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AO-40 Update

2001-11-06, AO-40 UPDATE

Late last week a short program was uploaded to cycle the power on and off 
to the S1 Tx.    The purpose of this test was to determine if the 
controller circuit to the S1 Tx, or the S1 Tx itself had an intermittent 
problem relating to power up.  This program turned the power on or off 
every second.  When on, it checked to see if the S1 Tx was actually drawing 
any current.  If so, the program would stop, leaving the S1 Tx on.  This 
program ran for approximately 45 minutes.  Thus, the power was cycled on 
(and off) approximately 1350 times.  During this time, the S1 Tx was NEVER 
detected to be drawing current.  Accordingly, we must assume that the S1 Tx 
cannot be recovered.  Nonetheless, we will repeat this test from time to 
time on the remote chance that an intermittent problem has corrected itself.

The above test will also be performed on the solid state component of the 
X-band Tx shortly.

Draws power and warms up, but no output signal is detected. Additional 
testing will be done listening with EME class stations.  Though this may 
provide evidence for what's wrong with the V-Tx, ultimately it appears lost.

We are currently at 6/2 ALON/ALAT and attempting to "station keep" that 
orientation against the mystery effect for several orbits.  Following that 
we will move back towards 0/0.  The magnetorquing interval has been 
decreased from MA=224-32 to MA=240-16.  Due to the high altitude, the extra 
time either side of perigee had no effect.

A few months ago we encountered a problem with the middle beacon (and 
passband) not turning on after the RUDAK session.  This was traced to 
problems with the S2 Tx AGC due to the SCHEDULE routine disconnecting the 
RUDAK, followed by a brief (milliseconds) delay with no input to the S2-Tx 
and then abruptly connecting the middle beacon and passbands (break before 
make).  The S2 AGC did not like this rapid fluctuation and would 
occasionally go into a low power mode requiring powering the S2 Tx off and 
back on to recycle things.  The temporary solution to this was an 
intermediate schedule line which turned the middle beacon on for one MA 
before the RUDAK was disconnected.  This worked fine but wasted a schedule 
line. The SCHEDULE routine in the IHU has now been modified to a "make 
before break" approach for the IF Matrix connections, and the intermediate 
line no longer appears necessary.

This freed schedule line will be used in the future for additional testing 
including L-band only uplink to S2 downlink to test the L-band receivers 
and passband downlink without the U-band, K-band only downlink with S-band 
uplink to test the S-band receivers, etc..  Watch the N-block and the 
amsat-bb for the status changes.

Misconceptions heard on the passband
I'd like to briefly comment on a few recurrent misconceptions that I've 
heard on the passband many times.  Obviously, the bulletin board readers 
know better, but if you hear others making these comments, please feel free 
to correct them! :-)

1. "You're signal is not quite as loud as the middle beacon so you are OK!"
Remember, this is not the GB on AO-13.  The middle beacon is about 10 dB 
louder than your signal should be.  Do NOT try to equal the strength of the 
middle beacon.  You'll only drive up the AGC for everyone else.

2. "Something must be wrong with Leila, my signal isn't that strong and it 
hit me."
Remember that Leila doesn't know what your downlink signal sounds like, it 
only knows about your uplink.  The U-band patches may be receiving you very 
well and the receivers on AO-40 are incredibly sensitive, but because of 
range and offpointing, your downlink may sound weak.  Still, you are 
exceeding the input level and Leila will respond appropriately.  When the 
S1 was functional, we had a DRAMATIC example of how well AO-40 can hear us, 
when the downlink isn't the limiting factor.

3. "Leila hits some folks more than others."
This may not be a misconception and is related to how you speak, 
essentially the duty cycle of your voice.  Along these lines, Leila seems 
to almost ignore CW and SSTV.  However, the AGC, does not, so please keep 
your power low.  CW, in particular, hammers the AGC very hard.  There is no 
reason to run more than QRP for CW on AO-40.  Less than a watt will get a 
good CW contact if the pointing angle is remotely good.

4.  "Leila is broken because it hits blank spaces in the passband."
Leila does hit apparently "dead air" but it's not broken.  We're not 
completely sure what the cause of this is, but it may be related to high 
powered RADAR signals.  Along these lines, it is instructive to watch the 
U-band AGC which often shows 9+ dB of suppression when the passband appears 

5. "They've turned down the transmitter power."
There is no ground control of transmitter power.  The AGC is not adjustable 
from the ground.

6. "When they open the solar panels and turn up the power, the signals will 
really be strong."
....as above.

Testing and development continues on the 3-axis control system, to account 
for significant changes in our final orbit, the mystery effect, and the 
loss of some sensors.  Expect further feasibility testing and announcements 
on this shortly.  We are approaching the end of the favorable solar angle 
"season", so within about one month we will have to either initiate 3-axis 
control or offpoint for several months until the solar angle improves.  No 
shift to 3-axis control will be made without adequate testing of a 
mechanism to revert back to spin control.

--- S.E. Mills, W4SM, for the AO-40 command team

  Stacey E. Mills, W4SM    WWW:    http://www.cstone.net/~w4sm/ham1.html
   Charlottesville, VA     PGP key: http://www.cstone.net/~w4sm/key

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