What is Coaxial cable?
Coaxial cable, a specially designed copper cable with a robust metal shield, acts as a safeguard against signal interference. This type of cable, commonly known as coax or coaxial cable, serves as a crucial link for cable TV companies, connecting their satellite antenna facilities to residential and commercial premises. Telephone companies also employ coaxial cable for connecting central offices to telephone poles in close proximity to customers. While some homes and offices still utilize coaxial cable, its extensive use as an Ethernet connectivity medium in enterprises and data centers has been largely replaced by twisted pair cabling.
The most common coaxial cable sizes are RG-6 and RG-11, where RG stands for “radio grade” or “radio frequency.” RG-6 is suitable for drops shorter than 150 feet, while RG-11 is preferred for longer distances due to its enhanced performance. These cables used in homes have an impedance of 75 ohms.
Oliver Heaviside, an English engineer and mathematician, invented and designed coaxial cable, which he patented in 1880. AT&T’s creation of the first cross-continental coaxial transmission line in 1940 was an important milestone for coaxial cable. Alternatives to coaxial cable have evolved as technology advances, such as twisted pair copper wire and fiber optical, which vary based on carrier technology and other considerations.
How Coaxial Cables Work
|Center Conductor||Responsible for transmitting the cable’s signal, typically made of pure copper or copper-coated steel/aluminum.|
|Dielectric Insulator||Acts as an insulator between the center conductor and outer shielding, helps maintain center conductor position. Common materials include Foamed Polyethylene (FPE), Teflon, Polyethylene (PE), Polypropylene (PP), and Polyvinylchloride (PVC).|
|Braided Shield||Protects against electromagnetic interference (EMI) caused by external signals. Expressed as percent coverage, higher coverage offers better protection.|
|Foil Shield||Optional shield made of aluminum foil, covers 100% of inner parts, protects against radio frequency interference (RFI).|
|Outer Jacket||Flexible PVC (polyvinyl chloride) jacket that holds the cable together and provides protection against external elements.|
Coaxial cables are made up of concentric layers of electrical conductors and insulating material, resulting in a design that effectively encloses signals within the cable and prevents electrical noise interference. This multilayer structure ensures that transmission is reliable and free of interruptions caused by external disturbances.
The central conductor layer of coaxial cables is made up of a thin conducting wire that can be solid or braided copper. A dielectric layer consisting of an insulating material with specified electrical properties surrounds this conductor. This dielectric layer is subsequently encompassed by a shield layer made of metal foil or braided copper mesh. The entire assembly is wrapped in an insulating jacket for added protection. The coaxial cable’s exterior metal shield layer is typically grounded at the connectors at both ends, acting as a shield for the signals and a way to dissipate any stray interference signals.
Coaxial cable design relies on exact control over cable dimensions and materials. A consistent characteristic impedance for the coaxial cable is attained by carefully regulating these parameters. This characteristic impedance is critical in preserving signal integrity. When there are impedance mismatches, particularly at higher frequencies, a portion of the high-frequency signals may be reflected, resulting in mistakes and transmission disruptions. To reduce impedance variations and ensure reliable signal transmission, precise control over cable dimensions and materials is required.
A coaxial cable’s characteristic impedance varies with the frequency of the signal being sent. When operating at frequencies above 1 GHz, cable manufacturers must use a dielectric material that reduces signal attenuation while avoiding changes in characteristic impedance that could result in signal reflections. The cable can maintain a stable characteristic impedance across a wide range of frequencies by carefully selecting an appropriate dielectric material, ensuring effective signal transmission without considerable loss or disturbances.
Coaxial cable electrical parameters are critical for obtaining optimal performance and vary depending on the application. The following are two regularly used standard characteristic impedances:
- 50 ohms: This characteristic impedance is appropriate for moderate power situations where signal transmission must be dependable. It is widely used in a variety of applications, including telecommunications, data networks, and high-frequency electrical systems.
- 75 ohms: This characteristic impedance is often used in antenna connections and in home installations. It is commonly used in cable television (CATV), video transmission, and audio systems to ensure effective signal transfer and minimize signal loss over comparatively lengthy distances.
Coaxial cables can provide reliable and high-quality signal transmission in a variety of settings by selecting the suitable characteristic impedance depending on the unique application requirements.
Types of Coaxial Cables
There exists a wide variety of coaxial cables, each designed for specific applications and requirements. Here are a few examples:
- Triaxial cable: Triaxial cables have an additional grounded layer of shielding, which provides improved protection for signals transmitted down the cable. This additional layer reduces interference and external noise, making triaxial cables acceptable for applications requiring excellent signal integrity.
- Hard-line coaxial cable: This cable is made of spherical copper tubing and has a shield made of a combination of metals such as aluminum or copper. It is widely used to connect a transmitter to an antenna, ensuring efficient signal transmission in a variety of communication systems.
- Rigid-line coaxial cables: These cables are made of twin copper tubes and are designed as rigid pipes. They are generally used to connect high-power radio frequency (RF) transmitters indoors. Rigid-line coaxial cables provide long-term endurance and minimum signal loss, ensuring reliable transmission in high-frequency situations.
- Radiating cable: Radiating cables have the same components as hard-line cables, but they also have tunable spaces in the shielding. These slots are matched to the RF wavelength of the cable, allowing the cable to function as a radiating element. Radiating cables are used in elevators, military equipment, and underground tunnels to provide dependable distribution of signals in challenging environments.
These are just a few examples of the numerous coaxial cables available, each designed to suit specific technical criteria and enable effective signal transmission in a variety of industries and settings.