https://urgentcomm.com/wp-content/themes/ucm_child/assets/images/logo/footer-new-logo.png
  • Home
  • News
  • Multimedia
    • Back
    • Multimedia
    • Video
    • Podcasts
    • Galleries
    • IWCE’s Video Showcase
    • IWCE 2022 Winter Showcase
    • IWCE 2023 Pre-event Guide
  • Commentary
    • Back
    • Commentary
    • Urgent Matters
    • View From The Top
    • All Things IWCE
    • Legal Matters
  • Resources
    • Back
    • Resources
    • Webinars
    • White Papers
    • Reprints & Reuse
  • IWCE
    • Back
    • IWCE
    • Conference
    • Special Events
    • Exhibitor Listings
    • Premier Partners
    • Floor Plan
    • Exhibiting Information
    • Register for IWCE
  • About Us
    • Back
    • About Us
    • Contact Us
    • Advertise
    • Terms of Service
    • Privacy Statement
    • Cookie Policy
  • Related Sites
    • Back
    • American City & County
    • IWCE
    • Light Reading
    • IOT World Today
    • Mission Critical Technologies
    • TU-Auto
  • In the field
    • Back
    • In the field
    • Broadband Push-to-X
    • Internet of Things
    • Project 25
    • Public-Safety Broadband/FirstNet
    • Virtual/Augmented Reality
    • Land Mobile Radio
    • Long Term Evolution (LTE)
    • Applications
    • Drones/Robots
    • IoT/Smart X
    • Software
    • Subscriber Devices
    • Video
  • Call Center/Command
    • Back
    • Call Center/Command
    • Artificial Intelligence
    • NG911
    • Alerting Systems
    • Analytics
    • Dispatch/Call-taking
    • Incident Command/Situational Awareness
    • Tracking, Monitoring & Control
  • Network Tech
    • Back
    • Network Tech
    • Interoperability
    • LMR 100
    • LMR 200
    • Backhaul
    • Deployables
    • Power
    • Tower & Site
    • Wireless Networks
    • Coverage/Interference
    • Security
    • System Design
    • System Installation
    • System Operation
    • Test & Measurement
  • Operations
    • Back
    • Operations
    • Critical Infrastructure
    • Enterprise
    • Federal Government/Military
    • Public Safety
    • State & Local Government
    • Training
  • Regulations
    • Back
    • Regulations
    • Narrowbanding
    • T-Band
    • Rebanding
    • TV White Spaces
    • None
    • Funding
    • Policy
    • Regional Coordination
    • Standards
  • Organizations
    • Back
    • Organizations
    • AASHTO
    • APCO
    • DHS
    • DMR Association
    • ETA
    • EWA
    • FCC
    • IWCE
    • NASEMSO
    • NATE
    • NXDN Forum
    • NENA
    • NIST/PSCR
    • NPSTC
    • NTIA/FirstNet
    • P25 TIG
    • TETRA + CCA
    • UTC
Urgent Communications
  • NEWSLETTER
  • Home
  • News
  • Multimedia
    • Back
    • Video
    • Podcasts
    • Omdia Crit Comms Circle Podcast
    • Galleries
    • IWCE’s Video Showcase
    • IWCE 2023 Pre-event Guide
    • IWCE 2022 Winter Showcase
  • Commentary
    • Back
    • All Things IWCE
    • Urgent Matters
    • View From The Top
    • Legal Matters
  • Resources
    • Back
    • Webinars
    • White Papers
    • Reprints & Reuse
    • UC eZines
    • Sponsored content
  • IWCE
    • Back
    • Conference
    • Why Attend
    • Exhibitor Listing
    • Floor Plan
    • Exhibiting Information
    • Join the Event Mailing List
  • About Us
    • Back
    • About Us
    • Contact Us
    • Advertise
    • Cookie Policy
    • Terms of Service
    • Privacy Statement
  • Related Sites
    • Back
    • American City & County
    • IWCE
    • Light Reading
    • IOT World Today
    • TU-Auto
  • newsletter
  • In the field
    • Back
    • Internet of Things
    • Broadband Push-to-X
    • Project 25
    • Public-Safety Broadband/FirstNet
    • Virtual/Augmented Reality
    • Land Mobile Radio
    • Long Term Evolution (LTE)
    • Applications
    • Drones/Robots
    • IoT/Smart X
    • Software
    • Subscriber Devices
    • Video
  • Call Center/Command
    • Back
    • Artificial Intelligence
    • NG911
    • Alerting Systems
    • Analytics
    • Dispatch/Call-taking
    • Incident Command/Situational Awareness
    • Tracking, Monitoring & Control
  • Network Tech
    • Back
    • Cybersecurity
    • Interoperability
    • LMR 100
    • LMR 200
    • Backhaul
    • Deployables
    • Power
    • Tower & Site
    • Wireless Networks
    • Coverage/Interference
    • Security
    • System Design
    • System Installation
    • System Operation
    • Test & Measurement
  • Operations
    • Back
    • Critical Infrastructure
    • Enterprise
    • Federal Government/Military
    • Public Safety
    • State & Local Government
    • Training
  • Regulations
    • Back
    • Narrowbanding
    • T-Band
    • Rebanding
    • TV White Spaces
    • None
    • Funding
    • Policy
    • Regional Coordination
    • Standards
  • Organizations
    • Back
    • AASHTO
    • APCO
    • DHS
    • DMR Association
    • ETA
    • EWA
    • FCC
    • IWCE
    • NASEMSO
    • NATE
    • NXDN Forum
    • NENA
    • NIST/PSCR
    • NPSTC
    • NTIA/FirstNet
    • P25 TIG
    • TETRA + CCA
    • UTC
acc.com

content


Triaxial radiating cables improve subway communications:

Triaxial radiating cables improve subway communications:

Achieving proper radio frequency coverage for emergency police communications has become an increasing concern for subway transit authorities. Electrical,
  • Written by Urgent Communications Administrator
  • 1st May 1997

Achieving proper radio frequency coverage for emergency police communications has become an increasing concern for subway transit authorities. Electrical, mechanical and combustion characteristics are important.

Obtaining adequate radio coverage in enclosed areas such as subway tunnels and underground transit stations poses a challenge. The use of point-source antennas results in dead spots, and RF energy will not propagate along the length of a tunnel.

Many terms such as radiating cables, leaky feeders and antenna cables have been used to describe a cable designed to provide RF coverage in enclosed or confined areas where point-source antennas are not practical. These cables have been used as a way to provide RF coverage for two-way radio, paging, cellular and, most importantly, radio communications for police and emergency workers in the event of an accident or fire within a tunnel or enclosed area.

In 1985, the New York City Transit Authority (NYCTA) began a system-wide upgrade of its transit police radio system. This upgrade involved the removal of an existing twin-lead antenna cable and replacing it with radiating cable. The NYCTA was looking for improvements in coverage of communication dead-spots within the tunnel system, improved reliability and the capability to add communications for other purposes in other frequency bands.

The NYCTA approved two radiating cable constructions to replace the existing twin-lead design. One construction was the traditional slotted corrugated copper design. The second construction was a split-shield triaxial design. After testing and qualification, the low-smoke-producing, flame-retardant triaxial design was chosen over the conventional slotted corrugated design for the IRT, the largest portion of the New York Subway System, extending into all five boroughs.

Fischbach and Moore Transit Group was chosen to install the more than 300,000 feet of TRC-1250-size cable (1.760″ outside diameter) that was used. Because of the height restrictions within the tunnel, a maximum reel size of 72 inches was allowed, which provides as much as 2,000 feet of continuous length to be installed before any connector attachment is needed. These cables are directly mounted to tunnel walls, providing easier installation.

Cable design As with all RF cables, the most important function of a radiating cable is to transmit RF energy from one point in a system to another with minimal degradation or loss of signal power. The difference between radiating transmission lines and conventional shielded coaxial designs is that this cable must also allow a controlled amount of RF energy to couple out of the cable and into the surrounding environment without sacrificing too much in downline attenuation.

Figure 1 on page 10 shows the construction of the triaxial cable design. Depending on the cable size, either a copper-clad aluminum conductor or a hollow copper tube is used for the center conductor. The dielectric material is a high-velocity, closed cell structure of foamed polyethylene, which offers a tough, low-loss medium for the transfer of RF energy between the center and outer conductors. The outer shields consist of a semi-circular bonded smooth aluminum tape, which is separated by a layer of solid polyethylene. Braided drain wires are used to provide contact with the two outer shields when connectors are attached.

The outer jacket consists of a dual extrusion of low-smoke, low-toxicity polyolefin material. This proprietary flame-retardant material offers a tough weather- and ozone-resistant jacket, while maintaining the flexibility that is required when installing these cables within enclosed areas.

Theory of operation All radiating cables are affected by their environment. The environmental effect on the cable is a degradation of downline attenuation and coupling loss of varying degrees. The extent of the degradation depends on both the cable design and the environment in which it is installed. Cable performance will exhibit different results under different conditions, such as free space, inside a building or next to a conductive or high-dielectric-constant material (such as lying on the ground or attached directly to a tunnel wall.) The triaxial cable designs exhibit a more stable and predictable performance over these environmental conditions than the conventional slotted corrugated designs because of the different operating mechanisms. With the corrugated constructions, rows of milled openings are created, which provide a means for coupling energy to the surrounding environment. These rows of oval apertures occur periodically along the length of cable and, therefore, contain electromagnetic fields that have a component in the direction of propagation of the cable, which results in the total energy not being transmitted in the transverse electromagnetic mode (TEM). With the triaxial design, the aperture that is created by the separated shields does not store energy but transfers a small amount of energy to the outer surface. These cables are continuous and, therefore, have no fields in the direction of propagation. Figure 2 on page 11 demonstrates the effects of a section of steel piping on the attenuation performance of the two radiating cable designs. Both constructions exhibit similar attenuation characteristics from 100MHz through 1,000MHz. With the introduction of this piping at the input end of the cable, the triaxial design was virtually unaffected, whereas the slotted design showed a significant effect. This is important to system installers because cable standoffs are no longer required, decreasing cable installation costs.

An added benefit of direct mounting is the elimination of hanging cables, which offers a more appealing cable installation. Another benefit is the additional protection from the effects of vibration and damage from contact with moving vehicles.

Electrical performance The attenuation and coupling loss of the triaxial cable is controlled by the separation of the split shields. This approach optimizes the tradeoff between downline attenuation and coupling loss, and they are tightly controlled by the shield width tolerances, as well as dimensional tolerances on both the dielectric core and interlayer. Table 1 above gives values of three of the standard size triaxial designs. The attenuation and coupling loss values are typical of directly mounted conditions. These cables were all mounted directly to the tunnel walls within the New York City transit system, which resulted in easier cable installation and reduced overall cost.

Mechanical considerations In addition to the electrical design performance of these radiating cables, other considerations such as mechanical, physical and environmental issues had to be addressed. The NYCTA required a series of qualification tests to be performed before any cable would be considered for installation within the transit system. Table 2 on page 17 is a partial listing of the environmental, physical and mechanical specifications that the cables were required to meet.

Because of the harsh physical environment that these cables would encounter, additional testing was performed to determine the crush strength of the triaxial designs. Both the corrugated construction and the triaxial design were subjected to a flat plate crush strength test, using the reverse mode on a tensile testing machine. The triaxial cable exhibited increased crush strength to more than twice that of the corrugated copper design. This is primarily due to the tough foamed polyethylene dielectric, along with the protection of the layers of polymeric jacketing material. In addition to the overall higher crush strength, the elastic memory of the materials allowed the triaxial design to return to within one-half ohm of its original impedance, whereas the corrugated construction remained in a crushed state. This increased crush strength and memory may provide the difference in replacing a cable that has been damaged by some outside physical force. The triaxial design is also much more flexible and easier to route than the corrugated copper cable.

Fire safety There have been well-documented mass transit system fires over the years. Death and injury due to toxic products of combustion and smoke have accompanied several of them. As a result, in the last decade, many mass transit systems worldwide have required low-smoke-producing, flame-retardant materials for all products installed in subway tunnels. Events such as the fire at the London Kings Cross Road subway and the tragic loss of 300 lives in the Baku (former Soviet Republic of Azerbaijan) subway fire have ledto an increased awareness of the safety of the materials that are specified and used within enclosed are as.Table 3 on page 17 lists some of the flame performance and products of combustion testing that the triaxial cables meet. With the recent advances in flame-retardant technology and available materials, the triaxial cables are able to meet the required level of flame performance without the need for expensive barrier tapes. In addition to the flame retardance, all materials used in the construction of this cable are non-halogen. When subjected to a flame source these cables exhibit extremely low levels of smoke generation, toxic emissions and corrosive offgassing.

System interconnects For those sections within the transit system that did not require RF communications, or where system interconnects were needed, shielded low-loss coaxial designs were used. These flame-retardant constructions provide lower downline attenuation because of the non-radiating nature of the designs. Both the low-loss coaxial cables and the triaxial radiating designs can be routed much more easily than corrugated copper cables. The flexibility and non-kinking nature of these cables allows them to be routed and bent into tighter areas, reducing installation time. The interconnect cables are also required to meet all the physical, mechanical, environmental and combustion properties of the radiating cable designs.

Because of the varying nature of environments in which radiating cables will be installed, exact electrical performance can be difficult to predict. The triaxial cable designs have exhibited that environment affects performance minimally. These triaxial constructions were chosen by the NYCTA for the various benefits and predictability of performance. The installed cables were tested after installation and exhibited high-quality signal levels when subjected to survey test procedures that were required prior to operation of the system-wide police radio system. The ease of connectorizaton, elimination of cable standoffs and the flexibility of these constructions were also benefits provided to the installation contractors.

Over the past three years, the transit police radio communications system has been operating with no defects or downtime.

Fedor is product manager, cable, for Times Microwave Systems, Wallingford, CT.

Tags: content

Most Recent


  • Triaxial radiating cables improve subway communications:
    Newscan: Securing the Internet of Things is quite a challenge
    Also: EWA requests dismissal of 900 MHz applications; TIA names tech and policy priorities for 2014; IJIS Institute names Shumate Award winner; App makes bus waits more tolerable; a Blackberry comeback may be in the offing.
  • Triaxial radiating cables improve subway communications:
    Newscan: FCC certifies Carlson Wireless's white-space radio
    Also: Congress looks to revamp telecom law; Obama to place some restraints on surveillance; IEEE to study spectrum-occupancy sensing for white-spaces broadband; Major Swedish transport operator opts for Sepura TETRA radios; RFMD to partner on $70 million next-generation power grid project; NENA opens registratiuon for "911 Goes to Washington."
  • Triaxial radiating cables improve subway communications:
    Newscan: A look at the critical job of 911 dispatchers
    Also: NYC launches website for tracking 911 response times; Oregon implements 911 on pre-paid cell phones; LightSquared wants to keep spectrum assets; Harris receives multiple government orders; FCC extends rebanding financial reconciliation deadline; Zetron gear at core of communications system upgrade; Ritron debuts wireless access control system; EWA seeks policy review of VHF vehicular repeater system deployments.
  • Triaxial radiating cables improve subway communications:
    Newscan: Average peak data rates of 144 MB/s average realized in tests with CAT 4 LTE device
    Also: Verizon, T-Mobile to swap unused spectrum to improve coverage; Internet giants oppose surveillance--but only when the government does it; FCC Chairman says incentive auction will be delayed until middle of 2015; FCC chair announces staff appointments; Alcatel-Lucent names Tim Krause as chief marketing officer; New Jersey county deploys TriTech CAD system; Toronto airport deploys 26-position Zetron console system;

Leave a comment Cancel reply

To leave a comment login with your Urgent Comms account:

Log in with your Urgent Comms account

Or alternatively provide your name, email address below:

Your email address will not be published. Required fields are marked *

Related Content

  • RugGear: Contributing to the future of mission-critical broadband communication review and market vision
  • Photo gallery: 2014 Communications Marketing Conference (CMC) in Tucson
  • Triaxial radiating cables improve subway communications:
    Top 5 Stories - Week of Sept. 22
  • Triaxial radiating cables improve subway communications:
    RCA plans to expand this year's Technical Symposium

Commentary


Updated: How ‘sidelink’ peer-to-peer communications can enhance public-safety operations

  • 1
27th February 2023

NG911 needed to secure our communities and nation

24th February 2023

How 5G is making cities safer, smarter, and more efficient

26th January 2023
view all

Events


UC Ezines


IWCE 2019 Wrap Up

13th May 2019
view all

Twitter


UrgentComm

Gallery: The last day of IWCE 2023 dlvr.it/SllQKJ

30th March 2023
UrgentComm

Video: Opening of the Expo Hall on day three of IWCE 2023 dlvr.it/SlkyNy

30th March 2023
UrgentComm

Verizon officials highlight role of 5G tech for responders during IWCE keynote dlvr.it/Slkh9n

30th March 2023
UrgentComm

Day three of IWCE 2023 features the opening of the Expo Hall dlvr.it/Slhgvr

30th March 2023
UrgentComm

Gallery: The Expo Hall opens on day three of IWCE 2023 dlvr.it/SlhfPT

29th March 2023
UrgentComm

Rescue 42 launches miniCRD deployable for FirstNet dlvr.it/SlgdtY

29th March 2023
UrgentComm

RT @IWCEexpo: 📽️ More sights from Day 2 at #IWCE23. It's been a fantastic start so far... Thanks to you! Tomorrow is another awesome spea…

29th March 2023
UrgentComm

RT @IWCEexpo: Ildefonso De La Cruz Morales, Principal Analyst-Critical Communications @OmdiaHQ takes the stage and kicks off tonight’s Keyn…

29th March 2023

Newsletter

Sign up for UrgentComm’s newsletters to receive regular news and information updates about Communications and Technology.

Expert Commentary

Learn from experts about the latest technology in automation, machine-learning, big data and cybersecurity.

Business Media

Find the latest videos and media from the market leaders.

Media Kit and Advertising

Want to reach our digital and print audiences? Learn more here.

DISCOVER MORE FROM INFORMA TECH

  • American City & County
  • IWCE
  • Light Reading
  • IOT World Today
  • Mission Critical Technologies
  • TU-Auto

WORKING WITH US

  • About Us
  • Contact Us
  • Events
  • Careers

FOLLOW Urgent Comms ON SOCIAL

  • Privacy
  • CCPA: “Do Not Sell My Data”
  • Cookie Policy
  • Terms
Copyright © 2023 Informa PLC. Informa PLC is registered in England and Wales with company number 8860726 whose registered and Head office is 5 Howick Place, London, SW1P 1WG.