[amsat-bb] Re: AO-51 Down??

Alan Cresswell alancresswell at xtra.co.nz
Tue Jun 15 20:41:51 PDT 2010

Hi Drew,

The point of my email was to suggest that based on my observations, and
knowledge of operations "down under", the fact that AO-51 is sometimes on in
eclipse may not necessarily be caused by bad operators.  There seems to be
evidence to indicate that the transponder can be triggered for other
reasons.  There is only a very small group of regular operators in VK and I
am the only currently active ZL on AO-51 and we are all well aware of the
eclipse problem.  A turn on at 1758z for example is 3:58am local time in VK.
None of the regular operators operate at that time of the day.  I can not
guarantee of course that some rogue operator who never otherwise appears on
the satellites is triggering the system but it seems unlikely.  
As a general observation I would point out that operations in this part of
the world differ markedly from the Northern hemisphere.  I have never to my
knowledge exchanged a grid square.  A typical pass consists of 2 to 5
stations, all well known to each other, and we simply have a round table
discussion. It is this fact that gives me reasonable confidence as to
whether or not there is operation in eclipse.


-----Original Message-----
From: Andrew Glasbrenner [mailto:glasbrenner at mindspring.com] 
Sent: Wednesday, 16 June 2010 02:14
To: Alan Cresswell
Cc: 'Rick - WA4NVM'; 'AMSAT BB'
Subject: Re: [amsat-bb] Re: AO-51 Down??

Alan Cresswell wrote:
> Hi Drew,
> Well the southern hemisphere is a big place and I can assure you there is
> operation in eclipse from VK/ZL.  I monitor almost all evening passes here
> which occur shortly after the eclipse and on a number of occasions I have
> noted that the transponder was on at my AOS.  It also tends to drop out
> shortly after AOS so given the length of the timer this would indicate a
> turn on somewhat south of ZL.  This would also correspond to the time
> comes out of eclipse.  My first guess would be that sometimes the
> transponder is triggered as it comes out of eclipse as there are no
> south of ZL to trigger it.  There is also continual switching between the
> normal and reduced power levels during the evening passes.  I presume this
> indicates a marginal condition so perhaps usage down this way should be
> limited for a time after eclipse as well to give the batteries time to
> recover.
> Alan
I'm looking at a Whole Orbit Data file right now from 6/12 that 
indicates use at 2116Z and 1758Z, over Australia and New Zealand, in 
eclipse. Other files show similar patterns. I'm sure however that we 
will have the exact same problems, and worse, over the northern 
hemisphere during our winter eclipses! It may also be that the PL 
decoder is occasionally decoding falsely, which would mean a longer 
sample time might help.

The software does not increase power after eclipse until a set voltage 
is reached. I think the solution will be to lower the intermediate power 
step to zero, as the low one is, and then there will be no use possible 
during eclipse, but also with occasional periodic dropouts during poor 
attitudes during the rest of the orbit. Regardless, my comment was not 
meant as a slight to anyone, and was merely based on observation of the 
WOD. We can see pretty much everything that happens in 30s intervals.

Thanks for the observations.

73, Drew KO4MA

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