AN EXTENDED PHASE-LOCK TECHNIQUE FOR AIDED ACQUISITION

Abstract

In a phase-locked PM demodulator, the input signal is modulated by a periodic waveform, particularly when the loop bandwidth is less than the sideband to carrier spacing, and thus discrete sidebands are apt to appear about the carrier frequency. This frequently results in a sideband locking instead of phase-locking to a selected carrier and aided-acquisition is then required. Conventional techniques such as discriminator-aided-acquisition have been implemented by Mostrom¹ and Victor et al.² to correct this problem, however, this approach necessitates a large carrier to noise ratio (CNR) in the bandwidth of the discriminator. The current study describes a novel approach to extend the threshold for a phase-locked loop designed for Hartman Systems’ telemetry receiver. By phase remodulating the error signal, the network reduces the phase swing of the signal and restores the carrier power so as to provide anti-sideband properties for biphase and PM modulation up to 1.3 radians deviation at all modulation frequencies and at a signal level where CNR is greater than 5 dB above PM threshold.