Re: [amsat-bb] Help measure AO-40 spin rate

["Richard D. Burgan" <wc8j@xxxxxxxx>]

Hi All,

I have two ways of measuring the spin.  The first is entirely
manual
and the second involves recording the signal amplitude on a
strip
chart and counting the peaks over time.  I'll describe the
manual
system since I feel its the most accurate.

I listen to the audio from my 2.4 GHz receiver in USB mode. 
(The
same signal goes to the 400 bps psk modem)  I use head phones
so I
can hear very clearly.  The signal has a distinct
Swish-swis-swis-Swish-swis-swis repetitive pattern caused by
the
side lobes of the antenna pattern.  This is an amplitude
modulation
and it can be seen on your S-meter if you set your receiver
AGC to
fast.  It may help to watch the S-meter.  I simply count the
number
of repetitive pattern groups for about two minutes and
calculate to
spin rate.  I use a stop watch and time from the first Swish
until
the first one after two minutes has passed while marking each
Swish
on a piece of paper.  Then I calculate the spin rate.  I
repeat the
process three times.  If the three measurements are very close
I
average them.  If they differ I re-measure.

Example:  Date 1/22/2001 01:36 EST 
2 minutes 5.43 seconds - 37 Revs. (Swish's)
 or that is Date 1/22/2001 06:36 UTC 
  37 Revs / 125.43 seconds = 0.295 Revs / Second
 or 0.295 * 60 = 17.69 Revs / Minute = 17.69 RPM

Please note:  I HAVE JUST PROVED MYSELF WRONG!  I claimed that
my
measurement showed that AO-40 had slowed from 17.6 to 17.2
RPM.  I
was wrong due to my counting error.  I went back and got the
paper
that I recorded the marks and times on and recounted and
recalculated the results for the above example.  Originally I
counted 36 and not 37 counts.  I'll try to be more careful in
the
future.  Sorry I mislead all of you.  I'm glad I had the lab
notebook!

73's de Rich Burgan @ WC8J

----

Dave Guimont wrote:

> >It appears that the command team has started magnatourqing at
> >perigee to slow the spin rate.  Yesterday the spin had slowed
> >from 17.6 to 17.2 RPM just after perigee.  Also, the WOD data
> >showed that the battery voltage was lower around perigee,
> >possibly indicating that the magnets were on.
> >
> >If you can here the bird why not measure the spin rate and
> >post it here?  Even if you cannot copy telemetry you can count
> >the number of spin modulation cycles per unit time and post it
> >here.  (The spin rate indicated by telemetry has been wrong
> >since December.)
> Hello Rich,
>
> How can you tell which frequency variation to zero in on?
> The indications I get on my psk decoder are rapid, and variable.
> I try to get on every pass I can...and will be happy to count if
> I know how!!
>
> >It might even be helpful to the command team to get early
> >indication of spin changes here.
>
>             73, Dave wb6llo@amsat.org
>                     Disagree: I learn....
----
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