If *any* code they link to was GPL, their code is GPL or in violation of the GPL. This is true of code they cut-and-paste, code they use as a library and link to, but not code where they call an unmodified GPL external program.
The idea behind the GPL is that you cannot freeload on the work of the community. If you improve a tool, the improvements must be returned to the community under the same terms as you received the original tool. As far as subaudible tones are concerned, the real issue is how they would affect the (human) mode. In SSB, they'll look like fixed carriers offset from zero. This is easy to detect as "signal, thus busy", even if you can't reliably decode them (you need to know what their "dial frequency" and USB/LSB setting is to know what that carrier represents, but then you don't *need* to know) For FSK, they would be pointless, as there's already one or another carrier that is itself detectable. They would also create a two-tone situation which would cause problems with linearity and crest factor. There are similar issues with PSK and similar. With CW, there's also no reason. I would expect that AM voice would be detectable (due to the carrier), ssb would be difficult, any of the wide/noise-like modulations would be difficult to detect as well. Anything narrow, or with high energy in a narrow bandwith, should be easily detected. Multitone modes with relatively few carriers would be easy for this reason; numerous carriers "spread" the energy and make it harder to detect unless you know exactly where the carriers are expected to be. I can think of several relatively trivial ways to detect the high-energy/narrow easy cases, but SSB voice and broadband/"noise-like" modulations... those are the real challenge. Just off of the top of my head, say, take a one-second-window FFT of the signal, find the total energy in the spetrum, then find if it's relatively evenly spread or concentrated in a few buckets. The second case is likely a busy channel. On 9/18/07, Rud Merriam <[EMAIL PROTECTED]> wrote: > The code for busy detect, ARQ, etc was not GPL'd. It was their own work. > Since it was all research it probably was not the cleanest implementation. > > While replying to your previous message I was wondering about sub-audible > tones being included in transmission, ala repeater tone usage. > > > Rud Merriam K5RUD > ARES AEC Montgomery County, TX > http://TheHamNetwork.net > > > -----Original Message----- > From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] On > Behalf Of Robert Thompson > Sent: Tuesday, September 18, 2007 1:57 PM > To: digitalradio@yahoogroups.com > Subject: Re: [digitalradio] Re: Busy Detectors > > > > If there was GPL code involved, they are in violation of the license of the > code they borrowed. Distributing only a binary (with or without suicide > timers) is to put it mildly, EXTREMELY in violation of the spirit as well as > the letter of that license. Of course, if they themselves wrote *all* of the > code in use, there is no limitation on what they can themselves do with it. > (This exception vanishes if they "release" their code as GPL to make it > compatible with other GPL code they're using, then fail to actually comply > with the GPL for their own code. > > <snip> > > A practical solution may also require some change in expectations on the > part of pure human-to-human qso partners, too. > > Regards, Robert Thompson > > > Announce your digital presence via our Interactive Sked Page at > http://www.obriensweb.com/drsked/drsked.php > > Yahoo! Groups Links > > > > > > > > Announce your digital presence via our Interactive Sked Page at > http://www.obriensweb.com/drsked/drsked.php > > Yahoo! Groups Links > > > > -- Regards, Robert Thompson ==================================================== ~ Concise, Complete, Correct: Pick Two ~ Faster, Cheaper, Better: Pick Two ~ Pervasive, Powerful, Trustworthy: Pick One ~ "Whom the computers would destroy, they first drive mad." ~ -- Anonymous ====================================================
