https://urgentcomm.com/wp-content/themes/ucm_child/assets/images/logo/footer-logo.png
  • Home
  • News
  • Multimedia
    • Back
    • Multimedia
    • Video
    • Podcasts
    • Galleries
  • Commentary
    • Back
    • Commentary
    • Urgent Matters
    • View From The Top
    • All Things IWCE
    • Legal Matters
  • Resources
    • Back
    • Resources
    • Events
    • 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
    • Cookies Policy
  • Related Sites
    • Back
    • American City & County
    • IWCE
    • Light Reading
    • IOT World Today
    • Mission Critical Technologies
    • Microwave/RF
    • T&D World
    • 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
    • Galleries
  • Commentary
    • Back
    • All Things IWCE
    • Urgent Matters
    • View From The Top
    • Legal Matters
  • Resources
    • Back
    • Events
    • Webinars
    • White Papers
    • Reprints & Reuse
    • UC eZines
  • IWCE
    • Back
    • Conference
    • WHY ATTEND
    • Exhibitor Listings
    • Floor Plan
    • Exhibiting Information
    • Registration Opens April 2019-Join Our Mailing List
  • About Us
    • Back
    • About Us
    • Contact Us
    • Advertise
    • Terms of Service
    • Privacy Statement
    • Cookies Policy
  • 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


Analog Multiplex systems: The basics

Analog Multiplex systems: The basics

Part 3 - Active analog mux systems are still in widespread use. An understanding of basic testing and troubleshooting techniques can distinguish a technician.Equipped
  • Written by Urgent Communications Administrator
  • 1st June 1999

Part 3 – Active analog mux systems are still in widespread use. An understanding of basic testing and troubleshooting techniques can distinguish a technician.

Equipped with a basic understanding of analog multiplex (mux) systems, two-way radio technicians can take the leap toward extending their duties beyond base station maintenance and into transmission systems.

This three-part series concludes with a brief discussion of mux system connections, VF and HF considerations and practical testing and troubleshooting techniques.

VF jackfield External circuits that interface with a mux modem should do so through a VF jackfield. The jackfield allows the “end equipment” (base station, telephone, etc.) to be isolated from the mux modem for testing purposes. There should be jack positions for the MOD, DMOD, and E & M leads of each mux channel. (See Figure 1.)

The top jacks are wired to the mux channel modem and are referred to as the line side of the jackfield. These jacks allow VF level testing into the mux modem MOD or out from the DMOD. The bottom jacks are referred to as the drop side of the jackfield.These jacks allow VF level testing into and out of the drop (“customer”) equipment. Without any test cords plugged in, the jackfield internally connects the line side to the drop side. If a test cord is inserted into either the line or drop jacks, the internal connection is broken and the two sides are electrically isolated.

The balanced connections to and from the VF jackfield have a circuit impedance of 600V. When test equipment is plugged into either the line or drop jacks, the instrument should have an internal terminating impedance of 600V. Because the line and drop jacks break (isolate) the two sides of the circuit, this allows the side under evaluation to be properly terminated into the test equipment for accurate measurements. A common mistake is to have the test equipment set up in the bridging rather than terminating mode when plugged into a breaking jackfield. This will not offer the proper termination to the circuit, and it will result in level readings being +6dB hotter than what actually exists without the test equipment in the circuit.

Often, a third monitor jack is located beneath the VF line and drop jacks. Plugging test equipment into this jack will not break the circuit, but it puts the test equipment in parallel with it. In this case, the test equipment must be put in the bridging mode to avoid a double-termination to the circuit under test. A double-termination will result in readings that are 23dB lower than what actually exists when the test equipment is removed.

When measurements indicate levels are 23dB lower or +6dB hotter than expected, the test equipment terminating/bridging mode switch should be checked. The mode switch only affects the receive portion of the test equipment.

VF test equipment Serious VF test equipment can accomplish more than just frequency and levels checks. Circuit performance parameters can be obtained from use of a transmission impairment measurement set (TIMS). Test results indicate various aspects of circuit quality. The telephone industry has established standards for many tests such as PAR (peak-to-average ratio), message circuit noise, noise-with-tone, signal-to-noise ratio, 3-level impulse noise, phase jitter, envelope delay, noise-to-ground and non-linear distortion, to name a few.

HF test equipment As the channel modems translate VF signals up to their assigned baseband frequency slots, a method is needed to measure the signal levels of the individual circuits while in the HF frequency range. A frequency selective device is required that can discriminate between the different frequencies on the baseband. Such a device is called a frequency selective voltmeter (FSVM), sometimes referred to as a selective level meter. This piece of test equipment has a variable bandpass “window” that can be tuned to any baseband frequency. It measures the power level (in dBm) of the energy within the bandpass being viewed. This allows measurement of individual multiplexed channel signals while filtering off all other baseband frequencies. The selective can measure broadband (3kHz) or narrowband (about 200Hz bandwidth) circuit levels and typically has both flat and C-Msg weighted filters offering different response characteristics.

A spectrum analyzer is another useful tool for viewing baseband levels. There are spectrum analyzers made specifically for baseband frequencies that have their horizontal baseline calibrated to read in terms of channel, group, supergroup and mastergroup numbers. Test tone level can be calibrated on the vertical axis (signal amplitude, in dBm) so that the whole baseband can be evaluated at a glance with regard to signal levels. Hot levels can be easily identified and zoomed in on down to the channel level.

As a tool in gain/loss measurements, a bridging HF signal generator may be connected to the baseband and used to inject specific tone frequencies at a specific levels. The HF frequency, when de-multiplexed, will produce a VF tone in the DMOD of the associated mux channel that occupies that portion of the baseband.

Video (HF) jackfield The multiplex system baseband connects to a microwave radio through separate receive and transmit coaxial cables. There should be an HF or video jackfield placed between the mux system and the microwave radio so that the two can be electrically isolated for testing and troubleshooting purposes. A monitor jack is usually provided in both the transmit and receive directions. This allows a FSVM, bridging HF signal generator or baseband spectrum analyzer to be plugged into the jackfield to gain access to the baseband without “breaking” the connection and disrupting traffic.

Potential problems Care should be taken to maintain proper signal levels within an analog multiplex system. Whether they be externally injected test tones or “live traffic,” excessive levels can drive analog mux circuitry into non-linear modes that wreak havoc on the baseband. Hot signals can not only splatter over to adjacent channel slots but produce sum and difference frequencies that affect circuits in other areas of the baseband spectrum as well. As mentioned previously, there should not be any signal on the baseband that exceeds TTL.

Another cause of baseband interference relates to poor shielding or bad solder connections in a mux/baseband assembly. Occasionally, local AM broadcast stations, which operate in the same frequency range as the baseband, can be heard on the baseband along with the mux signals. Although such interference typically affects only one or two mux channel slots, it can render those slots useless for “live traffic.”

Analog mux modems also require periodic maintenance. The operating frequencies of their on-board oscillators should be held to within +/-5Hz to eliminate problems with translation error.

Conclusion FDM systems have been in use for a long time. Although a lot of the latest wireless applications are employing digital technologies, active analog mux systems are abundant and employers need qualified technicians to maintain them. Many of these employers have microwave, mux and base stations at their hilltops and would much prefer having one technician “do it all.” With a basic understanding of analog multiplex systems, two-way technicians will find themselves better postured in today’s job market.

Tags: content

Related


  • RugGear: Contributing to the future of mission-critical broadband communication review and market vision
    As one of the leading international developers and manufacturers of rugged mobile phones, smartphones and tablets for professional use in extreme safety and working conditions RugGear is becoming an increasingly important player in the field of mission critical communications. With our high-performance mission critical flagship product RG760 we are proud to contribute to the future […]
  • Photo gallery: 2014 Communications Marketing Conference (CMC) in Tucson
    This photo gallery features scenes from the 2014 Communications Marketing Conference (CMC) in Tucson, Ariz.
  • Top 5 Stories - Week of Sept. 22
    Top 5 Stories - Week of Sept. 22
    Here’s a look at the most popular stories on IWCE’s Urgent Communications from the last week.
  • RCA plans to expand this year's Technical Symposium
    RCA plans to expand this year's Technical Symposium
    Recent presentations, given by both startups and major corporations, have included fractal antennas, LTE, emergency communications, "invisibility cloaks" using RF, disabling IEDs with RF and tropospheric ducting.

One comment

  1. Avatar Rami Safar 17th June 2015 @ 12:50 pm
    Reply

    Greetings,
    I am new in voice

    Greetings,

    I am new in voice MUX and in my work there are a lot of bulky VF jackfields used to troubleshoot E&M and Voice circuits. I want to know if there other new patch panels or other way of troubleshooting techniques to avoid using old VF Jackfield. As you know these backfields requires a lot of wireing and it’s trouble the wiring in MDF side.

    Regards,

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

  • Newscan: Indiana 911 dispatch-center deadline looms
  • Newscan: Texting 911 becomes an option for some Pennylvania cell-phone users
  • Newscan: Senator wants inventory of government spectrum
  • CMA conducts 40th conference this week

Commentary


Unlocking the power of ESInets: Different NG911 provisioning approaches exist; level of control is key differentiator

7th April 2021

Ransomware? Let’s call it what it really is: extortionware

21st February 2021

Redefining communications for today’s mobile workforces

18th February 2021
view all

Events


UC Ezines


IWCE 2019 Wrap Up

13th May 2019
view all

Twitter


UrgentComm

Newscan: Single sign-in for government services expands to states, localities dlvr.it/RxLQNR

9th April 2021
UrgentComm

‘Life-saving technology’: AST SpaceMobile CEO outlines capabilities of direct-to-smartphone LEO satellite service dlvr.it/RxKqvp

9th April 2021
UrgentComm

Handcuffs over AI: Solving security challenges with law enforcement dlvr.it/RxGtpD

8th April 2021
UrgentComm

Fujistsu: Cyber cretins are casing out private 5G dlvr.it/RxGnfN

8th April 2021
UrgentComm

Faster in-vehicle Wi-Fi dependent on faster connectivity dlvr.it/RxGnZL

8th April 2021
UrgentComm

Digital-health infrastructure benefits from cloud-to-edge architecture dlvr.it/RxFcjx

8th April 2021
UrgentComm

All actions monitored: The 10 most surveilled major cities in the U.S. dlvr.it/RxFZHV

8th April 2021
UrgentComm

Unlocking the power of ESInets: Different NG911 provisioning approaches exist; level of control is key differentiat… twitter.com/i/web/status/1…

7th April 2021

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
  • Microwave/RF
  • T&D World
  • TU-Auto

WORKING WITH US

  • About Us
  • Contact Us
  • Events
  • Careers

FOLLOW Urgent Comms ON SOCIAL

  • Privacy
  • CCPA: “Do Not Sell My Data”
  • Cookies Policy
  • Terms
Copyright © 2021 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.
This website uses cookies, including third party ones, to allow for analysis of how people use our website in order to improve your experience and our services. By continuing to use our website, you agree to the use of such cookies. Click here for more information on our Cookie Policy and Privacy Policy.
X