I would strongly suggest don't buy a Cobra 75 WX, WSTX, whatever it is (or any variant thereof). They seem to have the poorest sounding microphones I've ever come across. And unlike most hard-mount radios, you cannot swap the mic out for a better (aftermarket) one either (not without doing major microsurgery on the unit anyway). Our group almost always endures the muffled sound of at least one of those units by a person who unwittingly bought one when we're out with a large (or new) group. Some comments go along the lines of: As bad as two soup cans with a string, but with socks stuffed into the cans. Occasionally it
is that bad, they can be completely garbled, depending on the person's voice characteristics.
Cobra once made very good units, but except for a few of their "legacy" units (the 29-LTD and 148-GTL for example), they're junk nowadays (and even the legacy units are not as good as they once were).
If an all-in-the-hand-mic type unit is what you're after, get the
Midland 75-822. It is a MUCH better sounding unit, and to top that off, you have the freedom to use it as an actual hand-held radio too (though not very effectively due to the extremely short antenna, but it'll still work fine for spotting another driver thru a trail obstacle).
Of course even the Midland falls far short of the good clean sound you'd have with a
Uniden PRO-520XL ( a small under-dash unit). And the Uniden is FAR cheaper to boot.
I am far from an expert an cb antennae and the likes , but a good friend of mine is. He says actual antenna length does not matter but that the length of cable and antenna should be divisible by 3 foot. Because the CB radio waves are 3 ft from peak to valley. I'm sure some one with more knowledge can correct me if I'm wrong.
Yeah your friend is completely wrong (first time I've heard something about a 'divisible by 3-foot' thing
Usually people tout 18 feet, which is also wrong for many reasons).
Length of the antenna itself matters immensely, not just for CB, but for any radio, transmitter or even just a receiver. A very short antenna (less than 1/8 wavelength, or about 4' for CB) has a very small (or steep, in layman terms) radiation resistance (a tiny fraction of the 50-ohm system impedance) and it only gets steeper the shorter you go. This causes most of your transmitted energy to be dissipated as heat (resistive losses) in the antenna's load coil (basically it works more like a dummy-load than an antenna).
Best length for a (vehicle-mounted) CB antenna is between 102-108". This represents approx ¼ of the 11-meter wavelength of the CB band and provides about a 40-50 ohm input impedance, which matches well with the 50 ohm output impedance of the radio unit.
However I also know some people don't like antennas that tall on their vehicle, so shorter-length antennas are commonplace. However, know that if you go
too short, you come to a point where performance starts to drop off extremely fast (falling off the "knee" if you were to graph it), which is generally right about 54-60" for CB antennas.
IMO, a 60" antenna is a good compromise for those who don't want a full 102" tall one. Field tests I've done showed about a 2-3 dB difference between antennas 60-66" tall, and a 102" tall antenna, which in most cases is difficult to discern. Testing 36" and shorter antennas however showed large drops in both transmitted and received signal strength, even though the SWR was good.
Length of the antenna cable is irrelevant when your SWR (match) is good. If changing the cable length affects your setup significantly, then it's because you have a bad SWR (mismatch) and/or a poor ground somewhere. The only thing important in regard to cable length is that you have the shortest length practical, as this will minimize the losses in a longer-than-necessary length of cable.
The Firestik link posted earlier is mostly good, but even there, I still found plenty of mistakes.
I have the 5½' tall
Francis CB-26 Hot-Rod antenna mounted on a triple-magnet mount similar to
this one on mine. A
spring keeps the antenna from getting damaged or knocked over by low trees and/or drive-though overhangs.
Regarding comments earlier about MURS, GMRS, etc., I do have to agree, the 27 MHz segment of CB radio, due to having had no significant regulatory updates in decades, has become quite antiquated since each of those other services generally uses FM where squelch circuits work far more effectively to block noise & static from busting through the speaker while driving through towns or other populated areas. Of MURS, GMRS, FRS, and HAM, I think MURS is by far the most versatile, although for whatever reason it has not gained much popularity, probably partly because there are no commercially-made mobile (hard-mount) radios available, you have to repurpose a hand-held if you want a mobile unit in your vehicle, or modify a ham radio or some other unit to work there. There are some hard-mount GMRS units that have hit the market recently that look promising, though to do it correctly you have to purchase a license (authorization) from the FCC to use a GMRS unit legally (though few do).