Re: [RTTY] HAL ST-8000 and 6000 vs. Sound Cards

[Kok Chen <chen@mac.com>]

On Jan 29, 2005, at 9:12 AM, Neal Campbell and Sarah Ferrell wrote:

> As I believe in Don's recommendation to have a couple of different 
> modem types for diversity, I would tend to take a soundcard-based 
> modem (MMTTY or RITTY) and a hardware based one (I have ST-8000, AEA 
> PK-900, etc.)

Why not just build in the "algorithmic diversity" into one single 
multiple-demodulator software modem?  That is what cocoaModem does.

Speaking of diversity (in the radio engineering sense) -- it is not 
difficult to expand the soft-decision multiple-demodulator based modem 
idea into a space or polarization diversity RTTY system.  Feed one 
receiver/antenna into some of the demodulators and a second 
receiver/antenna into another bunch of demodulators and some algorithm 
to steer the decision (e.g., the receiver bank which has more of its 
demodulators agree with one another wins out).  It should work better 
than summing the audio signals from the two receivers into one single 
demodulator (think of it as working with the conditional probability of 
two uncorrelated vectors versus working with the average of the same 
two vectors) .  I have this as something in my stack of "things to try 
out one day when I have time."

However, I have to interject a really odd comment -- wold you believe 
that a better demodulator can lead to a more frustrating operating 
experience?

The reason is that there are now more people that you can print that 
cannot print your signal!

What is more important is that every rare DX or rare contest mult gets 
a good modem :-).

73
Chen, W7AY

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