The Antenna.

This must be a special CB antenna - do NOT use an antenna that was not designed for use on CB.
The type you use is one of the most important choices to make when buying a CB system. If you have limited money, save on the radio and spend on the antenna.

In the UK, the maximum size is restricted to 1/2 wave (about 18 foot / 5.46Metres) for a dipole type or 5/8 wave (about 22 foot / 6.8Metres) for a monopole type. The width is also restricted - 55mm maximum width. Within these limits, there are a wide range of different sizes available.

The size will affect performance - a small antenna can be useful for limited space and will be less obtrusive, but will not perform as well as the larger ones.

Each antenna performs differently. They can only put out only the power you put in, but some may be more efficient and some may concentrate the signal more in certain directions than in others.

Antennas can be made to send more signal in one direction than in others. This can be either vertical or horizontal directivity. All antennas will be directional to a certain degree.

All antennas should be tuned for the frequency they are going to be used on. As CB uses different frequencies in different countries, they will not usually come ready tuned.
Tuning usually just involves adjusting the length and checking the tuning with a SWR meter.