The simple rebuttal to this post is "its already been done". SCAMP
demonstrated a highly-effective busy frequency detector running on a
PC and soundcard more than a year ago.
73,
Dave, AA6YQ
--- In [email protected], "mulveyraa2" <[EMAIL PROTECTED]> wrote:
>
> --- In [email protected], Bill Turner <dezrat@> wrote:
> >
> > ORIGINAL MESSAGE:
> >
> > At 01:41 AM 6/22/2006, expeditionradio wrote:
> >
> > >I can sit here and decode and participate in an Olivia 500/16
> > >QSO on 20meters that I cannot hear by ear and I cannot see any
signal
> > >on the waterfall. Is that frequency "busy"?
> >
> > *********** REPLY SEPARATOR ***********
> >
> > Of course it is "busy". If software can find a signal, that
channel
> > is busy. Whether you can hear it by ear is irrelevant.
> >
>
>
> And therein lies the problem.
>
> The software would need to be able to determine whether any of
> *dozens* of possible signals are present in the passband. In the
case
> of some of the more exotic ( and even less exotic modes ), it
needs to
> try to decode multiple bandwidths and bitrates. This takes quite a
> bit of time.
>
> Of course, along with that, you need to deal with frequency
> offsets. So there may be an Olivia signal at some frequency F+N,
at
> which point the detector can decode it. But if the detector is
> starting to scan at frequency F, it needs to then attempt to decode
> all of those possible signals at F, then F+1, then F+2, etc, until
it
> finally gets to F+N, where the target signal is functioning. This
can
> take a lot of time. And in modes where even a 10hz offset causes
> problems, you can have a real problem.
>
> But - ooops! A new signal has just popped up at F+N-X, which
the
> busy detector had already determined was empty of signals. Or the
> Olivia signal at F+N just had a turn-around, so it appears empty.
Or
> the QSB had dropped the signal just far enough that it can't be
> decoded, and therefore doesn't appear to be a valid signal.
>
> So determining when a passband is busy is actually a very, very,
> tough problem to crack.
>
> - Rich
>
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