Coaxial Cable Standards and Designations
Selecting the right coaxial cable requires more than just picking a wire; it requires an understanding of the complex alphanumeric codes used by manufacturers and regulatory bodies. These designators provide critical information regarding the cable's physical dimensions, electrical properties, and intended application, ensuring that connectors and hardware are compatible across different systems.
From the ubiquitous RG series used in consumer electronics to the high-precision hardlines used in telecommunications, these standards ensure consistency in signal transmission and attenuation across global industries.
ไม่มีภาพประกอบKey Facts
- RG Designators: Primarily used to identify compatible connectors rather than guaranteeing specific electrical characteristics.
- Impedance: Common standards include 50 Ω (often for radio and data) and 75 Ω (common for video and cable TV).
- Velocity Factor (VF): A measure of how fast a signal travels relative to the speed of light, determined by the dielectric material.
- Shielding: Ranges from single braid to quad-shielding to reduce electromagnetic interference.
- Dielectrics: Materials like Polyethylene (PE) and Polytetrafluoroethylene (PTFE) significantly impact cable performance and temperature resistance.
Understanding Cable Designators
The RG Series (Radio Guide)
The RG prefix is an industry series prefix. While widely used, there is no single standard that guarantees the electrical and physical characteristics of a cable labeled as "RG-# type." Instead, these designators help users identify connectors that fit the inner conductor, dielectric, and jacket dimensions.
- Suffixes A, B, C: Indicate revisions of the base RG cable type (e.g., RG-58A).
- /U: Denotes a universal or general-use cable (e.g., RG-58A/U).
- /UQ: Indicates a quad-shield version for superior interference protection (e.g., RG-6/UQ).
National and Military Standards
Different regions and sectors use specialized coding systems to ensure rigorous quality control:
- U.S. Military (MIL-SPEC): Uses the M17 designation (e.g., M17/75-RG214) for military-grade coaxial cables.
- JIS (Japanese Industrial Standards): Uses a specific system where "C" indicates 75 Ω and "D" indicates 50 Ω. Dielectrics are coded as "2" for polyethylene and "F" for foamed polyethylene.
- British Standards: Includes URM (British military), BT/RA (British Telecom), and PSF (BBC) designations.
European Standards (EN)
European cables often follow the EN prefix. The EN 50117 series is the standard for analogue and digital systems, with suffixes indicating specific uses:
- -1: Generic specifications.
- -9-3: Indoor drop cables (5 MHz to 6,000 MHz).
- -10-2: Outdoor drop cables (5 MHz to 3,000 MHz).
- -11-1: Distribution and trunk cables (5 MHz to 1,000 MHz).
Additionally, the EN 50575 standard governs fire performance (CPR), using Euroclass suffixes (e.g., B2ca) and additional classifications for smoke (s), flaming droplets (d), and acidity (a).
Commercial and High-Performance Alternatives
Beyond standard RG cables, commercial manufacturers offer low-loss and semi-rigid alternatives for specialized high-frequency applications.
- Low-Loss Prefixes: LMR, HDF, CFD, EMR, and H (e.g., LMR-400) are common alternatives to standard RG cables.
- Semi-Rigid/Hardline: UT (semi-rigid), LDF/AVA (corrugated HELIAX-style), and HCA (semi-flexible air-dielectric) are used for high-power or very low-loss requirements.
- QR Series: Low-loss hardlines often used to replace RG-11.
Technical Specifications and Materials
Dielectric Materials and Velocity Factor
The dielectric—the insulating layer between the center conductor and the shield—determines the Velocity Factor (VF), which is the ratio of the speed of signal propagation in the cable to the speed of light in a vacuum.
| Code | Dielectric Material | Typical Velocity Factor (VF) |
|---|---|---|
| FPE, PF | Foamed Polyethylene | 0.78 – 0.88 |
| PE | Solid Polyethylene | ~0.66 |
| PTFE | Solid Polytetrafluoroethylene | ~0.70 |
| Foamed PTFE | Foamed Polytetrafluoroethylene | ~0.84 |
| Air | Air | ~1.00 |
Comparative Cable Performance
Cable choice depends on the balance between diameter, attenuation (signal loss), and flexibility. For example, RG-58/U is common for thin Ethernet and amateur radio, while RG-6/U is the standard for satellite and cable TV due to its low loss at high frequencies.
For extreme performance, LMR series cables (like LMR-600) use copper-clad aluminum or bare copper tubes to achieve significantly lower attenuation than standard RG cables.
Frequently Asked Questions
What is the difference between RG-6 and RG-59?
RG-6 is designed for high-frequency applications like satellite and cable TV with lower loss, while RG-59 is typically used for baseband video in CCTV systems and is generally less effective for high-frequency signals over long distances.
What does "Quad Shield" mean in RG-6/UQ?
Quad shielding means the cable has four layers of shielding (typically alternating foil and braid) to provide superior protection against electromagnetic interference compared to the one or two layers found in standard RG-6.
Why is the Velocity Factor important?
The Velocity Factor is critical for calculating the electrical length of a cable. This is essential in RF (Radio Frequency) engineering for matching impedances and ensuring signals arrive at the correct time in phased systems.
When should I use a semi-rigid cable like RG-402?
Semi-rigid cables are used in high-frequency interconnects where minimal signal loss and high stability are required, and where the cable does not need to be frequently bent or moved.
What is the purpose of the EN 50575 standard?
EN 50575 is a European fire-performance standard (CPR) that classifies cables based on their reaction to fire, including smoke production, acidity, and the presence of flaming droplets.