[dajjhman] wrote in to show us how he added a microphone jack to the handset of his Yaesu radio while retaining the DTMF functions. He states that there were some adapters available on the market ...

It relies on the fact that almost every ham radio designed for field use incorporates a DTMF encoder in the microphone or in the transceiver itself. Hams have used Touch Tones for in-band ...