--- In [email protected], Bill Turner <[EMAIL PROTECTED]> 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 ------------------------ Yahoo! Groups Sponsor --------------------~--> Great things are happening at Yahoo! Groups. See the new email design. http://us.click.yahoo.com/TISQkA/hOaOAA/yQLSAA/ELTolB/TM --------------------------------------------------------------------~-> Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
