The IMD shouldnt be a significant problem unless something is overdriven. However, you see that with PSK31 and to a lesser extent RTTY fairly often on the bands, although most of what i see is 60 cycle hum and audio harmonics related to that, rather than just pure overdrive. AFSK, etc., is the way to go if you can keep it clean (vs FSK).
PSK31 is too slow for contesting, so the first shift required is to PSK63. 73, Ty K3MM Jul 20, 2010 04:00:06 AM, digitalradio@yahoogroups.com wrote: > > > > --- In digitalradio@yahoogroups.com, k...@... wrote: > > > > Quite frankly, RTTY could easily be replaced with PSK63 as the prime > > digital >contest mode. However, many PSK operators are so clueless and often downright >rude >when it comes to contests that its an extremely uphill battle. We could fit a >lot >more PSK63 signals on the band than RTTY... > > > > It would be interesting to see what happened if a semi-major RTTY contest >was moved to PSK63 only. > > > > Agreed, though the IMD might be a problem, especially as many RTTY contesters >use class C amps. Of course, you could also argue that they wouldn't need to >use >as much power... > > As a not completely unrelated aside, a few of us have been helping to test >G4HYG's APRS Messenger software which at the moment is an experiment to find >an >alternative publicly documented mode to FSK300 packet that gives better >performance >on the HF bands. We had been using PSK63 but very recently have been trying >the >GMSK modes (63, 125 and 250) which are implemented in the MMVARI free software. > > I don't know (and don't at the moment have time to find out) what exactly the >technical differences are between PSK and GMSK but the performance seems to be >even >better, and apparently it doesn't have the amplitude variations that cause IMD >products >when using PSK. > > Just because a mode is better doesn't mean that people will want to use it, >though, and I guess both RTTY and PSK31 are so established now that you'll >never >persuade people to give them up. > > Julian, G4ILO > >
