On Thursday 17 February 2005 07:32 pm, Marcus D. Leech wrote: > In the analog world, do they implement squelch using > detected RF power levels (i.e. prior to FM demod), or > something else?
It is usually done by measuring detected noise. Recall, in FM, audio output level is independent of the carrier level, except at very low signal levels. As the signal gets stronger, detected noise decreases. The usual way that squelch works is to use a high pass or band pass filter on the output of the detector, to filter out the signal. This leaves only high frequency noise. Then sense the level of that detected noise. When the noise goes down below the set level, open it. Using carrier level does not work well. Atmospheric noise would be able to open the squelch. Also, remember that the IF amp is a limiter. The level at the input to the detector does not vary at all with signal strength. There is enough gain so the front end noise is brought up to hard limiting. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
