Re: Using "Q"PSK?


Steve W3HF
 

Erika -

I'm answering to QPSK-calls and mostly the om's are surprised to get
an answer, but actually I don't have the impression that it is much
better than BPSK.
In theory, the QPSK-plus-FEC implementation in PSK31 is 3-6 dB
better than the BPSK option. But you would only achieve 6 dB in
an already-very-good channel. And if your print is 100% already,
you won't see it.

At the marginal cases, the improvement may be only 2-3 dB, or
less than 1/2 of one S-unit. And I believe most HF QSB is much
deeper than that, so it will be hard to see this difference too.

There's probably a class of signals that are just in the middle,
where the improvements are noticeable. But I don't know how
common they are.

My software shows in the tuning indicator a cross
when I'm tuned on a QPSK-signal, seems that some softwares don't show
any difference, that might be the reason why you get not so many
answers.
Any software that has a phase scope will see this--it's a function of
the signal, not the software. BPSK has two phase states--0 and
180 degrees--so the "perfect" signal looks like a straight line.
QPSK has four states--0/90/180/270 degrees--so the signal looks
like a cross.

I think the problem is that most people don't know what the phase
scope means, and either don't use it or don't recognize what it is
telling them. No one is expecting QPSK, so they don't even think
to try it.

Steve
W3HF

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