GB1357187A - Heterodyne circuits - Google Patents

Abstract

1357187 Frequency changing; automatic frequency control SIEMENS AG 19 Aug 1971 [20 Aug 1970] 38889/71 Headings H3A and H3T In a heterodyne circuit for v.h.f. a mixer stage M, Fig. 1, is supplied with a harmonic of an oscillation supplied by an oscillator G which is overdriven to such an extent that the required harmonic is produced with significantly more energy than is required in the mixing stage, the oscillator output being fed to the mixer stage M via a filter circuit BP which filters out the desired harmonic and passes this to an attenuating element DR 1 for setting the required energy level; the oscillator G is provided with an automatic frequency control circuit AFC operating at the fundamental frequency. In the embodiment the output of the oscillator G is fed to a stage W comprising a high-pass HP and a lowpass TP filter in parallel, the output of the first of which feeds the bandpass filter BP and the output of the second feeds the AFC circuit via an attenuator DR2, The output of the attenuator DR1 feeds the mixer M via a circulator RG, to the second input of which is applied the signal frequency via a band-pass filter BPE. A construction comprises a screening box divided into three compartments I, II, III, Fig. 2 by separators. The first compartment I contains the oscillator tuning element, comprising a line K i tuned by adjustable capacitor C D , and having coupled to its lower end varactor diode D K1 to which the AFC voltage is applied. There is also coupled in a second varactor diode D K2 which serves for modulating the oscillator. The second compartment II contains oscillator transistor T which operates in the common collector mode, its base being coupled to the line K i via a capacitor C 1 <SP>1</SP>. The output from the emitter of transistor T is fed via capacitor C 2 <SP>1</SP> into the third compartment III and thence into a highpass filter comprising capacitor C3 and inductor L3: this feeds the third harmonic of the oscillator frequency into a bandpass filter comprising inductors L 4 , L 5 and capacitors C 4 , C 5 , C 6 . A low-pass filter comprising inductor L 6 and capacitor C 7 selects the fundamental oscillator frequency and feeds this, via an attenuator comprising resistors R , R 2 , R 3 to the AFC circuit.