Rebuilding the radio station in May. Restructuring the May radio station Rebuilding the Mayak radio station on 144 MHz

Is it possible to make a station at home that is not inferior to the bourgeois one? (meaning 144 MHz). You decide. In terms of characteristics, Mayak is capable of surpassing bourgeois consumer goods. The MAYAK radio station was widely used in professional VHF radio communications. It is distinguished by high reliability, good technical characteristics and high stability of the main parameters.

The sensitivity of the receiver is 0.4 µV with a signal-to-noise ratio of 12 dB. However, with proper adjustment of the operating modes of the UHF cascades and some adjustment of the spiral resonators, the sensitivity can easily be increased to a value of 0.2 µV and higher. By adding a switchable UHF on the gallium arsenide field-effect transistor AP325A-2 without altering the Mayak input stages, the radio station on the air is no longer inferior to potbelly stoves in sensitivity, and when connecting an antenna amplifier it is superior. The selectivity of the receiver over the adjacent channel is determined by the use of a monolithic quartz filter. In terms of selectivity, noise immunity and overall reliability, the station is superior to many domestic and imported ones. The noise reduction system is not made according to the classical principle of amplification and detection of the IF signal, however, it provides good quality noise reduction and, when the regulator is brought to the front panel, it responds to the appearance of any weak carrier.

The transmitter power amplifier contains 4 amplification stages, an automatic power control circuit, a low-pass filter, and a receive/transmit switch on pin diodes. From the point of view of reliability and security, the scheme is designed quite well. The output power is 10 watts, but the applied element base makes it possible to obtain an output power of more than 50 watts without altering the circuit. The current consumed by the radio reaches 8A at 13.8 volts and is provided by a modified power supply from the PC/AT.

I tried to bring together all the achievements of radio amateurs and translate them “in metal.” I propose a technique for converting a radio station for use in a mobile-stationary amateur version. Appearance in photo 1.

To obtain a good appearance and ease of operation in amateur radio conditions, the control unit has been mechanically modified. The front panel is milled. The recess contains a printed front panel with protective plexiglass 1 mm thick. It has a 10 k connector for connecting a headset with speaker and microphone or a computer. The use of an electret microphone makes the signal clear and the voice natural. The microphone amplifier is assembled on two KT315s according to the original Mayak circuit and is located in the headset. To connect a computer, a PTT signal, a noise suppressor signal, and a signal for CW manipulation of the power amplifier are output to the connector. When connecting a PC, it becomes possible to work with digital modes of communication, connect DSP filters, programs for a digital tape recorder, beacon, echo repeater, high-quality external ULF, equalizer, use reverberation, etc.

The UHF is assembled according to the scheme of Igor Nechaev (UA3WIA) and Nikolai Lukyanchikov (RA3WEO), published in Radio magazine No. 9, 2000. The tuning technique is also given there.

The S-meter was assembled with minor changes according to the schemes of Igor Nechaev (UA3WIA) published in the magazine “Radio” No. 11 for 2000 and No. 8 for 1998.

The printed circuit board with K174 UR5 is located in the main unit and is shown in the figure, and the K1003PP1 indication chip is installed in the control unit and the location of the elements is visible in the photo.

The front panel also has 12 S-meter LEDs, an indication of the TX mode, UHF on, a switch for two-level change in output power and a maximum power indicator, a volume control, buttons for turning on the standby mode for using the pilot tone, call tone, turning on the UHF and controlling the frequency synthesizer .

The main difficulty when converting a radio station is usually the frequency control device. I used a synthesizer control device made according to the excellent design of E.Yu. Dergaev. UA4NX and allows you to control the frequency of the MAYAK radio station in the range of 144.5-146.0 MHz. A detailed description and firmware are available on the author’s home page http://www.kirov.ru/~ua4nx and on this site (Control of the frequency synthesizer of the “MAYAK” radio station on an AVR microcontroller). In repeater and anti-repeater modes, the transmission frequency is indicated. The program stores 63 channel frequencies and one VFO in non-volatile memory, including repeater spacing +600 kHz, anti-repeater spacing -600 kHz, with a tuning step of 25 kHz. Writing frequencies to each memory cell is guaranteed 100,000 times. In the “SCAN” mode, scanning occurs from memory channels 53 to 63, in the “DUAL” mode, scanning occurs between any memory channel and “VFO”. When the power supply voltage drops, dashes appear on the indicator. When you turn off the power or press the “CLOCK” key, the indicator enters clock mode. Key presses are confirmed by a short, high-pitched beep. For “LOCK” mode in transmit mode, pressing “H” will lock the keyboard. To remove the lock, press “L” in transfer mode.

The controller itself is built into the Control Panel, power supply is +13.8 V. The control buttons are from computer mice with long rods. The indicator is an analogue of NT1611, used in caller IDs. Unfortunately, to work on SSB sections, the firmware needs to be modified.

On the main unit, an IF signal is output through a 10 pF capacitor to the connector for receiving digital, SSB and CW signals through an additional receiver.

The installation of additional boards is visible in the photo.

The radio station has been in use for more than 5 years, worked in the field during the “Valley” expedition and showed high reliability. Many connections have been made with regions 1 and 3 of Russia, the Baltic states, and the Kaliningrad region through repeaters. The maximum communication range in the direct FM channel with a 5/8 antenna at tropo was 611 km ( LY3UV QTH KO14WU). When you are in the radio visibility zone, you can clearly hear the work of the International Space Station repeater on 145,800 kHz FM.

In the future, it is planned to install a “Radio-76” board in the main unit with EMF on both sidebands, CW and work in a package via satellite.

For those who want to experiment with domestic devices and those who prefer to go on the air with hand-made transceivers, I will answer all questions and invite you to the home page for discussion on the forum. Other improvements will also be posted there, the diagram and design of the RS switching unit - radio station, photos and dimensions of the 5/8 “bottle” antenna, sketches of printed circuit boards, because the boards were developed “in pencil” and corrected when drawing on PCB. I believe that creating a modern home radio requires the efforts of various specialists (circuitry, programming, radio communications, antennas, etc.). Therefore, I invite those who wish to unite and express their opinion. Come to our forum “Novgorod Council of Radio Amateurs”. I ask the “cool aces” not to be distracted by such trifles.

Veliky Novgorod 2004

Radio stations come in quartz and synthesizer types.

The operating frequency of quartz radio stations is determined by the quartz of the receiver and transmitter. Therefore, to rebuild a quartz radio station, you need to change two quartz, one in the receiver, and the other in the radio transmitter. Consequently, for each frequency there is a pair of unique RK169MA crystals. The receiver quartz determines the local oscillator frequency of the radio station according to the formula: 2Fkv-10.7 MHz, and the transmitter quartz determines the operating frequency according to the formula: 4Fkv.

If the frequency to which you want to rebuild your radio stations differs from the previous frequency by one or two channels (25 and 50 kHz), then you can limit yourself to replacing the quartz, but if it is more, you will have to adjust the circuits.

At the same time, do not forget that the entire frequency range from 33 MHz to 57.5 MHz is divided into three subranges: 33-39 MHz, 39.025-48.5 MHz, 57-57.5 MHz, and the board of the first range will not work with quartz at 57 MHz.

With synthesizer radio stations the situation is a little more complicated, although there are many similarities - the same three subranges. But this is where the similarity ends, and the differences begin. The frequency of the synthesizer radio station is determined by the program located in the K556RT4A chip. Eight frequencies can be programmed into this chip, given that they must lie in the 200 kHz band. If you need to make a multi-channel version, with a separation between extreme frequencies of more than 200 kHz, then this requires changes in the radio station circuit and it would be better if you contact us.

Therefore, in order to rebuild a synthesizer, you need to change the microcircuit. There is also quartz in the synthesizer room, but it does not determine the operating frequency of the radio station, but serves as a support in the master oscillator of the KR1015ХК2А microcircuit and its frequency is the same in all radio stations - 12.796 MHz. Although within small limits: 1-2 kHz it affects the operating frequency of the radio station (this can be noticed if you twist the construction capacitor next to the quartz).

If you need to rearrange radio stations from one range to another, then

you need to change the circuits, if only four need to be changed in the receiver, then all eight in the transmitter! It is easier to replace entire boards from one range to another.

All of the above also applies to Len-B radio stations (Bulgarian production), but you need to take into account that the quartz from Len-B will fit into the Len-B receiver, but in the transmitter the frequency will be shifted by half a channel (12.5 kHz) and you need to change the circuit slightly inclusion of quartz.

We will help you in rebuilding Len radio stations, both quartz and synthesizer, we have a large assortment of quartz in stock:

1. RESTRUCTURING a quartz RADIO STATION - 600 rubles

2. RESTRUCTURING a synthesizer RADIO STATION - 550 rubles

3. COST of a set of QUARTZ (two RK169MA quartz) - 360 rubles

4. COST of programmed K556RT4A - 80 rubles

The cost of rebuilding radio stations includes the cost of crystals and microcircuits. The price shown is for a rebuild within the range. The price for restructuring per range must be agreed upon in each specific case with the customer.

1. RESTRUCTURING MAYAK RADIO STATIONS

The frequency of the radio station is determined by jumpers in the synthesizer. At the same time, there are different synthesizers - old and new. The main difference is that in the new synthesizer, jumpers C and D groups simultaneously affect the reception and transmission frequencies, while in the old one they need to be calculated for reception and transmission separately. Therefore, in the new synthesizer it is easier to make a multi-channel version, but in the old one an additional board was installed for this - a decoder.

The entire range from 146 MHz to 172 MHz is divided into sub-bands of 2 MHz each.

In this case, each subband relies on its own VCO and its own spiral resonators, and when tuning to another range, they need to be changed. Don't forget to change

capacitors K21-9-11V on the power amplifier board - they are also range.

146000/25 = 5840 - transmission code

5840 - 428 = 5412 - reception code

This means: A in transmission 5 and in reception 5; B in transmission is 8, and in reception is 4; C in transmission 4, in reception 1; D in transmission 0 in reception 2. Now we convert these numbers into binary code: A transmission 0101, reception 0101; B transmit 1000, receive 0100; C transmit 0100, receive 0001, D transmit 0000, receive 0010.

Next we solder the jumpers: A1 to 1 both in reception and transmission, B1 and B2 0 always, B3 1 in reception, and 0 in transmission, B4 vice versa, C1 1 reception, 0 transmission, C2 0 always, C3 1 transmission, 0 reception , C4 and D1 0 always, D2 1 receive, 0 transmit, D3 and D4 0 always.

Now, if there is 1 in reception and 0 in transmission, then solder this command to the PRM bus, if vice versa, then to the PRM, if 0 is always, then do not solder anywhere, and if 1 is always, then solder to the 9 Volt bus.

COST OF RESTRUCTURING THE MAYAK RADIO STATION - 500 rubles

The price is based on rebuilding within the range. When tuning out of range

additionally 1020 rubles VCO and 900 rubles a set of spiral resonators for the receiver.

My radio station is on 144 MHz

The UHF is assembled according to the scheme of Igor Nechaev (UA3WIA) and Nikolai Lukyanchikov (RA3WEO), published in Radio magazine No. 9, 2000. The tuning technique is also given there.

The S-meter was assembled with minor changes according to the schemes of Igor Nechaev (UA3WIA) published in the magazine “Radio” No. 11 for 2000 and No. 8 for 1998.

The main difficulty when converting a radio station is usually the frequency control device. I used a synthesizer control device made according to the excellent design of E.Yu. Dergaev. UA4NX and allows you to control the frequency of the MAYAK radio station in the range of 144.5-146.0 MHz. A detailed description and firmware are available on the author’s home page http://www.kirov.ru/~ua4nx and on this website ( Controlling the frequency synthesizer of the radio station “MAYAK” on an AVR microcontroller). In repeater and anti-repeater modes, the transmission frequency is indicated. The program stores 63 channel frequencies and one VFO in non-volatile memory, including repeater spacing +600 kHz, anti-repeater spacing -600 kHz, with a tuning step of 25 kHz. Writing frequencies to each memory cell is guaranteed 100,000 times. In the “SCAN” mode, scanning occurs from memory channels 53 to 63, in the “DUAL” mode, scanning occurs between any memory channel and “VFO”. When the power supply voltage drops, dashes appear on the indicator. When you turn off the power or press the “CLOCK” key, the indicator enters clock mode. Key presses are confirmed by a short, high-pitched beep. For “LOCK” mode in transmit mode, pressing “H” will lock the keyboard. To remove the lock, press “L” in transfer mode.

On the main unit, an IF signal is output through a 10 pF capacitor to the connector for receiving digital, SSB and CW signals through an additional receiver.

The installation of additional boards is visible in the photo.

In the future, it is planned to install a “Radio-76” board in the main unit with EMF on both sidebands, CW and work in a package via satellite.

For those who want to experiment with domestic devices and those who prefer to go on the air with hand-made transceivers, I will answer all questions and invite you to the home page for discussion on the forum. Other improvements will also be posted there, the diagram and design of the RS switching unit - radio station, photos and dimensions of the 5/8 “bottle” antenna, sketches of printed circuit boards, because the boards were developed “in pencil” and corrected when drawing on PCB. I believe that creating a modern home radio requires the efforts of various specialists (circuitry, programming, radio communications, antennas, etc.). Therefore, I invite those who wish to unite and express their opinion. I ask the “cool aces” not to be distracted by such trifles.

The FT857D opens up for transmission in exactly the same way as the FT897D.
We unscrew all the screws holding the top cover (don’t forget on the sides), pull out the internal speaker connector, and remove the cover.
We look around the board, looking for the location of the jumpers:

In details:

By the list:
1 - solder,
2 - solder,
3 - solder,
4 - don't touch
5 - don't touch
6 - solder,
7 - remove the SMD element,
8 - don't touch
9 - don't touch it.
Please note that an SMD element is installed on the seventh jumper: it can be completely unsoldered, or you can simply lift it on one side.
Then close the lid, and while holding the F and V/M buttons, turn on the transceiver.
Enjoy!

It all started when Valera and I took out a *BEACON* UX7UX. The stations are solid, good, and most importantly Soviet. Well, don’t let the people’s good go to waste. Here is the MAYAK radio station before it was rebuilt.

Then I wanted to bring them into divine form, so that it would be pleasant and convenient to work on it on air. I personally get great pleasure from working on air on a device I made myself - rather than on a ready-made import. This situation prompted me to start this development. The whole rework, including painting the body, took two days. Plus a day to write a program for the firmware and five days to debug it.

The appearance of the converted *LIGHTHOUSE* is shown in the picture. Four such devices were manufactured. I remade UR5UFQ, UX7UX, UR5UHW and UY5UM myself with all my help.
Many thanks to Valery Shevchenko UX7UX ex ER1DX. For thorough testing of his device at the collective radio station UT4UWD of the concern *ALEX*. All correspondents of the city of Kyiv noted the good quality of the signal and modulation!!! And also many connections were made through the Kiev repeater *R3* with other regions of Ukraine such as: Chernigov, Cherkasy, Poltava, Dnepropetrovsk, Kirovograd, Sumy, Chernivtsi, as well as with correspondents from Belarus and the Bryansk region of Russia.
Description:
The device is implemented on an ATmega8 microcontroller from ATMEL Fig.1.

The ATmega8 microcontroller controls the operation of the radio synthesizer, transmitting to the transceiver unit on IC2 and IC3 74HC164 (shift registers installed directly next to the synthesizer Fig. 2.)
serial frequency code, analyzes the state of the keyboard, pressing the PTT switch, the state of the BUSY noise suppressor, and transmits information to a liquid crystal two-line 16-bit indicator with an HD44780 controller (with green LED backlight, backlight power varies from manufacturer to manufacturer, so read the datasheet). The power supply is stabilized by a 7805 stabilizer, the voltage is 5 volts. The BUSY signal is removed from D16 K561LA7 pin 10 (on the LF board). TX (push-to-talk) signal, pin 35 of the same low-frequency control board.

Device functions:
This device allows you to control the frequency of the “MAYAK” radio station in the range of 144-146 MHz with a grid step of 25 kHz. In half-duplex mode, the TX frequency is indicated during transmission. The repeater spacing varies from 25 kHz to 2 MHz, plus or minus. If the frequency goes beyond 144-146 MHz, the transmission is automatically blocked and the message *NO TX* is displayed on the LCD. There is a scanning mode. The control device has 8 buttons:
*UP* and *DW* - channel switching. When held, they have auto acceleration.
*M1* *M2* *M3* - 3 direct memory access buttons. When pressed, a call is made from the channel memory; when held, the current channel is recorded (as in car radios).
*SCAN*-scanning.
*SHIFT* - half duplex. Short press to turn on and off the spread. While holding, we enter the spacing settings menu. Using the *UP* and *DW* buttons we change the spacing itself from 25 kHz to 2 MHz and the *SCAN* button the direction of the spacing plus or minus. Everything is clearly and accessiblely displayed on the LCD Fig.4.
*TON* - CTCSS support. 38 standard frequencies from 67Hz to 250.3Hz. A short press turns the support on and off. Holding the button opens access to the support frequency selection menu. The frequency is indicated on the LCD. Frequency selection is made using the *UP* and *DW* buttons.
All procedures are accompanied by sound beeps. In my version, a ZP-eshka is used (a simple tweeter without a generator), but if desired, the BEEP signal can be sent to a ULF radio station.

Installation:
The capacitor for powering the IC2 and IC3 microcircuits 74HC164 (2200μ * 6.3V) was installed for good reason. It must be installed near the microcircuits, since the latter are critical to power clicks. The capacitor guarantees their reliable operation. Using resistor R1, in the LCD power supply circuit, we set the brightness of the indicator segments. The circuit does not require adjustment and, if assembled correctly, works immediately. One single setting is to set the CTCSS support deviation. It should be within 600Hz.
The entire device is mounted on an additional front panel which is placed on the transceiver block and screwed with two M5 screws on the sides into the original holes of the block Fig5.
It is cut and soldered from 1.5mm double-sided fiberglass. Dimensions: width - 24 cm, height - 6 cm, length - 3 cm, and sides are 6 cm long. Fig.6.
The LF board is pulled out from the remote control and installed in the transceiver instead of the decoder board on the right Fig7
the second board (tone calls) with the remote control is discarded. As a result, we have one transceiver unit with a front control panel Fig.8.

For ease of control, the front panel includes volume knobs, noise reduction knobs, a PTT connector, a headphone jack, and a speaker. In the beacon tube there is a microphone amplifier with 2 transistors, I assembled the same one in one in my Motorola PTT. The original antenna connector was replaced with a standard PL Fig.9.
My MAYAK was originally at 168 MHz. I had to tinker with it to get it to 145 MHz. I wound up spiral resonators in UHF, two and three links (based on a turn at 10 MHz). The heterodyne two-link spiral resonator was tuned with screws, since I moved the synthesizer from bottom to top, that is, the frequency of the synthesizer when receiving is 10.7 MHz higher than the received signal. In the synthesizer, the TX gun circuit was rebuilt (a 3pf capacitor was added in parallel to the circuit). The transmitter power was increased by adjustment to 30 watts. Instead of capacitor C20 (which I didn’t have), I installed a 5/25 pF trimmer on the left Fig. 7. I slightly adjusted the circuits in the screens in the output stage, and moved the trimmer resistor R26 (driver voltage regulator) all the way counterclockwise. The most important thing in the receiver is to change the resistor that is located in the emitter of the mixer (according to circuit R22). Instead of the 27th, you need to solder in the 10th, but do not short-circuit it tightly! The sensitivity of the receiver will noticeably increase to 0.2 µV.
The controller board with buttons is made on a technology board; therefore, a printed circuit board was not developed.

For now I'm posting demo firmware. In the demo firmware, the CTCSS/ DUPLEX/ MEMORY/ SCAN functions are disabled; it simply works as a 144-146 MHz radio station. For complete firmware, contact the author by email.
mail:
[email protected]
[email protected]

Firmware:
You need to flash two files HEX (flash memory) and EEP (eeprom memory)
and depending where your synthesizer frequency is on the received frequency
from above or below we select firmware +10700kHz or -10700kHz.

Download the article in one archiveIcoMayak.
Pavel Gunko UR5UFQ. Irpen, Kyiv region.
This educational and instructive article is for free distribution!
Photos were taken with a *FUJIFILM E550* camera.
73!
Pentogonych Corporation(C) All reserved. 2007

UHF IN THE RADIO STATION "MAYAK"

In the May and June issues of the magazine "Radio" 2000. The control unit for the Mayak and Transport radio stations, modified to operate on the amateur band of 2 meters, was described. The recommendations of the authors of the published article will allow the owners of such stations to significantly increase their sensitivity.

Radio amateurs widely use industrial-made multi-channel VHF FM radio stations, such as "Mayak" (16Р22В-1) and similar ones, to operate on the air. However, their sensitivity does not really satisfy the owners. Trying to increase the sensitivity of the receiving path, many replace the UHF input transistor (KT399A) with ones that have a lower noise figure (for example, KT3101A-2, KT3115A-2, KT3132A-2, etc.). But this does not always have a positive effect.
According to the authors of these lines, it is possible to significantly increase the sensitivity of a radio station by installing an additional single-stage UHF on a low-noise gallium arsenide field-effect transistor. Since maximum sensitivity is not always needed, to increase the reliability of the radio station, it is advisable to make the additional UHF switchable. It is precisely this option for finalizing the Mayak radio station that is proposed in this article.
The UHF field-effect transistor circuit is shown in Fig. 1
. Its gain is 18...21 dB. The sensitivity of the radio station with an amplifier increased to 0.1 μV (with a signal-to-noise ratio of 12 dB and a frequency deviation of 3 kHz).
When the amplifier is de-energized (as shown in the diagram), the input signal through the normally closed contacts of relay K1,
a piece of coaxial cable and contacts of relay K2 are supplied to the input of the receiving path of the radio station. When the supply voltage is applied, the relays will operate and the signal from the antenna will go to the input circuit L1C2, tuned to the center frequency of the 2 meter range. The amplifier stage is assembled according to a circuit with automatic bias. The magnitude of the drain current is set by resistor R1. The back-to-back diodes VD2, VD3 and VD4, VD5 protect transistor VT1 from possible breakdown by a powerful signal from the radio station transmitter or static electricity. The amplified signal through the matching P-circuit L3C7C8 and the contacts of relay K2 is supplied to the input of the receiving path of the radio station.
The UHF is powered by a parametric voltage stabilizer on the zener diode VD1 and a current source on the transistor VT2.
Depending on the response voltage, relays K1 and K2 can be switched on differently. If it does not exceed 6 V,
then their windings can be connected in series. In this case, blocking capacitors C 10 and C11 are installed parallel to the windings. And if the operating current of each relay is no more than 25 mA, they can be used as a ballast resistor for the zener diode and eliminate the field-effect transistor VT2 and resistor R2 (see Fig. 2).
The following parts are used in the amplifier: transistor VT1 - AP343A-2, and when changing the board topology - AP324A-2, AP331A-2. Trimmer capacitors are KT4-25, and it is advisable to use permanent capacitors K10-17v, K10-42. KM, KD, KLS are also suitable, but with minimal dimensions and with a minimum length of leads. Resistors - R1-12, R1-4, MLT, S2-33. Relay - RES-49. Coils L1 and L3 are wound turn to turn with PEV-2 0.9 wire on a mandrel with a diameter of 5 mm. L1 has 4 turns with a tap of 0.5...0.7 turns, L3 - 6 turns. Inductor L2 is wound with PEV-2 0.3 wire on a mandrel with a diameter of 3 mm (the number of turns is 12-15).
All amplifier parts are placed on one side of a printed circuit board made of double-sided foil fiberglass, a sketch of which is shown in Fig. 3.
The dimensions of the board were chosen based on the ease of installation inside the radio housing. The second side of the board is left metallized and connected to the common wire along the circuit of the board using foil.
Setting up the amplifier begins with setting the drain current of transistor VT2 (within 15... 20 mA) by selecting resistor R2. Then the drain current of transistor VT1 is set (5 mA for AP325A-2, 10 mA for APZ31 A-2) by selecting resistor R1. The input circuit is tuned with capacitor C2 to the center frequency of the range. By changing the location of the tap from coil L1, you can vary the bandwidth of the amplifier input circuit within 2...10 MHz. The P-circuit is adjusted to the maximum transmission coefficient. If the amplifier is self-excited, then a ferrite bead must be placed on the drain terminal of the transistor or a resistor with a resistance of 5...20 Ohms must be connected to the drain circuit.
Slightly worse sensitivity results can be obtained by using low-noise bipolar transistors in the amplifier. A fragment of the circuit of such a UHF is shown in Fig. 4 , and the corresponding fragment of the printed circuit board is shown in Fig. 5 . In this design, coil L1
wound with bare copper wire with a diameter of 1.2 mm on a mandrel with a diameter of 5 mm. It contains 6 turns with a tap from the 1st turn. Winding length - 10 mm.
The setup begins by setting the required current through the transistor by selecting resistor R4 to minimize the noise figure (by ear when receiving weak stations). The input circuit with capacitor C2 is adjusted to the middle of the range. Its capacity should be close to maximum. If this is not the case, then you need to stretch the coil turns and repeat the circuit adjustment procedure. The amplifier can use transistors KT3101A-2, KT3114A-6, KT3115A-2, and with a slight change in the board topology - KT3120A-2. The gain of the prototype of this amplifier was about 20 dB, and the sensitivity of the radio station was 0.12 μV.
The placement of UHF in the radio body is shown in Fig. 6 . Its installation is facilitated by the fact that in the radio station itself the receiver is connected to the power amplifier board by short pieces of wire. Therefore, you need to connect this board to the UHF input with a coaxial cable, and its output with the same cable to the receiver input. +12 V power can be supplied through any small-sized switch, which is placed in a convenient place. The board itself is secured with screws using the holes on the back wall of the radio.
An experimental test of the efficiency of a field-effect transistor amplifier was carried out on a 41 km long route (Kursk - Fatezh, Kursk region). The transmitter power could be changed in steps of 1 dB. The test showed that without UHF, for satisfactory reception of signals, a transmitter power of 2.5 W was required, and with UHF - 0.25...0.3 W. These numbers speak for themselves.

APPLICATION OF RELAY REV-14

The search for a compact connection of two REV-14 coaxial relays led to a very simple design solution and made it possible to eliminate unnecessary coaxial connectors and, as a result, unnecessary losses.

Everything is very simple, to connect the relay, a regular housing from a coaxial connector CP-50 or CP-75 is used, their housings are absolutely identical, all the giblets are first removed from the connector. On the relay body - indicated by a white arrow - the protruding part of the thread is removed with a file - this is done so that the relays can be moved as close as possible.

After this, the core of the connector is made which will connect the two relays. It is made of copper with a diameter of 3 mm and a length of 30 mm, the ends are sharpened like a connector. Next, take a copper tube with a diameter of 6 mm and a length of 15 mm, which is placed on the previously made 3 mm core exactly in the middle and soldered along the edges - this finished part is indicated by a green arrow.

The photo shows one of the options for connecting preamplifiers to the reception; the cable used here is RG-142; it is heat-resistant and allows the use of such a design.

In order not to be soldered to the relay core, copper pins are made that are inserted into the core and the central core of the cable is soldered to them, but you can also solder directly, the length of these pins is 5mm in diameter and also 3mm - the part is indicated by a red arrow. The cable braid is soldered directly to the relay connector body. The yellow arrow indicates the place where the hole is drilled in the connector for the cable. The blue arrow indicates a plug which has a diameter of 17 mm and is sealed onto the end of the connector with an overlap after soldering the cable. If you can make it and plate it with silver, that’s even better, meaning the central pin of the connector.

I use this system not only on predicators, but also in power amplifiers, only there are input and output connectors. By the way, this design was used on PD this year even at 1296 MHz and, as practice has shown, everything works. By the way, to ensure a tight seal, the end of the connector must be sealed with a sealant if it is intended to be installed outdoors, just do not use our domestic automotive sealant for this; it reacts horribly with copper and brass, not to mention silver.

AGAIN ABOUT REV-14

During operation of the REV-14 relay, a defect is often observed. There are relays with loose bolts securing the connector to the relay body to the point that there is not even electrical contact between the relay body and the connector, this happens due to the fact that the paint that is painted on the relay penetrates under the connector and under the fastening bolts / one thing is not clear - how these relays are painted / getting rid of this is quite simple - you need to unscrew the connector, plug the hole with a piece of gauze or bandage and carefully remove with a flat file the paint that is under the connector, after all this, put everything back together as it was in reverse sequence, not forgetting to put all the gaskets and washers under the connector. This was found out after drawing a design assembled from two relays, they introduced a huge deterioration in the SWR of the entire antenna-feeder device. I hope this advice is useful to someone.