I have had good success in obtaining a COS signal from an 'unknown circuit' by opening the lead to the front panel LED that indicates receive activity. Place the diode of an opto isolator in series with the LED and then use the transistor section of the opto isolator in your circuit as the COS signal. You can use the transistor to pull up a resistor to a positive voltage if you need a positive going COS ( with the other end grounded) or you can pull a resistor to ground for a negative going COS (with the other end connected to a plus voltage ).
I have no idea if your radios have this front panel activity LED, but most do. The PTT and mic inputs are pretty straightforward, and the speaker audio can be used in a pinch, if the knob is removed from the audio gain control to discourage folks from 'tweaking'. 73 - Jim W5ZIT --- On Tue, 7/1/08, dakaratcaptivereefing <[EMAIL PROTECTED]> wrote: From: dakaratcaptivereefing <[EMAIL PROTECTED]> Subject: [Repeater-Builder] RELM SMUxx Link Radio? To: [email protected] Date: Tuesday, July 1, 2008, 12:42 PM I've recently been tasked to link a couple of VHF repeaters with a UHF link.. not too difficult, however the link radio's provided are Relm SMUxxxx's, they are all programmed and ready to go. I'm just having trouble finding any good docs on locations to tap for Rcv/Tx audio and maybe COS in these radios. On the plus side, I've bought an extra controller for myself and have an extra mobile rig of the same model to experiment with before tackling the repeaters... might as well make a mobile remote base for my RV to play with while out fishing etc... Can anyone recommend a good starting point or some docs? Even better I like pics :) Thanks Dave - N0TRQ
