I have just installed a GM300 for my transceiver and I configured it to put out TPL /DPL det on the accessory plug. Signal looks OK about 2.59 volts for low and 13.5 volts for HI. I can see this change correctly when I use TPL or when I don't. I set RTCM menu item line 12 external CTCSS to non-inverted. line13 External COR to 0 normal. The problem is audio passes into the system no matter if it has tpl tone on the incoming carrier or not. I can see the top green light (RX) on the RTCM module no matter if the carrier coming in has tone or not. I'm out of ideas on how to fix this. I want the RTCM to respond to the incoming CTCSS control line from the GM300. Any ideas on what is happening here????? Bill Hurlock CPCommunications 856-234-1661 Office 856-264-1010<http://www.totalrf.com/> Cell www.cpcomms.com<http://www.cpcomms.com/> WA2TQI