GB1384338A - Microwave signal detector - Google Patents

Abstract

1384338 Radio receiving arrangements N A BENNETT 19 Sept 1973 [15 Nov 1972] 52696/72 Heading H3Q A microwave signal detector comprises radiation receiving means associated with a detector diode D1, Fig. 1, and a chopping diode D2 which is fed with a signal derived from noise which has passed through a narrow band pass filter FL and then amplified and clipped to produce a square wave which is applied to the diode D2 to switch it: the diode D1 detects a received microwave signal which is modulated at the switching rate of the diode D2, the detected signal being passed through the filter FL to produce a positive feedback loop. In the embodiment the amplified output from filter FL is also applied to an output stage OP to produce an indication by means of loudspeaker LS; alternatively an optical indication may be given. In a detailed embodiment, the detector diode D1, Fig. 2, is coupled to a first amplifier A1 comprising D.C. coupled transistors TR1, TR2, TR3 with stabilizing negative feedback over resistors R5, R6, R7 and capacitor C2. The output is applied over resistor R8 to filter FL comprising circuit L1, C3 tuned, e.g. to 1 KHz. The output of filter FL is applied to a second amplifier A2 comprising integrated circuit IC1, the gain of which can be adjusted by variation of negative feedback by means of potentiometer VR1. The output from amplifier A2 is applied to the limiting amplifier A3 comprising integrated circuit IC2, the output of which is applied over capacitor C7 to the chopping diode D2; a further diode D4 provides D.C. restoration. The output from amplifier A2 is also applied to output circuit OP comprising a transistor TR4 driving loudspeaker LS, resistor R12 limiting the current through the loudspeaker. The output circuit is arranged to have a threshold value, diode D3 providing D.C. restoration.