Hilbert Transform Applications to Asynchronous Demodulation Methods for RZ SSB, Multichannel ISB and ISB-Based AM Stereo Modulated Signals Propagating through Fading Path

Abstract

Previous studies have revealed that both AGC (automatic gain control) and AFC/PLL (automatic frequency control/phase-locked loop) circuits for demodulating SSB/ISB (single sideband/independent sideband) modulated signals cannot cope with severe fading at all. The author therefore decided to develop an asynchronous demodulation scheme for SSB/ISB signals using a DSP processor, i.e. without AGC or AFC/PLL circuits. The adverse effects of fading on the amplitude and phase components of the received signal must be first removed at the receiver side. The introduction of the Hilbert transform has certainly enabled successful asynchronous demodulation. The paper presents asynchronous demodulation methods for three modulated signals such as RZ SSB (Real Zero SSB), multi-channel ISB and ISB-based AM (amplitude modulation) stereo signals propagating along a fading path. The demodulation circuit can be implemented in a feedforward configuration.