Re: [RTTY] PSN Modulation & PSK31 with Icom

[Kok Chen <chen@mac.com>]

On Nov 29, 2004, at 6:07 PM, Don Hill AA5AU wrote:
> Can someone tell me what this PSN modulation is and what advantage it 
> is for SSB
> (not PSK31 obviously).  My guess is it should be turned off for PSK31.

I think PSN stands for "phase shift network," used to suppress the 
adjacent sideband in SSB systems.  Like the old time phasing SSB rigs, 
but Icom is probably using a digital Hilbert Transform to do the phase 
shifting, rather than the lattice of resistor and capacitors that we 
used to build to try to get 90 degrees of phase shift across the voice 
spectrum.

A good Hilbert transform can null out the opposite sideband more deeply 
than SSB filters do.

That said, I have no idea why it does not work well with PSK31.

Did the VU4 say they will operate PSK31 rather than RTTY?

PSK31 is a better choice than RTTY actually, if there is no multipath.  
 If they go split, people with software that can receive at multiple 
frequencies will have an advantage <grin>.

(cocoaModem users: Just option-click on the VU4 in the waterfall to 
print them them on xcvr-2, then click around in the waterfall to use 
xcvr-1 to search for the QSX and also to transmit through.)

I can imagine some people plastering the band with 70 watts and a 
crummy -20 dB IMD signal, though.

Wink, wink, nod, nod:  remember that a clean PSK31 signal is also 
easier for the DX to print correctly.  The over-modulated guys are just 
making themselves harder to copy - the resultant demodulated waveform 
does not match an optimal matched filter for the raised cosine envelope 
of a PSK31 signal.

73
Chen, W7AY

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