As Mitch mentioned, I worked out a way to do this. Both the local head and the one connected with RemoteRig work in parallel, simultanously. If you've ever played with a TS-2000 with the RC-2000 panel attached, it has the same feel (except the TS-480 head is much nicer than the RC-2000.)
My scheme is based on a B and B Electronics PTC serial port combiner. The PCB I developed, which Mitch posted the link to, merely does TTL-to-RS232 level translation for use with the serial port combiner, using the same 6-conductor modular jacks on the TTL side as the radio-to-head cable.
It works great and I like the idea of having local control while the remote is in use.
I also developed a small three-channel mic audio mixer so that the local mic, RemoteRig, and an auxilliary mic input which can be attached to, for example, your computer sound card or the speaker output of a TM-D710A when using as the Transporter for a Sky Command setup. To facilitate local use of VOX, the local mic audio is always live except when the RemoteRig or Aux PTT inputs are active, in which case the local mic audio is muted. However, if the local operator picks up the mic and presses the PTT the local mic is given priority and the other mic inputs are muted, giving the local operator the ability to censor the remote operator. All accomplished by a quad op-amp, 4053 CMOS switch, and two CMOS logic gate chips, the 4025 and 4001. Eight-conductor modular jacks with Kenwood mic standard connections are used, and the mixer draws it's power from the 8V power on the mic line from the radio.
Between the serial port combiner and the mic multi-source, my TS-480 interface to RemoteRig allows for a great deal of flexibility while retaining a great deal of simplicity due to use of modular connectors wired to be compatible with Kenwood's.
Not everyone will require or even desire to emulate my setup, but for those who do, the ExpressPCB designs are available free of charge. (See the link Mitch posted.)
73
Brad KB9BPF
