Because it’s commonly used in radio work, every ham should be familiar with coaxial cable, often simply called coax.
Coaxial cable is most often used between the transceiver (or T/R switch) and antenna. In this application coax acts as the feed line (AKA transmission line) to carry transmitted and received RF signals between the antenna and radio. Other types of feed line can be employed but coax is used by many hams because it is easy to work with and readily available.
Coax is a type of electrical cable that has an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield. Most coaxial cables also have an insulating outer sheath or jacket. The term coaxial comes from the inner conductor and the outer shield sharing a geometric axis.
To be useful coaxial cable must be terminated with mating RF connectors. An experienced ham may terminate their own coax; at greater cost they may purchase ready-made and tested assemblies.
A wide variety of coaxial cable and assemblies are available with different characteristics. A quick summary of the important features:
- Characteristic impedance
- Signal loss
- Power capacity
- Environmental resistance
A seventh important characteristic of coax is velocity factor but that is a more advanced topic of lesser importance so we’ll simply mention it here.
Coaxial cable selection for each installation may be a compromise between features, requirements, and cost. The ham has to factor in what he needs or wants, what is available, and what it costs.
A quick look at these features of coaxial cable: Continue reading