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Re: Lets use the 3 1200 baud PSK sats!



In a message dated 01-03-29 12:26:47 EST, Bob Bruninga writes:
> All you need is:
>  
>  1) A 2 meter FM HT or mobile rig on the uplink and OMNI antenna
>  2) A UHF all mode downlink (downconverter to HF is fine) and small beam
>  3) A manchester encoder (this is only an XOR gate combining the 1200
>  baud AX.25 data with its own 1200 baud clock.  OR KA2UPW's SOUNDCARD
>  program...
>  
>  4) A PSK demodulator.  (Drum rolll please.... THIS IS WHAT IS NEEDED)
>  

All,

   I guess I should take this as a hint to finish the demodulator
half of the soundcard PSK mo-dem (my dem works, but the
bit sync-clock recovery algorithm should really be much better
than it is, and the software doppler tracking needs work
....email me if you of know a better bit sync algorithm or a good
software doppler tracking algorithm...Or start up a discussion 
on the amsat-bb about how to compensate in software for 
high doppler shift with relatively low bit rates (20:1).... I found that 
having the software pulse the MIC-DOWN button doesn't
work well because you'll under/overshoot your correction at high 
doppler rates given the latency of getting the audio from 
soundcard through the OS to your application.  Got a better 
idea?  Email me. This isn't an issue with other soundcard 
demodulators because they don't have to deal with a large 
*changes* in doppler in a short period of time all while looking at 
the audio from several seconds back...)    But I digress...

   I know Bob is interested in a soundcard PSK modem for
the PACSATs,  and I'm interested, but is there really 
all that much interest out there in the rest of satellite hamdom?  

</soapbox on>
   In the whole time I've had my UPW modulator program 
available on my web site, I've only received email from a 
handful of people who were trying to hook up the soundcard 
to their radio.   Is that just typical for the amount of feedback 
people don't send to software authors?  I definately get the
impression that no one would use a soundcard PSK modem 
except a handful of amateur radio operators.   That's fine.  
I had fun writing the soundcard PSK modulator and still have 
fun using it to digipeat APRS packets though the PACSATs.   
But, I'd like to work on projects that other people will use have 
fun using too.

    I'm in this for the fun factor, and I have lots of fun projects 
to work on, and this is just one of my many fun projects 
on my personal list.   I'll bump this up on my to-do list if there 
are actually people who might use it.  Otherwise, I'll keep
working on it at the current pace I'm working it and I'll get to
it after the current satellite modem I'm finishing up.

   How many people are actually interested in a 1200 baud
soundcard PSK modem?  (Regardless of the whole
Linux / Windows thing.)

   Would you, yes *YOU*, use a soundcard PSK modem 
for the PACSATs?

   Speak up.  

   Send me email off the list.

Douglas KA2UPW
dquagliana@aol.com
"Or if you know of a good simple algorithm for extracting bit clock...
or compensating for high doppler shift in software...then email me too."
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