Here are three PDF files of Eagle board designs for the SX-28.
All are single sides so that the user can make these at home.
The red is a wire jumper on the top side of the board.
The blue is all the printed circuit on the bottom.
Included are the following...
A. An SX without regulator and two ribbon cable interfaces.
B. An SX with a TO-92 7805 regulator and two ribbon cable interfaces.
C. An Sx without regulator, but with the MCP3208 ADC and three ribbon cable interfaces.
One can easily use headers instead of the ribbon cable interfaces. Power is intended to be limited to low power uses.
All have an SX-key programing interface.
IF YOU LIKE WHAT YOU SEE, YOU CAN USE OR MODIFY FOR YOUR OWN USE IN EAGLE.
I USED VER 7.2XX