BUILT-IN GROUP DELAY TESTING ARRANGEMENT FOR AN FM RADIO SYSTEM

A BUILT-IN GROUP DELAY TESTING ARRANGEMENT FOR AN FM RADIO SYSTEM by ABRAM FROESE LARRY Y. Onotera ALVIN Liebelt Muhammed Jamil Abmed The baseband input to a frequency modulation transmitter is switchably connectable to a square-wave generator, the amplitude of the square-wave being adjusted to provide a predetermined deviation of the FM radio transmitter. The output signal of a pilot oscillator is also applied to another input of the transmitter. This pilot signal is subjected to phase modulation because of group delay which exists in the system and this adversely affects the signal during transmission through the system. In contrast, the prior art uses commercial test sets which are expensive. At the receiving end of the radio system, the receiver output includes the pilot signal which has been phase modulated by the group delay slope in the system, because of the square-wave test signal. This phase modulation is detected in a phase lock loop, prior to being amplified, rectified and applied to a meter so as to provide an indication of the group delay slope in the system.