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Re: AO-51 Mode S Antenna question



Hi Ron!

By the way, thanks for the QSO this (Saturday, 5 April) afternoon
on AO-27.  I was parked SE of Flagstaff AZ, dealing with a strong
wind while working that pass.

><snipped reference to K5GNA-modded S-band downconverter>
>
> With this setup, can I mount the Mode S downcoverter and have a
> reasonable chance at getting it to work or should I look at some type of
> patch antenna to get better signal picket ?  Is mode S a little less
> unforgiving so that I have to have it more directed at the satellite
> than I can get away with on my current VHF/UHF antenna setup ?

For AO-51, you can receive it easily with just the dipole and corner
reflector on that downconverter.  Some have replaced the dipole
with a Yagi, and you could even go with some of the 2.4 GHz WiFi
antennas.  AO-51 is transmitting on S-band at 2 or 2.5W when it
is there, so in a low orbit you should be able to hear it.

As for dealing with the Doppler at S-band, computer-control of
your downlink radio is desireable.  It *can* be done manually, but
with the shift of around 55 kHz +/- you are adjusting the receive
frequency almost all the time.  When I have worked AO-51's
S-band downlink, I would not have the benefit of computer control
for my portable setup.  I would be almost constantly adjusting the
downlink frequency, but with 5 kHz tuning steps on my downlink
receiver (VX-2R connected to the downconverter) I did OK.

Good luck and 73!



Patrick WD9EWK/VA7EWK
http://www.wd9ewk.net/
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