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Overview of the Coaxial cable
Coaxial cable is a type of copper wire specifically designed with a metal shield and additional components to prevent signal disruption.
A coaxial — or coax — cable is mainly utilized by cable TV providers to link their satellite antenna systems to customers’ residences and commercial establishments. Occasionally, telephone companies employ coaxial cable to connect their central offices to telephone poles near customers. While some residences and offices still use coaxial cable, twisted pair cabling has largely replaced coaxial cable as the primary medium for Ethernet connections in enterprises and data centers.
The term “coaxial cable” derives from its construction, which includes a single physical channel that transmits the signal, surrounded by another concentric channel, both aligned along the same axis. The innermost channel is usually a copper conductor, encased by an insulating layer separating it from the outer channel. The outer channel acts as a ground, typically made of copper mesh. An additional insulating layer encases both the inner and outer channels. Multiple such cables or coaxial tube pairs can be encased within a single outer sheath, and with the use of repeaters, can transmit information over long distances.
Coaxial cable was created in 1880 by English engineer and mathematician Oliver Heaviside, who patented the invention and design in the same year. AT&T implemented its first transcontinental coaxial transmission system in 1940. Depending on the transmission technology and other variables, twisted pair copper wire and optical fiber serve as alternatives to coaxial cable.
How Coaxial Cables Function
Coaxial cables operate through layers of electrical conductors and insulating material arranged in concentric fashion. This setup ensures that signals remain contained within the cable, safeguarding against interference from electrical noise.
The central conductor layer consists of a slender conducting wire, either solid or braided copper. Surrounding this wire is a dielectric layer made of insulating material with specific electrical properties. Enveloping the dielectric layer is a shield layer composed of metal foil or braided copper mesh. The entire structure is encased in an insulating jacket. The outer metal shield layer of the coaxial cable is typically grounded at both ends of the connectors, serving to shield the signals and providing a pathway for stray interference signals to dissipate.
The design of coaxial cable relies on precise control of cable dimensions and materials. This control ensures a consistent characteristic impedance for the coaxial cable. Errors can occur when high-frequency signals encounter impedance mismatches, leading to partial signal reflections.
Characteristic impedance is sensitive to signal frequency. For frequencies exceeding 1 GHz, cable manufacturers must select a dielectric material that minimally attenuates the signal and maintains the characteristic impedance to avoid signal reflections.
The electrical characteristics of coaxial cables are contingent on their application and are critical for optimal performance. Two standard characteristic impedances are commonly encountered:
– 50 ohms, suitable for moderate power environments.
– 75 ohms, frequently used for connections to antennas and residential installations.
Types of Coaxial Cables
There are various types of coaxial cables, including the following:
Hard-line coaxial cableuses round copper tubing and a mix of metals for shielding, such as aluminum or copper. These cables are typically used to link a transmitter to an antenna.
Triaxial cable features a third shielding layer that is grounded to safeguard the signals transmitted through the cable.
Rigid-line coaxial cables consist of twin copper tubes that act as rigid pipes. These cables are designed for indoor applications between high-power radio frequency (RF) transmitters.
Radiating cable resembles many aspects of hard-line cable but includes tuned slots in the shielding that match the RF wavelength at which the cable operates. This type is often used in elevators, military equipment, and underground tunnels.
Types of Connectors
There are numerous types of coaxial cable connectors, divided into two categories: male and female connectors. Connector types include the following:
Bayonet Neill-Concelman (BNC): Used for television, video signals, and radio frequencies below 4 GHz.
Threaded Neill-Concelman (TNC): A threaded version of the BNC connector, employed in cellphones and capable of operating up to 12 GHz.
SubMiniature version A (SMA): Utilized in cellphones, Wi-Fi antenna systems, microwave systems, and radios, with an operating range up to 18 GHz.
SubMiniature version B (SMB): Suitable for telecommunications hardware.
QMA A quick-locking version of SMA connectors used in industrial and communications equipment.
Radio Corporation of America (RCA): Employed in audio and video applications, recognizable as the grouped yellow, white, and red cables used with older televisions. RCA connectors are also known as A/V jacks.
F connectors: Also referred to as F-type connectors, these are used in digital and cable televisions, typically with RG-6 or RG-59 cables.
Uses of Coaxial Cables
In households and small offices, short coaxial cables find application in cable television setups, home video equipment, amateur radio setups, and measuring instruments. Historically, coaxial cables served as an early Ethernet medium, supporting speeds up to 10 Mbps. However, twisted pair cabling has predominantly replaced coax in this regard.
Nevertheless, coaxial cables remain extensively utilized for cable broadband internet connections. They are also employed in automotive systems, aircraft, military and medical apparatus, and for linking satellite dishes, radio, and television antennas to their respective receivers.
Coax Standards
Most coaxial cable specifications maintain impedance values of 50, 52, 75, or 93 ohms. Due to their prevalent use in the cable television sector, RG-6 cables boasting double or quad shields and a 75-ohm impedance have emerged as a de facto standard across various industries.
Nearly 50 distinct standards govern coaxial cables, tailored for specific applications in amateur radio or low-loss cable television. Examples include RG-59/U, utilized for transmitting broadband signals from closed-circuit TV systems, and RG-214/U for high-frequency signal transmission.
Coax Connectors
Coaxial connectors span from simple single connectors employed in cable TV systems to intricate assemblies comprising multiple thin coaxial links, coupled with power and other signal connections, housed within semi-customized bodies. Such assemblies are prevalent in military electronics and avionics.
Mechanical stiffness can vary significantly, contingent upon the internal structure and intended use of coaxial cabling. For instance, high-power cables often feature thick insulation and exhibit high stiffness.
Certain cables are intentionally crafted with thick central wires to induce skin-effect resistance. This resistance arises from high-frequency signals traveling predominantly on the surface of the conductor rather than throughout. A larger central conductor yields a rigid cable with minimal loss per meter.
Difference Between RG-59 and RG-6
RG-59 and RG-6 cables are both commonly used in satellite television and cable modem installations. Older systems typically used RG-59 cables before the adoption of RG-6 cables.
RG-59 Cable:
– Gauge: Thinner at 20 American Wire Gauge (AWG)
– Center Conductor: Copper
– Applications: More commonly found in older buildings, well-suited for CCTV and analog video systems
RG-6 Cable:
– Gauge: Thicker at 18 AWG
– Center Conductor: Copper
– Applications: Used with high-bandwidth and high-frequency equipment, suitable for internet and satellite signals that operate at higher frequencies compared to traditional analog video
The choice between RG-59 and RG-6 largely depends on the frequency requirements. For applications requiring frequencies above 50 MHz, RG-6 cable is recommended.
