Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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There are many descriptions of modern transceivers in amateur radio literature, but not every novice radio amateur dares to repeat them. The lack of experience in designing and setting up such equipment, as well as economic problems, sometimes force us to use developments that have become classics for radio amateurs in our country.

For decades, "old men" - transceivers of the UW3DI design have been faithfully serving us, remaining for many the only opportunity to spend time on the air with enthusiasm. Over the past years, there have been many publications in various literature on the refinement and improvement of these transceivers. With a focus on a beginner radio amateur and based on my own experience, I propose some changes in the design and scheme of the original author's publication of the UW3DI-1 transceiver (see "Radio", 1970, No. 5,6).

Automatic gain control

The introduction of the AGC system will significantly improve the operation of the transceiver. The AGC scheme of the UW3DI-II transceiver was taken as a basis (with some additions, see Fig. 1). In this and subsequent figures, the reference designations of elements without denominations correspond to the reference designations of the circuit in the author's publication with a slight modification - L7 is replaced by VL7, RZ-to short-circuit, etc. - on 6K9P. It should be noted that before installing the 4K6P lamp in the transceiver, it is necessary to swap the conductors connected to the legs 13 and 6 of the lamp socket. The pinouts of the lamps 1K5P and 6Zh4P are the same.

The low-frequency signal from the VL7 ULF lamp through the emitter follower on the transistor VT1 is fed to the AGC detector (diodes VD1 \ VD2). Capacitor C3 determines the AGC delay time, Zener diode VD3 determines the AGC threshold. Resistor R9 carry out manual gain control. At the loudest signals, the voltage on the AGC bus reaches -10 V.

The AGC unit is assembled on a printed circuit board made of foil fiberglass. It is installed in the basement of the chassis.

UHF input loop

It is possible to improve the selectivity of the receiving path by installing a high-quality narrow-band circuit at the UHF input (Fig. 2). Coil L1 is made on a ferrite magnetic circuit with holes (the so-called transfluxor), which is used, for example, in television indoor antennas. It contains 50 turns of PEV-2 wire 0,23 mm. The tap for the 80 m range is made from the 25th turn, for the 40 m range - from the 10th turn (counting from the end of the coil connected to the common wire). The antenna communication coil is one turn of the same wire.

Coil L2 is made on a frame with a diameter of 15 mm and has 20 turns of silver-plated wire with a diameter of 0,7 mm. Winding step - 1 mm. The taps are made from the 1st and 12th turns, counting from the end of the coil connected to the common wire.

S-meter and exit indicator

This refinement (Fig. 3) allows using the transceiver's measuring device as an S-meter when receiving and an output indicator when transmitting. To switch the measuring device, a free group of short circuit relay contacts is used. The milliammeter is replaced by a microammeter with a total deflection current of 50-100 μA. When receiving, the device is calibrated according to the generally accepted method by selecting resistor R4, and when transmitting, by trimming resistor R3 (at the maximum signal at the transceiver output).

When initially setting up the P-circuit (by selecting capacitors C53 - C55), a 150-200 mA milliammeter should be connected to the anode circuit of the output stage lamp. In the future, the setting of the output circuit is controlled by the output indicator.

microphone amplifier

To work with low-impedance microphones, you need to add a cascade on the VT1 transistor (Fig. 4). VOX, AntiVOX systems and VL14 lamp are excluded. The output of the capacitor C 105, which is freed at the same time, is connected to the common wire, as shown in Fig. 4. The right output of the resistor R87 is connected to the bus, which combines the cathodes of lamps used only in transmission mode. Variable resistor R5 adjust the output level of the microphone amplifier.

Mode switching

The transceiver has three modes: CW, SSB and tuning. When setting up, the transceiver is switched on for transmission with the SA2 switch (Fig. 5). When working CW and SSB, a pedal is used for this. Resistor R1 is selected depending on the type of relay used.

Author: Vladimir Zhitkov, Ust-Donetsk, Rostov region.

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