I put a cb in my truck a little awhile ago and was wondering if 2 antenna's are better then 1?

 

Two antenna's are better than one, but it depends where they are. On the other hand they won't be that much better if you place the first on in a great position!
The ideal position is the center of the metal in your truck that would be the back center of your cab. An antenna's reception is based on it's position relative to the ground plane. Simple put this means if it is in the center it will radiate and pick up signals equally all around the the rig. If you put the antenna in the front center (middle of the front bumper) it will receive better from the rear.

Having said all this the biggest factor in your reception will be where you are relative to the radio you are talking to. Height is the biggest factor so a higher antenna is the best. Bottom line is decent reception is a 7 mile radius without any mountains, hills or buildings to block you, so buy fiberglass antenna as tall as you can handle and mount it as high as you dare!

Don't get sucked into the more power is better game, it helps but not as much as antenna height. Also more power has huge problems with reception in radios that are too close, which is true of CB radios in other rigs.

 

Great post and explanation of how ground plane works....
While dual antennas look cool, it is important to know that you should space them about 8 foot apart from each other...

When you do decide to do an install, find someone with an SWR meter if your CB does not have one built in. Your radio will operate most efficiently when the SWR is 1:1. I would recommend doing what basilkies says and mount a good 5 ft fiberglass antenna. Firestick, and Wilson are good brands and have an adjustable tip. (Adjustable tips will help you get your SWR down as close as possible to that 1 to 1 ratio.)

 

I agree with all that has been said except that power doesnt matter. A friend and I both had K-40s mounted on top of cab and top of van. We both had 100 W amps and we talked over flat ground mobile to mobile 48 miles.

 

I suspect that something else was helping you or that the fact that your antenna's were fairly high on your rigs and helped more. Antenna height will help more than power because radios mostly talk when they aren't blocked out by the earths curvature. Six feet off the ground this is about 7 miles the distance increases as your antenna gets higher.

Also, the word mobile is misleading in your comment because I'm guessing that you were both parked which is more like a set location operating with a generator (your alternator or/and battery). My buddy and I played around with extra power and found it to have only one advantage, blasting over the guys that had less, but the price was a distorted voice or signal that was annoying to listen to when at closer ranges.

 

We were both moving at the time we were talking. We added the power to combat the skip that was really bad at that time. There was a guy called "Music man" from FLorida that would blank out the whole area when he keyed up.

 

Ah, there's that "other" thing I was talking about. clouds and skip! I'm not sure how power helps on skip days but it must be an advantage to be able to blast over multitudes of talkers.

 

I have the antennas on my truck bed one behind the drivers seat as far as I could put it to the left n them same thing on the right side n both r 3ft fiberglass whip antennas

 

Those 3 ft dual fiberglass antennas are made for over the road big rigs. The mirrors that they are generally mounted to are 7 to 8ft off the ground, and are approximately 8ft apart from each other.

Like others have posted in here have said, I recommend a centrally mounted 5ft fiberglass antenna with a tunable tip.

 

yeah i would of gotten a 5ft fiberglass whip antenna, but i wouldn't be able to get it in the garage unless i take it off all the time