| 摘要 |
<p>A superhet receiver in which an input signal is frequency down- converted in a first mixer (14) to produce a first IF signal comprising a wanted channel signal and an image channel signal. The first IF signal, without image rejection filtering, is frequency down-converted in a second mixer (24) to produce a second, lower IF signal comprising at least the wanted channel signal having a bandwidth corresponding to a predetermined passband of a channel filter (32) coupled to the output of the second mixer. The local oscillator signals used in the first and second frequency down conversion processes are varied in order to produce successively different image channel signals in the first IF signal and to maintain the wanted channel signal in the second IF signal within the passband of the channel filter (32). By rapidly hopping the local oscillator signals in the frequency domain the wanted signal can be made to remain stationary within the bandwidth of the channel filter whilst other unwanted frequencies are spread across a wider bandwidth and have their amplitudes averaged in the filter (32).</p> |
