Improvement of the RA3AO transceiver. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Civil radio communications
Comments on the article
For balancing receiver mixer it is desirable to install a tuning resistor. A fragment of the circuit is shown in Fig.1.
Ris.1
The sensitivity of the transceiver on the bands of 21 and 28 MHz still did not satisfy. Therefore, it was added switchable URCH. Structurally, the URC is made on the "patch" on the free space of the board of the node A2. Resistor R2 is selected so that the current through the transistor is 30 - 40 mA. Relay K1 - type RES-47 (RES-48), you can use the QSK button of the transceiver to turn it on.
In some cases, there are problems with the operation of the node adding one to the division factor at node A6 (DPKD). To eliminate this, it is enough to turn on the blocking capacitor (2200 pF) from pin 10 of the DD6 microcircuit (Fig. 1.b in [L]) to ground.
In my transceiver, it was not possible to obtain an SSB signal level on the L2 coil of node A19, sufficient for the normal operation of the transmitting path. This problem was solved by introducing additional amplification stage after EMF node A18 (Fig. 3). Standard IF circuits from small-sized receivers were used as circuits. Structurally, the assembly is made on a small printed circuit board soldered at an angle of 90° to the A18 board near the EMF outputs.
Ris.3
Often, especially at a low IF frequency, it is not possible to obtain telegraph local oscillator frequency tuning range regulator R3 (fig.28 in [L]) within ±300 Hz. In addition, the power adjustment range of the output stage with resistor R2 (Fig. 28 in [L]) by 5 times is often insufficient.
Both of these shortcomings are eliminated very easily - the output of the resistors R2 and R3 (Fig. 28 in [L]) installed on the A17 board, which is upper in the circuit, is sufficient to be disconnected from the "ground" and apply +12 V to them. After such an alteration, the tone adjustment range telegraph signal increases significantly, and the power of the output stage becomes possible to reduce almost to zero.
Literature
L. Drozdov. Amateur KB transceivers. M. 1988.
Author: O. Shishov (UC2WCJ), Polotsk; Publication: N. Bolshakov, rf.atnn.ru
See other articles Section Civil radio communications.
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