Instead of a toggle switch relay, instead KPE - resistor

When designing small equipment often raises the question of how all the controls to place on the front panel, simultaneously satisfying the requirement arrangement, for example, toggle switches near the respective cascades.

In such cases, can be successfully used small variable resistor, the transistor and the relay (Fig.1). This replacement is often more convenient toggle switch, because it allows us to place the relay in the vicinity of switched circuits, which may be high frequency, and thus greatly reduce the possibility of self-excitation and increase the stability of the whole device. Relay it is desirable to use low current consumption, type RES, RES, although the resistor gives you the ability after the operation of the relay to reduce the current to the desired value for the retention of contacts that may be useful in equipment with independent power supply.

Fig.1

When designing QRP-transceiver with quartz stabilization and conventional scheme slip frequency (Fig.2)

Fig.2

Instead of C1 can also use a variable resistor [1]. The values of C1, C2, R1 (Fig.3) are selected for specific quartz by the maximum slip frequency. The scheme was tested in the range of 3.5-14 MHz and provided almost the same frequency as with KPE 10/100 pF (C1 in Fig.2) with the same non-uniformity of the amplitude of the output signal.

Fig.3

Literature

1. G. Baghdasaryan. About frequency tuning LC-oscillators. Radio No. 7, 1994

Author: Igor Grigorov, RK3ZK, Belgorod; Publication: N. Bolshakov, rf.atnn.ru