Instantaneous measurement of a varying frequency
L U Hibbard, D E Caro · Journal of Scientific Instruments · 1952
It is shown that it is possible to observe the instant of passage of a rapidly varying frequency through a specified value by beating it with a fixed frequency reference signal. The method is particularly suitable for frequency-time functions which are linear or have an inflexion at the point of observation. Errors due to non-linear functions are examined. The accuracy of measurement is dependent only on the rate of change of frequency. A feature of the method, with repetitive functions, is the automatic phasing of the fixed reference oscillator with respect to the varying frequency signal at the point of observation.