Attached is a cheat sheet for those looking for a proven way to interface the SunSDR2DX to an Elecraft KPA1500 amplifier.
Using an HD15 cable wired as shown, the SunSDR2DX PTT enable and BCD band data are automatically passed to the Elecraft KPA1500, as described in the books.
The "Ext Ctrl" band setting table are also shown for the SunSDR2DX.
Setting it up like this, the amp now automatically follows the rig band changes, and the TX enable (PTT in) for the Elecraft are also satisfied.
Enjoy, and 73
N1KIN