Improvements in or relating to apparatus for providing a representation of the difference between the frequencies of two periodic signals

摘要

1,085,575. Indicating frequency differences. GENERAL ELECTRIC CO. Ltd. March 7, 1966 [March 25, 1965], No. 12699/65. Heading G1U. Two frequencies f 1 , f 2 to be compared are fed to a mixer circuit 3 and the resulting difference frequency is fed to a trigger circuit 5 the output from which switches a reactance 9 across the input at frequency f 2 during alternate half cycles of the difference signals. The sense of the resulting phase shift in the difference frequency signal at the instant of switching is determined by whether f 2 is greater or less than f 1 and differentiation of this signal by unit 6 results in a train of positive or negative going pulse which are used to trigger monostable circuits 13 or 14. If f 2 is greater than f 1 the resulting pulse train is of such a polarity not to trigger circuit 13 but when inverted by inverter 15 with trigger circuit 14 and flash the "High" lamp 17. Conversely if f 2 is lower than f 1 lamp 16 is flashed. The flash rate gives an indication of the difference frequency and in addition the output from trigger 5 may be used to operate a further switch 8 controlling the charge and discharge of capacitor 18 so that a voltage proportional to the frequency difference is fed to meter 23.