| 摘要 |
<p>In a QAM microwave radio communications system an IF (intermediate frequency) input signal is amplified (12) and predistorted (14), and the amplified IF signal is mixed with a local oscillator signal (18) to produce an RF (radio frequency) signal which is amplified in a power amplifier (22) for transmission, the predistortion compensating for non-linear gain of the power amplifier. Clipping in the power amplifier is controlled by down-converting (30) part of the RF signal to produce an IF output signal representative of the output of the power amplifier, monitoring signal compression by comparing (38) the IF output signal with the IF input signal, and controlling (36) the IF amplifier gain in dependence upon the monitored signal compression.</p> |
