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[Linrad] Re: Running Linrad on 2 computers through a network : Help

Hi John,

> For  what it worth, FM squelsh works on quieting so is always less 
> sensitive than the receiver.  
That would not be true if I would add a squelch in Linrad.
The baseband is available in several forms and I guess
the most sensitive squelch would be based on the same
spectral information used to produce waterfall graphs.

I think the FM squelch is a well defined problem, few operators
use Linrad for FM as far as I know so priority is low....

> We would rather squelsh on subaudible tone 
> or some digital pattern.  These are not available in the standard ssb 
> signal. I once worked for Harris RF, they had an ssb (reduced carrier) 
> squelsh that worked on the recovered carrier, again not available here.
OK. - But we need backwards compatibility to conventional SSB:-)

An SSB squelch could be based on RMS power in the passband. That
would open it on lightening crasches and any other noise burst.
One could look at RMS power in relation to the surrounding noise 
floor. That would be problematic in crowded bands. One could
look for a non-flat power spectrum which would not open the squelch
for stations using really heavy speech processing.

I can hear by ear when a station is properly tuned. Also when 
speech processing is allowed to distort the signal heavily. I
have tried, but failed, to find an algorithm that could do the 
tuning automatically in the computer. It must be possible since
my ear-brain system can do it, but I do not know how to compute
whatever cross-correlation in the frequency or time domain that
would say "yes. This is a voice signal and the carrier frequency 
is....." Once I know what is needed for that, any output would
be a suitable control signal for squelch/muting.


Leif / SM5BSZ

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