GB971291A - Improvement in and relating to apparatus for measuring frequencies - Google Patents

Abstract

971, 291. Measuring frequencies of electric Signals. SUD-AVIATION SOC. NATIONALE DE CONSTRUCTIONS AERONAUTIQUES. March 15, 1963 [March 19, 1962 ], No. 10453/63. Heading G4H. To enable the frequency of a signal to be measured over a short period by counting cycles, the unknown frequency 2, Fig. 1 is multiplied by a fixed number at 1 and cycles of the product frequency 3 are counted at 4, the frequency 2 being determined by dividing the count by the multiplier number and the time interval. The multiplier 3 may consist of a series of doublers as shown in Fig. 2, the transistor 6 giving antiphase signals on the collector and emitter which are halfwave rectified by diodes at 7 and added to obtain a series of positive halfcycles. This signal is smoother at 8 to provide a double frequency signal. Instead of using transistor 6 a transformer with centre-tapped secondary may be used. Because of harmonics this sort of multiplier is unambiguous only if the frequency does not vary over a range of 1-1. 5. For greater expected variations the range of operation of the multiplier is reduced by adding a large constant frequency in a single side band modulator 10, Fig. 4 multiplying as before and subtracting a frequency equal to that added times the multiplier number. The modulator frequency may be derived by dividing the demodulator frequency by a number equal to the multiplier number. This may be 256 obtained by using 8 doubling and halving stages.