Independent detuning in the RA3AO transceiver. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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The functionality of the transceiver or KB-receiver can be somewhat expanded by introducing the so-called "independent detuning" (hereinafter NR) about them. In essence, HP is an additional channel for receiving and transmitting.

Normal detuning is used by the operator to work at split frequencies and to listen to stations near the main tuning frequency. In the latter case, if a station of interest to the operator appears, then you have to turn off the detuning and tune in with the main knob. Using HP, you can make a connection without additional manipulations, and the frequency of the main tuning will remain the same.

The figure shows a two-channel HP circuit implemented in practice in a RA3AO design transceiver (V. V. Drozdov "Amateur KB transceivers" ed. "Radio and Communications", 1988). In the initial state, the "zero detuning" voltage is supplied to the HP varicap from the divider R1R2. This position is used to tune the transceiver with the main knob. Relay contacts K 1.1, K2.1 include one of the HP channels.

The voltages on the relays K1 and K2 come from the modified A15 board (the designation of the blocks and the elements located in them corresponds to the book mentioned above).

The following changes have been made to the RA3AO standard design.

1. In place of the regulators "IF Gain", "LF Gain" variable resistors R4 n R7 of type PPZ-40 are installed.

2. The "IF Gain" knob is set to the "TX Level" position, the last to the "CW Tone" position. The "LF Gain" and "CW Tone" controls are excluded from the diagram, but if necessary, they can be placed on the rear wall of the transceiver.

3. In block A5 (GPA), an additional detuning circuit R'C'VD' is mounted, which is later used as HP.

4. In the front wall of the A5 (GPA) case, an additional feed-through capacitor Cdop with a capacity of 4700 pF is installed.

5. Nuts of resistors R4 and R7 on the false panel fixed a board with dimensions of 40x50 mm, on which fixed resistors of HP dividers, a relay of the RES49 type (passport RS4.569.421-0,1), stabilizer elements and coil L1 (100 turns of PEV 0,2 per resistor MLT-0,5 1MOhm).

Elements VT15, VT1, VT2, VT3 are removed from board A 6. R5, R8, R9, RIO, R11, R14, R16, R17, R18, R19 and C2, and on the vacant sites solder two transistor switches that control the operation of relays K1 and K2.

With the ratings indicated on the diagram, the detuning limits turned out to be the following:

The frequency overlaps by resistors R4 and R7 are different. This is done intentionally by the choice of resistor values ​​R3, R5, R6 and R8 in order to cover more frequency bands with HP channels. When working on the air, you can follow the following procedure:

use the main knob to tune in to the middle of the section of the range of interest (general call work), with resistors R4 and R7 to frequencies above and below the main one (search work).

The disadvantage of HP, compared with a separate additional local oscillator, is the relatively narrow range of overlap and tuning of the HP channels when the fundamental frequency changes. But the proposed option captivates with the simplicity of the scheme and the possibility of organizing several channels.

For smoother tuning at the HP station, it can be made in the form of an electric vernier, i.e. R4 and R7 are replaced by two series-connected potentiometers with ratings that differ by 10 times.

Coaxial potentiometers are very convenient for this purpose. The inclusion of HP should be accompanied by an appropriate indication.

Author: Falat Sharapov (RA4PC), Leninogorsk, Tatarstan; Publication: N. Bolshakov, rf.atnn.ru

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