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

Wes Johnston aprs at kd4rdb.com
Fri Jul 8 01:39:26 UTC 2005


What about q15x25? mix32 (or is it mix-w) supports it... agwpe is
supposed to Real Soon Now. q15x25 is 15 PSK carriers with an aggregate
bit rate of 2500 baud on normal channels, and FEC. It's just a tweak
processor intensive to encode and decode.

Wes


Gerry Creager wrote:

> 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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>
>





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