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Author Topic: Why Accommodate for Doppler on AO-91 Uplink?  (Read 970 times)
K6LCS
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Posts: 1995


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« on: November 24, 2017, 07:37:31 AM »

An interesting inquiry: AO-91 has Automatic Frequency Control built into it. So
why is it recommended to adjust the Uplink frequency for Doppler?

Lab testing of '91 "corrected" to  +/- 8.5kHz deviation in the uplink. Hmmm ...

Keep working it, and document your signal reports!

Clint


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Clint Bradford, K6LCS
http://www.work-sat.com
KF0QS
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Posts: 17




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« Reply #1 on: November 25, 2017, 11:45:36 PM »

I have yet to work AO 91.  However, I did check out the AMSAT BB and found this discussion of the subject (check out the link below).  Apparently, you can still try and get away without adjusting the uplink frequency throughout the pass, but will get into the bird better if you do adjust.  The AFC is meant to make it easier to uplink, but folks who adjust for doppler on the uplink will have a better chance of getting into the bird, particularly when competing with other users.

http://www.amsat.org/pipermail/amsat-bb/2017-November/065590.html
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K6LCS
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Posts: 1995


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« Reply #2 on: November 26, 2017, 09:03:25 AM »

Operators will be experimenting with it during "off-peak-time" passes ... In the interim, it is suggested that we DO accommodate for Doppler on the uplink, per the frequency chart here -

http://www.work-sat.com

Clint
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Clint Bradford, K6LCS
http://www.work-sat.com
WD9EWK
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Posts: 508


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« Reply #3 on: November 26, 2017, 09:32:24 AM »

I have yet to work AO 91.  However, I did check out the AMSAT BB and found this discussion of the subject (check out the link below).  Apparently, you can still try and get away without adjusting the uplink frequency throughout the pass, but will get into the bird better if you do adjust.  The AFC is meant to make it easier to uplink, but folks who adjust for doppler on the uplink will have a better chance of getting into the bird, particularly when competing with other users.

http://www.amsat.org/pipermail/amsat-bb/2017-November/065590.html

I think your statement I put in bold above will be the case with AO-91's AFC. Unless I know I have the strongest signals at the satellite, daytime passes are so crowded you won't want to rely on AFC. It can be a different matter for the overnight passes, and maybe things will be less hectic once the "new car smell" wears off AO-91. Until then, I'll probably continue using the 5 tuning steps to work AO-91.

73!
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Patrick WD9EWK/VA7EWK
http://www.wd9ewk.net/ - Twitter: @WD9EWK
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