Frequency measuring circuit in a passive radar receiver

Abstract From the Canadian patent

Passive frequency measuring circuit comprising a number of frequency discriminators to obtain a digital code representing the frequency of an appliedr.f. signal. Each discriminator is tuned to different frequency ranges and, provided with a plurality of similar frequency analysers for the phase detectionof the applied r.f. signal passed through different delay lines. As each discriminator delivers an ambiguous code at the boundaries of its characteristic, a digital filter is incorporated to resolve the ambiguity. If such an ambiguity is established, an adjoining discriminator is activated to deliver information for obtaining a digital code representing an unambiguous frequency value.