I didn't even think of two ways. Trying to tune a VOX would be rough, so a old fashion keyed mike would have to work.
The frequency determines the range characteristics. AM will follow the curve of the earth, but get absorbed quicker, FM and higher is straight line, so you could bounce off the ionosphere for greater range, given same output wattage.
There's sure to be a unit somewhere that will control multiple outputs, but your still probably talking cables plugged into it and then one connected to the speakers.
Then there's the mounting issues. I wonder if just a holster for the hand unit wouldn't be the easiest solution.
Heh, I can just see a dirt bike with electronics mounted across a bar above the handlebars , you'd need to install an extra battery, trick out the stator, and run dual regulators. It would pretty much destroy the low profile. Might as well put a 600 watt speaker bank on each side of the electronics array. roflmao.. you'd be pimpin..
As for the units I got, you are correct, it is pretty much line of sight only. We were able to hear each other but very garbled when we rode parallel one block apart, then it got clear when we were line of sight again.
So the ones I have won't work if someone is a mile away in a forest, unless there is cell coverage, the we could just call.
You could just take a hand held CB and run the output through an amp. In the military we used single side band AM with 1000 Watt output, and could talk half way around the world on a good day. The only problem with that is the amp will draw a ton of power and it's illegal, you could blow out local receivers. It used to be common on truckers with the old 23 channel. I haven't kept up with the technology in 20 years, and my HAM license expired a long time ago.
I'm still going to look up those radios, throw a set in the hydro backpack. Could really save the day.