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AO-40 Update, 2003-05-18




Passbands
-----------------
The passbands will be operational again within a few days from 
approximately MA 20 to 100.  This interval will change as we follow the sun 
and ALON increases toward 360. We are awaiting one more good set of images 
and verification of ALON/ALAT before activating the passbands.


Experimental AO-40 Downlink Telemetry Coding
--------------------------------------------
At the 2002 AMSAT Annual Meeting in Ft Worth, Texas, Phil Karn KA9Q presented
his proposal for a forward-error-correcting (FEC) format for AO-40 downlink
telemetry.

When links are poor due low signal-to-noise ratio, spin modulation or both,
FEC promises error free telemetry. The link improvement can be as much as
8db.

The software to do the encoding on the AO-40 satellite has now been written
and will be exercised from time to time as a proof of concept. It will run
on the IHU-2 (the experimental flight computer), so there is no risk to the
spacecraft.

When downlink FEC is in use, both the normal uncoded A-blocks and their FEC
encoded versions will alternate. First an A-block is sent and you collect it
in exactly the same way as you do at present. Immediately following will be
the same data FEC encoded into 650 bytes, which takes 13s to send. Then
there are a few seconds of inter-block idle, and the sequence repeats. The
repeat period is about 27s.

People
------
The FEC format and a generic 'reference encoder' (in the "C" language) was
designed by Phil Karn KA9Q and all aspects of his work are documented at
http://www.ka9q.net/ao40/

Conversion of the 'reference encoder' to IPS, the spacecraft's native language
was performed by Jonathon Naylor G4KLX, his first exercise in the genre.
Jonathon used IPS running on an IBM-PC as his test bed. Big hug, J.
For IPS info see: http://www.amsat.org/amsat/sats/ao40/ips.html

Minor edits to the encoder and devising the IHU-2 test framework was done by
James Miller G3RUH.

--W4SM for the AO-40 Command Team



-- 
  _______________________________________________________________________
  Stacey E. Mills, W4SM    WWW:    http://www.cstone.net/~w4sm/ham1.html
   Charlottesville, VA     PGP key: http://www.cstone.net/~w4sm/key
  _______________________________________________________________________

----
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