UHF CBs use Frequency Modulation (FM) to transmit/receive. Since UHF signals generally travel in a straight line, the terrain impacts how well the signal is transmitted or received. For example, UHF CB radios will perform poorly in hilly or forested areas and perform well in flat open countryside. UHF CBs can also access repeater stations that re-transmit the signals on another channel which can provide much further coverage. So invest is a good antenna to compliment your UHF CB radio.
The antenna is a device for transmitting and/or receiving signals – the eyes and ears of your UHF radio. A good antenna is designed to be “in-tune” to the signal you are seeking – your radio “sees” the signal and you hear a clear conversation. Use a poor antenna or mount the antenna is a bad location, will greatly reduce your range and clarity.
Mobile antenna should radiate in a symmetrical pattern 360° around the antenna. However depending on where you mount your antenna, the way the antenna radiates will be affected. The best location for an antenna is in the middle of you roof however this is generally not practical. Most UHF CB antennas are mounted the front guard or bull bar. In these cases, it is essential that you A) use a ground independent antenna B) mount the antenna away for vertical metal sections like windscreen pillars, other antennas etc. and C) mount the antenna as high as possible.
While the radiation pattern is important, antenna gain increases the antennas performance. As gain is increased, the radiation gets compressed into a thinner pattern and reaches out further to the side. The more gain an antenna has the thinner the pattern becomes and the further the signal can travel or reach. However a thinner radiation pattern may prevent strong signal reception when driving through hills. A summary of the ideal gain for each situation is as follows; low gain antennas (2-4 dBi) are good for hilly terrain but lack range in flat terrain; medium gain antennas (5-7 dBi) are good all round antenna which works well in hilly and flat terrain and high gain antennas (8+ dBi) are good in flat terrain but poor in hilly terrain.
Ground independent antennas are antennas that have been designed to simulate a ground plane which allow it to perform efficiently with a minimum or no ground plane. Hence they are ideal for mounting on bull bars or guards etc.