Double Shielding of Antenna Cables for Low Signal Loss

Interference and Cable Shielding

Shielding protects against both leakage and absorption of stray radiation of electrical noise by cables.

• Electrical "signal noise" interferes with the operation of antennas and antenna cables.
• Cables carrying high-frequency charge naturally pose the risk of EMI transfer - both from shedding and accepting interference.

While insulation protects antenna cables from physical damage due to the forces of impact or compression, shielding deflects the environmental challenges of EMI (electromagnetic interference).

High levels of EMI radiation should be expected where appliances with heavy charge transference are present, like transformers (for example).

How Shielding Works

Shielding within the composition of a coaxial cable functions in two ways:

1. It reflects any EMI generated by the inner conductor (which carries the electrical charge/signal) and
2. It catches external noise while grounding it, thus sparing the inner conductor from interference & preserving the inner signal transmission.

No shield protection within cabling is impenetrable, but the aim is to sufficiently dampen (attenuate) the noise such that it doesn't interfere with the signal carried.

Shielding methods vary. Increased shielding is required in especially noisy environments challenged by many sources of high-load interference, and the converse is expected in less noisy locations.

Is there any downside to cable shielding?

Shielding reduces flexibility and increases the diameter of cables, which can be an issue in tight spaces, such as device cases and enclosures.

Cable shielding comes at a budgetary cost, so a carefully calculated trade-off should be considered, but without compromising mission-critical signal transmission quality.

Types of Shielding in Coaxial Antenna Cables

1] Aluminum foil shield

A layer of aluminum, reinforced for strength, is usually girded by polyester. This type of shield covers the conductor 100%—i.e., the aluminum shield has no breaches in its integrity. This makes for a good shield.

2] Copper braided shield

These comprise braided strands of copper metal, which, by nature of the formation, do not offer 100% coverage (due to gaps between braided bunches). However, tighter braids can be used for increased coverage. Braided shields typically offer between 70% and 100% coverage.

Which shield is more effective?

Contrary to what you may think (according to the concept of coverage), the copper braided shield offers the greatest noise attenuation.

Why? The density of the braided copper material simply blocks out more noise. However, more material is more expensive and also heavier.

Is there ever cause to use both shields?

Yes, aluminum and copper braided shields are used in boisterous environments.

Where wires are twinned together in a cable, aluminum is used as an inner cover to prevent 'cross-talk' between conductors, and then the outer cabling is shielded by dense copper braiding.

Grounding the noise

The key to good shielding is ensuring the noise is grounded once it is picked up by the shield. So, good practice would be to have every cable grounded to carry away the noise, maintaining the effectiveness of your shield.

 RG58 Compared to LMR-200 & LMR-100 Coax: Shielding & Signal Loss

RG58 Coaxial Cable Specifications

RG58, LMR-100, and LMR-200 all have the following characteristics in common:

• 50 Ohm impedance
• A weather-resilient polyethylene (PE) dielectric
• PVC outer jacket

·         Structural comparison of RG58 and LMR-100 (aside from what is mentioned above):

• LMR-100 is a 50 Ohm coaxial cable that shares structural and material similarities with RG58 but has an overall lower diameter of 2.79mm (0.110 inches).
• RG58 and LMR-100 have the following key differences:
• LMR-100 carries a solid bare copper-covered steel (BCCS) central conductor of 0.46mm.
• LMR-100 is a double-shielded coaxial cable. The inner shield is made from aluminum tape, and the outer shield is braided, tinned copper.

·         Structural comparison of RG58 and LMR-200 (aside from what is mentioned in the first paragraph above):

• LMR-200 is a larger diameter (6.1mm 0.24inches) low-loss coaxial cable that has double shielding (meaning less loss of signal along the length of the cable), with braided tinned copper and aluminum tape layers coating the dielectric and inner conductor.
• LMR-200 possesses a more prominent conductor of 1.42mm diameter made from bare copper (BC) 

About RG58

Electrical characteristics of RG58: The typical impedance is within a 2 Ohm range of 50 Ohm. It operates at frequencies up to 5GHz. The conductor resistance is 38.4 Ohm. The dielectric resistance is 500 Ohm.

Structure and material composition of RG58 cable

Like all other coaxial cables, RG58 comprises an inner conducting wire surrounded by an insulating layer and outer conducting shielding. It is typically manufactured to the U.S. specifications MIL-C-17F and MIL-C-17G 9.

• The conductor has a diameter of 0.91mm (0.036 inches) and is made from stranded (7 or 19 strand tinned copper wire, which has added resistance to oxidation and is readily soldered. Solid conductor variants are also available.
• The dielectric diameter is 2.95mm (0.116 inches), made from solid polyethylene (PE). Polythene is heat stable up to a maximum operating temperature of 80 degrees Celsius (176 degrees Fahrenheit) and provides flexibility, fire resistance, resilience against abrasions, and weatherproofing.
• RG58 is shielded with flexible and heat-stable tinned copper wire braid, with coverage between 70% and 95%, depending on the manufacturer.
• The outer jacket of the RG58 cable is made from UV-resistant PVC, which is heat-stable but has limited resistance to acids, alkalis, and inorganic solvents.
• The overall diameter of this cable is 5mm (0.2 inches).

RG58 is a coaxial cable type for antenna cables made to strict U.S. government specifications. The ‘RG’ prefix stands for ‘Radio Frequency Government,’ and the number refers to the gauge of the cable.

RG58 applications

This coax cable performs well for various radio frequency communication applications in a low-power setting. Key applications include:

• Testing and measurement
• Ham and emergency services radio
• Marine VHF
• WLAN antennas

RG standard of Coaxial Cable

RG is a robust coaxial technology standard - one of the original standards for coaxial cable technology, created for the US military in the 1960's. RG is not a specific manufacturer's standard: All coax manufacturers can use RG and a standard by using the letters RG ("Radio Guide") followed by a number corresponding to a certain standard with a particular set of specifications. Sometimes, the letter "/U" follows the number for the "Universal" standard (i.e., the cable construction is intended for universal applications).

There is no standardization among manufacturers to ensure that every aspect of the cable is constant, so it helps to know the specifications of the cable you need.

RG technology is used in military and commercial applications in various environments.

Generally, 75 Ohm cables are used in audio/video applications, and 50 Ohm cables are used in data applications. The 50 Ohm RG cables typically lose too much signal through attenuation to be appropriate for wireless applications unless the cable is short. Low-loss coax is the only viable solution for antenna cables of longer lengths.

RG-174 compared to LMR-100 Coax : Shielding and Signal Loss

LMR-100 and RG174 Coaxial Cable Comparison

• RG174 and LMR-100 are compatible with Wi-Fi, Cellular, and most IoT wireless applications.
• LMR-100 is double-shielded and suitable for outdoor as well as indoor use. 
• RG174 has a single shield and is unsuitable for long-term outdoor use.

RG174 is a small, flexible coax for antenna cables with an American Wire Gauge of 26. Its diameter is 2.79mm (0.11 inches). Its relatively small diameter, flexibility, high speed, and efficient data transfer make it an ideal choice for  a wide range of contemporary and consumer applications, including:

• Security and access control
• Automation and IoT networking
• GPS
• Wireless networking such as LAN/WAN:
• For Wi-Fi: Most typically RP-SMA,  cables
• For LTE: SMA cables or N-Type cables

RG174 Physical Characteristics:

RG174's structure is typical of coaxial cables and is comprised of the following layers and materials:

• Central conductor: 7 strands of stranded copper-clad steel (CCS) with a diameter of 0.483mm (0.019 inches).
• Dielectric: Low-density polyethylene (LDPE), which contributes water resistance and flexibility to the cable. The dielectric diameter is 1.55mm (0.06 inches)
• Outer shielding: A single layer of tinned copper with coverage between 88% and 90%, depending on the manufacturer.
• Jacket: Polyvinyl Chloride (PVC), a flexible weather-resistant coating with good flame resistance. Due to its material composition (plastics), the operating temperature of this cable is between -40 and 80 degrees Celsius (-40 degrees to 176 degrees Fahrenheit).

Electrical profile of RG174

The impedance of RG174 is typically 50 Ohm. The conductor resistance is a maximum of 142.4 Ohm, and the dielectric resistance is at least 1000 Ohm. This cable transmits a maximum frequency of 6GHz.

Comparison of RG174 and LMR-100 coax cable

Key Features:

• RG174:
• Diameter: Typically around 2.79mm.
• Impedance: Standard 50 ohms.
• Velocity of Propagation: Approximately 66%.
• Attenuation: Higher than LMR-100, especially over longer distances.
• LMR-100:
• Diameter: Roughly 2.79mm, similar to RG174.
• Impedance: Maintains the 50 ohms industry standard.
• Velocity of Propagation: Slightly higher than RG174 at around 70%.
• Attenuation: Provides better performance with lower loss over extended distances.

Materials Composition:

• RG174: RG174 coaxial cables often consist of a silver-plated copper center conductor surrounded by a dielectric insulator, typically solid polyethylene. This assembly is then covered by a shield, usually made from tinned copper, followed by an external PVC jacket.
• LMR-100: This cable features a copper center conductor, often silver-plated, and a gas-injected foam polyethylene dielectric core. LMR-100 is recognized for its dual shielding, with the inner layer being aluminum and the outer layer made from tinned copper braid, all enveloped in a durable polyethylene jacket.

Types:

RG174 and LMR-100 come in various versions specially designed for specific environments. You can find these cables in their regular form as ultra-flexible versions, or even with UV resistance for outdoor installations.

Associated Wireless Technologies:

• RG174: Due to its higher Attenuation, RG174 is commonly employed in low-power, short-distance applications, such as Wi-Fi antennas, GPS systems, and mobile communications.
• LMR-100: LMR-100, with its superior Attenuation performance, finds applications in a broader range of wireless technologies, including 2G/ 3G/4G cellular, WLAN, RFID, and more.

Applications & Suitability for Specific IoT Applications:

IoT revolves around connectivity, requiring reliable transmission lines.

• RG174: Suitable for indoor IoT applications where the cable run is short. Ideal for connecting Wi-Fi-based IoT devices, short-range sensors, and indoor antennas.
• LMR-100: Given its low loss characteristics, LMR-100 is more appropriate for indoor and outdoor IoT deployments, particularly where longer cable runs are involved. If you're looking at IoT applications such as outdoor weather stations, smart agriculture, or city-wide sensor deployments, LMR-100 stands out as the preferred choice.

Conclusion:

Coaxial cables have been at the forefront of telecommunication and radio-frequency transmissions for decades. As technology advances, the requirements for more efficient coax cables grow, especially in the Internet of Things (IoT) domain. Two significant contenders in this arena are the RG174 and LMR-100 cables.

When comparing RG174 and LMR-100 coax cables, understanding their key features and associated applications is essential. For short-distance, indoor IoT applications, RG174 may suffice. However, LMR-100, with its enhanced performance metrics, is the superior option for more extensive and demanding scenarios, especially outdoors. As the landscape of IoT continues to evolve, ensuring you're equipped with a suitable coaxial cable can be the difference between seamless connectivity and unwanted transmission losses.