GB604773A - Superheterodyne radio receivers - Google Patents

Abstract

604,773. Superheterodyne receiving circuits. STANDARD TELEPHONES & CABLES, Ltd. Sept. 11, 1945, No. 23454. Convention date, July 22, 1944. [Class 40 (v)] The tuning range of a superheterodyne receiver is extended by the use of a second mixer fed from an aerial and the local oscillator, the output being applied to the normal input of the superheterodyne receiver. The normal receiver comprises an aerial 1 coupled to a H.F. amplifier valve 17 feeding a mixing valve 24, energy from the local oscillator valve 25 being injected over coupling coil 29. The extended frequency range is received over aerial 11 and fed to a second mixer valve 35 also supplied from the local oscillator 25 over coupling coil 36, the output being fed to the first mixing valve 24 which further reduces the frequency and feeds the common I.F. amplifier 6. A switching circuit 14 controls a trigger pair of valves 40, 41 which provide a paralyzing bias on valves 17, 35 to render one or other channel inoperative, the circuit also controlling a switching circuit 14a to displace the trace on indicator 10. By arranging a tuning motor 16 to rotate the tuning capacitors and to operate the switching circuit after a complete sweep through the tuning range, the received signals from the two aerials are displayed in separate traces on the indicator 10.