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Re: AO-27 (TOPR?) SCHEDULE



Hello Eric,

I looked at this issue last spring.  AO-27 is turned on each pass in the 
Northern Hemisphere for 8(7 analog) minutes.  Exactly when changes, but it 
should be on in the CONUS every pass, half or more of the pass depending 
upon the maximum elevation

The AO-27 site and the Java scheduler program will show you the on/off times 
each day, then you need to compare this with the pass times for your 
location to see when it will be on - and you are good to go.

I know of no tools that tell you when you can work AO-27 for a particular 
QTH.

73,
Gould, WA4SXM

----- Original Message ----- 
From: "Eric Fort" <eric.fort@gmail.com>
To: <wd9ewk@amsat.org>
Cc: <amsat-bb@amsat.org>
Sent: Thursday, September 13, 2007 1:47 PM
Subject: [amsat-bb] Re: AO-27 (TOPR?) SCHEDULE


> 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@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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