| 摘要 |
A signal receiver, for use on a Doppler radar system for example, discriminates between coherent received signals and background or jamming noise on the basis only of the phase of the input signal, rather than its amplitude. The output of a given Doppler filter 11 is supplied via a hard limiter 12, which detects the zero crossings, to a monostable 13. A low-pass filter 14 detects the mark-space ratio in the monostable output, which ratio will vary randomly when only noise is being received but will become steady when a coherent signal (i.e. of regular frequency) is present. Band pass filter 15 blocks such steady outputs, so producing a signal E which remains steadily at zero when a coherent signal is present. This condition is sensed by a threshold detector 16 which provides a logic 1 level when signal E is substantially zero and whose integrated (17) output will thus rise to exceed the threshold of detector 18 only when signal E remains at zero for some time. Large reflected signals interfering from adjacent Doppler frequency bands are blocked by network 21-23, and a signal representing Doppler frequency is derived at 24. |
