Originally Posted by 2five22
Get a CB antenna based on the wavelength or an appropriate wavelength fraction [1/2, 1/4, loading coil, etc.], not based solely on how many feet it is. 100 feet is not 10 times better than a 10 foot antenna.
Sorry for the confusion, I was posting from my phone.
2five22 is much more accurate then I was.
Warning: detailed brain dump follows:
Most of your fiberglass wrapped antennas are actually the same wire length (108"), however they compress the "length" of the wire by looping it around a piece of fiberglass.
In the commercially available lengths of fiberglass antennas my doubling math works. This math does not work in antennas in general.
This kind of antennas come in 2ft, 3ft, 4ft, and 5ft lengths. This kind requires tuning with a SWR meter to get them dialed in or they won't work well. They don't come with a meter when you buy them, but the meters are like $20.
There is also a 108" steel whip antenna that does not require tuning and works better then any other kind of CB antenna on Jeeps. The problem is that this antenna is ~8ft tall.
108" whips are fun in the desert and on the freeway, but not very useful anyplace where you are either going fast offroad (sand) or going under stuff (trees) because it whips around and hits stuff. If you want one of these, you need a "heavy duty" spring with the antenna, as the antenna designers assumed you would run one. The length isn't correct without the spring. The "heavy duty" springs are all standard lengths.
In case you didn't already guess, I am an engineer by trade. Since antennas are not that expensive, I put a quick disconnect on my CB setup and got one of each antenna to try them all. I then resold the "not so good" ones on craigslist.
I've found in my personal experience that the 2ft ones are garbage and not worth your time, I personally could never get it below 3 (in the "not good range") on the SWR meter. The 3ft ones are very picky about their mounts, they would get good SWR on the hood mount, but not on the license plate mount. The 4ft and 5ft ones work reasonably well but require a little tuning to zero them in.
In my testing, the 5ft antenna got about the same distance from my base station's antenna as the 4ft one did in a dense urban area. It got about 1.5 miles despite having to go through many building full of computers. This gets 2-3x better in open areas to about 4 miles reliably, maybe 5 miles if you are really lucky.
The furthest I've gotten the 108" whip to work to a base station antenna was about ~8ish miles in open terrain. 6 miles is a more practical working distance for my whip when I'm not in the city. In the city I'll get 2 miles at best.
I got rid of the 2ft and the 5ft and kept the 3ft, the 4ft, and the whip antenna. When I'm in the city and I park in garages I'll keep the 3ft on as it is the same height as the top, even though the 3ft one really doesn't work. The 4ft is what I run when I go out to nature.
I use the whip only when I'm goofing off with the radio.
Some other random thoughts:
Don't run dual antennas on a Jeep. They are harder to put in, and really don't work that well. I got much better results with a single antenna then with dual ones. Base loaded (magnetic) and mid loaded (trucker antennas) kind of work on a Jeep, but only get ~60% to ~80% of the range of what the top-loaded kind mounted to the same radio in the same mount get.
NGP (no ground plane) antennas do work on the Jeep, but not as well as the regular kind. They also cost more.
Don't buy crappy no-name antennas. I saw a cheapo ($3) 4 ft antenna in Fry's Electronics so I picked one up to see how it works. In short: it didn't work at all. It got about 300 yards, which is less then what my handheld CB can do.
If you want to be busy for a week, here is some "light" reading: Tech-Docs Index
If you only read one thing, read this: Listen Up
Also: what is the "base"? Is this a house? They make really nice base station CB antennas that work amazingly well, but they are 1/2 wave (~18 foot) in length so not practical to deploy from a moving vehicle.