The Spectra, while a great radio for analog, and configurable like all get out (multiple heads, handsets, etc.), doesn't have a good place to pick up true discriminator (flat) audio with enough fidelity to drive the mmdvm. It was made for analog service, and their detection circuit just doesn't extract a good signal for digital use. Add to that the self-destructing capacitor issues on both the motherboard and display board (which will destroy the traces if left unrepaired), and the fact they're over 20 years old at this point...there are better (and not expensive) options. I've used, successfully with no more than 5 wires to the back connectors (flat rcv, gnd on the rx side, flat audio in, ptt, gnd on the tx side), both the GM300 and cdm750 radios both on allstar via a URI and digital through the mmdvm. Program for 25k bandwidth (let the sw handle bandwidth limiting, etc...don't put the hw in the way), if using the 300s, make sure the jumpers are set correctly on the board, program up with rss for the 300, CPS for the cdm, hook up and go. I do suggest, if you don't block TG 3100 on brandmeister, that you have a decent muffin fan blowing on the rear of the tx; because 3100 is almost constantly keyed up. measured the fin temps with the fan on, and with almost constant us, never gets more than 10 degrees F above room temps... Just for the heck of it, I did connect up an old hamtronics 440 machine I had that was on my freq, and even it worked, because it is a true discriminator rcv and the tx input is through a varactor right to the oscillator...not that I'd ever keep that in service, mind you... Just some thoughts. -- Bryan Sent from my iPhone 6S...No electrons were harmed in the sending of this message.