Abstract: A tunable oscillating limiter threshold extension demodulator capable of demodulating video and other wide band width FM signals is described. A steering signal is generated to tune the oscillating limiter in response to the video output signals from an FM discriminator to which input signals from the oscillating limiter are applied. The steering signal is generated so as to be in proper phase relationship to track the frequency of the FM signal for modulating frequencies within certain critical regions and is reduced in amplitude over another region where proper phase relationship is not achievable because of unavoidable delays in the system. The steering signal generating circuit may be provided by a filter having a phase response characteristic such that the total phase lag of the system is small at the low frequency end of the band width and about 360.degree. at the high frequency end of the band width.

Abstract: Apparatus for lowering the noise threshold at which FM and other angle modulated signals may be demodulated is described wherein an oscillating limiter provided by an amplitude limiter having a bandpass filter in regenerative feedback relationship therewith is connected ahead of the demodulator. The bandpass filter is made tunable in response to a steering signal developed by processing the frequency proportional signal at the output of the demodulator to attenuate high frequency components thereof which are outside the baseband of the signals and adjusting the amplitude of the signal so that the center frequency of the bandpass filter is caused to substantially match the frequency of the frequency modulated signal.