent.

The preselector is adjusted in the same way: “down” - with the L2 coil, “up” - with the C6 trimmer according to the maximum undistorted volume of the stations. For more precise tuning, the length of the antenna can be reduced.

Coil L1 does not need to be adjusted.

A little about the antenna. At first I decided to make a "printed" one and install it in the same place where the magnetic one stood in the "original" Youth. For fastening, I used 2 double wire corners. In antennas, to put it mildly, I am not strong, so I just drew 2 options in the form of "snakes". The total length of the conductor of one snake turned out to be 440 mm, the other - 390 mm. But it turned out that these antennas work very poorly ... I tried both, selected the parameters of the circuits, tried to make some kind of "dipole" out of them - all in vain. Perhaps there are printed antennas for this range, perhaps you need to make the correct matching - I don’t know, I repeat once again, I’m not strong in antennas. So far, I see only one solution - a telescopic antenna. And so you don’t want to “perforate” the body ... (Fig. 18, 19).

Although, one hole has already been made - for the fine-tuning LED (between the tuning dial and the volume control - everything is "on the verge of a foul" in terms of placement). It must also be installed in place, after marking the hole in the top cover of the receiver.

Next, we install the board into the case using standard Yunost brackets. (Fig.20). Under the fixing screws, which are located closer to the KPI and the volume control, it is imperative to lay washers made of insulating material.

We close the back cover and enjoy our work (Fig. 21). JMounting a telescopic antenna is as you wish and who will find which antenna ...

Vitsan Sergey Viktorovich

Saint Petersburg,

This transceiver was developed in 1998, when our salary did not allow us to buy an extra kilogram of potatoes, and radio components even more so. Therefore, at that time I decided to make the device for "grassroots" radio communication as simple and almost free as possible.

The device has quite satisfactory sensitivity, has an output power of about 1.5 watts, operates in amplitude modulation mode, but is also capable of receiving broadband FM (after all, it is a super-regenerator), for example, in the range of 66 - 74 MHz.

The receiver of the transceiver is built according to the scheme of a super-regenerator without UHF. The super-regenerative cascade is made on a high-slope tetrode, and the ULF is on a double output triode. The scheme is so simple that explanations on the work are almost not required.

In the transmission mode (TX), the switch group P1.3 connects resistor R2 to the control grid L1 through the inductor Dr2, which switches the super-regenerator to the “classical” generator mode.

At the same time, by group P1.2, the ULF input is disconnected from the super-regenerator and connected to the microphone, and also by group P1.1, the power supply circuit of the super-regenerator is connected to the anode ULF circuit.

Details

In my version, the L1 and L2 coils were made on a carbolite frame with a brass trimmer from an ancient KVN TV (I found it in a gutter, near a summer cottage).

L2 has 5 turns in the groove of the frame, 3 layers of paraffin paper are tightly wound on top of it (at least, because there is anode voltage on L2, and L1 “sits” on the ground!), And on paper, from the lower end of the coil according to the scheme wound L1 (3 turns). The wire in both cases is PEL 0.6-0.7 mm.

Inductors Dr1 and Dr2 - factory, with an inductance of 50-100 microhenry, Tr1 - from any tube receiver, Gr1 - at least 1 watt. M1 - any dynamic microphone, P1 switch - any suitable one, R3 - any tuning non-wire.

R1 - 12MΩ, R2 - 7.5KΩ, R3 - 100KΩ, R4 - 270KΩ, R5 - 20KΩ, R6 - 2KΩ, R7 - 680Ω, R8 - 270KΩ.

C1 - 5/40 pf, C2 - Zpf, SZ - 51pf, C4 - 0.01mkf, C5 - 560pf, C6 - 0.025mkf, C7 - 2700pf, C8 - 0.01mkf.

C9 - 47 microfarad x 20v, C10 - 0.1 microfarad x 160v, C11 - 0.01 microfarad, C12 - 0.01 microfarad. L1 - 6E5P, L2 - 6N6P.

Antenna - designed for the frequencies used (GP, Dipole, etc.).

Setting

In receive mode with an antenna connected, achieve characteristic super noise by adjusting R3. Then you need to try to tune in to some radio station (broadcast, or airfield weather service). Further, according to the best reception quality, adjust R3 again.

It should be borne in mind that when adjusting R3, the tuning to the radio station will go away, so you need to adjust R3 in stages, i.e.: R3-C1 -R3-C1 - R3 - C1 - etc. until you get a good, high-quality reception.

In conclusion, it should be noted that any non-UHF super-regenerator is capable of causing some interference to closely spaced receivers.

It is more profitable to choose the transceiver range in the range of 27-140 MHz, because at frequencies below 27 MHz, it is more difficult to set up the super-regeneration mode, and above 140 MHz, the reception bandwidth expands too much.

To ensure volume control, you can include a variable resistor with a nominal value of 100 KΩ in the RX contact circuit of switch P1.2 next, as follows (highlighted in color):

Sincerely, Patriot.

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

Currently, you can relatively inexpensively purchase multi-channel portable VHF transceivers from world famous companies - " YAESU”, “KENWOOD”, “ALINCO ”, which, in terms of their parameters and ease of use, are significantly superior to both home-made equipment in the 145 MHz band and converted industrial equipment - Palms, Lighthouses, Violas.

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

This material is devoted to the manufacture of simple home-made 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 band, thick wire is usually used - with a diameter of 1 to 10 mm (sometimes thicker vibrators are used, especially in commercial antennas), then 145 MHz band antennas 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 band.

For tuning 145 band antennas MHz You must have an SWR meter. It can be both a home-made device and industrial production. On the 145 MHz band, radio amateurs practically do not use bridge antenna impedance 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 VHF antennas. But even using only an SWR - a pass-through type meter, it is quite possible to tune home-made VHF antennas. The power of 0.5 W, which is provided by imported portable radio stations in the " LOW "and domestic portable radio stations of the VHF range of the Dnepr type,"Viola", "VEBR", is quite enough for the operation of many types of SWR meters. Mode " LOW » allows you to tune antennas without fear of failure of the output stage of the radio station for any input impedance of the antenna.

Before starting to tune the VHF antenna, it is advisable to make sure that the SWR meter readings are correct. It's a good idea to have two SWR meters rated for 50 and 75 ohm transmission paths. When setting up VHF antennas, it is desirable to have a control antenna, which can be either an "elastic band" from a portable radio station or a home-made quarter-wave pin. When tuning the antenna, the level of field strength created by the tuned antenna relative to the control one is measured. This makes it possible to judge the comparative efficiency of the tuned antenna. Of course, if a standard calibrated field strength meter is used in the measurements, an accurate estimate of the antenna's performance can be obtained. When using a calibrated field meter, it is easy to take the antenna pattern as well. But even using home-made field strength meters for measurements and having received only a qualitative picture of the distribution of the electromagnetic field strength, one can fully conclude about the efficiency of the tuned antenna and approximately estimate its radiation pattern.

Consider the practical design 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. A metal corner is attached to the window frame from the outside (Fig. 2) or from the inside on an extension wooden bar, 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 is the minimum required length. 4 counterweights 50 cm long are attached along the edges of the corner. 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 a coaxial cable with a characteristic impedance of 50 ohms can be used to power it. With the help of the tilt angle 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 the branded "elastic band", you can temporarily use an antenna made of 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 A simple outdoor VHF antenna

Figure 2 Construction of a simple outdoor VHF antenna

The VHF antenna, made of a coaxial cable with the outer braid removed, works reliably. The cable is terminated in the RF connector similar to the connector of the "proprietary" antenna (Fig. 3). The length of the coaxial cable used to make the antenna is 48 cm. Such an antenna can be used in conjunction with a portable radio station to replace a broken or lost standard antenna.

Figure 3 A 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 jack of the radio station and antenna. The antenna can be connected to such a piece of cable using a high-frequency tee (Fig. 4). In this case, an “elastic band” antenna is connected from one end of the tee, and counterweights 50 cm long are wound from the other end of the tee, or another type of radio technical “ground” for the VHF antenna is connected through the connector.

Figure 4 A simple remote VHF antenna

Homemade portable radio antennas

If the standard antenna of the portable radio station is lost or broken, you can make a home-made 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 50 cm of copper wire with a diameter of 1-1.5 mm is initially wound. To tune a twisted antenna, it is very convenient to use a frequency response meter, but you can also use an ordinary SWR meter. Initially, the resonant frequency of the assembled antenna is determined, then, biting off part of the turns, shifting, pushing the turns of the antenna, tune the twisted antenna to resonance at 145 MHz.

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

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

Half wave field antenna

For efficient operation of quarter-wave antennas, it is necessary to use several quarter-wave counterbalances. This complicates the design for a field quarter-wave antenna, which must be placed in space relative to the VHF transceiver. In this case, you can use a VHF antenna with an electrical length of λ/2, which does not require counterweights for its operation, and provides a directivity pattern pressed to the ground and ease of installation. coaxial cable. An antenna with a length of λ/2 and a diameter of 1 mm will have an input impedance on the 145 MHz band of about 1000 ohms. Matching with a quarter-wave resonator, which is optimal in this case, is not always convenient in practice, since it requires the selection of connection points for the coaxial cable to the resonator for its efficient operation and fine tuning of the antenna pin to resonance. The dimensions of the resonator for the 145 MHz band are also relatively large. Destabilizing factors on the antenna, when it is matched with a resonator, will manifest themselves especially strongly.

However, at low powers supplied to the antenna, quite satisfactory matching can be achieved using a P-loop, similarly as 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 pin is chosen to be slightly shorter or longer than the length λ/2. This is necessary because even with a small difference in the electrical length of the antenna from λ / 2, the active resistance of the antenna impedance noticeably decreases, and its reactive part at the initial stage increases slightly. As a result, it is possible to match with the help of the P-loop of such a shortened antenna with greater efficiency than the matching of an antenna with a length of exactly λ/2. It is preferable to use an antenna with a length slightly greater than λ/2.

Figure 5 VHF antenna matching using a P-loop

In the matching device, air tuning capacitors of the KPVM-1 type were used. Coil L 1 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 an SWR meter in the antenna cable path and at the same time measuring the level of field strength created by the antenna by changing the capacitance of variable capacitors C1 and C2, compression-stretching of the coil turns L 1 achieve the minimum readings of the SWR meter and, accordingly, the maximum readings of the field strength meter. If these two maxima do not match, you need to slightly change the length of the antenna, and repeat its tuning again.

The matching device was placed in a case soldered from foil fiberglass with dimensions of 50 * 30 * 20 mm. When working from a stationary workplace of a radio amateur, the antenna can be placed in the window opening. When working in the field, the antenna can be hung from the upper end on a tree using a fishing line, as shown in Fig. 6. A 50 ohm coaxial cable can be used to power the antenna. Using a 75 ohm coaxial cable will slightly increase the efficiency of the antenna matching device, but at the same time it will require the radio's output stage to be tuned to work with a 75 ohm load.

Figure 6 Mounting the Antenna for Field Operation

Foil Window Antennas

Based on the adhesive foil used in burglar alarm systems, very simple designs of VHF window antennas can be built. Such foil can be purchased already 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 instantly sticks securely. Foil without an adhesive base can be glued to glass using varnish or Moment type glue. But for this you need to have some skill. The foil can even be fixed to the window with adhesive tape.

With proper training, it is quite possible to make a high-quality solder connection of the central core 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 only rosin, some can be soldered with soldering fat, other types of foil require the use of active fluxes. The flux should be tested on the particular type of foil used to make the antenna well in advance of installation.

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

Figure 7 Connecting Antenna Foil to Coaxial Cable

Let us analyze the practical designs of window antennas built on the basis of foil.

Vertical window dipole antenna

The scheme of a vertical dipole window VHF foil-based antenna is shown in fig. 8.

Figure 8 Windowed vertical dipole VHF antenna

The quarter-wave pin and counterweight are angled at 135° to bring the antenna system's input impedance closer to 50 ohms. This makes it possible to use a coaxial cable with a wave impedance of 50 ohms 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 on the glass for as long as possible.

Foil Loop Window Antenna

More efficient than a dipole vertical antenna, a VHF loop antenna, shown in fig. 9. When feeding the antenna from the side angle, the maximum of the radiated polarization is located in the vertical plane, when feeding the antenna in the lower corner, the maximum of the radiated polarization is in the horizontal plane. But at any position of the feed points, the antenna radiates a radio wave, with a combined polarization, both 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 VHF Loop Window Antenna

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

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

Foil antennas can deliver significant power levels, up to 100 or more watts.

Outdoor vertical antenna

When placing an antenna outdoors, the question always arises of protecting the opening of the coaxial cable from atmospheric influences, using a high-quality antenna support insulator, moisture-resistant wire for antennas, etc. These problems can be solved by making a protected outdoor VHF antenna. The design of such an antenna is shown in Fig. 10.

Figure 10 Protected outdoor VHF antenna

A hole is made in the center of a plastic water pipe 1 meter long, into which a coaxial cable can tightly enter. Then the cable is threaded there, protrudes from the pipe, exposed at a distance of 48 cm, the cable screen is twisted and soldered at a length of 48 cm. The cable with the antenna is brought back into the pipe. Standard plugs are put on top and bottom of the pipe. Moisture-proofing the hole where the coaxial cable enters is not difficult. This can be done with automotive silicone sealant or fast curing automotive epoxy. As a result, we get a beautiful, moisture-proof protected antenna, which 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 pipe with the antenna can be installed on a window frame, on a non-metal mast, or placed in another convenient place.

Simple coaxial collinear antenna

A simple collinear coaxial VHF antenna can be made from 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 A simple collinear VHF antenna

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

Antenna dimensions in fig. 11 are indicated in centimeters for a coaxial cable with a velocity factor of 0.66. Most PE insulated coaxial cables have this shortening factor. The dimensions of the matching loop are shown in fig. 12. Without this loop, the SWR of the antenna system may exceed 1.7. If the antenna turned out to be tuned below the 145 MHz band, it is necessary to shorten the upper section a little, if it is higher, then lengthen it. Of course, the optimal tuning is possible by proportional shortening and lengthening of all parts of the antenna, but this is difficult to do in amateur radio conditions.

Figure 12 Matching loop dimensions

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 slats, as shown in fig. 13. The antenna can withstand significant power supplied to it up to 100 or more watts and can be used in conjunction with both fixed and portable VHF radios. The use of such an antenna in conjunction with low-power portable radios will give the greatest effect.

Figure 13 Installing a collinear antenna

Simple collinear antenna

This antenna was assembled by me similar to the design of a car remote antenna used in a cellular radiotelephone. To convert it to the 145 MHz amateur band, I proportionally changed all the dimensions of the "telephone" antenna. As a result, an antenna was obtained, the circuit of which is shown in Fig. 14. The antenna provides a near-horizon directivity pattern and a theoretical gain of at least 2 dB over a simple quarter-wave pin. The antenna was powered by a coaxial cable with a characteristic impedance of 50 ohms.

Figure 14 Simple collinear antenna

The practical design of the antenna is shown in fig. 15. The antenna was made from a whole piece of copper wire with a diameter of 1mm. Coil L 1 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 the design is made exactly in size, the antenna practically does not require adjustment. It may be necessary to slightly adjust the antenna by compressing and stretching the turns of the coil to achieve a minimum SWR. The antenna was placed 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 tube. They were threaded, and with the help of nuts they were fixed on a plastic pipe. Counterweights can be 2-4 mm in diameterdepending on the ability to cut threads on them. For their manufacture, you can use copper, brass, or bronze wire.

Figure 15 Construction of a simple collinear antenna

The antenna can be mounted on wooden rails on the balcony (as shown in Fig. 13). This antenna can withstand significant levels of power supplied to it.

This antenna can be considered as a shortened HF antenna with a central extension coil. Indeed, the antenna resonance in the HF band, measured with a bridge resistance meter, turned out to lie in the frequency region of 27.5 MHz. Obviously, by varying the diameter of the coil and its length, but at the same time maintaining the length of its winding wire, it is possible to ensure that the antenna operates both in the 145 MHz VHF band and in one of the HF bands - 12 or 10 meters. To operate on HF bands, four counterweights with a length of λ / 4 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 experimenting with 145 MHz radios, it is often necessary to connect the antenna under test to its output stage to check the operation of the radio's receive path or to tune the transmitter's output stage. For theseI 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 the extension coil, and the other end to the 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 to a coaxial cable with a wave impedance of 50 or 75 ohms by connecting to different turns of the coil, and there may be a slight shortening of the tuning section. The antenna circuit is shown in fig. 16. Antenna design is shown in fig. 17.

Figure 16 Diagram 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 Plexiglas cylinder with a diameter of 19 mm and a length of 95 mm. A thread is made at the ends of the cylinder, into which the antenna vibrator is screwed on one side, and on the other side it is screwed to a piece of foil fiberglass with dimensions of 20 * 30 cm, which serves as the "ground" of the antenna. A magnet was glued to the back of it.old speaker, 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 distributed over the frame. The tap to the coaxial cable is made 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 ground foil of the antenna. The antenna provides SWR in the cable no worse than 1:1.3. The antenna is tuned by shortening its upper part with wire cutters, which is initially slightly longer than necessary.

I have carried out experiments to install this antenna on a window pane. In this case, an aluminum foil vibrator, originally 125 centimeters long, was glued to the center of the window. The extension coil was used the same, and was installed on the window frame. Counterweights were made of foil. The ends of the antenna and counterweights were bent slightly to fit on the window pane. The view of the window 5/8 - wave VHF antenna is shown in fig. 18. The antenna is easily tuned to resonance by gradually shortening the vibrator foil with a blade, and gradually switching the coil turns to minimum SWR. The window antenna does not spoil the interior of the room and can be used as a permanent antenna for operation 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 a "ground" for its work and when working over long distances it gives a gain compared to a standard "elastic band" up to 10 dB. These are quite real numbers, given that the physical length of a half-wave antenna is almost 10 times longer than the "gum".

The half-wave antenna is powered by voltage and has a high input impedance that can reach 1000 ohms. Therefore, this antenna requires a matching device when used in conjunction with a radio with a 50 ohm output. One of the variants of the matching device based on the P-loop 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. The scheme 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 matching device

The circuit coil contains 5 turns of silver-plated copper wire with a diameter of 0.8 mm, wound on a mandrel with a diameter of 7 mm along a length of 8 mm. The setting of the matching device consists in setting the circuit using a variable capacitor C1 L 1C1 into resonance, with the help of 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 C2must be with an air dielectric.

For the antenna vibrator, it is advisable to use a telescopic antenna. This will make it possible to carry the half-wave antenna in a compact folded state. It also makes it easier to set up the antenna with a real transceiver. During initial tuning of the antenna, its length is 100 cm. During the tuning process, this length can be slightly adjusted for better antenna performance. It is advisable to make appropriate marks on the antenna, so that later, from its folded position, install the antenna immediately to the resonant length. The box where the matching device is located should be made of plastic to reduce the capacity of the coilto the "ground", can be made of foil fiberglass. This depends on the actual operating conditions of the antenna.

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

When the antenna is double-operated 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 working on the radio station body, and the other risk corresponds to the minimum SWR when used together with the antenna extension coaxial cable. Usually these two marks are slightly different.

Vertical continuous antennas with gamma matching

Vertical antennas made from a single 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 wave impedance of both 50 and 75 ohms.

Very simple to implement and easy to tune is an inextricable half-wave VHF antenna, the design of which is shown in fig. 20. To power it through a coaxial cable, gamma matching is used. The material from which the antenna vibrator is made and the gamma matching must be the same, for example, copper or aluminum. Due to the mutual electrochemical corrosion of many pairs of materials, it is unacceptable to use different metals for antenna and gamma matching.

Figure 20 Uninterrupted half-wave VHF antenna

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

Figure 21 Setting the Gamma Matching Copper Antenna

If an aluminum wire from a power cable in plastic insulation is used for the antenna, then it is advisable to leave this insulation to prevent corrosion of the aluminum wire by acid rain, which is inevitable in urban environments. In this case, the gamma matching of the antenna 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 an SWR in the cable less than 1.5, then the length of the gamma matching must be reduced and the adjustment repeated again.

Figure 22 Adjusting the Gamma Matching Aluminum Copper Antenna

With sufficient space and materials, a continuous vertical VHF wave antenna can be installed. The wave antenna works more efficiently than the half-wave antenna shown in Fig. 20. The wave antenna provides a radiation pattern more pressed to the horizon 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 making these antennas, it is desirable that the coaxial power cable be at least 2 meters perpendicular to the antenna. The use of a balancing device in conjunction with a continuous antenna will increase the efficiency of its operation. When using a balancing device, it is necessary to use symmetrical gamma matching. Balancing device connection is shown in fig. 24.

Figure 24 Connecting a balun to a continuous antenna

Any other known balancing device can also be used as an antenna balancing device. 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 of vertical antennas shown in Fig. 20 and fig. 23 in their traditional vertical position is difficult, they can be placed by folding the antenna sheet into 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 a combined vertical and horizontal polarization, which is favorable for communications with mobile and portable radio stations. Although, theoretically, the level of vertical polarization will be higher with lateral feeding of round VHF antennas, in practice this difference is not very noticeable, and lateral feeding of the antenna complicates its installation. The side feed of the round antenna is shown in fig. 27.

Figure 25 Unbroken round vertical half-wave VHF antenna

Figure 26 Unbroken round vertical wave VHF antenna

Figure 27 Side feed of round VHF antennas

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

Passive "amplifier" portable station

When testing portable radios or working with them, sometimes there is not enough more “slightly” 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 securely open the squelch of the correspondent's 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 tinned coffee tin of a fairly large size (the bigger the better). A connector similar to the antenna connector of a radio station is inserted into the bottom of the can, and a connector for connecting to the antenna socket is soldered into the can's lid. 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 efficient "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 λ/4 copper wire pin simply inserted into the antenna socket.

Broadband survey antenna

Many imported portable radio stations provide reception not only in the 145 MHz amateur band, but also in the 130-150 MHz or 140-160 MHz survey bands. 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 circuit is shown in fig. 29 and the dimensions for different operating ranges are given in Table. 1.

Figure 29 Wideband VHF vibrator

Table 1 VHF broadband antenna dimensions

Table 1

Range, MHz	130-150	140-160
Size A, cm
Size B, cm

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

Zigzag Antenna

Some long-distance VHF service radios use antenna arrays consisting of zigzag antennas. Radio amateurs can also try to use elements of such an antenna system for their work. A 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 energizes the half-wave vibrators. Real antennas use up to five of these half-wave vibrators. Such an antenna has a narrow radiation pattern pressed to the horizon. The type of polarization emitted by the antenna is combined - vertical and horizontal. For the operation of the antenna, it is desirable to use a balancing device.

In antennas used in office communication stations, a reflector made of a metal mesh is usually placed behind elementary zigzag antennas. The reflector provides a 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 amateur VHF bands 145 and 430 MHz. For the manufacture of the antenna web, you can use an aluminum wire with a diameter of 4-12 mm from a power electric cable. In the domestic literature, a description of such an antenna, for the fabric of which a rigid coaxial cable was used, was given in the literature.

Antenna Kharchenko in the range of 145 MHz

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

Figure 31 Antenna Kharchenko

Both 50 and 75 ohm coaxial cable can be used to operate the antenna. The antenna is broadband, operates in a frequency band of at least 10 MHz on the 145 MHz band. To create a one-way radiation pattern, a metal mesh is used behind the antenna, located at a distance of (0.17-0.22)λ.

The Kharchenko antenna provides a beam width in the vertical and horizontal plane close to 60 o. To further narrow the radiation pattern, passive elements are used in the form of vibrators 0.45λ long, located at a distance of 0.2λ from the diagonal of the frame square. To create a narrow radiation pattern and increase the gain of the antenna system, several combined antennas are used.

145 MHz loop directional antennas

Loop antennas are one of the most popular directional antennas for 145 MHz operation. The most common on the 145 MHz band are two-element loop antennas. In this case, the 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

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 radiation of the vertical component, the antenna can be powered from the side. The input impedance of a two-element antenna is close to 60 ohms, and both 50 ohm and 75 ohm coaxial cable are suitable for working with it. 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 balancing device.

Circular polarized loop antenna

An interesting design for a circularly polarized loop antenna has been proposed in the literature. Antennas with circular polarization are used for communication via satellites. Dual power loop antenna with 90 phase shift° allows you to synthesize a radio wave with circular polarization. The power supply circuit of the loop antenna is shown in fig. 33. When designing an antenna, it must be taken into account that the length L can be any reasonable, and the length λ / 4 must correspond to the wavelength in the cable.

Figure 33 Circular 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 balancing device. The simplest balancing device is shown in fig. 34.

Figure 34 The simplest balancing device

145 MHz Industrial Antennas

Currently on sale you can find a large selection of branded antennas for the 145 MHz band. If you have money, of course, you can buy any of these antennas. It should be noted that it is desirable to purchase one-piece antennas already tuned to the 145 MHz band. 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, you must strictly follow all the instructions in the assembly instructions, and do not spare silicone grease for waterproofing connectors, telescopic connections and screw connections in matching devices.

Literature

1. I. Grigorov (RK 3 ZK ). Matching devices in the 144 MHz range // Radio amateur. HF and VHF.
-1997.-№ 12.- C .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 via satellite // Radio.- 1985.- No. 12.- S. 20.

5.D.S.Robertson ,VK5RN The “Quadraquad” – Circular Polarization the Easy Way //QST.-April.-1984.
-pages16-18.

The VHF FM receiver offered to readers (see figure) is made on the basis of a direct conversion radio receiver with a PLL, developed at one time by a radio amateur from Krasnodar A. Zakharov (see "Radio", 1985, No. 12, p. 28-30).

The radio-frequency receiver stage is assembled on a VT1 transistor and is a frequency converter with a combined local oscillator, which simultaneously performs the functions of a synchronous detector. The receiver antenna is a headphone wire. The signal of the broadcasting station received by it is fed to the input circuit L1C2, tuned to the average frequency of the received VHF band (70 MHz) and then to the base of the transistor VT1. As a local oscillator, this transistor is connected according to the OB circuit, and as a frequency converter, according to the OE circuit. The local oscillator is tuned in the frequency range of 32.9 ... 36.5 MHz, so that the frequency of its second harmonic lies within the boundaries of the VHF broadcasting range (65.8 ... 73 MHz). The L2C5 circuit is tuned to a frequency half that of the L1C2 input circuit, and since the conversion occurs at the second harmonic of the local oscillator, the difference frequency is in the audio frequency range. Amplification of the difference frequency signal is provided by the same transistor VT1, which, like a synchronous detector, is connected according to the OB circuit.

Amplifier 3H receiver two-stage. The pre-amplification stage is made on a transistor VT2, and the power amplification stage is made on a transistor VT3. Listen to the received transmissions on the head telephone BF1 (TM-4). The output power of the 3H amplifier at a load with a resistance of 8 ohms when powered by one A332 element (1.5 V) is 3 mW, which is quite enough to work on a head phone. The current consumed by the receiver from the power supply does not exceed 10 mA.

The receiver can be assembled in any small-sized case. Hanging installation. Resistors - MLT-0.125, oxide capacitors - K50-6, trimmers - any with an air dielectric, the rest are KM, KLS. Coils L1 and L2 are frameless. Winding inner diameter - 5, step - 2 mm. Coil L1 contains 6 (with a tap from the middle), and L2 - 20 turns of wire PEV-2 0.56. Coils L3, L4 each contain 200 turns of PEL wire 0.06. They are wound on a ferrite (M400NN) rod with a diameter of 2 and a length of 10 mm in two wires. Transistor VT1 can be replaced by KT3102B, while the sensitivity of the receiver will increase.

Setting up the receiver begins with a 3-hour amplifier. The operation mode of transistors VT2, VT3 is set by selecting resistor R5 until the collector quiescent current of transistor VT3 is equal to 6 ... 9 mA. The local oscillator mode is regulated by the selection of resistor R1, the level of the second harmonic of the local oscillator - capacitor C6. The boundaries of the received frequency range are set by changing the inductance of the coil L2. The input circuit is tuned by capacitor C2, focusing on the maximum holding band of the signals of the received radio stations. The receiver is tuned in range by capacitor C7.

Setting recommendations: C7 is not particularly twisted. Instead, catch the station by changing the length (inductance) of the coil L2. Capacitor C2 serves for fine tuning. When you have caught the station, then turn C2 until the sound becomes clear. Yes, and you may have to pick up the power of the receiver. Since 1.5V indicated on the diagram, in my case it was not enough. Powered by about 7 volts. You can also add an antenna to the bottom one according to the diagram, the output of the capacitor C1.? But this is if it is completely deaf.

List of radio elements

Designation	Type	Denomination	Quantity	Note	Shop	My notepad
VT1-VT3	bipolar transistor	KT315B	3			To notepad
C1, C5, C6	Capacitor	12 pF	3			To notepad
C2, C7	Trimmer Capacitor	6-25 pF	2			To notepad
C3	Capacitor	3000 pF	1			To notepad
C4, C8, C9		5uF 10V	3			To notepad
C10	Capacitor	100 pF	1			To notepad
C11	electrolytic capacitor	50uF 10V	1			To notepad
R1, R4, R6	Resistor	100 kOhm	3			To notepad
R2	Resistor	100 ohm	1			To notepad
R3	Resistor	1.3 kOhm	1			To notepad
R5	Resistor	5 kOhm	1			To notepad
L1-L4	Inductor		4	Manufactured by yourself