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


Troublesome telco line problems

Troublesome telco line problems

Ever had one of those days when nothing seems to work according to theory? Usually, it is something simple, and we technicians often tend to overlook
  • Written by Urgent Communications Administrator
  • 1st August 1997

Ever had one of those days when nothing seems to work according to theory? Usually, it is something simple, and we technicians often tend to overlook the simple problems in pursuit of the more complex and weird stuff.

After working many long hours for several weeks in an effort to meet a startup deadline for our new centralized dispatch center, my assistant, Hilton Crews, and I were beginning to see the light at the end of the tunnel. Little did we know that the light would turn out to be a speeding freight train. After all, the most difficult part of the journey was behind us, and the remaining tasks were fairly simple in comparison_or so we thought!

The Problem Part of this project included the installation of quite a few base stations and all that goes with that (antennas, control lines, grounding, lightning protection, etc.). At one location we installed three base stations with associated control lines leased from telco to allow remote control from the central dispatch point. The remote control system used the standard remote control audio tones (2,175Hz for transmitter keying).

After getting everything installed and wired up on both ends, we were ready to run initial tests on the three stations. The basic block diagram is shown in Figure 1 below.

Ready, set, go! It works!

No, it doesn’t.

Yes, it does!

Simply put, it worked intermittently. With 10 transmitter keying signals sent down the line, the transmitter would not key 100% of the time. The keying percentage would vary from 30% to 70%, with each series of 10 keying control signals.

Before installing the base stations at the remote sites, we had checked each one with the dispatch console to make sure each one worked. This included transmitter keying and modulation. The only thing different now was the interconnecting telco line_or was it? We decided to check the telco line for loss and frequency response. Maybe there was a severe attenuation notch at the 2,175Hz keying control frequency. It can happen, but on all three lines?

A fairly complete frequency response test did not indicate such a problem. From the test results, it would seem that the telco line should work. Hilton and I were using two identical-line testing instruments with a built-in intercom so that we could communicate and coordinate our test procedure. It was during one of these voice messages that I noticed that Hilton’s voice sounded as if he were talking through a fan. I communicated this to him, and he also noticed the “fan-voice” sound. It sounded much like a broadcast radio with a bad filter capacitor in the power supply, with the voice riding on top of the 60Hz hum (120Hz in the case of a full-wave rectifier).

As it turned out, this was the clue that ultimately led to the cure. However, another twist would lend more confusion to the issue. Having tried almost everything we could think of, it was almost desperation time! If you look at Figure 1, you will see a line protector that is used to protect the equipment from lightning surges on the telco line. Given our past experience with these devices, we never suspected that this device could play even a minor role in the problem we were experiencing. In a last-gasp attempt to find some common denominator to the problem, I asked Hilton to disconnect this line protector and to wire the telco line straight into the base station tone-termination panel.

Though neither of us was expecting to see any positive results from this procedure, we had nothing to lose. After Hilton made the change, the dispatch console sent 10 consecutive keying signals down the line to the transmitter.

“Okay Hilton, how many times did the transmitter key?”

“Ten for ten,” came the enthusiastic reply from Hilton. Then a few seconds of dead silence on both ends_neither of us could believe that we had overlooked this innocuous device for so long! Hilton made some ac voltage measurements and found the ac voltage (60Hz) on the line to be high. This accounted for the “fan-voice” effect. Apparently, the ac voltage was causing the line protector components to “fire,” which caused distortion preventing the tone-termination panel circuitry from recognizing the keying signal.

The Solution Obviously, we couldn’t leave the base station hooked to the telco line without any lightning protection device connected, so a means of eliminating the 60Hz ac voltage had to be found. In a conversation with some of the telco personnel, Hilton learned about a special filter that telco technicians use on occasion to eliminate certain line interference problems. Telco loaned us three filters to use on a trial basis. Unfortunately, the filters did not eliminate the interference problem, but they did lead to the solution. Hilton contacted the manufacturer of these filters only to learn that better filters were available to combat the 60Hz “power influence” problem.

Having made the call to SNC Manufacturing, Oshkosh, WI, Hilton soon had the proper filters in hand. In each case, the filter was installed between the line protector and the line itself. The result was amazing. The transmitters would now key reliably even with the line protector in line. Figure 2 on page 8 shows a block diagram of the circuit after the installation of the SNIX filter (Single Noise Interference Xterminator) from SNC Manufacturing, as shown in Photo 1 on page 8.

Summary Something can be learned from this_never be surprised at what you might find on a leased telco line. Expect the unexpected! Check for any induced 60Hz ac voltage on the line. Check for any dc voltage. Measure across the line and from each leg to ground. Check the line loss over the audio frequency range and especially at each of the control tone frequencies. Where bidirectional amplifiers are used, the loss and response tests should be conducted in both directions and compared. In short_be thorough.

Further information on these filter products can be obtained from SNC Manufacturing, 101 W. Waukau Ave., Oshkosh, WI 54901, or call them at 1-800-558-3325. Information is also available from SNC from their website at: www.sncmfg.com.

Until next time_stay tuned!

Kinley, a certifiied electronics technician, is regional communications manager, South Carolina Forestry Commission, Spartanburg, SC. He is a member of the Radio Club of America.Je is the author of Standard Radio Communications Manual: With Instrumentation and Testing Techniques, which is available for direct purchase. Write to 204 Tanglewylde Drive, Spartanburg, SC 29301. Kinley’s email address is [email protected]

Tags: content

Most Recent


  • Troublesome telco line problems
    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.
  • Troublesome telco line problems
    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."
  • Troublesome telco line problems
    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.
  • Troublesome telco line problems
    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
  • Troublesome telco line problems
    Top 5 Stories - Week of Sept. 22
  • Troublesome telco line problems
    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.