Re: [amsat-bb] Notes on 2.4 GHz beacon

[Clifford Buttschardt <cbuttsch@xxxxxxxxxx>]

Good to know that the 2.4 Gc downlink will be turned on MA 20-26.
For those of us on the West coast, the first window (MA 25) will be on 2
Dec at 20:30 UTC.  Then each day following at approximately 25 minutes
earlier.  Those in Southern California will see the bird a bit earlier and
those North a bit later of course.  Great opportunity!
   Nothing specific about these times, there just for planning purposes. 
Cliff K7RR

On Wed, 29 Nov 2000, Stacey E. Mills, M.D. wrote:

> Dear Group,
> 
> The 400 bps GB (telemetry just like the V-Tx MB) has been set up on the S1 
> transmitter (nominal freq. = 2400.2 MHz) from MA = 20 to 26. This is about 
> 2.77x6 = 16.6 minutes.  The MA chosen is a compromise of reasonable squint 
> angle and visibility.  The V-Tx will remain on during this time, as 
> well.  Keep a few things in mind.  First, the S1 antenna is highly 
> directional.  At squint angles greater than 35-40 degs, I don't know how 
> loud/weak the signal will be.  Also, at these relatively high offpointing 
> angles the normally right-hand circular polarization, may be predominantly 
> left-hand, which will also decrease the signal if you've got a right-handed 
> antenna.  Finally, as has been mentioned, doppler at this frequency and 
> this point in the orbit is going to be dramatic.  As a "guestimate", 20+ 
> KHz down is not unreasonable if the satellite is moving rapidly away from 
> you.  If you have doppler correction software, the current NORAD keps are 
> very good and should get you close to the frequency, but scan around.
> 
> BTW, whenever a change is made in the transmitter or antenna status of 
> AO-40, you may hear a change in the downlink signal (assuming the 
> transmitter you're listening to hasn't been turned off!!).  This is due to 
> two factors. First, the change in the loading on the 28v-buss caused by an 
> additional transmitter coming on or off line causes a small momentary 
> voltage change on this   buss and a momentary shift in the transmitter 
> output frequency.  Second, if antenna switching is involved, transmitters 
> are turned off for a fraction of a second for "cold" switching of the 
> antenna relays.  Users of AO-13 will remember this phenomenon.
> 
> 
> --
>   ________________________________________________________________________
>   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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