[RTTY] High speed RTTY

[Kok Chen]

On Jan 27, 2010, at 7:32 PM, Bill, W6WRT wrote:

> So, is the bottom line that PSK125 would be a better DX mode than the
> slower rates?

Only if the predominant error term comes from phase error due to multipath (what you had asked).  

Under quiet (AWGN-like) propagation conditions, minimizing the effects of mutipath will do nothing for you, and reducing the bit period will actually hurt because there is now less bit energy relative to noise density.  Again, I would refer you to this:

http://www.sss-mag.com/ebn0.html

When there is no multipath, faster PSK modes will definitely be worse than PSK31 in terms of weak signal capability because Eb/No suffers as you increase the baud rate.  But when there is multipath, *and* if your signal has good enough SNR (i..e, when you have plenty of Eb compared to No) then reducing the symbol period can reduce the influence of multipath and produce better print.

If by DX, you mean consistently make it across the pole on HF, a multitone FSK mode that includes FEC is a better option than either RTTY or PSK31.  In fact, DominoEX is as fast to tune and as interactive as RTTY (since you don't need to wait for the absolute tones to be identified in DominoEX as you do in MFSK16 -- like RTTY, once you hear one tone and then a second different tone, you can start the decoding process).  When you turn on FEC, DominoEX is very robust against flutter.  However, if your interest is in contesting, rather than in radio science, there are not many DominoEX contests.  I only remember one HF contest that specifically targeted DominoEX.   (More recently, there have been VHF contests that targeted DominoEX.  QST mentioned it not too long ago.)

73
Chen, W7AY