GB1492862A - Frequency discriminator - Google Patents

Abstract

1492862 Frequency discriminators; digital frequency measurement W J KEANE 26 Sept 1975 39631/75 Headings H3A and H3H A frequency discriminator of wide and adjustable band-width comprises an arrangement 20 for tuning a ferrimagnetic resonator, e.g. a YIG filter, to a quiescent centre frequency, an arrangement 19, 25 for electronically sweeping the resonator or the input signal over a given frequency range and an arrangement 32 determining the time relationship between the output of the resonator derived via a detector 28 and the sweeping signal from 25 to provide the discriminator output. The discriminator band-width is adjustable by varying at 19 the amplitude of the sweep signal. The discriminator output provides a measure of the frequency offset of an input signal from the discriminator centre frequency. The sweep signal may be derived as in Fig. 6A via an arrangement including a digital clock 38, a reversible counter 40 and a digital to analog converter 44. An output of the counter 40 may be applied to a digital read-out gate triggered by a pulse representative of the input frequency so that a digital measure of the input frequency offset can be obtained. Figs. 6B-7B (not shown) relate to arrangements receiving the detected output of the resonator and the sweep signal to provide frequency offset measurement. A frequency sweep arrangement (Fig. 8, not shown) involves a phase lock loop including the frequency discriminator and the desired number of oscillators operating over contiguous bands. The discriminator may initially be adjusted for maximum bandwidth to effect capture of the associated oscillator. Fig. 10 (not shown) releates to a heterodyne counter arrangement for determining the input frequency offset in respect of a comb line filter. Fig. 11 (not shown) releates to a frequency demodulator in which the output of the frequency discriminator is filtered in a RC circuit to remove the sample rate and to pass the modulation rate. In a tracking filter Fig. 12 (not shown), a tuning filter may be incorporated in the same magnetic housing as the frequency discriminator resonator and included in a feedback control loop for automatic tuning of the filter to an input frequency. Fig. 13 (not shown) relates to a broad band harmonic generator incorporating the frequency discriminator in a feedback loop.