[amsat-bb] AO-51 CTCSS/PL tone

Andrew Glasbrenner glasbrenner at mindspring.com
Wed Dec 13 14:07:21 PST 2006

The primary FM repeater modes on AO-51 have historically required a 67 Hz 
subaudible tone to access the satellite. This tone was originally designed 
to allow the downlink to be switched off when the satellite was not in use. 
Because of the difficulties in power management between orbits seeing heavy 
use and those with light use, this scheme is not practical with the current 
software onboard the satellite. The use of the subaudible tone access has 
also been problematic when trying to identify the seemingly growing 
interference issues experienced on most 2 meter uplink frequencies, and when 
the satellite is over areas of heavy use. Furthermore, despite the near 
ubiquity of subaudible tone enabled radios in North America, many areas of 
the world have limited or difficult access to this type of equipment, even 
in commercial off-the-shelf gear.

After careful evaluation and discussion, I have made the decision to suspend 
the subaudible tone access on AO-51 until such time as it becomes necessary 
or useful for power management. Please continue to listen to the downlink 
before and as you transmit to reduce QRMing other users. This means full 
duplex operation is the most courteous and efficient means of operating the 
FM satellites. Also, please continue with renewed vigor to help identify and 
eliminate both non-amateur interference, and amateurs operating outside of 
the established bandplan that interfere with our satellites.

I encourage those with questions or feedback regarding this policy to email 
me at ko4ma at amsat.org, and those with special mode requests to continue to 
submit them to ao51-modes at amsat.org for consideration. The Operations 
Committee will soon begin to put together the schedule for the upcoming 
month, and your input is welcome.

73, Drew Glasbrenner KO4MA
AMSAT-NA VP Operations
AMSAT LM 2332 

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