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/