Transverter for 430...435 MHz. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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Operation in the 27 MHz band showed that it is quite loaded with SL. There are quite frequent long-range passages of radio waves here, which also serves as an additional source of interference. This makes communication with moving objects difficult. For handheld and car radios in the 27 MHz band, there is a problem with antenna size, since. its efficiency is directly proportional to its geometric dimensions, and in the 27 MHz range, a quarter-wave antenna has a radiating pin size of about three meters and its installation on a moving object, and even more so in a portable radio station, is very problematic.

All shortened antennas are compromise and their properties deteriorate the more, the smaller their geometric dimensions. Nevertheless, there is a way to significantly increase the efficiency of radio communications, especially in urban areas, by transferring the frequency spectrum emitted by the radio station transmitter to the amateur band 430 - 435 MHz, and for the receiver - by performing the reverse conversion. Such a device is called a transverter and can be used with any radio stations in the 27 MHz band, both author's design and industrial production, domestic and foreign. The number of channels of the communication system thus obtained in the range of 430 - 435 MHz will be determined by the number of channels of the radio station used. In the range of 430 - 435 MHz, it becomes possible to use full-sized antennas with a length of l / 4 - for a pin it is only 16 centimeters, but the best results can be obtained with an antenna with a length of 5 / 8l.

Schematic diagram of the actual transverter is shown in fig. one.

Fig.1 (click to enlarge)

Let's take a look at his work. In the receive mode, the signal from the antenna with a frequency of 430 - 435 MHz is fed to pin 1 of the board and is amplified by a high-frequency amplifier based on a VT1 transistor of the 2P327B type. The circuits L1, C2 and L2, C5, L3, C6 are tuned to a frequency of 432 MHz. The amplified signal from the source of the transistor VT1 is filtered and fed to the first gate of the mixer on the transistor VT2 type 2P327B. The second gate of this transistor receives a local oscillator signal with a frequency of 405 MHz. The difference frequency in the range of 27 MHz is allocated on the circuit L4, C9, C10 and through pin 6 of the board goes to the radio station. In the FM transmission mode, a signal from a radio station with a level of 50 - 100 mW is fed to output 3 of the board and then to a mixer based on a VT7 transistor of the KP327B type. The second gate of this transistor receives a signal from a local oscillator with a frequency of 405 MHz.

In the source circuit of the transistor VT7, a signal with a frequency of 432 MHz is emitted and through a bandpass filter on the elements L17, C37, L18, C39 enters the base of the amplifier on the transistor VT8 type KT399A. The cascade on the VT9 transistor type KT399A is also an amplifier. The amplified signal is allocated on the circuit L21, C47 and through the output of the board 10 is fed to the power amplifier. The local oscillator of the transceiver is a crystal oscillator with subsequent frequency multiplication and signal amplification. The master oscillator is built on a transistor VT3 type KT316D. Its frequency is stabilized by a ZQ1 quartz resonator at a frequency of 15 MHz. The quartz resonator is excited at the third mechanical harmonic, i.e. at a frequency of 45 MHz. A signal with this frequency is selected on the circuit L5, C17, L6, C18 and goes to the first frequency tripler on a VT4 transistor of the KT316D type. In its collector circuit, a signal with a frequency of 135 MHz is allocated on the circuits L8, C20, L9, C21. Further, the signal with this frequency is fed to the second frequency tripler on a VT5 transistor of the KT399A type. A signal with a frequency of 405 MHz is allocated to the collector of this transistor. From the circuit L12, C25, this signal is fed to the receiving part of the transverter, and also goes to the amplifier on the transistor VT6 type KT399A, and from it to the second gate of the transistor VT7 of the transmitting part of the transverter. The power supply of transistors VT3 and VT4 is stabilized by a stabilizer on a DA1 chip of type KP 142EI 18A. On diodes VD1, VD2 and transistors VT10, VT11, an electronic "reception-transmission" switch is built. A schematic diagram of the power amplifier is shown in fig. 2.

Fig.2 (click to enlarge)

The signal from the transverter board with a frequency of 430 - 435 MHz is fed to pin 1 of the board. The first amplifier on the transistor VT1 type KT610A operates with a small initial current. Further, the amplified signal is fed to a line of amplifiers operating in mode C, on transistors VT4 - KT610A, VT5 - KT913A, VT6 - KT916A, VT7 - KT960A and having no features. The amplified signal is separated by a bandpass filter L25, C39, L26, C40 and through the contacts of the relay K1.1 type RPV 2/7 and output 7 of the board enters the antenna. Part of the output signal is detected by the diodes VD4, VD5 and fed to the automatic power control circuit (AWC). It is built on an operational amplifier DA1 type KR140UD7 and transistors VT2 type KT3117A and VT3 type KT837V. The power amplifier is controlled by the collector circuits of transistors VT1 and VT2 of the amplifier. The required power level of the amplifier is set by the resistor R1. AWS also protects the power amplifier in case of an antenna break and a short circuit in it or the feeder.

The connection diagram of the converter and local oscillator with a power amplifier is shown in fig. 3.

Ris.3

The radio station is connected to connector XS1. Relays K1, K2 of the RES-47 type are also included in the automatic transfer-reception switch. Switching to the "transmit" mode is carried out when a signal with a frequency of 27 MHz is received from the radio station, which is rectified by diodes on the conveyor board and leads to the operation of the corresponding relays. The antenna is connected via connector XS3 to terminals 7, 8 of the power amplifier board. The transverter is powered by the voltage of the car's on-board network 11 - 14V. It enters through the XS2 connector and is filtered by a filter on the transformer T1 and capacitors C1, C2. The transverter is made on two printed circuit boards made of double-sided foil fiberglass. Moreover, the foil on the side of the installation of radioelements is completely preserved. It is removed only around the terminals of elements that are not connected to a common wire by countersinking. The printed circuit board of the converter and the local oscillator has a size of 150 x 80 mm, and the power amplifier has a size of 190 x 70 mm. The winding data of the inductors of the transverter are given in Table. 1, and the power amplifier - in table.2.

Table 1

Table 2

The design of coils L1, L2, L3, L17, L18 of the transverter and L25, L26 of the power amplifier is shown in fig. four.

Ris.4

The transformer T1 of the power filter is wound on a ferrite ring with a permeability of 2000 NN and a size of K32 x 20 x 6 with an HB-0,14 wire and has 30 turns. Winding is carried out in two wires. The transverter is assembled in a housing measuring 200 x 200 x 40 mm. Setting up the transverter should begin with the local oscillator. First, the excitation of the quartz resonator at the third mechanical harmonic is achieved by stretching and compressing the turns of the L5 coil. Next, connecting in series an RF voltmeter to the bases of transistors VT5 and VT6, as well as to the L14 coil. Triples are tuned to frequencies of 135 MHz and 405 MHz, as well as an amplifier on the VT6 transistor - to 405 MHz for the maximum signal at the corresponding frequency. Then the receiving part of the transverter (converter) is adjusted. To pins 6, 7 of the transverter board, a radio station is connected, which is turned on for reception. The input 1 of the board is fed a signal with a frequency equal to Fc=405+Fr.st. where Fр.st. - tuning frequency of the radio station in the range of 27 MHz. By rotating the rotors of the capacitors C2, C5, C6 and the core of the coil L4, the maximum sensitivity of the converter is achieved. It should be no worse than 0,1 μV. Now we move on to setting up the transmitting part of the transverter board.

A signal with a frequency of 3 MHz is fed to the input of board 27, and an RF voltmeter is connected to pin 10. Sequentially rotating the rotors of the trimmer capacitors, they achieve the maximum readings of the RF voltmeter. Then proceed to setting up the power amplifier. To set it up, you need a frequency response meter like X1-48, X1-42 or similar. Tuning the RF part is reduced to obtaining the maximum output power at a load of 50 ohms. In this case, the AWP must be turned off (the resistor slider in the lower position). The maximum output power in this case can reach 20 watts. Next, resistor R1 sets the output power to 10 watts. The bandwidth of the amplifier should be about 30 MHz, and the shape of the frequency response curve on the meter screen should be bell-shaped. When changing the power using the resistor R1, the average frequency of the frequency response of the power amplifier should not be shifted. Then the entire transverter is assembled into the housing and the final adjustment is carried out. As a transverter antenna on a car, a 5/8l long pin on a magnetic base is used.

For the purchase of printed circuit board patterns and design features of the transverter, please contact the author.

Author: V. Stasenko (RA3QEJ), Rossosh, Voronezh region; Publication: N. Bolshakov, rf.atnn.ru

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