Feeder cable.

Purpose.
The feeder cable is designed to transport a signal from one place to another, often between a transmitter and antenna.
The perfect feeder cable would have no loss, no radiation and no signal pick up on the cable. All the signal would be delivered from one end to the other.

Types.
There are two main types of feeder cable in use, coaxial and parallel conductor. The coaxial type is the more commonly used type, and is the type used for CB radio installations.
Coaxial cable also comes in various types, according to it's characteristics.

Characteristics.
RF cable has several characteristics, and there are many different types to allow for different requirements.
Impedance is a preset characteristic, set by design and independent of length or frequency.
Loss is a measure of how much of your signal will be lost in the cable. The amount of loss will depend upon frequency, and is per stated length - more cable equals more loss.
Velocity factor is a measure of how fast the signal will travel along the coax. When in free space, radio waves travel at the speed of light. In coaxial cable, they will travel slower.
Diameter. Low loss cables may often be thicker.

Selection.
When selecting the cable to use, you need to consider the application.
Impedance must match that of the transmitter and antenna.
Loss, being per unit length, will be a question of how much you are using. It is not worth the extra cost and width for small runs, you will not notice the difference.
Velocity factor is fairly standard between many types of coaxial, and is not really important in most installations.
Diameter is only really important if you may have problems installing thick, stiff coaxial as opposed to thin, more flexible coaxial. Otherwise, pay more attention to impedance and loss.

Length.
Under normal conditions, if all is well, the length of coax makes no real difference. If the length of coax appears to change readings, there is a fault on the system somewhere. This issue is covered in more details on following pages in this section.

CB Radio     Electronics     Magazine     Privacy     Email     Accessibility     Site map
Copyright © 2001 - 2008.