[amsat-bb] Re: AO-7 is not OK

Wed Apr 14 10:00:05 PDT 2010

Mike, Piraja and all,

Please take a moment to visit the page on the AO-7 Web site that includes an essay from AO-7 Project Manager Jan King, W3GEY. You will find that essay here: http://www.planetemily.com/ao7/history.php?PHPSESSID=5cc1e3be993405e687967faffcac4407

According to Jan, AO-7 no longer uses batteries in its current condition. It is powered completely by the solar array. He explains fully what he believes to have happened. Here are some excepts for the full essay Jan wrote, which appears on the page I provided the link to (NOTE - scroll down toward the borrom of the page to find Jan's report):

"I am certain what has happened (and I know why): The battery did fail short. Virtually all of the cells failed in a shorted mode eventually. This shorted condition placed a shunt across the solar arrays and prevented current from going to the satellite loads (i.e. the transponders, in particular). Some time before G3IOR reported hearing the spacecraft again the short on one of the cells (1 out of 10) failed a second time. This time, it went from short to "open." When it went open this released the shunt that was pulling the array voltage down and allowed the current to pass to the satellite loads. Since there is no battery at all now (because one cell went open), when AO-7 goes into eclipse with each orbit, the satellite has no power to operate and shuts down in the dark."

Also:

"People should realize that the solar arrays are old and they don't put out more than a few watts now. That's the only power available to run the transponders.So, if they uplink too much power it will just cause the transmitter to sort of 'cave in.' The voltage on the satellite bus begins to sag badly when a heavy demand is placed on the transponder (by a large uplinking signal) since there is nothing there to regulate it and then the oscillators in the receiver and transmitter chain start changing frequency. People call this 'FMing' and that is what is going on."

Jan's entire essay is fascinating.

The primary reason I consider AO-7 the flagship of the amateur satellite fleet is her amazing story and legacy. I consider myself blessed and fortunate to have an opportunity to work the "Grand Old Girl" now, more than 25 years after she reached orbit. Even on her bad days - and today appears to be one, as I write this - I am able to clearly copy my CW signal on the downlink from about 20 degrees elevation running only 5 watts out of a Yaesu FT-817 from my handheld Elk dual-band yagi - and working from inside my home on the second floor, my uplink signal shooting through the second-floor ceiling and roof. I believe she spoils us on her good days with the ability to enable contacts that span oceans and continents - even with a station like mine.

I am grateful for every orbit during which I am able to hear such an amazing piece of amateur-radio hardware still working as hard as she can.

73 to all,

Tim - N3TL

________________________________
From: Mike Rupprecht <mail at mike-rupprecht.de>
To: ps8rf Piraja <ps8rf at hotmail.com>; amsat-bb at amsat.org
Sent: Wed, April 14, 2010 12:25:03 PM
Subject: [amsat-bb] Re: AO-7 is not OK

Hi Piraja,

Yes, I made similar observations. If the CW is active on 70cm you can hear
sometimes a very strong deviation in frequency.
The CW beacon partly not decodable. I agree with you it could be an effect
by low batteries or due heavy usage.
See some graphs here: http://www.dk3wn.info/p/?cat=21

73, Mike
DK3WN

-----Ursprüngliche Nachricht-----
Von: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] Im
Auftrag von ps8rf Piraja
Gesendet: Mittwoch, 14. April 2010 13:22
An: amsat-bb at amsat.org
Betreff: [amsat-bb] AO-7 is not OK

Some days we are seeing very strange behavior in the AO-7.  In some orbits
can only hear the feedback on the downlink when the satellite is approaching
my station at about 30 degrees elevation, before is impossible to hear any
signal via AO-7. Using two pre-amplifier, one in the  TS 2000x and the other
with 0.6 noise with 20 dB gain. During the orbits we transmiting power with
of 30 watts.  The satellite does not respond. Tried with 15 watts It was
then that we hear at certain points on the downlink audio too low. Its best
performance  is when the satellite is almost 90 degrees from my station.
Yet it seems that the satellite is asking for help.

This seems the batteries are not getting enough loads. Or maybe it's
excessive use of power by the users of the satellite.

Maybe it's time for the users of AO-7 rethink the best ways to keep QSO
through it, such as the use of LOW POWER so that over time the satellite is
stabilized.

"Long live the AO-7"

73'

Piraja, PS8RF

The Amateur Radio is supportive and helpful in any circumstance.

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