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Re: AO-7 Predictability.



Hi John,

Guess it's time for me to "weigh in" on the situation.

> Between the 9th and 19th of January I've observed the mode change from A
to
> B on AO-7 to be consistent and regular. This shows that the 24 hour timer
is
> functioning as it was designed to do ... 31 years! ago.

This appears to be the case!

> I assume the reason for the present "predictable" mode changes to be the
> fact that the satellite is not, nor will be, in eclipse until at least
> March.

This also appears to be true.

> After checking the log on "THE AO-7 RESOURCE PAGE" I estimated the
> switchover to be at
> approximately 08:30 UTC daily. However, on the 17th of January, I noticed
> the changeover happened at precisely 08:57 ... in the middle of a Mode-B
QSO
> with UA9CP ... so I immediately switched to mode-A and carried on the QSO
> ... therby confirming the time of the mode change on that particular day.

Here's an explanation of the 24 Hr Timer from Jan, W3GEY (with a comment
thrown it from me)
===
Jan:
AO-7 has a 24 hour timer that is a simple CMOS oscillator and a long chain
of divide by 2 FFs.  The logic simply picks off various clock rates that it
needs.  At the end of the chain is a one pulse per day logic output.

Mike:
> As I understand it, telemetry channel 2C is the one to watch. If the timer
> is working, we should see it increment between 0 and 95. When it reaches
95,
> we can expect to see a mode switch soon after. It's not precise, but gives
> an indication that the change is scheduled to happen. From the paperwork I
> have, the equation was:
>
> t=0.253N (Hours)

Jan:
[Yes, That's correct.  Ch 2C is an analog value proportional to where the
clock is in the 24 hour day.  If that seems to increment about every 15
minutes then the clock is still working. - Jan]
===

So what we really want to do is monitor the telemetry and see if Channel 2C
is really incrementing and that the switch occurs near 95 in the cycle.

One other thing I'd like to try is to command the satellite to reset the
timer. This should be fun!

Perhaps Emily could put up something on the AO-7 page so folks could record
any observations of Telemetry Channel 2C??

73,
Mike, N1JEZ
AMSAT #29649
A humble AO-7 commander
"A closed mouth gathers no feet."
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