I drive a '00 Peterbilt 379 with sleeper. If I were to use two antennas, and they were both tuned for say like 1.2 give or take 1, would I still have to have an 18' co-phase coax to make this work? What I'm trying to ask is will a shorter co-phase coax work or do I have to use an 18' co-phase coax? Anybody confused yet? I think I am, lol!