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[aprssig] I'm brainstorming, so don't beat me up!

Gerry Creager gerry.creager at tamu.edu
Thu Jul 7 17:34:59 UTC 2005


Actually, the 2-tone modem history pertains to telephone line 
optimization for tone detection.  Preemphasis and deemphasis were 
rampant, and tone detection was done with LC lumped constant filters.  A 
single tone detector had a higher error rate.  Once you get to two tone 
systems (remember RTTY?) one can start thinking about different encoding 
and modulation schemes.  When one is thinking in terms of 
bits/transition, multiple tones or constellations thereof start making 
sense.

I suspect we could create a high performance CW system using DSPs but 
we're talking now about transitions per bit rather than bits per 
transition.  For what we're talking about, does it make sense?

gerry


Curt, WE7U wrote:
> On Thu, 7 Jul 2005, Earl Needham wrote:
> 
> 
>>At 10:40 AM 7/7/2005, Curt, WE7U wrote:
>>
>>>While we're at it, would some other non-standard rate _between_ 4800
>>>and 9600 work?  What is the maximum rate we could get through
>>>voice-grade rigs without modification, even if we have to change to
>>>a different type of modulation?
>>
>>         If we're going to consider another form of modulation, I'd like to
>>enter my vote for 100 WPM (or faster) CW.  Maybe a LOT faster -- can we
>>design a system that does 1200 WPM CW?
> 
> 
> That's extremely fast!  What you're describing is (assuming 5-char
> words and a space between each one) 6 * 1200 chars per second, or 6
> * 1200 * 8 bits per second.
> 
> I assume you mean something equivalent to 1200 baud packet speed in
> terms of characters transferred.  That's 1200 bits per second.
> 
> I don't know whether a CW system could be designed that would
> compete with 1200 baud AX.25 packet.  There must be a good reason
> that people went with the 2-tone modem originally.  Perhaps coherent
> CW would suffice for this idea, which I think is a two-tone modem
> anyway isn't it?
> 
> --
> Curt, WE7U.   APRS Client Comparisons: http://www.eskimo.com/~archer
> "Lotto:    A tax on people who are bad at math." -- unknown
> "Windows:  Microsoft's tax on computer illiterates." -- WE7U
> "The world DOES revolve around me:  I picked the coordinate system!"
> 
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-- 
Gerry Creager -- gerry.creager at tamu.edu
Texas Mesonet -- AATLT, Texas A&M University	
Cell: 979.229.5301 Office: 979.458.4020
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