PL Tone Decode Pickup Point for COS (Carrier Operated Switch) Modification for the elderly Kenwood TM-411a.
I found the appropriate point through trial and error. I then run this point into an external PL Tone Decode Board then to a relay driver/relay for COS. Fortunately I did not damage the radio trying ! Schematics for a circuit to tie in a pl decoder board / relay from this line on my IRLP page. My 411A only had a plug for a Tone Encoder hookup but not decoder.