| 摘要 |
A low frequency tone detector filters out undesired frequencies in a received signal, than a latching circuit locks on when a given number of low frequency cycles are detected, having at least a predetermined peak amplitude. Thereafter, only a second given number of missing or low amplitude cycles will reset the latch. When the detector determines that the received signal is weak or of very poor quality, false detect signals are essentially prevented. The circuit is particularly suited to use with AM stereophonic signals where a low frequency tone is added to the difference channel for providing mono/stereo indication and mode switching.
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