Originally Posted by necromancer_tat
An antenna is designed to work for a certain frequency range, usually determined by the length of said antenna.
CB radio frequency range: 26.965 MHZ to 27.405
Car stereo FM frequency range: 88 megahertz to 108 megahertz
Car stereo AM frequency range: 535 kilohertz to 1,700 kilohertz
So a CB antenna would be between 8.68 to 8.54 feet long at a quater wavelength.
On FM a car stereo antenna would be between 2.66 and 2.167 feet long at a quarter wavelenth, so a full wave length would be between 10.62 and 8.67 feet long.
Most shortened CB antennas are longer than the are physically tall due to them having coils of wire wound in spirals around or inside the antenna shaft, that is how they achive the compromise of making the antenna shorter overall, but still having it function well.
A CB antenna used as a car stereo antenna would perform fairly decently, but a car stereo antenna being used as a CB antenna would perform poorly.
One thing to note though is that using a CB antenna as a car stereo antenna has the potential to cause your CB to become directional in how it transmits and receives.
Your explanation is very helpful and I think I might just go with a long whip mounted either on the rear bumped or (if I can find a suitable one) to the top of a spare tire carrier. I know it will work fine, but seeing as you seem to know about these things I was wondering if the body of the Jeep itself would inhibit the antenna's function (for example, transmitting to a forward location when the whip is attached to the rear of the Jeep).