Scanning device. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Nodes of amateur radio equipment
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In amateur radio practice, it often becomes necessary to periodically listen to a portion of the range. It is convenient to do this by changing the frequency of the transceiver's local oscillator using a scanning device. On fig. 1 shows a diagram of such a device used by the author in a tube-semiconductor transceiver [L].
Ris.1
It is made on transistors VT1-VT3 and operational amplifiers DA1 (follower), DA2 (comparator). When the SA1 switch is set to the "Scanning" position, the power supply to the varicap of the GPA transceiver comes not from the detuning unit, but from the emitter follower of the scanning device. At the same time, a sawtooth voltage of negative polarity with an amplitude of about 1 V is applied to point 5 of board 27 of the transceiver (Fig. 2).
Ris.2
At the same time, the supply voltage (-1.2 V) from the transceiver to the scanning device is supplied through the contacts SA50 and is stabilized by the stabilization element VD2 (selected with a voltage close to 30 V). When the scanning device is turned on, capacitor C2 starts charging (through normally closed contacts of the SB1 button and resistors R1, R2). Until the voltage on it reaches -27 V, the voltage at the output of the comparator DA2 will be about 0. Transistors VT3 and VT1 are closed. When the voltage across capacitor C2 becomes -27 V, a voltage of about -30 V will appear at the output of the comparator (Fig. 2). Transistors VT3, VT1 will open, and capacitor C2 will quickly discharge through the open transistor VT1. After that, the transistors VT3, VT1 will close and the process of charging the capacitor C2 will be repeated.
Thus, a sawtooth voltage of negative polarity will be formed at the output of the scanning device. By changing the position of the slider of the resistor R6, you can adjust the amplitude of the sawtooth voltage from 0 to 27 V and thus the scanning range. In the upper position of the resistor slider according to the diagram, the maximum scanning range is 50 kHz. Resistor R1 can vary the time constant of the charging circuit of capacitor C2. In the upper position of the resistor R1 slider according to the diagram, the maximum charging time is 30 s, in the lower position it is minimal, about 6 s. If during the scanning process the button SB1 is pressed, then the charging circuit of the capacitor C2 is broken and a constant negative voltage is supplied to the varicap of the GPA transceiver, corresponding to the moment the button is pressed. In the described device, you can use, in addition to those indicated in the diagram, operational amplifiers K140UD7, K140UD8, KM140UD20, K157UD2, KR1005UD1, etc. Transistors VT2, VT3 can use any of the series KT361, KT3107, KT502, etc. Capacitor C2 - K73 -17.
Literature
- Kudryavtsev Yu. Lamp-semiconductor transceiver. - Radio, 1974, No. 4, p. 20-25; No. 5, p. 22-25; No. 6, p. 23-25, 34.
Author: B. Chyzh (UB5BCJ), Ternopil; Publication: N. Bolshakov, rf.atnn.ru
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