Receiver circuit

A receiver circuit comprising:

• a) an antenna for receiving a frequency modulated carrier signal;
• b) a narrowband filter for converting the frequency modulated carrier signal to an amplitude modulated signal at a modulation frequency;
• c) a transistor connected to the narrowband filter and configured to operate as a detector of modulation of the amplitude modulated signal;
• d) a resonator circuit connected to the transistor and configured such that the transistor simultaneously self-oscillates at substantially the modulation frequency of the amplitude modulated signal to produce an oscillation signal;
• e) an oscillator quenching means for periodically quenching oscillation of the transistor;
• and
• f) oscillating sensing means connected to the resonator circuit and arranged to receive the oscillation signal and for sensing characteristics of a build-up of oscillation to indicate a presence of the modulated carrier signal.

A receiver circuit comprising:

• a) an antenna for receiving a phase modulated carrier signal;
• b) a narrowband filter for converting the phase modulated carrier signal to an amplitude modulated signal at a modulation frequency;
• c) a transistor connected to the narrowband filter and configured to operate as a detector of modulation of the amplitude modulated signal;
• d) a resonator circuit connected to the transistor and configured such that the transistor simultaneously self-oscillates at substantially the modulation frequency of the amplitude modulated signal to produce an oscillation signal;
• e) an oscillator quenching means for periodically quenching oscillation of the transistor;
• and
• f) oscillating sensing means connected to the resonator circuit and arranged to receive the oscillation signal and for sensing characteristics of a build-up of oscillation to indicate a presence of the amplitude modulated carrier signal.