Thanks for the replies.
FKP- it's not so much that it's demanding, it's a combination of (1) only having 1 pair, (2) on a mountain which is shaped in such a way that TED-400's don't work reliably (so I assume other brand transmitters as 2-way radios have issues also without a repeater) (3) where we need to transmit the serial feed to the top (there's only phone/data coverage at the top).
"You are going to end up with too much data noise if you try what you are suggesting and the headset will end up being discarded.": is it just the headset which would be compromised, or the start impulse also?
Rib Mtn Timer: we have 2 sets of TED-400's which I agree work well- we've used many times without issue. The problem on some hills is simply the local geography. In this case it's a MTB downhill, which starts a way behind the top of the hill, the signal simply does not curve far enough.
It may just end up that we run another pair on the ground, although if we can run a start impulse + RS485 on the same cable, that's an option, and we can find another way to transmit voice.
Thanks,
+M