Automatic search receiver tuner with capacity diode - has search band restricted by preset bias on tuning diode and circuit prevents tuning outside desired band

摘要

A circuit is used for an automatic search tuner for a radio receiver. The search process is initiated by operation of a push-button which causes a capacitor to charge, so producing a steadily increasing voltage which is applied to a tuning diode, with a holding system coming into operation when a signal is received producing a received signal exceeding a certain amplitude. The capacity diode (13) is pre-biased by part of the receiver supply voltage through a diode (8) to ensure that the research voltage starts only at this level. This avoids tuning over a wider range than the proper range of reception of the receiver. For example, in a VHF receiver it prevents locking on to a police or similar signal outside the broadcast band.