Nearly any CB antenna (or HF ham radio antenna, for that matter) will be a compromise. You're dealing with a height restriction, so generally you're looking at antennas that are physically shortened and use electrical tricks to simulate the correct resonant length. Unfortunately, those tricks equate to lower performance.
This antenna option has the lowest RF performance, but the greatest functional and aesthetic appeal. You can mount it to parallel your existing FM antenna (assuming the Expedition puts the antenna on the front fender, I'm not familiar with that vehicle). Gives you adequate road performance, a small antenna that won't collide with most overhead objects, and only requires a couple small holes in the inside of the fender, under the edge of the hood.
If you can mount something a little more substantial, but still need to keep it shortened, a top-loaded fiberglass whip is the next suggestion. I use a pair of phased Firestik KW4-R antennas on the bedrails of my pickup. http://www.firestik.com/ They're cheap, durable, and available at your favorite truck stop.
Firestik has been around forever, my father used them on his trucks and buses, and I used a pair of them as a rotatable-dipole antenna for the 10 Meter ham band as a kid. Worked everything from Jersey to Japan. The most important thing to remember, and Firestik makes sure to remind everyone on their site and packaging, is to tune the antenna in its final installed position on the vehicle. An SWR meter is a must if you really want to squeeze all the performance out of the limited power you've got in a CB system (or a QRP ham system, which I operate regularly). Firestik tries to ship all their antennas a little too long, and you just gently unwind the extra copper wire from the top, snipping it off a little at a time until you get the lowest reading at the center of the band.
If you can swing it, Tugrik's suggestion of the full whip (though it'd be a quarter-wave, not a half-wave - a half wave CB antenna would be 17 feet tall!) will give the best performance (it's not shortened, no electrical tricks). Just requires bending it down to clear obstacles. Radio shack sells the 102" whip for $19.99 - pretty good deal.
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First suggestion - A fender mounted whip. http://www.hamstick.com/f11.html
This antenna option has the lowest RF performance, but the greatest functional and aesthetic appeal. You can mount it to parallel your existing FM antenna (assuming the Expedition puts the antenna on the front fender, I'm not familiar with that vehicle). Gives you adequate road performance, a small antenna that won't collide with most overhead objects, and only requires a couple small holes in the inside of the fender, under the edge of the hood.
If you can mount something a little more substantial, but still need to keep it shortened, a top-loaded fiberglass whip is the next suggestion. I use a pair of phased Firestik KW4-R antennas on the bedrails of my pickup. http://www.firestik.com/ They're cheap, durable, and available at your favorite truck stop.
Firestik has been around forever, my father used them on his trucks and buses, and I used a pair of them as a rotatable-dipole antenna for the 10 Meter ham band as a kid. Worked everything from Jersey to Japan. The most important thing to remember, and Firestik makes sure to remind everyone on their site and packaging, is to tune the antenna in its final installed position on the vehicle. An SWR meter is a must if you really want to squeeze all the performance out of the limited power you've got in a CB system (or a QRP ham system, which I operate regularly). Firestik tries to ship all their antennas a little too long, and you just gently unwind the extra copper wire from the top, snipping it off a little at a time until you get the lowest reading at the center of the band.
If you can swing it, Tugrik's suggestion of the full whip (though it'd be a quarter-wave, not a half-wave - a half wave CB antenna would be 17 feet tall!) will give the best performance (it's not shortened, no electrical tricks). Just requires bending it down to clear obstacles. Radio shack sells the 102" whip for $19.99 - pretty good deal.