| 摘要 |
A circuit for rapidly assessing communications activity on a particular radio channel being jammed has a filter tuned to the receiver IF and to the input of which the incoming signal (at the receiver IF) is switched. The waveform of the resultant filter output for the signal on the particular channel-that is, falling within the filter passband-is produced in conjunction with interfering signals in adjacent channels. It is shown that the nulls in the waveform of the interfering signals occur at time instants dependent on the passband of the filter, not on the frequency of the interfering signals. The circuit therefore is timed to measure the level of the filter output at the instant of one or more of the nulls of the interfering signals, thus avoiding interference by the latter.
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