The 102" whip antennas with a 6" spring give a full 1/4 wavelength ground-plane antenna at CB frequencies (discounting velocity factors of various conductive materials). The higher the frequency, the shorter the antenna should be and vice versa. When tuned for minimum Voltage Standing Wave Ratio (VSWR) on Channel 19 (mid-band), the VSWR does not rise appreciably as you move to Channel 1 or 40... such antennas are relatively "wideband".

Full-length whips have better reception and a fairly low angle of radiation (transmission) for a 1/4 wave ground-plane antenna (meaning more power pointed along the surface of the earth where receiving radios are located, instead of up in the sky). HOWEVER, full-length 1/4 wave whips are seldom practical... especially in the woods. 

The 1/4 wave ground plane antenna depends on a conductive plane perpendicular to the antenna. Ideally, the ground-plane antenna would be mounted in the center of an all metal vehicle, up on the roof. With the birds eye view of the vehicle, the radiation pattern would be oval with more radiation out the front and back of the vehicle than out the narrower sides. If you mount the antenna on the left rear, the unit will transmit strongest to the right front. Kind of impractical to put a full-length whip in the center of the vehicle, on the roof, especially on a softtop.

Bowing a full length whip makes it overall less efficient than, say, a 3-5' continuously loaded whip, but you do have the option of unclipping the front if longer range transmission is necessary. The reason deals with polarization. While TV transmissions are horizontally polarized (the reason TV antenna elements are horizontal), most CB or other radio transmissions are (supposed to be) vertical. For maximum reception of received signals, and max transfer of your transmitted signal to a receiving vertical antenna, your antenna should be vertical. Also, if you look at the radiation pattern of a bowed antenna, there's very little energy going to the front or back of the vehicle (which are basically looking into the hole of the donut shaped pattern) and most of the energy is directed up in a wide weak area, down into the vehicle in a small, highly focused area (health risks?), and out the sides of the vehicle in a wave 90 degrees to most receiving antennas.

 The radiation pattern is a donut with the 1/4 wave whip up the center. More ground plane on any side (up to 1/4 wavelength) will concentrate energy in that direction. Less (or none) on any side will reduce the radiation in that direction. Tilting (or bowing) the antenna from vertical "squeezes" the pattern on the side the antenna is being pulled towards (and lowers the radiation pattern) on that side and does the opposite on the other. And finally, loading, as previously described effects the angle of radiation, or how high the donut is off the ground. You want it as low as possible so the fattest part of the donut, looking at it from the side, is along the ground, giving you more range. There are other (omnidirectional, vertically polarized) antennas with lower angle of radiation than the 1/4 wave ground plane (which also allow them to be mounted higher, clearing obstacles), such as the 5/8 wave, or center-fed coaxial 1/2 waves, but they're WAY too long for vehicle use.

Shorter than 1/4 wl antennas can be made to appear electrically longer (to the radio's output circuits) with parallel capacitance, or series inductance the former being seldom used. This tricking of the circuits does narrow the bandwidth of the antenna (VSWR on Channels 1 and 40 is higher), but it makes the antenna a much more practical length. The shorter the antenna, and the more you depend on loading, the worse the reception/transmission, and the narrower the bandwidth (other factors being equal).

The loading coil (inductance) can be placed anywhere along the antenna. Typically, you'll see a coil at the base of the antenna. This has the worst (highest) angle of radiation, but puts the coil where it places the least wind drag on the antenna. There are also center loaded antennas with the coil in the middle, which offer a lower angle of radiation. Top loaded antennas have a lower angle of radiation, but aren't too practical on vehicles. Another style of loading is continuous loading, usually done by wrapping the coil around the full length of the antenna... you see this with the shorter fiberglas whips. It has about the same angle of radiation as a center loaded antenna.

But as I stated before... vehicle installation is a compromise... a lot of folks are using a variety of less than ideal setups to meet their needs just fine. The best compromise I've seen was a 3' center loaded whip permanently mounted on the roof, and in the center of a Pinto station wagon. Signal strength was an nice strong oval, with a little more strength in the front, due to the lowered ground plane (the hood lower than the roof) pulling the radiation pattern down a bit in the front. The problem with this setup was that it could transmit farther than it could receive from most other vehicles... partly due to their less than ideal antenna setups and reduced transmit range, and partly due to the Pinto's short antenna length putting less metal up to grab signals. An Oldsmobile wagon or full-size van with that setup would be even better due to more ground plane. 

Dual antenna's interfere with each other unless they are 1/4 wavelength (9') apart... their radiation patterns aren't round, and are affected by the length of the cables feeding them... forget 'em. RG-58 is the appropriate cable for vehicle CB radio's (RG-8 has less loss for long runs but is too stiff and thick for vehicle use).

For drawing the power for a CB, the best bet is a direct connection (fused) to the battery or closest terminal. Shielding the power cable also prevents RF noise from the engine compartment getting into the radio (but coax isn't a good power cable... buy separate shielding). Good ground connections are essential... scrape any paint or rust off before making grounds. I prefer to get radio ground at the battery. Make sure ground straps for the hood, trunk, doors, frame, etc are on good, clean connections.

Another hint is to make sure the engine is running when you want power... i.e. making an emergency call from deep in the woods. CB's (and other vehicle electronics) are designed for an average input of 13.8 or so volts... without the engine running you only have 12 volts or so from the battery. I've run tests with an RF wattmeter that showed radios putting out a full- legal 4 watts with the engine running, but only 2 - 2.5 watts with it off. If you absolutely must mount the antenna on the rear of the vehicle, point the vehicle in the direction you want the broadcast to go (preferably nose slightly downhill) before making your emergency call.

CB Radio: SSB vs AM

AM (Amplitude Modulation) transmits the same as AM 'radio' does.. it 'encodes' information by varying the 'power' or 'amplitude' of the wave. AM also has a habit of creating 'resonant' frequencies. An AM broadcast will transmit on its given 'frequency' as well as produce harmonics that are slightly above and slightly below the 'given frequency'. SSB (or Single SideBand) works on this principal. SSB transmits ONLY one of the harmonics. SSB also does not transmit a 'carrier'. When you 'dead-key' or just hit the x-mit button on a AM radio without saying anything, it will 'dead-key' transmit 4 watts (or something similar). On a SSB radio, the 'dead-key' transmission will be zero. SSB only transmits what you actually say. The end result is that you get roughly 3 times the power (you're legally allowed 12 wattts (vs 4) of power on SSB) and an additional 80 'channels'. The SSB 'channels' actually reside *between* the regular 40 AM channels. Since SSB transmits on the harmonics of regular channels, people with 'standard' CBs will be able to hear what you say.. sort of.. it actually sounds a lot more like Charlie Brown's mother or teacher on the cartoons.. generally indistinguishable.. Now, the benefits are you get 8 more watts, and channels that are generally a lot more 'clear' and less congested than 'conventional' CB channels. The down side is that most people don't have SSB capabilites. If you're in trouble and using an SSB to get out farther, that's great.. but the guy on the other end has to be able to understand you! SSB CBs can also x-mit in AM mode with the flip of a switch, but you're back to 4 watts of power.. so the person who heard your garble might not hear your 'regular' speech. SSB also allows a greater amount of 'privacy'.. *most* people won't be able to understand what you say.. some will, but most won't. SSB is something useful to have, but if you go 4x4ing with a group, I'd guarrantee that at least (and probably the other way around) one person will not have an SSB CB and you'll all get stuck talking AM. If, however, you become seperated from the group, an SSB rendezvous channel might come in handy.

Miscellaneous