[amsat-bb] AO-40 Status, Orbit 349

["Stacey E. Mills" <w4sm@xxxxxxxxxx>]

2001-08-02 AO-40 Status
--------------------------------------
The command/RUDAK team currently plans to do testing and software loading 
on 2001-08-03 for one hour from approximately 0200U to 0300U.  This will be 
early in Orbit 349 (the latest NORAD keps, day 211, remain 1 orbit 
low).  By MA=36, testing should be complete.  If testing starts somewhat 
earlier, it should finish earlier, as every effort will be made to limit 
this to about one hour.  During testing the passbands will be closed and 
the middle beacon will be off or intermittently off and on.  Once the 
middle beacon is back on continuously, the passbands will have been restored.

Finding Yourself
------------------------
I get questions about once a day regarding the transponder frequencies, 
equations, etc.  In truth, I have not measured these any more precisely 
than was done just before launch.  This is something that anyone with 
proper, calibrated equipment and accurate keps can do.  As a note of 
caution, many downconverters, drift considerably in frequency with 
temperature, particularly if the LO crystal is not oven stabilized.  My own 
downconverter, which is otherwise quite good, drifts 0 to 20 KHz depending 
on outside temperature.  This is my main excuse for not making the above 
measurements.

It should be noted that the middle beacon is, almost precisely, in the 
middle of the passband.  So, to find yourself when the MB is active, here's 
the simple method that I use.  You may well have a better technique, but 
this works for me.

1. Note your frequency reading on the middle beacon.
2. Move your receive frequency up or down, about 100 KHz or so from the 
middle beacon, to a good clear region near the top or bottom of the 
passband with no one around +/- 10 Khz
3. Note the above offset from the MB frequency, for example, +110 KHz
4. From the chart, calculate the middle frequency of the uplink passband 
you want to use.
5. Move the transmit offset amount in the opposite direction, for example, 
-110 KHz from the mid-band frequency.
6. Make a calculated or estimated doppler adjustment to the above transmit 
frequency.  Early in the orbit, AO-40 is generally moving away from you, so 
the Tx freq. at your QTH will have to be somewhat higher, to give the 
calculated Tx. freq. at the satellite.
6. Transmit an intermittent carrier and keep the transmit frequency 
constant (please!).
7. Tune the receive frequency to find yourself.
8. Note the Rx/Tx frequency values and calculate your equation, or set this 
offset in your rig as required.
....off you go.

The above technique is relatively fast, it avoids the middle beacon and 
should avoid stepping on other users.  The passband of AO-40 is 250 KHZ and 
finding an dead spot near the top or the bottom for this is not difficult 
(at least for the moment), even with lots of activity, much of which seems, 
for some reason, to cluster in the 2401.350 to 2401.400 region.

Once you have done the above once or twice, it is seldom necessary to go 
through all the steps again, and you should be able to find yourself 
quickly at the high or low end of the passband, well away from the beacon 
and active QSO's.

..good luck and enjoy!



-- 
  ________________________________________________________________________
  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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