GB799674A - Improvements in or relating to apparatus for determining the frequency of electrical signals - Google Patents

Abstract

799,674. Frequency measuring. RANK CINTEL, Ltd., [formerly CINEMA-TELEVISION, Ltd.]. Sept. 14, 1956 [Sept. 15, 1955], No. 26434/55. Class 37. Apparatus for measuring the frequency of electric signals; particularly intermittent signals such as a keyed carrier in which each signal portion is too short for satisfactory measurements comprises a first means 5 operative only during the reception of input signals above a predetermined amplitude to allow these signals to be passed to a counter 8 and indicating means 9, and a second means 7 for applying constant frequency signals to a second counter means 11 which on receipt of a predetermined number of signals operates to prevent further application of the input signals to the first counter means 8. The incoming signal is passed through a gate 2 which is opened by a start pulse from 3 (supplied for example by an operator) and closed on receiving a suitable signal from counter 11. After passing through the gates the signal goes to a detector 4 and trigger 5 and also to gate 6. Trigger 5 opens gates 6 and 7 when the amplitude of the signal exceeds a predetermined value, and closes them when the strength of the signal falls below this value. The output of gate 6 is fed to counter chain 8 and the state of the count is indicated at 9 either continuously or on reception of the stop pulse from 11. Gate 7 controls the supply of a constant frequency source 10 to counter chain 11 and when the count on 11 reaches a certain predetermined value the stop pulse is produced which closes gate 2. The total time period provided by counter 11 being known, the indicator 9 may be used to determine the frequency. The start pulse received at 3 can be used to zero counters 8 and 11 and indicator 9. Preferably, this zeroizing is triggered by the leading edge of the start pulse and the opening of gate 2 by the trailing edge. Specification 743,528 is referred to.