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

J. Lance Cotton joe at lightningflash.net
Fri Jul 8 13:41:00 UTC 2005


Andrew Rich wrote:
> psk31 for aprs ? on hf
> 
> -----Original Message-----
> From: Wes Johnston [mailto:aprs at kd4rdb.com]
> 
> 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.

PSK31 is an order of magnitude slower than HF 300 baud. Plus it has zero 
error detection/correction. You definitely do not want mangled positional data!

I've played around (in a way) with q15x25, but at the time I had it up, I 
didn't have a 2nd person to test with. It does look promising because it 
ties in so well with AX.25 (but doesn't have to!).

The Linux q15x25 (also called newqpsk) modem is built into the soundcard 
modem system and so any linux APRS or packet program that utilizes the ax25 
network interface to the radio can use q15x25 instead of 1200 AFSK, 
transparent to the program.

It does look promising and even holds the 2500 bps (raw) data rate on HF 
channels. Though, of course, it was designed for SSB rigs, it may still work 
with FM, but without the weak-signal performance.

Unlike some other robust digital modes, q15x25 does not have a long sync 
time, which rules out so many for APRS use.

-- 
J. Lance Cotton, KJ5O
joe at lightningflash.net
http://kj5o.lightningflash.net
Three Step Plan: 1. Take over the world. 2. Get a lot of cookies. 3. Eat the 
cookies.




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