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Re: Another Satellite PSK-31 possibility.



> I was in Radio Shack today and they are selling these little $15 talking
> picture frames.  The audio sounded quite high quality.  10 seconds. 
> So I could build a 10 sec parrot Satellite Xponder on 10m that might be
> able to be left on all the time... [without impacting our mission?]

Im trying to figure out how this would work to see if it is worth doing...
Target ground user would be someone with a RS or other 10m rig.  Radio
after inital tuning is not touched during pass.  DIGIPAN or other software
watches the whole passband. the Parrot allows for bidirectional SIMPLEX
but there is 600hz doppler each way.  QSO's would need to stay within 1000
to 2000 Hz on the bird to allow for:

* APPROACHING:  User transmits 400-1400 Hz and hears himself 1600-2600
* GOING-AWAY:   User transmits 1600-2600 Hz and hears himself 400-1400
* Transponder would have a pilot pure carrier at 1000 Hz.  Easy to see
  on the water fall.  No one should operate below that tone, or he will
  find himself out of the pass band later in the pass.
* Since everyone hears the 10 second playback, everyone can find 
  themselves easily WITHOUT running full duplex.

OPS SCENARIO.  At start of pass, tune so PILOT is at 1600 and look only
for QSO's above 1600. To each user, the entire band will shift downward as
the pass progresses.  Idea is to keep everything within a fixed tuned
400-2600 Hz audio passband for everyone.  Problem is you have to hit your
uplink in the blind.

So to start, you make an intelligent guess, find yourself, and press a
button.  This causes your station to remember the instantaneous offset.
Now, find anyone in the passband, and your software will apply this
initial offset value to your UPLINK (minus 20 Hz).  Since the time
elapsed is 10 seconds, You will only be off by about 10 Hz each way and
HIGH.  SO we subtract 20 hz to counteract this.  (we actually want to
overshoot by about 10 Hz low so that the QSO walks down the band, not
up...  If we didnt subtract something from the offset, then the QSO's
would walk up the band and out of the passband..

This should be enough for the other guy to quickly CLICK on you.  When he
moves like that then his software also remembers the instantaneous shift
observed at his location and will use that when HE transmits.

We tweak these estimates so that all QSO's walk down the band together so
that to everyone everywhere, their uplink and downlink stay within the
original 400 to 2600 Hz passband.  Thus, no radio tuning required.
And you can do it almost manually.

All that the PSK-31 software needs to do is have an "offset memory" that
will remember your offset when ever you putsh a button that says to
"remember this offset"  and to reduce it by 2 Hz every second.  Yes, the
average rate of 2 Hz per second is not constant, but it is totally
predictible.  All you need to know is the peak elevation of the pass.  For
low passes, it is almost linear.  For very high passes it is quite low at
either end and very fast in the middle.

But since 90% of ALL passes are low to everyone else, and you do have to
click on the other guy each time, I think even a constant adjustment might
work well enough.  I want to do anything I can to avoid having to have the
PSK-31 software have to have updated KEPS to work...

Of course, a 10m UP and 12m down transponder would be trivial to do, but
it violates the principle of one-radio operation.  I'm leaning towards the
more convoluted challenge above, so that anyone with a cheap $149 10m xcvr
and a PC can work it.  If it is too hard to work as a parrot, then we
could go to the cross band approach but that significanly complicates the
ground station.  (for an entry level linear satellite).

de WB4APR@amsat.org, Bob

PCsat Design        http://web.usna.navy.mil/~bruninga/pcsat.html
CUBESAT Designs     http://web.usna.navy.mil/~bruninga/cubesat.html
APRS LIVE pages     http://web.usna.navy.mil/~bruninga/aprs.html
APRS SATELLITES     http://web.usna.navy.mil/~bruninga/astars.html
MIM/Mic-E/Mic-Lite  http://www.toad.net/~wclement/bruninga/mic-lite.html

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