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Are there any pieces of software or web tools that will allow the input of
qth and give pass data for ao-27 that shows transponder on passes only?  I'm
looking for a simple way to tell weather or not the pass (or portion
thereof) is workable.


On 9/13/07, Patrick STODDARD <wd9ewk@amsat.org> wrote:
> Hi Eric!
> > I just reviewed the pass prodictions for ao-27 on the amsat website.  I
> then
> > followed the link to ao27.org.  now I'm a bit confused.  On ao27.orgthere
> > is listed a TOPR schedule with little explanation of what TOPR is.  It
> > appears however that this causes the satellite to turn on and off it's
> > transponder at various times.  If this is the case how does one
> determine
> >  usable passes?  A satellite overhead without a functional transponder
> is
> > about as useless as mammaries on a bull! It seems it could be a source
> of
> > significant frustration if trying to work a pass only to find out the
> sat
> > had switched itself off!
> First of all, AO-27 is an old satellite - about 14 years old.  Its
> batteries, although
> functional, aren't what they used to be.  This satellite originally
> had a non-ham
> use along with its use as a ham FM cross-band repeater, but now it is
> pretty much
> just used by the hams.  To keep from ruining what's left of the
> batteries, the control
> operators of that satellite (most of the time, just Michael N3UC) have
> found a way
> to keep it functional through this summer despite its age.  Especially
> when
> considering that summertime is generally the "eclipse season", when
> the satellite
> is in darkness for a significant part of each orbit, not able to get
> its batteries
> fully charged to support full-time operations.
> Last year, the satellite was working through the winter into
> springtime.  In early
> May 2006, it started to operate intermittently, and then stopped
> working.  At
> that time, it was on as an FM repeater for 6 minutes per ascending pass
> (from
> South to North) over the Northern Hemisphere along with telemetry
> transmissions
> before and after the repeater time plus an additional telemetry
> transmission on
> descending passes (passes going from North to South).  It stayed
> silent until early this
> year, and - after many weeks of testing and tweaking - and now it has been
> on
> for 7 minutes per daytime pass over the Northern Hemisphere.
> The TOPR (previously TEPR) scheduling determines when the satellite is on
> and
> in what configuration - analog repeater or digital telemtry
> transmission, and the
> power level.  Most of the time the power level is "Med" (around
> 500mW).  For the
> past couple of years, the FM repeater would come on after 20 seconds of
> data
> and then there would be another minute or so of data after the repeater
> switches
> off.  Currently, the repeater switches on for 7 minutes once the
> satellite reaches
> approximately 28-29 degrees North latitude on any ascending pass (moving
> from South to North) where the satellite is in daylight.  The schedule
> is uploaded
> to the satellite, but the satellite's onboard clock runs a little fast.
> Officially, you can see AO-27's schedule for the upcoming 24 hours on this
> page:
> http://www.ao27.org/AO27/listing.shtml
> My observations show that the schedule listed on this page is about 5-6
> minutes later than the actual times.  There is a program you can download
> and run on your computer (Java-based) that will do the same thing.  It can
> be found at:
> http://www.cs.rit.edu/~cjh9783/programs/satsched.php
> If you don't have a program to unpack RAR archives, I can e-mail the
> AO-27 program to you in a ZIP archive.
> You can tell when the schedule was made from looking on the
> http://www.ao27.org/ homepage.  Look for the "TOPR Epoch" near the
> middle of the page.  The last time the schedule was updated was in
> late June, so you can determine the approximate difference between
> the satellite's onboard clock and the "real" time when looking at the
> schedule.
> For my location, I have two possible AO-27 passes this afternoon according
> to the pass-prediction utility on the AMSAT web site: 2137-2152 UTC, and
> 2317-2331 UTC.  The AO-27 Satellite Schedule program shows that, for those
> passes, the repeater should be on for 7 minutes starting at 21:42:51 and
> 23:23:40 UTC (before accounting for the satellite's clock discrepancy -
> about
> 40-60 seconds before these times).
> Is it frustrating that a satellite like this is only available for
> only portions of
> some passes?  Sure.  This has been the way AO-27 has operated for
> many years, and despite those limitations there are usually good crowds
> working the passes that cover most of North America.  In my satellite log,
> I
> have made almost 25% of my 2800+ satellite contacts on AO-27, despite
> its limitations and the fact it had been off for several months in 2006
> and
> into the start of 2007.
> Good luck and 73!
> Patrick WD9EWK/VA7EWK - Phoenix AZ
> http://www.wd9ewk.net/
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