in a bandwidth - limiting apparatus , control is performed of the oscillation frequencies of each of three local oscillators of three intermediate - frequency circuits , and the passband is limited by adjusting the width of and shifting the if , the intermediate frequency at the last stage being converted by a frequency conversion means to a low frequency suitable for processing , which is then bandwidth limited by a filter function of a digital signal processor . control of each passband is performed in linked fashion by control stored in a microcomputer circuit , and the sharp shape factor of the digital signal processor is effectively used to eliminate noise from the deviation passband . because noise is eliminated before the detection stage , there is no cause for the intrusion of wraparound noise , thereby eliminating the necessity to perform excessive bandwidth limiting .