Finalization of the transceiver designed by V. Drozdov. Scheme, description

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Finalization of the transceiver designed by V. Drozdov. 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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Currently, a transceiver designed by V. Drozdov (RA3AO) is popular among radio amateurs. In general, a good transceiver needs to be improved.

When repeating the transceiver in some instances, when receiving, there is a large number of affected points. The reason for this is the "crawling" of the constantly operating PLL system of the transmitter through parasitic connections into the receiver channel. It is not difficult to eliminate this effect, it is only necessary to make changes to the A4 board according to Fig. 1.

The QSK signal is taken from the A19 transmitter board. Otherwise, this scheme does not require explanation.

Finalization of the transceiver designed by V. Drozdov

Insufficient stability of the GPA caused by poor performance of +3,5 and -2 V regulators. UP3BD proposed a regulator circuit that has a high stabilization coefficient and good temperature stability (Fig. 2).

The stabilizer is assembled on a separate board, which is mounted on the GPA housing. Remove transistors VT6, VT2 and diodes VD9 - VD1 from the DPKD A8 board. The stabilizer is connected with conductors. Voltage -12 V is supplied to the stabilizer through a free contact on the XP1 connector.

Finalization of the transceiver designed by V. Drozdov

Interesting improvements were proposed by I.V. Goncharenko (RC2AV).

AGC system The transceiver does not have an amplitude delay element, so signals with a level less than S - 7 are noticeably attenuated by the AGC system. It is possible to eliminate this by introducing an amplitude delay element in the AGC control signal circuit. To do this, in block A4, in series with the diodes VD4, VD5, an additional two KD510 diodes are included in the same polarity. As a result, when receiving signals with a level less than S - 6...7, the receiver gain will become maximum and will not depend on the input signal level. The refinement does not affect the operation of the S-meter.

In the FOS block (A3), a not entirely successful method of matching the quartz filter with the first stage of the IF. In this case, with the inherent noise figure of the transistor VT1 2dB (typical value), the noise figure of the transistor will be 6...7 dB. After refinement, the noise figure of the amplifier will decrease to 2,5 dB, which will allow the use of more affordable transistors KP303, KP307 in it. The essence of the refinement is to include instead of the resistor R1 (A3) a resonant circuit similar to L1C1 (A4). The tap is made from 1/6 turns, counting from the grounded end (see Fig. 3). Replacing KP312A with KP303, KP307 practically does not worsen the noise characteristics of the cascade.

Finalization of the transceiver designed by V. Drozdov

Recommended introduce revision into the ULF (board A4). Between capacitor C38 and terminal 16 of the A4 board, turn on a low-pass filter with a cutoff frequency of 3 kHz, consisting of two capacitors according to YuN and an inductor of 100 mH. This refinement is especially useful when using stereo phones such as TDS, which effectively reproduce high-frequency noise components.

This does not exhaust all the possible improvements in the RA3AO transceiver that improve its performance. The editors are waiting for your messages about the upgrades of the transceiver that are not included in this collection, as well as the upgrades of other widely used transceivers, such as "Ural-84".

The numbering of elements on the diagrams is given in accordance with the book by Drozdov V.V. "Amateur KB transceivers". M. Radio and communication. 1988

Author: ABABAK (RC2AD); Publication: N. Bolshakov, rf.atnn.ru

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