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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Stationary FM transverter 144/27 MHz. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Civil radio communications The transverter is designed to work with a stationary CB transceiver with an output power of 2...6 W. It uses basically the same circuit solutions as in the previously described design ("Radio", 1999, No. 8. pp. 70-72). It features higher output power and higher sensitivity. This unit has been tested with Dragon SS-485, President Lincoln, Dragon SY-101+ transfers. With a supply voltage of 13,5 V, the output power of the transverter in the range of 2 meters was 5 watts. The sensitivity of the receiving path "transverter-transceiver" is not worse than 0,14 ... 0,15 μV. The presence of a smooth adjustment of the UHF gain allows you to adapt it to CB transceivers of various sensitivities. There are no electromagnetic relays in the transverter circuit, and the transition from the receive mode to the transmit mode occurs automatically when the transceiver transmitter is turned on. The transverter circuit is shown in fig. 1. Connector XW1 is for connecting the transceiver, connector XW2 is for the 11 meter band antenna, and connector XW3 is for connecting the 2 meter band antenna. External power is connected to sockets X1, X2. When the transverter is turned off, the transceiver is connected to the CB antenna through switches SA1.1, SA1.2, SA1.3 and is used for its intended purpose.
When switching switch SA1 to the "On." power is supplied to the transverter, the HL1 LED signals its inclusion. In this case, the CB antenna of the range closes to the body. This is done so that the signals from the CB antenna do not interfere with the reception of stations in the 2 meter band. In this design, they are attenuated by 65...70 dB. In the receive mode, the signal from the antenna through the L17 circuits plus the capacitance of the diodes VD7, VD8 and L18C37, tuned to the center frequency of the 2-meter range, is fed to the URF (transistors VT10, VT11). Its gain is set by resistor R18 within 15...30 dB. From the URF output, the signal through the VD4 diode goes to the L6L7C7-C9 band-pass filter and then to the balanced reversible mixer, made on transistors VT1, VT2. The mixer is loaded on the L4C5C6 circuit, tuned to the center frequency of the transceiver's operating range. Through the communication coil L3 and low-pass filter L1L2C2-C4 with a cutoff frequency of about 40 MHz, the signal is fed to the transceiver. The voltage of the local oscillator, made on transistors VT7-VT9, is applied to the gates of the mixer transistors. The frequency of the reference local oscillator (VT7) is stabilized by a quartz resonator. Cascade on transistors VT8, VT9 - frequency multiplier. In transmission mode, the CB signal of the transceiver through the low-pass filter and the L4C5C6 circuit enters the mixer, where it is converted into a 2-meter range signal. The signal selected by the L6L7C7-C9 band-pass filter is fed to a two-stage power amplifier made on transistors VT3, VT4 and then to the XW3 connector. At the same time, the output signal of the CB transceiver is rectified by the VD1 diode and fed through the stabilizer on the VD2 diode to the base circuit of the VT3 transistor, switching it to class AB mode. The HL2 LED, included in this purpose, indicates the presence of a transceiver signal at the input of the gransverter. Transistor VT4 operates without initial bias. LED HL3 - indicator of the presence of a signal at the output of the transverter. In order to exclude the influence of the URF on the operation of the power amplifier and the possibility of their joint self-excitation during transmission, the voltage rectified by the diode VD1 opens the transistor VT5, which leads to the closing of the transistor VT6. In this case, the RF transverter will be de-energized. Diodes VD5-VD8 also protect the RF transistors from the powerful signal of their own transmitter. Opening the diodes VD7, VD8 will cause detuning of the input circuits, and the diodes VD5, VD6 will limit the signal based on the transistor VT11. All parts of the transverter are placed on two printed circuit boards made of double-sided foil fiberglass, the sketches of which are shown in fig. 2 and 3. The second sides of the boards are left metallized and connected by a thin foil along the contour with a common wire of the first side. A large board is attached to the heat sink, on which transistors VT1-VT4 are installed. For these transistors, corresponding holes are made in the board. As a heat sink, you can use a 100x60 mm plate made of aluminum alloy 3...4 mm thick, as well as a transverter case, if it is made of the same material.
The URF board (Fig. 3) is soldered perpendicular to the large board, with parts towards the power amplifier, at the same time it serves as a shielding partition. The second screening baffle on the board is made from a strip of tin plate. The following types of parts can be used in the transverter: permanent capacitors - K10-17v, K10-42, KLS, KM, KD, trimmers - KT4-25. Fixed resistors - MLT, P1-4f C2-33, R1-12, tuned - SPZ-19. LEDs - any type with a working current of 10 ... 20 mA and preferably in different colors. Switch SA1 - type P2K or PK-61 with fixation. RF connectors - СР-50. Transistors can be replaced: VT1, VT2 - on KP905A-B; VT4 - on KT925B, KT934G; VT8, VT9 - on KT326A; VT7 - on KT316A-B, KT368A-B; VT10 - on KT3123B-2, KT3123V-2, KT363B, VT11 - on KT3101A-2. The choice of the frequency of the quartz resonator was described in detail in the article mentioned above. Parts are placed on the side of the printed conductors, and their leads are shortened to the minimum possible length. The design of the transverter is arbitrary. For example, you can place LEDs and a switch button on the front panel, and mount the RF connectors and power sockets on the back of the case. Inductors L1, L2, L5 - L7, L9, L12, L16 - L18 - frameless. They are wound on mandrels with a diameter of 5 mm. L1 and L2 each contain 7,5 turns of PEV-2 0,2 wire. Coils L6, L7, L16-L18 contain 3,5 turns each, and L9 and L12 each contain 2,5 turns of PEV-2 0,7 wire. The communication coil L5 is wound over L6 and contains one turn of doubled PEV-2 0,2 wire. Coils L7, L18, L19 are wound in increments of 0,5 mm between turns, leaving leads 7 ... 10 mm long. The taps at L7, L18 are made from 0,8 and the 2nd turn, counting from the "cold" end. Coils L3, L4, L15 are wound with doubled wire PEV-2 0,2 on a plastic frame with a diameter of 5,8 mm. L3 and L4 contain 10 turns each, L15 - 1,5 turns over L14, and L14 itself - 5,8 turns of PEV-2 0,4 wire. Trimmer for coils L14 and L15 - brand 7VN, size C2,8x10. Inductors L8, L10 are frameless, wound with wire PEV-2 0,2 on a mandrel with a diameter of 3 mm and contain 15 ... 20 turns. The inductor L11 is wound directly on the resistor R4 with a PEV-2 0,1 wire and contains 30 turns. The L13 inductor is wound with PEV-2 0.2 wire on an M1000NM ring ferrite magnetic core, size K10x6x3 mm. The number of turns is 10. The design of the device allows you to set up the URF and the transmitting path separately. First, adjust the URC for direct current. To do this, by selecting a resistor R20, a voltage is set on the VT10 emitter in the range of 5 ... Next tune the local oscillator. Trimmer coil L14 and capacitor C32 achieve stable generation and maximum local oscillator voltage at the gates of transistors VT1, VT2 (at least 6 ... 7 V). Voltage control should be carried out with a high-resistance RF voltmeter. Resistor R14 can change the value of this voltage. Capacitor C25 finely tunes the frequency of the local oscillator. In the author's design, a resonator at a frequency of 58997 kHz (third harmonic) was used and the local oscillator frequency was 118 MHz. If the frequency of the quartz resonator is slightly higher than required, the capacitor C25 should be replaced with an inductor. A load of 50 ohms and a power of at least 5 watts is connected to the output of the transverter. A signal with a power of 4 watts is fed to its input from the transceiver. Through a resistive divider 1:10, the output voltage is controlled by a broadband oscilloscope. Trimmer capacitors C7, C9, C14, C15, C19 achieve a "clean" signal with an amplitude of 15 ... 16 V. If necessary, adjust the coils L9, L12 by changing the number of turns or changing the winding pitch. Then finally adjust the URC. To do this, by adjusting the L17 coil and the C37 capacitor, the URF bandwidth is set to 5 ... 8 MHz. It may be necessary to clarify the connection points of the taps on the L18 coil. All coils and parts mounted by the hinged method should be fixed with a small amount of epoxy glue, and after its polymerization, the final adjustment of all nodes should be made. It is better to use a transverter with a transceiver that has a large operating frequency range (up to 10 grids), which simplifies the indication of the tuning frequency and the ability to move from zeros to fives. When they are paired with a resistor R18, the optimal gain of the URF is set, which provides maximum sensitivity of the receiving path "transverter - transceiver" with a minimum introduced noise level. The transverter works equally well with FM transceivers with an output power of 2 to 8 W, however, it should be noted that excess power will be dissipated on its elements, primarily on the field-effect transistors of the mixer. Authors: I. Nechaev (UA3WIA), I. Berezutsky (RA3WNK)
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