Why Coaxial Cables are Highly Insulated?

What is Coaxial Cable?

Coaxial cables conduct electrical signals using an inner conductor mostly copper or copper plated wire surrounded by an insulating wire and enclosed by a shield mostly one to four layers of woven braided aluminum or copper wire, and aluminum foil.

Common applications of coaxial cables include video and CATV distribution, RF and microwave transmission, and computer instrumentation and connectors.

Coaxial Cables Construction

Coaxial cable consists of a center wire which is mostly copper wires that is surrounded by insulation, a grounded shield, and a braided wire. Some of the cables consist of both braided wire and aluminum foil. Coaxial cabling is primarily used by the cable television industry and is also used for computer networks such as Ethernet.

Many coaxial cables have an outer insulating sheath which protects them from the external environment. The term coaxial (co-axial) comes from the inner conductor and shield sharing a geometric axis. Coaxial cables differ from those that carry high-frequency signals and those that carry low-frequency signals such as audio signals.

Operation of Coaxial Cables

During conduction of electricity through a conductor, say copper wire, not all the electrical energy gets to its destination as some of the energy is lost to the surrounding in form of heat. The energy lost is the energy used up when overcoming the internal resistance of the copper wire. The energy conveyed through the copper wire is done through its electrons. Electrical energy which is in form of heat is not the only thing the copper wire emits during conduction.

Electrons do get excited and when they receive or absorb the minimum amount of energy and when they do, they jump from one energy level to the other. During this process, electromagnetic radiation with a varying range of frequency, the wavelength is emitted.

Application of Coaxial Cables

Coaxial Cables are used as a transmission line for radio frequency signals. It can be used as a deadline connecting radio transmitters and receivers with their antennas, computer networks and is also used for distributing television signals.

An advantage that a coaxial cable has over other types of radio transmission lines is that in an ideal coaxial cable, the electromagnetic field carrying electrical signals exists only in the spaces between the inner and outer conductors. This makes it possible for the cables to be installed close to metallic objects such as gutter without having power losses occurring during transmission or propagation of the signals, unlike other transmission lines that leak the signals to the surrounding.

Signal Leakage in Cables

Signal leakage is the passage of electromagnetic fields and or electromagnetic radiations through the shield of cables that occurs in all directions. Signals can also pass from the surrounding of the cable into the cable which might cause interference. This process is called ingress. Interference causes noise. The signals propagated by the cables can likewise leak from the cable to the surrounding. When this happens, it leads to interference too. It is called egress. This process reduces the efficiency of the propagated signals.

Why Coaxial Cables are highly Insulated?

The electrical cables found in our homes are insulated. Electrical cables are insulated for safety purposes and also to minimize energy loss. The insulation offers great resistance to the leakage of energy to the surrounding. Since the loss of energy is minimal in such cables when there is excessive current, it damages the cables and that is why we have a fuse in our home devices. Just as electrical cables emit electromagnetic radiation and electrical energy in form of heat, coaxial cables can do the same but are hindered from doing so by insulating them. For a single core cable, the resistance offered by the insulation to electrical energy is given as                    

R_ins = ρdr / 2πrl

When integrated;

R_ins [ ρ / 2πrl (log_e (r₁/r₂))]

where ρ = resistivity of the conductor.

r₁ = radius of the conductor.

r₂ = radius of the insulator.

We are every day being bombarded by electromagnetic waves from all angles. There are lots and lots of waves passing through our homes all the time. These waves could be radio waves propagated from a nearby radio station, microwave, waves from our cell phones, infrared ray, and lots more.

There is a possibility that the waves propagated by the cables will have the same frequency or wavelength which can cause interference. Not only will the cables leak signals and cause interference and reduce the signals’ intensity, it can also absorb a signal that is passing close by.

With our cell phones switched on, our radio on and our TV set also on, if the coaxial cables were not highly insulated you hardly can hear a sound due to interference. Also notice that when you are close to a radio and a signal comes into your cell phone, the radio set begins to make unwanted noise due to interference of the waves.

Coaxial cables are highly insulated in order to prevent leakage of signals and prevent signals from the surrounding from penetrating to the inside of the cables. The cable does not only prevent leakage of signals but also electrical energy seeing that the materials used in insulating the cables are Non-conductors of heat and electricity.

The coaxial design makes the magnetic and electric field that is propagated along the conductor to be confined to the dielectric which serves as the insulator, giving room for little or no leakage of signal outside the shield.

Coaxial cables are a good choice when it comes to choosing cables that can convey weak signals and cannot tolerate interference from the surrounding or for higher electrical signals that must not be allowed to radiate or couple into adjacent structures or circuits.