AEA COMPUTER PATCH CP-1 Instruction Manual page 25

Some customers who have transceivers w ith a RTTY FSK position
built in have asked how they can use their CP-1 w ith FSK. Figure 1
shows a simple c ircu it consisting of a small signal type NPN transistor
(2N2222) and three resistors. This c ircu it can be wired inside the CP-1
and then connected to the DEMOD O UT jack (on rear panel), provided
the PCB traces to the Demod Out jack are CUT. Note that this circu it
gives low MARK, high level SPACE output. For high MARK output,
another inverter transistor stage should be added (SEE FIGURE 2).
Figure 2 shows a circuit used fo r SPACE low, MARK high. CP-1
serial numbers 1100 or higher already include the circu it of Figure 2. It
is Q13 and associated components. To make use of this circuit, lift the
middle leg of Q13 and connect it to pin 2 of the TTL plug.
For serial numbers less than 1100, wire the circu it in Figure 2 on a
piece of perf board and install it in the CP-1. Connect the output as
shown to the DEMOD O UT jack as per instructions above.
APPENDIX "D"
FSK APPLICATION