Perfect antenna location on big trucks?

On top and in the middle of the trailer would be good if the top is metal. Other than that, depends on the truck and your options are limited. 20 miles is a stretch on 19 except late at night when it's quiet.

 

I was told at OKC that as far out on the mirror as I could get on a 379 Pete. However after the way my Connex 3300hp sounds after he worked on it I'm not sure to believe it

 

Take a look at what other truckers do and that's what it takes. Usually you see antennas on top of the mirrors on the big rigs. From that position, you can achieve a height which won't exceed what's needed without hitting bridges etc, and be as far to the side as practical for the signal to "see" around to the rear. Twin antennas can provide some benefit, but it takes a lot of tweaking and special installations to get those benefits, which most drivers don't seem to want to bother with. See this site for lots and lots of info:
KØBG.COM

 

He means the RF signal gets around the rear of the big trailer that your trucks pulling. Haveing dual antennas on a big truck causes your signal to be more forward and rearward, rather than omni directional. Most drivers don’t care about distance to the side of their truck, mainly the truck in front or behind them. It’s called co-phasing (twin) antenna system, something they figured out that works well on big trucks back in the 50’s and 60’s.

 

The main drawback to the dual antenna system is that it can be more work to install, as Meteorgray pointed out. The radio basically sees both antennas as one antenna. So if you need to lower your SWR by cutting off 1/4 inch of the antenna on the passengers side, you need to cut 1/4 inch off of the drivers side antenna too. Both antennas need to be treated the same as far as making adjustment, therefore a lot more work. Also the antennas need to be 9 ft apart (1/4 wavelength for the cb band), although some guys claim you can move them closer for greater gain. I have no idea if thats true. As with all mobile antennas, they work better on a metal vehicles, unfortunately the modern trucks are going to fiber glass bodies which makes even a single antenna system difficult to tune.