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
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| Component | Description |
|---|---|
| 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.
Types of Connectors
Coaxial cable connectors are available in a variety of shapes, with male and female connectors being the most common. Here are some examples of common connector types:
- Bayonet Neill-Concelman (BNC): This connector is widely used with television, video, and radio signals with frequencies less than 4 GHz. It is often used in professional audio/video applications to ensure a secure connection.
- Threaded Neill-Concelman (TNC): TNC connectors, which are threaded versions of BNC connectors, are widely used in telephones and other devices. They are useful for high-frequency applications because they can operate at frequencies of up to 12 GHz.
- QMA: QMA connections, which are a quick-locking variation of SMA connectors, are widely used in industrial and communications hardware. They provide a dependable connection and are simple to install.
- F connectors: F connectors, often known as F-type connectors, are commonly used in digital and cable television systems. They are typically used in conjunction with RG-6 or RG-59 cables and provide a reliable connection for high-quality audio and video signals.
- SubMiniature version A (SMA): SMA connectors are commonly found in cellphones, Wi-Fi antenna systems, microwave systems, and radios. They can operate at frequencies of up to 18 GHz, making them appropriate for a variety of high-frequency transmission applications.
- SubMiniature version B (SMB): SMB connections are frequently utilized with telecommunications hardware and other electronic equipment that require a small and dependable connector solution.
- Radio Corporation of America (RCA): In audio and video applications, RCA connections, also known as A/V jacks, are extensively utilized. They can be identified by the grouped yellow, white, and red cables that are commonly found with vintage televisions and audio equipment.
These are only a few examples of coaxial cable connections, each adapted to certain purposes and frequency ranges. Choosing the right connector allows effective signal transfer and trustworthy connections in a variety of electrical devices.
Uses of Coaxial Cables
Short coaxial cables are used in cable television, home video equipment, amateur radio equipment, and measuring devices in household and small office environments. Coaxial cables were initially used as an early type of Ethernet, with rates of up to 10 Mbps. Twisted pair cabling, on the other hand, has largely replaced coax for Ethernet connectivity.
Nonetheless, coaxial cables are still widely utilized for cable broadband internet connections. They are also used in autos, aviation, military equipment, and medical devices. Furthermore, coaxial cables are used to connect satellite dishes, radio and television antennae, and receivers, ensuring dependable signal transmission in these situations.
Coax standards
| Coax Standard | Description |
|---|---|
| Impedance | Coaxial cables are available in standards with typical impedances of 50, 52, 75, or 93 ohms. RG-6 cables with 75-ohm impedance and double or quad shields have become widely accepted as a de facto standard in various industries, particularly in cable television. |
| Diverse Standards | There are approximately 50 separate standards for coaxial cables, catering to specific needs in areas such as amateur radio and low-loss cable television. Examples include RG-59/U, used for broadband communication in closed-circuit TV systems, and RG-214/U, used for high-frequency signal transmission. |
| Coaxial Connectors | Coaxial connectors range in complexity, from simple single connectors in cable TV systems to intricate combinations of multiple thin coax cables with power and signal connections. These connectors are commonly found in military and avionics applications. |
| Mechanical Rigidity | The mechanical rigidity of coaxial cables varies depending on their internal design and intended use. High-power cables often have thick insulation, resulting in a stiff cable structure. |
| Skin Effect Resistance | Some cables are intentionally designed with robust center wires to resist skin effects. Skin effect resistance occurs when high-frequency signals primarily travel on the surface of the conductor rather than throughout its entire cross-section. A larger center conductor creates a sturdy cable with minimal signal loss per meter. |
Interference issues with Coax
Coaxial cables are susceptible to many types of interference, which can degrade signal quality. One typical type is signal leakage, which occurs when an electromagnetic field penetrates the cable’s exterior shielding. Furthermore, external signals can pass through the insulation in some circumstances.
Straight-line feed cables to commercial radio broadcast towers provide little leakage and interference. These cables are outfitted with smooth, conductive shields with few gaps, offering good protection. Nuclear reactors, on the other hand, present substantial issues since they require specific shielding to prevent interference.
Difference Between RG-59 and RG-6
| Cable Type | Description |
|---|---|
| RG-59 | The RG-59 cable, which has a diameter of 20 American Wire Gauge (AWG) and is widely used in older installations, is thinner. It has a copper center conductor and is commonly seen in older structures. CCTV and analog video systems benefit more from RG-59. |
| RG-6 | The RG-6 cable has a larger diameter of 18 AWG with a copper core conductor. It’s typically seen in satellite TV and cable modems. Because RG-6 is designed for high-bandwidth and high-frequency hardware, it is perfect for internet and satellite signals that operate at higher frequencies than typical analog television. |
The frequency requirements heavily influence the choice between RG-59 and RG-6 cables. An RG-6 cable is suggested for frequencies above 50 MHz.
FAQ’s
What role does the center conductor play in a coaxial cable?
The central conductor is in responsible for transmitting the cable’s signal while also ensuring its electrical integrity.
What function does the dielectric insulator serve in a coaxial cable?
The dielectric insulator serves as an insulator between the center conductor and the outside shielding, reducing signal loss and maintaining the center conductor in place.
What is the mechanism by which braided shields offer protection against interference in coaxial cables?
By preventing external signals from accessing the inner conductor, braided shields defend against electromagnetic interference (EMI).
What role does the foil shield serve in coaxial cables?
Foil shields provide 100% coverage against radio frequency interference (RFI) by covering the interior components of the cable with aluminum foil.
What is the function of the outer jacket in a coaxial cable?
The outer jacket secures the cable and protects it from elements, giving mechanical protection and durability.
Are there various standards for coaxial cables?
Yes, there are over 50 different coaxial cable standards, each created for specialized demands in businesses such as amateur radio and cable television.
What considerations are important when choosing a coaxial cable?
When choosing a coaxial cable, consider impedance, shielding performance, frequency requirements, and the individual application or industry needs.
Is it possible to utilize coaxial cables for high-frequency signals?
Yes, coaxial cables can be utilized for high-frequency signals, with cables like RG-6 ideal for high-bandwidth applications like internet and satellite signals.
What are the benefits of using coaxial cables with low skin-effect resistance?
Low skin-effect resistance coaxial cables with a larger center conductor allow minimum signal loss per meter, preserving signal integrity for high-frequency signals.
Conclusion
Coaxial cables are essential in modern communication networks. Their unique design, which includes a center conductor, dielectric insulator, shields, and an outer jacket, enables for effective signal transmission while also protecting against interference. Coaxial cables are widely utilized in a variety of industries, including cable television, internet broadband, satellite communication, and others. The availability of many standards and specifications gives for flexibility in satisfying individual requirements. Coaxial cables remain a crucial component in our interconnected world, whether they are providing high-frequency signals or assuring dependable transmission. Coaxial cables are a reliable and proven choice for effective signal transmission because of reliability, longevity, and ability to handle a wide range of frequencies.
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