PSK etc

[Andre' Kesteloot]

drassew2@interalpha.co.uk wrote:

> >1. What means "stable" ?
> >2. I find it unfortunate that a linear TX is necessary,
> >   since it's bad efficiency compared to switched
> >   amplifiers. Is there a solution avoiding this ?
> >3. Is it better than AMTOR or RTTY at comparable
> >   speeds/shifts?
>
> PSK31 is considerably better than RTTY and has about the same speed in terms
> of words per minute as it uses variable length coding for the alphabet to
> improve coding efficiency.  AMTOR is only RTTY with error detection added,
> at twice the baud rate.  Both these modes are very wide for LF use, not as
> good as PSK31, and if not used with a linear transmitter will generate
> splatter that goes outside the band edges.
>
> By stable, I mean the frequency shifts caused by ionospheric propagation.
> In use, PSK31 shows a phase display and at night on skywave paths on 3.5 and
> 7 MHz the phase wandering due to reflections can be seen.  Whilst '31 is OK
> on all but polar paths with an active sun the 8 and 1 baud modes are
> unlikely to travel far.  The much reduced phase / frequency shift at the
> lower LF frequency should support the lower modes - but until I have someone
> to experiment with ie  with an EVM we won't know !!!
>
> ANdy  G4JNT