FM Transverter 144/27 MHz. Scheme, description

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FM Transverter 144/27 MHz. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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To organize operational communications, shortwaves usually use portable VHF FM radio stations operating in the 2-meter range. The development of this type of communication in the country is constrained by the fact that the cost of such factory-made radio stations is relatively high. And not every radio amateur can make them independently from scratch. Meanwhile, there are inexpensive (especially used) portable VHF FM CB radio stations on sale, which can be easily converted into 2-meter radio stations by adding a transverter to them. In this issue of the magazine, we bring to the attention of readers a miniature 144/27 MHz transverter for portable radio stations, and "on the way" we have a description of a similar transverter for a base station.

A transverter is an attachment to a transceiver (transceiver) that transfers the signals it receives and transmits to a new frequency band. They have been widely used in amateur radio practice for many years, in particular, for the linear transfer of signals from an amateur HF radio station to a 2-meter band (usually in 144/28 or 144/21 MHz versions). The advent of affordable CB FM radio stations and the development of a network of amateur VHF FM radio stations predetermined the creation of FM transverters 144/27 MHz.

The transverter, which will be discussed in this article, can practically be used with any portable CBS radio station with an output power of about 1 W, but best of all - with radio stations that have an extended operating frequency range (up to ten grids), as well as a frequency indication settings and the ability to move from "zeros" to "fives" (for example, "Dragon SY-101+").

The proposed transverter does not have electromagnetic relays, which are usually used in such devices to switch from the receive mode to the transmit mode. This made it possible to simplify its scheme, reduce dimensions and power consumption.

The sensitivity of the receiving path "transverter-radio station" is not worse than 0,5 μV. When a signal is supplied from a CB radio station with a power of 0,7 ... 1 W, the output power of the transverter in the range of 2 meters will be about 1,5 W. For a portable radio, this output power level is optimal because its power supply is limited. The current consumed by the transverter during reception is in the range of 15-18 mA, and during transmission it depends on the set output power. The transverter is assembled in a housing measuring 18x53x78 mm and placed on the rear wall of a portable CB radio station (see Fig. 1).

FM Transverter 144/27 MHz

Connect it between the antenna and the radio station, as shown in fig. 2. It is connected to the radio station with a short length (8 cm) of coaxial cable with an RF plug at the end.

FM Transverter 144/27 MHz

The transverter circuit is shown in fig. 3. The output of the CB radio station in the switch position SA1 "11 m" is connected to a 2-meter band antenna, which is used in the CB band with an L15 extension coil.

(click to enlarge)

When the switch SA1 is set to the "2 m" position, the transverter is supplied with power, and it is activated by input and output. When receiving, the signal from the antenna through the L14C28 and L13C27 circuits, tuned to the center frequency of the 2-meter range, is fed to the UHF (transistors VT6, VT7) with a gain of 20 ... 25 dB. It is chosen relatively high to compensate for losses in the passive mixer. Diodes VD3, VD4 protect the UHF input from overload by the power amplifier signal of the transverter's transmission path. From the UHF output, the signal goes to the bandpass filter L5, L6C7-C9, and from it to a passive mixer made on transistors VT1, VT2. Mixer load - L2C1C2 circuit, tuned to the center frequency of the operating range of the CB radio station. It comes to it from the communication coil L1.

The gates of the mixer transistors VT1 and VT2 are supplied with the RF voltage of the local oscillator, which is made on the transistor VT3. The local oscillator frequency is stabilized by a quartz resonator.

When transmitting, the signal from the output of the CB radio station through the L2C1C2 circuit enters the mixer, where it is converted into a 2-meter range signal. The signal selected by the bandpass filter L5L6C7-C9 from part of the turns of the coil L6 is fed to a two-stage power amplifier (transistors VT4, VT5). To reduce the connection between the output and input of the UHF receiving path and eliminate the possibility of its self-excitation, the VT5 transistor operates without an initial bias, and the bias is applied to VT4 only when a signal appears in the transmitting path. The output signal of the CB radio station is rectified by the diode VD1 and through the voltage stabilizer on the diode VD2 is fed into the base circuit of the transistor VT4, switching it to class B mode. IN.

Almost all parts of the transverter are placed on a printed circuit board made of double-sided foil fiberglass, a sketch of which is shown in fig. 4. The second side of the board is left metallized and connected with a thin foil along the contour to the common wire of the first side. Switch SA1 and socket XS1 are installed directly on the board. To reduce the dimensions of the device, the heat sink screws of the transistors VT1, VT2, VT4 are neatly sawn off at the very base, and the screw of the VT5 transistor is shortened to a size that allows it to be placed in the transverter case.

FM Transverter 144/27 MHz

The parts are placed on the side of the printed conductors, while their conclusions are made as short as possible. The mixer transistors are placed one above the other in "two floors", and their gates are soldered directly to the contact pad. The remaining conclusions are connected to the circuit with conductors of minimum length. The L15 coil is installed above the XS1 socket.

The dimensions of the board allow the use of parts of the following types: trimmer capacitors - KT4-25, constant capacitors - K10-17v and K10-42 (preferably unpackaged), KM, KD with leads shortened to a minimum length. Resistors - MLT, P1-4, C2-33. Using small-sized parts - resistors R1-12 (RN1-12) and capacitors KT4-27 (tuning), K10-17v (unframed), you can reduce the dimensions of the transverter by 1,5 ... 2 times, but the board will have to be reworked.

The XS1 jack is any small-sized RF socket with sufficient mechanical strength to allow a whip antenna to be connected to it. Switch SA1 - small, preferably high-frequency, two positions and three directions. Transistors VT1, VT2 are interchangeable with KP905B; VT3, VT6 - on KT363A; VT7 - on KT399A; VT4, VT5 - to equivalent other types, but in this case it will be necessary to select the parameters of the matching elements.

The quartz resonator must necessarily be harmonic, and it is desirable that it operate no more than at the fifth harmonic (otherwise the local oscillator may operate unstable). The frequency of the resonator should be selected based on the frequency range of the radio station and the 2-meter range section in which FM radio communication is allowed. To cover this entire section, the resonator frequency can range from Fv2 - Fv11 to Fn2 - Fn11, where Fn2 and Fv2 are the lower and upper frequencies of the FM section of the 2-meter range, and Fn11 and Fv11 are the lower and upper frequencies of the CB operating range radio stations. For the "Dragon SY-101+" radio station, the frequency of the quartz resonator can range from 116,145 to 119,340 MHz. If not the entire FM section of the 2-meter range is covered, then the resonator frequencies may go beyond the specified limits. It is desirable to choose the frequency of the resonator as a multiple of 10, 100, and even better, 1000 kHz - this will make it easier to read the frequency in the range of 2 meters.

Inductors L1, L2, L4, L5 and L15 are wound on plastic frames with a diameter of 5,8 mm without trimmers, the rest of the coils are frameless. L1, L2 are wound with double folded wire PEV-2 0,2 mm turn to turn and they contain 8 turns each, L5 contains 3,5 turns of wire PEV-2 0,41 mm, L4 is wound with double folded PEV-2 0,2 mm and contains two turns, which are connected in accordance with the diagram and placed close to L5 from the side of the output connected to the common wire. Coil L15 contains 30...50 turns of wire PEV-2 0,2 mm. Frameless coils L3, L6, L8 and L13 each contain 3,5 turns of PEV-2 wire 0,41 mm on a mandrel with a diameter of 5,8 mm, L11 and L12 - 2,5 turns each, L14 - 4,5 turns. Coil taps: L3 - from 1,5 turns, L6 - from 0,5 turns, L13 - from 1 turn. Inductors L7 and L10 are wound with PEV-2 wire 0,21 mm on a mandrel with a diameter of 3 mm and contain 25 turns each. The winding of the inductor L9 is wound directly on the resistor R9 with a PEV-2 0,1 wire and contains 30 turns.

Establishment begins with the UHF setting for direct current. To do this, by selecting a resistor R14, a voltage is set on the collector of the transistor VT6 in the range of 4,5 ... 5 V. Then, the UHF input circuits are pre-tuned to the center frequency of the 2-meter range and, by selecting the capacitor C19, the maximum UHF gain is set at this frequency. After pre-setting, all coils (and some parts) should be securely fixed with epoxy.

By tuning capacitors C3 and C6, stable local oscillator generation is achieved. In this case, the RF voltage at the gates of the mixer transistors should be 5 ... 6 V. The same capacitors can change the generation frequency within small limits (several kHz).

Having applied a signal with a frequency of 145 MHz from the generator to the L4 coil, capacitors C7 and C9 adjust the filter to this frequency according to the maximum RF voltage based on the VT4 transistor.

Then a 50 ohm load is connected to the output of the transverter. A signal with a power of 1 W is fed to its input from a CB radio station, and through a 1:10 resistive divider, the output voltage is controlled by a broadband oscilloscope. Trimmer capacitors C7, C9, C15 and C16 achieve a "clean" signal with an amplitude of 10 ... 12 V. By controlling the frequency of the output voltage, adjusting the capacitors C3 and C6 change the frequency of the local oscillator to obtain the calculated value of the output signal frequency.

After that, the final adjustment of UHF by ear in the receive mode is carried out. By adjusting the capacitors C27 and C28, maximum sensitivity is achieved.

The transverter for transmission worked stably with a whip antenna 35...40 cm long and with a remote antenna powered by a cable with a wave impedance of 50 ohms. By controlling the field strength during transmission, the optimal length of the whip antenna is selected.

If a radio amateur does not have quartz resonators at his disposal that provide the required local oscillator frequency at the fifth harmonic, then it can be performed on more common resonators by applying frequency multiplication. The scheme of such a local oscillator is shown in Fig. 5 (numbering of elements continued from Fig. 3). A master oscillator is assembled on the VT8 transistor (its frequency should be half the calculated one), operating on the third or fifth harmonic of the quartz resonator, and on transistors VT9, VT10 - a balanced frequency doubler. This oscillator works stably and provides more voltage at the gates of field-effect transistors, which means less attenuation in the mixer. Coils L16, L17 are made on a frame with a diameter of 5,8 mm with a trimmer made of carbonyl iron (diameter 4 mm). They contain 7 turns of wire PEV-2 0,21 mm. L17 is wound with doubled wire close to L16.

FM Transverter 144/27 MHz

Establishing the circuit comes down to obtaining a stable generation and setting its frequency with the trimmer of the L16 coil. Capacitor C3 tunes the L3C3 circuit to the maximum of the second harmonic signal. The RF voltage on this circuit (7 ... 8 V) is set by selecting the resistor R18. In this case, the current consumed by the generator and doubler should not exceed 10 ... 15 mA. The board will have to be slightly changed, but there is a place to install new parts on it.

The description of this transverter aroused great interest among the readers of the magazine. In their letters, the most common question is: "Can this transverter be used with other types of radio stations and how will its parameters change?" Here is what the authors of this development told us.

"There are no fundamental restrictions on the operation of an FM transverter with different types of CB radio stations. It can work with both multi-channel and single-channel radio stations of the Ural-R type and similar ones.

One of the conditions for its normal operation is that the output power of the radio station used must be within 0,8 ... 1,5 W. With more power, the FETs will overheat, and with less power, the output power of the transverter may noticeably decrease.

The second condition concerns the supply voltage. It should be within 7 ... 12 V. In this case, the output power varies from 0,7 to 2 W. At a lower voltage, the transistors of the transmitting channel do not work well (special low-voltage ones must be used), and at a higher voltage, the output transistor can become very hot, since it does not have an effective heat sink.

The sensitivity of the transverter-radio receiving path depends very little on the supply voltage.

In addition, we inform you that the description of the FM transverter at 144/27 MHz for the base radio station is being prepared for publication and will be published early next year.

Authors: Igor Nechaev (UA3WIA), Igor Berezutsky (RA3WNK)

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Goga
Those were the days in the 90s! To work at 145, they made a transverter to the SVshka. And now for $50, you can get a used radio station for 136-174.

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