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Encyclopedia of radio electronics and electrical engineering / Civil radio communications
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The RA3AO HF transceiver described in [1], which in its main parameters is not inferior to high-class foreign-made transceivers, does not have such a high service required when working on busy sections of the KB bands.
One of the most important nodes is a device that allows you to smoothly narrow the bandwidth of the transceiver's receiving path while maintaining high path selectivity (VBT). To do this, a device is introduced into the IF path of the transceiver, the functional diagram of which is shown in Fig. 1, which is a frequency converter of the IF transceiver to a lower one, followed by filtering with an electromechanical filter and further transfer to the frequency of the main IF.
(click to enlarge)
The converter stand generator shifts the frequency response of the EMF relative to the bandwidth of the quartz filter of the receiving path, narrowing the total bandwidth of the receiving path of the transceiver, without shifting the frequency of the received station, from above or below (Fig. 2) [2].
Ris.2
A diagram of such a device is shown in Fig. 3 and contains two balanced mixers, a quartz oscillator with a frequency shift of a quartz resonator. The device is assembled on a printed circuit board with dimensions of 120x70 mm from one-sided textolite.
Fig.3 (click to enlarge)
Transformers T1 - T4 are wound on ring magnetic cores K12, 600NN and contain 3x9 turns of twisted wire PEV 0,1 ... 0,2. An electromechanical filter of the EMF-DP-3.1N type, but any one can be used, with any passband and sideband, but preferably not wider than 3,5 kHz, since a large non-working zone will appear when the stand generator is rebuilt.
Resistors R1 and R7 type SP4-1. Quartz resonator ZQ1 in B-1 case.
The device can be used in other transceivers and receivers (with the appropriate replacement of the quartz).
The place of inclusion is in the IF path, after the main selection filter.
Literature
1. V.V. Drozdov. Amateur KB transceivers. Radio and communication. M.1988.
2. S. Kazakov. Designers of communication equipment report. Radio N10,: 1987, p.26.
Author: V.Teteryuk (YL2GL), Livny; Publication: N. Bolshakov, rf.atnn.ru
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