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RE: Contacts on AO-10



Regarding AO-10's fades and antennas:

>1) Immediately prior to a fade, the AO-10 transponder (and the beacon) will
>first drop in frequency by 30-40 Hz, then drop off rapidly as the power runs
>out.  The first and the second drops occur over the space of two or three
>seconds.

This is typical, as you say, of a power loss fade.  Either the sun is 
hitting the ends of the S/C or one or more solar panels/BCR's  are now bad.

>2) When the fade ends the transponder and beacon frequencies quickly
>stabilize at their original positions.
>3) The received signal strength is very steady until the frequency drops and
>returns to its pre-fade level as soon as the power comes back on.
>4) These observations were the same at near perigee and to about half way
>out (at my LOS)
>
>The interesting part about all this is that I could not detect deep fading
>of the received signal other than that associated with the loss of power
>when the sun falls on the end of the spacecraft.

In the past, it has been possible to detect the two types of fades.  One 
with freq. drop, ie. a power fade and one without, ie. an antenna pointing 
fade.  If one or more of the solar panels or their matching BCR's doesn't 
work any more, that would give you a power fade during a very slow 
rotation, without the sun hitting the end of the S/C.

>  Given the above, the
>satellite must be using the *omni* antennas rather than the high gain
>antennas as was previously believed.  If the high gain antennas were in use
>there should be much more deep and regular fading of the signal as the
>satellite rolls/tumbles on its axis.
>Comments?

The two strongest arguments that the hi-gains are on (or at least were on) are:

1. High signal levels occasionally obtained near apogee, inconsistent with 
no-gain omni.
2. The downlink and uplink antennas appear to be circularly polarized.

...however, things may certainly have changed.
Anyone currently noting polarization on the  downlink or the effect of 
polarization on their uplink??



--
  _______________________________________________________________________
  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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