If it's simply an encoder, you should be able to figure out the PTT line and Tx Audio Line's rather easily. First thing I would do is to take the lid off the unit and determine where the PTT relay is and using an ohm meter, verify the terminals. It will be a simple contact closure across two of the terminals. The next thing is to find the Tx Audio Line(s). Get an O-Scope or a simple Butt Set (Telephone Line Mans telephone) and have it generate a page, start by looking at each of the terminals, with exception of the 12vdc power and PTT that you have just found. Attach the minus lead to chasse ground and then do several pages until you find the correct audio + lead. Then continue chasing with the minus lead until you achieve maximum audio levels, if it’s a 600 ohm balanced line. Should not be that hard of a task.
What radio are you attempting to interface it to? You will have to have some way to set the Tx Level to achieve the desired transmit deviation, generally this is done using a service monitor but I suspect that you don’t have one of those so you can use a receiver and find where the unit starts clipping out of the receiver and back the level off by about 50% or so. If you have a pager you can also play with it to get a good decode. Generally, you don’t have to have a perfect tx level to get things to go.
If you are setting this up for public safety use, you absolutely will need to get a proficient radio tech to do the final adjustments.
Have fun, it should be difficult to blow any thing up…
-Mike
