Quartz filter matching. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Civil radio communications
Comments on the article
When I assembled the transceiver for the first time, I could not achieve good matching of the quartz filter with the first stage of the IF, and also get a sufficient gain and low noise. After conducting several experiments and trying out several methods of matching, I settled on the following scheme, Fig.1.
Ris.1
Resistor R1 is equal to the wave impedance of the filter, but it is still desirable to select it directly in the IF circuit. The circuit L1, C1 is equivalent to the oscillating circuit L1, C6 in the intermediate frequency amplifier of the transceiver. The tap should be made from 1/6 of the turns, counting from the grounded end. Resistor R2 sets the bias at the gate of the field-effect transistor, and capacitor C2 is selected for maximum gain. An increase in capacitance C2 to 100 pF leads to an increase in both gain and noise, and its further increase only leads to an increase in noise.
A few general recommendations
(The reference designations of the RA3AO transceiver are preserved in the text)
** In block A18, instead of resistor R1, a resistance of 50 Ohm +/-10 Ohm should be put, and capacitor C5 should be connected in series with the EMF winding (from either end). In block A21, to improve the symmetry of the circuit, the input circuit should be changed, Fig. 2
Ris.2
and for better matching with a coaxial cable, it is necessary to redo the output transformer, Fig.3.
Ris.3
** To increase the brightness of the dots on the light panel in block A7 (ChTM), resistor R42 should be connected to the +50 V power bus.
** You can improve the balance of the pointer device to "0" if you change the resistor values in block A13: R6 = 3,9 kOhm and R5 = 1,8 kOhm.
** Sometimes there is not enough supply voltage for the band-pass filter relay, especially when the mains voltage is low. This drawback can be eliminated by changing the values of resistors R10 ... R6, R9 ... R19 in block A22 by 1,5 kOhm.
** You can eliminate the self-excitation of the output stage if you swap the ends of the input winding of the transformer T21 in block A1. If it does not help, then you should shunt it with a 1 kOhm resistor and again select the phasing of the primary winding.
Literature
1. V. Drozdov "Amateur KB transceivers".
2. S. Bunimovich, L. Yaylenko "Technique of amateur single-band radio communication", 1970
Author: S.Volkovinsky, RA9FOR, Perm; Publication: N. Bolshakov, rf.atnn.ru
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