Discriminator Output:

"Although  it  will  void  your warranty, it's easy to add a baseband audio
 output jack to connect the BC9000XLT to a CTCSS or DTMF  reader,  such  as
 the  CSI  CD-1.  You  only need to drill a hole on the rear panel, mount a
 phono jack, and wire it to the  appropriate  point  on  the  main  printed
 circuit board (Figure 1).

 Drill  and  deburr  a  1/4"  hole through the BC9000XLT rear panel, in the
 vicinity of the jack labeled DC13.8V. Mount an RCA-type phono jack  (Radio
 Shack  #274-346)  through  the hole and fasten with the supplied hardware.
 On the top of the main board, find the test  point  labeled  TP3,  located
 about 3  inches  behind  the AUX jack.  You can choose to solder a wire to
 TP3 from either the top or bottom of the printed circuit board,  but  it's
 easier  to  solder  it  to  the  bottom  because  the bottom solder pad is
 larger.

 Connect a wire from TP3 to the center pin of the newly added jack.  It's a
 good idea to use very small diameter coaxial cable,  e.g.    RG174/U,  but
 ordinary hookup  wire  will  suffice.    If  you  use hookup wire, connect
 another wire from the ground lug of the new jack to a ground  pad  on  the
 printed circuit board, or place a solder lug under the nearest screw which
 holds  the  board  to the chassis and solder the ground wire to the solder
 lug...."  (Copyright 1996, Bob Parnass)