[amsat-bb] Re: AO-27 (TOPR?) SCHEDULE

[Bob Stewart]

The AO-27 transponder is generally on while it's over the US.  Mostly
I see it go into its data mode and then shut down at more-or-less the 
Canadian border on ascending passes.  I can't think of a pass where it 
was off since I've been using it - about 2 1/2 months.  I have no idea 
whether this changes during other times of the year.

Bob - AE6RV

--- Eric Fort <eric.fort at gmail.com> wrote:

> 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.
> 
> Eric
> KG6KQT
> 
> On 9/13/07, Patrick STODDARD <wd9ewk at 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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