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@amsat.org, and those with special mode requests to continue to submit them to ao51-modes@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