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Re: Question on AO-40 FEC telemetry



At 11:47 PM 2003-10-25 +0900, JJ1WTK, Kazu Sakamoto wrote:


>A Question on AO-40 FEC telemetry ;
>
>Stacy says in the latest update announcement;

It's Stacey with an "e" :-)

> >  FEC mode requires loading the IHU-2 each orbit and
> > this is not always possible; however most orbits have FEC active.
>
>Why can't the FEC mode step out ? Would this restriction be released by
>upgrading the FEC routine ?

The FEC routines do not need upgrading, but they are very computationally 
intensive and must run on the IHU-2.  It would take the 1802
processor in the IHU-1 about 100 seconds to compute one FEC 
block.   However, as has been indicated on the amsat-bb several times 
before, the IHU-2 is crash prone.  Rather than leave the IHU-2 on all the 
time and have it possibly crash when no command station is readily 
available to fix it, perhaps losing all telemetry for more than an entire 
orbit, we have elected to cycle the IHU-2 power off with a timer at the end 
of each orbit.  As soon as the IHU-2 switches off, the IHU-1 regains 
control of the MB and begins sending standard telemetry.  It takes a 
command station about 5 minutes or less to reset the IHU-2 in FEC mode so 
this is not a problem.  The other reasons not to send FEC telemetry all the 
time are the need to download 1. message blocks,  2. event blocks,  3. 
D-blks.  Cycling to standard blocks for 0 to 16 minutes of the hour, solves 
1 and 2.  FEC is turned off for D-blk downloading.

I hope that this helps explain things.



-- 
  _______________________________________________________________________
  Stacey E. Mills, W4SM    WWW:    http://www.keplerian.com
   Charlottesville, VA     PGP key: http://www.keplerian.com/key
  _______________________________________________________________________

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