This is pretty much covered but here is what I learned as a CBer back in the mid 90s. No I was not a trucker. About the max height unless mounted one front and one rear is the standard 4.5' whips. What happens is if they are any larger is it will send the signal from one into the other and it cancells them out. If the tips of the antennas touch then they e=are too close. Now I a sure they are still around (I bought mine from a guy) a black box that boosts the output works best. My CB would reach around 27 miles. I heard some guys that could play skip with like Mexico and stuff. Now mind you it is an illegal mod. They are hard to find. If you have anymore questions just ask.
