Frequency deviation testing and adjusting system for frequency modulated

Abstract

Deviation of a frequency modulated oscillator (FMO) is set by applying a square wave test signal to the input of the oscillator so as to generate a predetermined amount of symmetrical periodic frequency shift above and below the rest frequency, i.e., the carrier frequency of the FMO, for a desired setting of the FMO's modulation sensitivity. The FMO frequency is divided down so as to be within the range of a programmable divider in the automatic phase control circuit of the oscillator. The carrier frequency is set by program switches which are connected to an interface logic unit that provides the control information to set the divisor of the programmable divider. During testing, the square wave test signal is also applied to a control input of the interface logic unit, for adjusting the divisor so as to provide at the output a binary signal having a predetermined pulse repetition rate when the modulated signal is applied to the input to the programmable divider and the deviation is correctly set. A reference oscillator provides a separate binary signal which has a pulse repetition rate equal to that of said predetermined pulse repetition rate. These two binary signals are compared in a deviation test circuit and the modulation sensitivity of the FMO is adjusted until the difference between the two binary signals is at a minimum.