Go to Radio shack and purchase 3ea. 1n4000, or 1n4001, or 1n4002, or 1n4003, or 1n4004 , or any 1 to 3 amp silicon rectifiers.......

It should cost less than 2 bucks...... DO NOT PURCHASE SCHOTTKY RECTIFIERS as they have a lower series voltage drop. You want a silcon rectifier in the range of 1 amp to 3 amps.....

Put three in series. Each rectifier will provide a stable voltage drop of .6~.7 volt dc. Wire these in series with your 12 volts and viola, you have 10 volts!

The series connections would be: (follow the package illustration for clarification) Diode1-anode to Diode2-cathode to Diode3-anode.

You cab surround the three diodes with a piece of heat shrink tubing.

Now connect Diode3-anode to you transmitter battery connector positive terminal. Connect Diode1-anode to the positive 12 volt supply. Connect the 12 volt return (negative) to the transmitter battery negative input.

Viloa, you now have a stable 10 volt source.