Hi Dave,

Yes, what you have observed and described is exactly what we can expect from AO-51! It is almost exactly like a HT with low batteries--you transmit, it goes OFF. Unkey, it comes back on...you can key for a sec, but then it goes OFF again...

We will see a little of this going on with AO-51, but our goal is to keep it to a minimum...otherwise it's just plain annoying ;)

Just before entering eclipse, and just after exiting eclipse, you can expect the power to go UP and DOWN as you have observed. There is *just* enough power to keep the transmitter ON, then battery voltage drops (from less sun), and the transmitter goes OFF. The voltage bounces back UP because there is no load on the batteries, so the transmitter goes ON. Then the voltage drops/sags, and it goes OFF. Eventually, the bird sees even less light, and it's not enough--so it stays off, and we are effectively in eclipse (or insufficient sun to keep it running...)

As it exits eclipse, a bit of sun hits the solar panels, and battery voltage goes UP. Eventually, it's just enough for the transmitter to come ON. Then, the voltage sags, and it goes OFF. Eventually there is sufficient sun for the battery voltage to stay up when the transmitter is ON, and we are effectively out of eclipse.

Keep in mind this happens every 100 minutes (once per orbit). So if it's over a populated area, you'll observe this--as you have, Dave!

The good news is that eclipses are pretty short right now and are occurring at early local time in the Northern Hemisphere. So many aren't even awake yet..but those that are will see what you've seen.

Looking longer term--by early March 2011 (this year) we will have a period of full sun again, that lasts a couple of months. Then we are back into eclipses for a long, long--and we'll have eclipses that will get up to 30 minutes in length!! If that's over your QTH, that means you can't work AO-51 potentially for a whole pass..but it remains to be seen exactly what the orbit/eclipses will look like.

If anyone is the least bit interested, I can suggest two programs to predict eclipses:

Mike DK3WN's "Illum" program is great at giving you a quick graphic view of what a satellite is going to see for the next 60 days. http://www.dk3wn.info/software.shtml

John KD2BD's PREDICT is great at giving even longer term eclipse projections. http://www.qsl.net/kd2bd/predict.html

Happy eclipse predicting :)

73!

Mark N8MH

On Thu, Jan 6, 2011 at 9:47 AM, David Palmer dave@zdap.com wrote:

Hi Mark and Amsat,

Just wanted to report that I heard AO51 come over nicely this morning (2011-01-06 at around 1420z).  I put out a quick call, nice audio on downlink, and heard Loren K7CWQ come back.  On my return to him, the bird suddenly disappeared about 10 seconds in .... Loren replied, it cut off on him after about 5 seconds ... and on my repeat reply, it cut off after about 3 seconds.  Didn't hear it again on that pass. Sounded just like someone trying to transmit with an HT on low batteries!  :-)

A quick check showed AO51 was barely in eclipse (screenshot from my SatPC32 below):

http://3.bp.blogspot.com/_JEsfS-puDmk/TSXUKQFKhEI/AAAAAAAAATc/bsapXtrj1cM/s1...

So this sounds exactly like the behavior Mark was describing AO51 would do.  Even though the bird was heard at first, I flagged it as "not heard" on the oscar.dcarr.org page just to note that it dropped off early during the QSO.

73 all!

Dave KB5WIA / CM88