CW-SSB electronically commutated filter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Knots of amateur radio equipment. Quartz filters
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In modern communication equipment, electronic switching is widely used, which sometimes makes it possible to significantly simplify the design of a transceiver, receiver, or transmitter. A schematic diagram of a combined CW~SSB filter with such switching is shown in Fig.1.
Depending on the position of the switch S1, either quartz resonators B1, B3, B1, B4 or resonators B5, B8, B2, B3 are connected to the input and output circuits of the filter and to the oscillatory circuit formed by the inductor L6 and capacitor C7. The switching elements are diodes V1 - V8. So, with the switch position S1 shown in the diagram, a constant voltage of + 9 ... 12 V is supplied through resistors R2, R6, R7 and R10, respectively, to the anodes of diodes V1, V4, V5 and V8. These diodes open. The total current of these diodes creates a voltage on the resistor R4, which closes the diodes V2, V3, V6 and V7 (their cathodes are connected through resistors R3, R5, R8, R9 and the contacts of the switch S1 with a common wire).
Ris.1
The inductance of the coil L1 (it has a tap from the middle) and the capacitance of the capacitor C3 depend on the quartz resonators used - the resonant frequency of the oscillatory circuit formed by these elements should approximately correspond to the middle frequency of the passband of both filters. The final characteristic of the filter is also affected by the resistances of the resistors R1 and R11. They should be selected during tuning, observing the condition R1=R11.
The frequency of the series resonance of quartz B1 should be the same with quartz B5, and for B4 - with quartz B8 (for the second filter, respectively, for B2 - with B6, and for B3 - with B7). The frequency spacing between these pairs of resonators depends on the required bandwidth of the filters. It can be found in fig. 2, which shows the dependence of the filter bandwidth dF1 on the frequency separation dF2 of the successive resonances of the quartz that form the filter.
Ris.2
As switching diodes, you can use any modern high-frequency silicon or germanium diodes, for example. KD503A. GD507, etc.
Literature
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CQ (USA), 1978. No. 7
Publication: N. Bolshakov, rf.atnn.ru
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