| 摘要 |
<p>A high frequency SSB radio transmitter has an envelope amplitude modulator (3) for varying the envelope of an r.f. signal source based on an error signal from envelope detectors detecting the envelope of the input and output waveform. It also has a phase modulator (4) in a main feedback loop for varying the phase of the input waveform based on differences detected in phase detector (10) between the instantaneous phase of the input and output r.f. signal. To overcome the problem of spurious outputs from phase detector (10) resulting from the cross-over points of the SSB waveform when there are carrier breaks and other problems, a subsidiary, phase lock loop (12) feeds a signal derived from the error signal to phase modulator (13) to tend to hold the input A, B in such a phase relationship that the output is zero. To cope with large phase shift errors between input waveform and output resulting from when the power amplifier changes frequency or temperature variations e.g. at the antenna, a broadband phase shifting network (17) is brought into operation when a dual voltage comparator (19) senses that the signal fed to modulator (13) passes a value corresponding to its extremes of adjustment.</p> |
