Noise-dithered hard-limit loran c/d receiver

Claim 1

An improved method of processing RF signals of the type used in Loran navigation systems wherein pulses in pulse groups are received on a 100KHz carrier and wherein there is performed an envelope measurement and a cycle reading for determining the time difference between pulsed signals from a master transmitting station and a slave transmitting station comprising: receiving said RF signal; combining internally generated RF noise with said RF signal; amplifying the combined signal in a hard-limit amplifier to form substantially zero transistion times between positive and negative states; sampling the output of said hard-limit amplifier at a predetermined time from the beginning of each pulse resulting in a statistical signal average SAV (2/ square root pi )(S/N) wherein (S/N) is the signal-to-noise ratio; accumulating said samples over a group of n pulses; subtracting said accumulated signal from a predetermined noise reference corresponding to (n/2) (2/ square root pi )(S/N) resulting in a difference signal corresponding to a noise gain error signal; smoothing said noise gain error signal; continuously integrating the smooth error signal; and controlling the amount of RF noise combined with said RF signal to drive said noise gain error signal to zero using said integrated signal.