The radio station operates in the ultrashort wave range 144-146 MHz and has a separate receiver and transmitter, which makes it possible to carry out both half-duplex and full-duplex communications. The transmitter uses frequency modulation, which has a number of advantages over amplitude modulation.
The communication range reaches 1-1.2 km when working with such a radio station and can be slightly increased if the correspondent uses a more powerful transmitter and a receiver with increased sensitivity.
The antenna is a quarter-wave rod 47 cm long, but you can also use a flexible wire or high-frequency cable from which the outer braided shielding has been removed.
Scheme. The radio station is assembled on six transistors (two P403 types and four P14 types).
The receiver is made according to a direct amplification circuit with a super-regenerative detector (T1) and two low-frequency amplification stages (T2 and T3) (Fig. 25).
The super-regenerative detector has self-quenching of the auxiliary frequency, carried out by resistance R1 and capacitor C2. The super-regeneration mode is determined by capacitor C3. The oscillatory circuit of the super-regenerator (L1C4) is adjusted by capacitor C4.
Generator high frequency in the transmitter it is made according to a self-excitation circuit on transistor T4, the frequency modulator is on transistors T5 and 76. Frequency modulation is carried out on the base of high-frequency transistor T4. Compared to modulation on the collector or emitter (as well as with grid modulation in tube circuits), in this case the modulator power is required significantly less.
The choice of the operating point of the high-frequency generator is made based on considerations of the constancy of the amplitude of the generated signal with small changes in voltage at the base of the triode. The operating point of the generator is determined by the values of resistances R7, R8, R9. The current consumed by the generator is 12 mA.
Rice. 25. Diagram of a radio station using transistors with frequency modulation of the transmitter.
The frequency deviation in the transmitter is 200 kHz. To do this, you need to change the voltage at the base of the triode within ±0.1-0.15 V. At such voltages based on the triode, the dependence of the generator frequencies on the modulating voltage is almost linear.
The transmitter circuit (L2 C10) is tuned to a frequency of 146 MHz, the receiver circuit (L1 C4) is tuned to a frequency of 144 MHz.
The antenna is connected directly to the base of the T4 triode; it is connected to the receiver circuit (L1 C) through capacitance C1.
Details. Many of the parts used in the radio are similar to those used for the transistor radios described above.
Transformer Tr is wound with wire PEV 0.05; winding I contains 5,000 turns, and winding II contains 2,500 turns. To make a transformer, you can use
Build the frame and plates from the output transformer for the “Sound” hearing aid, which is made on Sh-6 permalloy with a package thickness of 10 mm.
For the manufacture of loop coils L1 and L2, silver-plated copper wire with a diameter of 0.8–1.0 mm is used, which is wound with tension on a ceramic or polystyrene rod with a diameter of 12 mm. Coil L1 contains three turns with a total length of 8 mm, coil L2 contains two turns with a length of 6 mm. The ends of the wire in coils L1 and L2 are firmly fixed to the edges of the rods.
Capacitor C4 is an air tuning capacitor with a capacity of 3 to 10 pF. It can be made in the same way as shown in Fig. 3. C10—ceramic tuning capacitor.
High-frequency chokes Dr1 and Dr2 are wound turn to turn on high-resistance resistances VS-0.25 with PEV 0.1 wire; they contain 40 turns each. Data for all other parts are shown in the diagram in Fig. 25, when choosing them, you should be guided by the considerations noted in the description of previous radio stations.
The insulator for the antenna can be made according to Fig. 4, reducing the indicated dimensions by 2 times.
The radio station uses a high-impedance telephone with a coil resistance of 1000 ohms and a piezoelectric microphone from hearing aids.
The antenna is a pin made of a copper or aluminum tube with a diameter of 4-6 mm with a total length of 47 cm. For communication on short distances(up to several tens of meters), the role of an antenna can be performed by a flexible mounting wire 47 cm long.
Design and installation. The radio station along with power supplies is mounted in a flat box measuring 150X70X24 mm. The design of the box is similar to that shown in Fig. 10. The cover is made in the form of a flap that fits into the grooves on the radio body.
In Fig. Figure 26 shows the arrangement of parts in the radio housing. The leads of all parts and transistors are soldered to the pins of the support posts, the design of which is shown in Fig. 12. The supporting insulating struts are attached to the radio body using BF-2 glue.
The Tr transformer is attached to the radio body with a clamp made of an aluminum strip.
The power switch and the switch for switching from receiving to transmitting are located on the side of the box near the power sources. Installation of the radio station must be done carefully and accurately. This especially applies to the installation of high frequency generators. First of all, you need to strive to ensure that the installation wires have a minimum length.
Rice. 26. Internal view of a radio station using transistors with frequency modulation of the transmitter.
You should also shorten the leads of high-frequency transistors to 1 cm. Special care must be taken when soldering these leads. To avoid overheating during soldering, they must be clamped with pliers or tweezers, which in this case act as a heat sink.
Power supplies. To power the radio, two 3-FMTs-20M (“Light”) batteries are used, each of which has a voltage of 2.6 V. These batteries, when installed in the radio housing, are connected to each other in series. Any other small-sized batteries or accumulators with a total voltage of 4.5-6 V can be used as power sources for the radio station.
Due to the fact that the radio station is designed to operate in the amateur VHF range of 144-146 MHz, high-frequency transistors with a maximum generation frequency fa = 140-150 MHz must be selected in the cascades of the supergenerative detector (T1) and generator (T4). For this purpose, from several transistors it is necessary to select those that have the highest maximum generation frequency.
The procedure for setting up a radio station is similar to those described above. Before turning on the radio station, in accordance with the circuit diagram, the correct installation is checked, then the power supplies are turned on and, using the TT-1 tester, the operating mode of the transistors is selected, which is indicated in the diagram in Fig. 25.
After this, you should check the operation of the receiver without connecting an antenna. At normal operation The receiver in the phone will hear super-regenerative noise, which should be uniform over the entire range of received frequencies. A complete absence of noise or a whistle in the phone means an incorrect choice of the super-regenerator operating mode or a malfunction of the low-frequency amplifier. In this case, first of all, it is necessary to check the low-frequency amplifier and, having made sure that it is in good working order, move on to setting up a super-regenerative detector cascade (T1). First, the presence of high-frequency oscillations in the L1C4 circuit is checked. To do this, a milliammeter is used to monitor the change in current in the collector circuit. When coil L is closed, the instrument readings should increase by 1.1-1.3 times. By selecting the values of capacitors C2 and C3, as well as resistance R1, the best operating mode of the super-regenerative detector is achieved. For the same purpose, you can slightly change the voltage on the collector of triode T1 (by sequentially connecting a damping resistance of 1-10 kohms into its collector circuit), and also swap the ends of the connection in the circuit of one of the windings of the transformer Tr.
If the transistor used (for example, type P403) does not operate in super-regenerative mode, it is necessary to do the following: disconnect the end of resistance R1 from the radio body and connect it to the plus of a separate battery (voltage 2-5 V), the minus of which is grounded. The voltage from this battery should be changed by applying it through a potentiometer of 10 koz, so that the emitter current of transistor T1 is about 2-3 mA.
After setting up the receiver is completed, they begin to check the operation of the transmitter. Having checked the operating modes of transistors T4, T5 and T6 in accordance with the voltages indicated in the diagram, we begin to determine the operation of first the low-frequency amplifier (T6 and T5), and then the high-frequency generator (T4). Checking the low-frequency amplifier in the transmitter is similar to checking the low-frequency amplifier in the receiver. A high-impedance telephone is connected to the positive end of the electrolytic capacitor C13 and the radio body. The quality of the amplifier is checked by listening to the words spoken in front of the microphone in the telephone.
The presence of high-frequency oscillations in the oscillatory circuit (L2 C10) is determined in the same way as was done when checking the super-regenerative cascade of the receiver. In the absence of high-frequency oscillations in the L2 C10 circuit, it is necessary to correctly select the operating mode of triode T4, which is achieved by changing the values of resistances R7, R8 and R9, as well as changes within small limits in the voltage of the power source.
Frequency deviation is achieved by changing the modulating voltage applied to the base of transistor T4. To obtain narrowband frequency modulation, the modulating voltage must be several millivolts.
After connecting the antenna, the operation of the radio station is checked with another VHF radio station, whose transmitter is tuned to a frequency of 144 MHz and the receiver to 146 MHz.
Some features:
The radio station is made primarily using SMD elements and consists of two boards. Transceiver boards and synthesizer boards, which are connected to each other through connectors soldered into them and form a single structure. All controls ( volume control, encoder, PTT) are connected to the corresponding terminal blocks. The vertically positioned synthesizer board has an LCD display, function buttons, and transmit-receive LEDs, and in general the board is an integral part of the front panel. All this makes it easy to assemble the entire structure in any housing to your taste, with a minimum number of connecting wires. Thanks to the widespread use of low-noise field-effect transistors in the circuit, it was possible to obtain a low receiver noise level, high sensitivity, stable operation of the transmitter and a clean emission spectrum.
Specifications:
- Supply voltage 12-14 volts
- Output power at 13.2 V. no less than 9 watts.
- Receiver sensitivity is better than 0.1 µV.
- Clogging resistance is no worse than 80 dB.
- There is an output to the S-meter
- Prompt shutdown of the ShP
- There is control of the transmitter output level
- Frequency tuning using a valcoder
- 59 channels of non-volatile memory
- Frequency or memory scanning mode
- Wide range of configuration options
- Design dimensions 77 X 80 mm.
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| Transceiver circuit |
To generate the operating frequencies of the receiver and transmitter, two separate VCOs are used, (Voltage Controlled Oscillator) which operate on a common load and are controlled by a synthesizer. This makes it easier to pair settings when switching from receiving to transmitting. The VCOs are assembled on field-effect transistors VT6, VT7 according to a capacitive three-point circuit. VT6 operates in receive mode, VT7 in transmit mode. The receiving path is made according to a double frequency conversion circuit and consists of UHF VT1, mixer VT2, intermediate stage VT3, functional IF-FM microcircuit DA1, and ULF DA2. In reception mode, the signal received from the antenna circuits through C1 is isolated by circuit L1, C2 and amplified by a cascade at VT1. The UHF is loaded onto a two-section filter L2, C5, C6, C7, L3, which allocates the operating frequency band. The signal from it is supplied to the 1st gate of the mixer transistor. The 2nd gate receives the signal of the first local oscillator from the VCO, through the switching stage VT8, capacitance C10 and is isolated by circuit C9, L4. The signal of the first IF 10695 KHz is isolated on resistor R5, passes through quartz filters F1, F2 and goes to an intermediate stage with a slight gain assembled at VT3. This cascade serves to compensate for attenuation in the filters and makes it possible to obtain an overall gain of the path sufficient for the correct operation of the S-meter at weak signal levels. Then, through C13, the signal goes to the second mixer included in DA1. A 10240 KHz signal is supplied to the other input of this mixer from the synthesizer’s quartz oscillator through the R14, C14 chain. The second IF signal of 455 KHz is isolated by the main selection filter F3 and detected by the DA1 chip. The low-frequency signal is removed from the filter chain R24, C23. In the absence of a useful signal, this circuit is shunted to the housing by the output of the trigger as part of DA1. (14th leg of MS). Diode D4 is locked in this state and cuts off a small residual low-frequency signal from the ULF input, and freely passes it when the noise suppressor opens. This design of the circuit ensures accurate operation of the ShP system, without popping noises in the dynamics when triggered, which are present in some stations. The response threshold is set by resistor R21. It is not necessary to take it outside, since the system works according to the signal/noise ratio, is not triggered by interference, and also reliably turns on when signals are weak, bordering on intelligibility. In order to listen to something in the noise, there is a button for quickly turning off the S3 Silk Silencer. When it is pressed, R12 closes to the case, transistor VT4 opens and supplies a positive voltage to pin 12 of DA1 and holds the ShP in the open state. If there is a working station and the ShP is opening, the positive voltage applied to diode D4 is used to control the scanner stop key and is removed from its cathode and C25. The VT5 transistor contains a matching stage for the S-meter. VT12 is a key that switches the power supply of the receiver. The circuits of the receiver, synthesizer, and the first stages of the transmitter are stabilized by the DA3 microcircuit.
In transmit mode, S2 closes circuit 2 of the circuit to the body. In this case, switch VT12 de-energizes the receiver, voltage is removed from gate VT6 and the VCO of the receiver stops working. The VT8 switching stage is also locked and disconnects the receiver circuits from the VCO output. This is necessary to eliminate their influence on the stability of the transmitter. Circuit 2 also switches the operating mode of the synthesizer. The synthesizer board diagram is shown in (Fig). It consists of the digital part itself, microcircuits U1, U2, U3, microphone amplifier VT1, VT2, LEDs for transmitting and receiving, function control buttons, and an LCD display. (The frequency control encoder is connected to the board via a ribbon connector.) By controlling circuit 2, logical “0” puts processor U1 into transmit mode. (Conclusion 16). The VT3 key also opens and supplies power to the microphone amplifier VT1,VT2, LED LD1. Further along circuit 5, it opens VT7, starting the VCO of the transmitter, also supplies power to the pre-power amplifier VT9, and through circuit R43, D7 additionally locks VT6 to avoid starting this generator when exposed to strong RF fields. From the VT9 pre-power amplifier, through C45, an RF signal with a level of about 100 mW is supplied to the next two stages of the transmitter operating in class “C”. Before the transmission is switched on, the cascades are locked and power is supplied to them constantly. From the collector VT11, through the matching circuits, the signal enters the antenna, and through the capacitance C54 to the RF meter.
Setting up.
The setup should begin by checking the VCO frequency locking mode in receive and transmit modes. It is better to de-energize the transmitter output stage for a while by removing inductor DR4. Turn on the station, set the operating frequency to 145 MHz on the display. Measure the voltage of circuit 3. Rotate core L6 to set its value to about 2 volts. Then press gear and rotating core L7 also set to 2 volts. Next, configure the receiving path. In the simplest case, you can get by with a GSS and an HF voltmeter. First, you should turn off the noise suppressor by adjusting the position of R21. The presence of noise in the dynamics is a preliminary indication of the serviceability of the path. Rotate core L5 to set position maximum volume noise. Apply a signal from the generator to the antenna input. Set the generator level to about 1-5 µV and adjust the frequency to achieve reception. Use resistor R29 to set the S-meter readings to the middle of the scale. Then adjust L1, L2, L4 by moving the coils apart and rotating the core L3 according to the maximum readings of the S-meter and constantly reducing the level of the GSS output. Next, increase the GSS level to 15 µV (9+10 dB) and set the S-meter readings at the end of the scale with resistor R29. Then reduce the GSS level and measure sensitivity. It should be no worse than 0.1 µV and the S-meter readings should be about 10% of the entire scale. Check the L5 setting again for FM modulation from a generator with a deviation of 3-4 kHz, for the loudest and most undistorted sound.
Next, set up the transmitter. Its setup is very simple. Connect a voltmeter to the output and, with the output stage de-energized for now, moving the turns of coils L8, L9, L10, L11 apart in turn, increase the readings of the device. You should not achieve the maximum yet. In this position, set the exact frequency value according to the frequency meter using trimming capacitor C9 in the synthesizer. Set the deviation to 4 KHz with resistor R27 when talking close to the microphone. This can be done at the control station, achieving a loud, but not distorted sound. Then solder in DR4, connect the equivalent of a 50 ohm load to the output and adjust the maximum readings by re-configuring all transmitter circuits. The RF output voltage should be around 22 volts, which corresponds to an output power of just over 9 watts. Next, use resistor R56 to set the transmitter output level readings on the S-meter in the region of 75% of the scale. Using these readings during operation of the station, one can judge the proper operation of the transmitter and antenna-feeder system.
Details.
The printed circuit boards of the radio station are made according to modern technology with metallization of holes and with a protective mask. The mounting locations for the receiver inductors are all the same and are designed for installation of standard coils in shields with ferrite cores. Although in this version some of the receiver coils are frameless, this is done for versatility and the possibility of manufacturing this radio station for the low-frequency ranges of 28 - 50 MHz. The synthesizer program allows this. All coils of the radio station (except for L3, L5, L6, L7) are frameless and are wound with PEL-0.5 wire on a 3 mm mandrel. Coil L5 is wound on a standard frame from the inverter circuits using PEL-0.1 wire. For L3, L6, L7, frames and screens are also used from standard coils, from which the ferrite cup is removed, and instead of a ferrite core, a brass core 5 mm long is used. The turns of these coils are laid one turn per frame section using PEL 0.3 wire. The number of turns is given in the table. A 100 micron head was used as an S-meter. Any electret microphone with two terminals can be used. For the 1st IF, 10.6M15A quartz filters with a central frequency of 10695 KHz are used. For the 2nd IF, piezoceramic CFU455D or similar. All diodes in the KD521-522 station, except VD10 which must have a forward current of at least 2A and serve to protect against power reverse polarity. If the station is used in a car, power must be supplied through an additional filter that has a choke, since it is not provided on the board. If the S-meter is not used in the station, then the MC3371 chip can be replaced with the more accessible and cheaper MC3361. A heat-conducting plate is screwed to the output transistor VT11, which is also attached to the radiator or to the radio body. Structurally, the heat sink terminal of the 2SC1971 transistor is connected to the emitter so that insulating gaskets are not required. To obtain maximum power, you must additionally connect it with a jumper to the ground of the board at the nearest point.
The capabilities of the synthesizer program are as follows:
- smooth tuning, - tuning in steps of 5,10,15,20,25 KHz, within 144-146 MHz (tuning limits are programmable)
- tuning according to the pre-programmed transmission of each channel is set individually, i.e. Each channel can be used as a repeater with an arbitrary frequency spacing.
- scanning in a given frequency range (scanning area is programmable)
- scanning through channels in a given frequency range (scanning area is programmable)
The synthesizer is controlled by a valcoder and two buttons: “F” (Function) and “Scan”. - "F" - switching between smooth tuning and tuning modes using pre-programmed channels.
- "Scan" - enable scanning mode. When a working radio station is detected and the squelch is activated, the scanning process pauses for 3 seconds and then continues. You can stop scanning by pressing the "Scan" button or pressing the PTT button or turning the encoder.
If you press the "F" button and hold it down to turn on the radio station, the synthesizer will enter the channel tuning mode - selecting the channel to be tuned. In this mode, the number of the channel being configured is selected using the encoder. After selecting the channel number, press the "F" button. In this case, the synthesizer goes into the mode of adjusting the reception frequency of the selected channel. The receiving frequency is displayed on the indicator as F1, the transmitting frequency as F2. By default, the transmitting frequency is equal to the receiving frequency, and if you do not need to change the transmitting frequency, then press the “F” button to exit this mode and set up the next channel. If you plan to work in repeater mode, then use the encoder to set the transmission frequency of the selected channel. After installation, press the "F" button. If the reception and transmission frequencies in a channel do not match (repeater mode), this is reflected on the indicator with the letter “P”. To exit the channel tuning mode, press the "Scan" button.
Notes:
- Channels from No. 1 to No. 59 are tuned.
- When tuning in channel mode, only tuned channels are displayed.
- In order to disable a channel, you need to write the frequency 146025 into it, i.e. take it outside the allowed range
- Regardless of the set tuning step, the memory channels are tuned with a step = 5 kHz.
Service channels: - Channel No. 60 is the last frequency used. There is no point in programming this cell; the program will rewrite it anyway.
- channel No. 61 - range boundaries. The default is 144000 - 146000
- channel No. 62 - boundaries of the scanning area. The default is 144500 - 145800.
- channel No. 63 - intermediate frequency and reference quartz frequency. By default, 10695 and 10240 are written
- channel No. 64 - tuning step and service cell (the adjustment is not saved). Default step = 25 kHz.
To fully initialize the synthesizer and restore the “default” settings, you need to press the “Scan” and “F” buttons simultaneously and while holding them down, turn on the radio station. After 5 seconds, release. All old settings are erased, the starting frequency is 145300, channel 01 is set to a frequency of 145300, the synthesizer is ready for use.
My radio station is 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. When adding switchable UHF to 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 amplifying and detecting 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 get good appearance and ease of operation in amateur radio conditions, the control unit has been mechanically improved. 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 sound signal high tone. 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. I ask the “cool aces” not to be distracted by such trifles.
This radio station can be used not only in stationary mode, the 12V power source allows the use of a car or other battery, and the compactness of the VHF antenna allows it to be successfully placed in a car, boat, or used in camping mode.The radio station consists of a main unit, which is mounted on a moving object or in a housing suitable for field conditions, and a speaking tube, which contains AF amplifiers with a microphone and speaker, a switch for receiving and transmitting modes, a tone generator, and a volume control.
The position of these controls on the handset body is designed so that you can operate the radio station with one hand, which is convenient when driving a vehicle.
Radio station characteristics:
1. Range - three channels in the 144 MHz range.
2. Modulation type - FM with a deviation of 3 kHz.
3. Receiver sensitivity with a signal-to-noise ratio of 3:1 - 2 µV.
4. Transmitter power - 4W.
5. Current consumption during transmission - 1A.
6. Receiving current consumption is 50mA.
7. Supply voltage - 12-14V.
Schematic diagram the main unit is shown in Figure 1. The receiving and transmitting paths are selected separately, this significantly simplifies switching. The transmitter is made on three transistors VT1-VT3. The master oscillator is made using transistor VT1. Its frequency is stabilized by a quartz resonator at 48.2 MHz, and the collector circuit is tuned to the third harmonic of 144.6 MHz. Good results are also obtained with a resonator other than 24 MHz, but starting it at the sixth harmonic is much more difficult. Any other resonator at 48-48.5 MHz is suitable. To receive multiple channels, entered
a switchable circuit for shifting the resonant frequency of the resonator on three switchable coils L1-L3 and capacitor C11. In the process of setting up a radio station by adjusting their inductances, you can get three channels within 200-300 kHz from a frequency of 144.6 MHz.
To ensure the ability to work with more complex radio stations that have a frequency synthesizer, a function has been introduced to adjust the transmitter frequency within small limits using a VD1 varicap. Frequency modulation is performed using another varicap VD2.
This is followed by two power amplification stages, at the output of the latter a 144 MHz loop vibrator is turned on. When switching the receiving and transmitting modes to the output stage, power is supplied constantly, the power of the master oscillator is switched (the output transistors of the transmitter operate without an initial bias and, as a result, in the absence of a signal from the generator, practically do not consume current).
In reception mode, the signal from the antenna through capacitor C16 is supplied to the RF amplifier on the field-effect transistor VT4. In transmit mode, it is protected from overload by a diode limiter. The gain of the cascade is set by tuning
resistor R10. The input and output circuits of this stage are configured to the middle of the received range (middle channel). From the output of the RF frequency converter, the signal is supplied to the frequency converter on microcircuit A1. The K174PS1 microcircuit has a built-in local oscillator, but in this case it is necessary to provide quartz stabilization and use the third harmonic of the resonator, as well as provide a resonance frequency shift and a mode for adjusting the local oscillator frequency, so the local oscillator is made separate on the VT5 transistor.
Its circuit and operation are similar to the master oscillator of the transmitter, but this oscillator has significantly less power. Switching of channels occurs by switching inductances connected in series with the resonator, and adjustment is done by changing the capacitance of the shifting circuit using a varicap VD4. The resonator is taken at 46 MHz, but is also suitable for 23 MHz, if it is possible to start the generator at the sixth harmonic.
At the output of the converter, circuit L12 C26 is turned on, tuned to an IF frequency of 6.5 MHz, the signal from this circuit is supplied to the universal module UPCHZ-2 from the 3-USTST color TV. This module contains a complete amplification and detection path for the FM IF signal, including piezoelectric filters at the input and in the phase-shifting circuit of the frequency detector.
The use of this very affordable module greatly simplifies both the manufacture and configuration of the receiving path. Power is supplied to the receiver only in receive mode. The schematic diagram of the handset is shown in Figure 2. It contains two ultrasonics, the first on VT1 VT2 amplifies the signal coming from the M1 electret microphone (a microphone from an imported handset is used), the second on VT3-VT5 amplifies the signal from the detector of the receiving path and at its output a dynamic sound emitter from the same imported handset is included (and the handset body is also from a handset).
Switch S1 - P2K is not latched; when free, it turns on power to the receiving path, and when pressed, to the transmitting path. SK1 is also without fixation; when pressed, the amplifier on VT1 VT2 turns into a ringing signal generator. Resistor R8 is the volume control.
The handset is connected to the main unit using a seven-pin 2PM18 type connector from military equipment, but you can also use a standard LF connector with 6 connections.
The radio station is designed to operate in the amateur band 144-146 MHz. The main attention in the development of this radio station was paid to the simplicity of the design, the absence of scarce components and the low complexity of setting it up. The radio station operates on one of the fixed frequencies of the amateur band, depending on the quartz resonators available to the radio amateur.
- operating frequency range.............................144—146 MHz;
- modulation...,...................................frequency with deviation 3 kHz;
- receiver sensitivity at signal-to-noise ratio 3:1......0.1 µV;
- transmitter output power.............................................1 W;
- supply voltage................................................ ................12 V.
A schematic diagram of the receiving part of the radio station is shown in Fig. 46. It is made according to a double frequency conversion circuit. The signal from antenna WA1, switched by switch SA1.3 (Fig. 47), is supplied to the tap of coil L1. Circuit L1C1 is tuned to the operating frequency of the radio station. Here it is partially switched on from the antenna side to match the resistances. The input impedance of the receiver is 50 Ohms. Next, the signal is amplified by a UHF transistor VT1 type KT399A and isolated by circuit L2C4, which is also tuned to the operating frequency of the receiver. Then the amplified signal through the coupling coil L3 and capacitor C6 is supplied to the base of the transistor of the first mixer VT2 type KT399A. The local oscillator voltage is supplied to the emitter circuit of this transistor.
A signal with an intermediate frequency of 10.7 MHz is isolated on the L4C7 circuit and then filtered by a quartz filter Z1 type FP1P2-436-15 or similar. Taps from coils L4 and L6 match the input and output resistance of the filter with the corresponding stage. The L6C9 circuit is also tuned to 10.7 MHz. From its tap, the filtered signal is fed through the capacitor SY to the amplifier of the first IF, made on a VT3 transistor of the KT368A type.
Boosted signal allocated on the L7C12 circuit and through the L8 coupling coil it is supplied to the DA1 K174XA26 multifunctional microcircuit, which performs the functions of a second mixer, a second local oscillator, a second amplifier, a frequency detector, a preliminary ultrasonic amplifier and a noise reduction system.
The second local oscillator is built on part of the DA1 microcircuit and elements ZQ1, L10, C15, .C16. When selecting a second IF of 465 kHz, the frequency of the ZQ1 crystal can be 11.165 MHz or 10.235 MHz. After the mixer, the signal to the second IF is filtered by a piezoceramic filter Z2 type FP1P1-61.08 at a frequency of 465 kHz or similar. The second IF signal filtered by filter Z2 is amplified by the second IF and then detected by a frequency detector. The L11C23 frequency detector reference circuit is set to 465 kHz. Resistor R18 is selected when tuning to minimize nonlinear distortion.
The detected and amplified signal 34 from pin 10 of the DA1 chip, through the pre-emphasis correction chain C28R17C31, is supplied to the low-pass filter on the DA3 chip of the KR140UD7 type. The low-pass filter has a cutoff frequency of 2.5 kHz and reduces the noise level in the dynamics when the noise reduction system is turned off. Then the signal from pin 6 of the DA3 chip is fed through capacitor C43 to an ultrasonic sounder made on a DA4 chip of type K174UN4A. From the output of the microcircuit, the ultrasonic signal is fed through switch SA1.1 to dynamic head B1 type 0.2GD-6 or any other with resistance alternating current 8-30 Ohm.
The master oscillator of the first local oscillator is built on a VT4 transistor (KT316B). Quartz resonator ZQ2 is excited at the fundamental harmonic. Cascades on transistors VT5 and VT6 type KT316B are frequency triplers. Circuit L12C49 is tuned to the third harmonic of the frequency generated by the master oscillator, and circuits L13C52 and L14C53 are tuned to the ninth. The voltage in the base circuits of the local oscillator transistors is stabilized by a zener diode VD2. From the L14C53 circuit, the local oscillator signal is supplied to the emitter circuit of the first mixer.
The power supply circuits of the UHF, mixer, amplifier of the first IF and the DA1 microcircuit are also stabilized by a stabilizer based on transistor VT7 and zener diode VD3.
Resistor R10 can be used to adjust the noise reduction threshold to a level of -30 dB. The noise component amplified by the DA2 microcircuit is detected by the diode VD1 and goes to pin 14 of the DA1 chip to control the switch that shunts the useful signal 34 through pin 16 of this chip. The HL1 LED indicates the activation of the noise reduction system or the appearance of a useful signal. Button SB1 is used to disable the noise reduction system.
A schematic diagram of the transmitting part of the radio station is shown in Fig. 47.
The sound signal from the microphone, the role of which is played by dynamic head B1, is fed through switch SA.1.1 to amplifier 34, made on transistors VT1, VT2 type KT3102E. Resistor R1 sets the best operating mode of the amplifier. Through resistor R7, the AF signal is supplied to the varicap VD2.
The master oscillator of the transmitter is built on a transistor VT3 (KT316B) according to a capacitive three-point circuit, and frequency modulation is carried out using a varicap VD2. Transistors VT4 and VT5 are used to triple the frequency of the signal coming from the master oscillator through capacitor C12. Circuit L1C14 is tuned to the third harmonic of the input signal of the master oscillator, and circuit L2C19 is tuned to the ninth.
A buffer amplifier is built on a VT6 transistor of type KT399A. The useful signal with the operating frequency is isolated on the L3C22C23 circuit and then fed to the final amplifier on a VT7 transistor of type KT913A or KT610A, operating in mode C.
The voltage in the base circuits of transistors VT3-VT6 is stabilized by a zener diode VD1. The amplified signal with the operating frequency from the collector of transistor VT7 is filtered by a P-filter on elements C26, L5, C27 and through switch SA1.3 is supplied for further filtering to elements SZO, L8, C31, L9, C32 and then through connector XI to antenna WA1 . The last filter works both on reception and on transmission. Its switching is carried out by a group of switch contacts SA1.3. It serves to match the antenna with the receiver input and transmitter output. Switch SA1 is installed on the transmitter board and is necessary to switch the “receive-transmit” modes.
NKGTs-0.5 batteries were used as power supplies for the radio station. The radio station is made on two printed circuit boards made of double-sided foil fiberglass 1.5 mm thick, and the foil on the installation side of the elements is completely preserved and serves as a common wire and screen. Around the terminals of elements not connected to the common wire, the foil was removed using the countersink method. On one of the boards there is a receiver, and on the other there is a transmitter, a transmit-receive switch and an input P-filter. The high-frequency stages of the receiver and transmitter are separated by shielding partitions made of thin copper foil. They have a height of 12 mm.
The radio station uses resistors of types MLT-0.125, S2-23, S2-33. The variable resistor of the volume control is type SPZ-4gM; its switch serves as a switch for the radio station's power supply.
Electrolytic capacitors - types K50-35, K50-40, K50-51 for an operating voltage of at least 16 V, other capacitors - types K10-176, KM-4, KM-5, KM-6, KD-2.
The antenna of the radio station is a quarter-wave pin. Instead of the KR140UD7 microcircuit, you can use other operational amplifiers. K174UN4A can be replaced with K174UN7, K174UN9, K174UN14 if they are included in the circuit accordingly. Receiver filter Z1 - FP1P2-436-15 or any other at a frequency of 10.7 MHz with a bandwidth of 15-18 kHz, filter Z2 - FP1P1-61.08 or another piezoceramic at a frequency of 465 kHz, transistor VT7 - KT913A, KT610A, KT606A, KT911A , varicap VD2 - KB 110A, KV109, KV124 with any letter index. P2K switches can be used as switch SA1 and button SB1.
Receiver coil winding data Table 8
Winding data of transmitter coils Table 9
The winding data of the receiver inductors are given in table. 8, and the transmitter - in table. 9. Most receiver and transmitter coils are frameless and are wound on mandrels of the appropriate diameter. Coils with MP-100 type cores are made on frames with a diameter of 5 mm, machined from organic glass.
This design was tested with a similar one and showed good results. When tested in mountainous areas, the communication range between these radio stations reached 90-95 km.
Literature: A.P. Family man. 500 schemes for radio amateurs (Radio stations and transceivers) St. Petersburg: Science and Technology, 2006. - 272 pp.: ill.