Build A COS Detector

We need a way to detect the presents of a carrier on the receiver since the radio does not has a audio/squelch board.  There are several ways to accomplish this.  We could use a CTCSS decoder to provide the COS but that requires the user to us PL which may not be desirable during times of emergencies.  We could build a COS detector like the one below or we can fiddle around in the radios receiver to see if we can find a way to detect the presents of a carrier.  I'm still working on the last option.

This simple circuit measures the noise on the discriminator audio, when the noise level falls the circuit enables the COS output.  C1 along with the 47K resistor make up the high pass circuit. 

Another option is to build the famous Micor squelch circuit.  The details of this circuit are detailed at Kevin's site, the repeater technical builders page.