Military data tranmission X-Codes.

The X-Codes are generally associated with "link 11" nets.

These code are like the radio 'Q' codes and can be treated
as a question, a command, or, an answer.
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XAA - Transmitting primary set-up sync tone.
XAB - Synchronized with primary sync tone.
XAC - Transmitting secondary set-up sync tone.
XAD - Synchronized with secondary sync tone.
XAE - Transmitting net operations sync tone, sent by Net Control Stn (NCS).
XAF - Synchronized with net operations sync tone.
XAG - Sending data to NCS.
XAI - Synchronized for short reports with station...
XAJ - Mode 1 - transmitting mode 1 ping-pong.
      Mode 2 - transmitting mode 2 ping-pong.
      Mode 3 - transmitting mode 3 ping-pong.
XAO - Not receiving alligator data.
XAP - Receiving alligator data.
XAQ - 
XAR - 
XBG - Set transmitter power to maximum.
XBH - Set transmitter power to minumum.
XBL - Experiencing technical difficulties with equipment.
XBO - Alligator transmissions suspended for ...(specified time).
XBP - Alligator transmissions to recommence in ...(time specified).
XBT - Mode 1 - 
      Mode 2 - 
XBV - Maintenance complete and ready to begin transmissions.
XBW - Transmissions stopped to carry out maintenance.
XCB - 
XCC - Change your track (track number) to my track (track number).
XCJ - Cease data transmission of track (track number).
XCK - Is your track showing my track number ...(track number)?
XCL - Identify all parameters on ...(track number).
XCP - Track full data dump transmission.
XDA - Off air for maintenance, (duration usually specified).
XDB - 
XDD - Leave the net.
XJG - Transmit all available data on ...(track number).
XYI - Receiving a Mode 1 radar squawk code from track ...(track number).
XYO - I am not receiveing your PU.
XYP - I am receiveing your PU.

(This list is compiled from various sources.)