Titre: Better RX with BayCom From: PY2IAV@PY2ZE.SP.BRA.SA To : BAYCOM@WW Hi everybody, thanks for reading. For you who use serial BayCom modem with TCM3105 at 1200 baud. Often this circuit is used not at audio power level got from speaker circuitry like external connector. I prefer extract audio signals at low level, before volume control, because this leads to a more confortable operation, since I can keep volume control off all the time. Usually this procedure is done at pre-amplifier output or at volume poten- ciometer. Most of Kenwood VHF transceiver, and also Alinco (some Yaesu, too) utilize a 8 pin standard microphone connector. In all of them, pin #6 is free of use (NC = not connected), and this pin is very suitable to put out the low level audio to the BayCom mode. This seems to be a must: only a 3-way shielded cable is enough, without another cable coming from external speaker rear connector. To improve this, locate a good place in rig circuitry to extract the low level audio signal, like the high fixed level edge of volume potenciometer. Solder a small capacitor about 50 nF at this point and also to pin #6 of mic jack (the exact value is not important, and isolation may be very low). If needed, use a shielded cable to wire between. And it is done!!! However (why not?), some trouble may occur. The fact is: most of 1305 BayCom implementations have low impedance input, which is a practical short-circuit for the high impedance that is caracteristic of low level signals. So, the audio level comes down, receiving may be deteriorate whith a lot of rejected frames, and this overload can be seem dangerous to you rig. Solution? Yes, there is. Observe your BayCom modem. Input circuit may look like this: R1 C o------/\/\/\/\-----x-------||-------- ..... | \ R1 is about 100 Ohms / R2 R2 is about 100 Ohms \ / | ----- / / / Simply wire-out the grounding resistor R2. Unsolder it and now the modem has high-level input impedance. Gee!!! Good packeting, OM. 73, Savio PY2IAV @ PY2ZE.SP.BRA.SA