| 摘要 |
PURPOSE:To attain complete squelch operation, by performing the squelch operation based on the characteristics through the digital measurement of the distribution of converted points of demodulated digital codes. CONSTITUTION:A demodulated digital signal from a demodulator (not shown) of a receiver and a bit synchronizing signal of digitized audio signals are applied to a transient detection circuit 13 and window circuit 16. A signal via the circuit 13 is converted into an impulse signal corresponding to the changing point and inputted to an up-down counter 15. The counter 15 is shaped with the circuit 16 and counted up by a signal being ''1'' before and after said changing point and counted down at other parts to count said impulse signals. Then, the counter 15 performs up-count only when the signal-to-noise ratio of the demodulated signals is large and performs down-count only when small. When the count value reaches a prescribed value or below, the output of the decoder (not sown) can be interrupted by a squelch output signal. |
