Radio Shack HTX-242 COS / COR Mod

This is a mod for the Radio Shack HTX 242 radio.


It allows this 2 Meter Ham Radio mobile to allow COS /COR sense to be used for a repeater RX or other use requiring squelch or signal sense.

Open the bottom cover on the radio by removing the 4 screws.





On the radio's front right, find the 3 transistors about 1 inch in from both the front and right side.
There is a resistor with a "473" printed on it, just below the top transistor. Tap off the RIGHT side of this resistor.






This will provide ~ +3VDC when no signal is present, and will drop to 0v when there is a signal.
This is a High to Low signal point. Most repeater controllers can be switched to select the correct setting. If not, you can make a small signal transistor switching circuit.