Fm-pm receivers with increased sensitivity

Abstract

Signal processing apparatus (410), for processing angularly modulated signals, provides improved sensitivity by reducing both the deviation of the modulation and the frequency of the bandwidth filter below the value calculated by Carson's rule. The signal processing apparatus (410) includes a closed loop (438) and a phase locking oscillator (270, 304, 318, 332, or 392) that is interposed into the closed loop (438). Both the frequency of the angularly modulated signal and the deviations of the angular modulation are reduced in the closed loop (438), and the demodulated output of the angularly modulated signal is produced in a conductor (436) of the closed loop (438). The phase locking oscillator (270, 304, 318, 332, or 392) includes both a forward path (204) and a feedback path (206), and an output frequency of the phase locking oscillator (270, 304, 318, 332, or 392) is phase locked to a reference frequency. The phase locked output frequency, in a conductor (230), is used as an input to the closed loop (438), and a derived signal, in the conductor (436) of the closed loop (438), which is the demodulated output of the angularly modulated signal, is used to vary the phase locked output frequency in the conductor (230). This varying of the phase locked output frequency includes separately modulating a frequency in the forward path (204) and a frequency in the feedback path (206) of the phase locking oscillator (270, 304, 318, 332, or 392). Modulation of frequencies in both paths (204 and 206) is accomplished without changing the reference frequency.