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[aprssig] Looking for 9600 baud equipment

Scott Miller scott at opentrac.org
Fri Oct 3 23:21:43 UTC 2008


As long as you're on FM, you're never going to do better than FM - I 
don't think multiple tones over FM is going to make any difference. 
Flutter is going to take out all of the tones at the same time.  Now, if 
you were running SSB, then I agree, COFDM would be great.  You may be 
right about the pre-emphasis thing though.

Scott
N1VG

Jack Spitznagel wrote:
> A "dumb" question:
> 
> Why can or can't multiple parallel tone modem systems be used? They work
> pretty well on some pretty terrible paths on SSB with MFSK and OLIVIA.
> 
> We are using FMN so the inherent SSB problems are not there. Would
> mobile flutter problems be offset by the advantage of staying a a slower
> bit rate with higher throughput? Wouldn't one be able to ignore
> pre-emphasis adjustment in a properly designed system? Most newer sound
> chips can handle multi-tone pair modes very well well.
> 
> Rough example of advantage: 8 tone pairs at 1200 "8-bit characters"/sec
> is theoretically 8 times faster than 1200 bits/sec. at the same
> transmission rate. Could you push the speed limit with a bit rate of 4800?
> 
> Just curious.
> 
> Jack - kd4iz
> 
> Patrick Green wrote:
>> Phone models spend a good 20 seconds syncing up.  Totally unsuited for
>> APRS.  Not to mention you aren't going to get the best speed if there
>> was any fading during the "training" process.
>>
>> 73 de Pat --- KA9SCF.
>>
>>
>>     Not at 56k, I don't think.  I'm pretty sure 56k requires a direct
>>     T-carrier connection on one end.  They should only be able to do 33.6k
>>     peer-to-peer.
>>
>>
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>>
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