Audio receiver with capacitive tuning - switches out tuning circuit at end of range to prevent reception of adjacent frequency signal

摘要

The receiver has automatic tuningusing diode capacitances (4), switching in and out of operation by an electronic switch (8). This is controlled by the output (24) of a comparator (9) which compares the tuning voltage (UA) for the diode capacitances (4) with a DC reference voltage UV). This differs from one of the two extreme voltages defining the tuning range by an amount corresp. to the reception range of the tuning circuit, so that the switch (8) is controlled to switch out the tuning circuit (5) when the tuning voltage (UA) exceeds the reference voltage (UV) and is closer to the end of the tuning range. Pref. the reference voltage (UV) is provided by an adjustable voltage divider (29) coupled across the voltage source (11) feeding the tuning potentiometers (12,13), each of which is associated with a respective channel selection switch (16). The tuning circuit prevents tuning-in to an unrequired transmitter in an adjacent frequency band.