Tuning circuit for two different varactor tuning diodes - has single potentiometer with negative logarithmic relation between output voltage and angle

摘要

The tuning circuit, for radio receivers, tunes, a first varactor with CV-characteristics for the AM band and a second varactor with CV-characteristics for the FM band. The circuit has only one potentiometer. This rotary potentiometer has negative logarithmic relation between output voltage and the angle at which the potentiometer is set. For the second varactor the potentiometer's direction of rotation and the order of its connections are reversed. The potentiometer is in series with a fixed resistor. The advantage lies in needing only one potentiometer with a scale for both varactors that is as uniform as possible.