Problem of speech pulling and its implementation for the design of phase-locked SSB radio systems

In the paper, the effect of speech interference on the performance of long-loop phase-locked VHF SSB radio systems is evaluated, It is shown that unless the system´s reference tone is adequately protected by suitable filtering in the transmitter´s audio processing, the problem of `speech puffing¿¿ may occur with severe degradationin intelligibility. Furthermore, residual FM modulation of the VCO´s control line (the first local oscillator) through speech interference degrades the oscillator´s output spectrum with possible reduction in adjacent-channel rejection. After analysing the effect of interfering sinusoidal signals on in-lock-loop per formance, filter design criteria are established for pilot-carrier and in-band-tone SSB systems, and the theoretically predicted results are verified experimentally. Finally, alternate phase-locked receiver configurations are suggested in an attempt to overcome first-oscillator spectrum degradation in long-loop receivers.