H - Electricity – 04 – B
Patent
H - Electricity
04
B
325/89
H04B 1/10 (2006.01) H03D 3/00 (2006.01) H03G 3/34 (2006.01)
Patent
CA 1060101
ABSTRACT OF THE DISCLOSURE The present invention relates to an improved squelch circuit for use with an FM demodulator. One of the most troublesomenoise problems in radio communications is the noise bursts which frequently appear at the beginning and/or end of a demodulated transmission due to the finite times required to detect the commencement or termination of a signal and to thereafter activate or deactivate the receiver output circuits. These bursts are caused by short periods of noise signal. The present invention provides improved squelch circuit for FM demodulators including a low pass filter for filtering out-of-band noise from the demodulator output signals, a delay line for time delaying the filtered signals, a gate for selectively passing the filtered demodulated output signals to an output terminal, and a control circuit for controlling the gate. The control circuit includes a high pass filter for passing the out-of-band noise in the demodulated signals, a detector for detecting the noise level of the noise passed by the high pass filter, and a comparator for comparing the detected out-of-band noise level to a reference to develop a gate control signal which causes the gate to be opened when the out-of-band noise level is relatively low and to be closed when the out-of-band noise level is relatively high.
255987
Altstatt John E.
Bush John A.
Lance Drew R.
LandOfFree
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