Improvements in or relating to apparatus for comparing the frequencies of electrical signals

摘要

1,089,373. Frequency discriminators. GENERAL ELECTRIC CO. Ltd. and D. L. CLAY. July 9, 1965 [July 9, 1964], No. 28368/64. Heading H3A. The difference between approximately equal frequencies #1 and #2 is measured by deriving pulses at these frequencies and using them to sample higher non-related frequencies (which may be the same frequency #3) thereby deriving two beat frequencies which are compared by mixing in a modulator 6 and counting the cycles of the difference frequency. If #3 = a# 1 + #SP1/SP = a# 2 + #SP11/SP the beat frequencies derived by sampling are #SP1/SP and #SP11/SP, so the difference frequency #SP1/SP-#SP11/SP = (# 3 -a# 1 )-(# 3 -a# 2 ) = a(# 2 - # 1 ). The difference frequency has thus been multiplied by a factor a, which may be 100, -without any frequency multiplication, and the accuracy is increased in the same ratio. In a modification, the reference frequency # 3 is a sawtooth wave; consequently the beat frequencies are also sawtooth waves which may be compared as in Specification 1,089,372.