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
    • Product Guides
  • 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
    • Product Guides
  • 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


Measuring 800 MHz interference

Measuring 800 MHz interference

Accurate readings will help to ensure performance of public-safety networks
  • Written by Urgent Communications Administrator
  • 1st March 2005

In recent years, 800 MHz public-safety systems have encountered increasing amounts of interference. Much of that interference has to do with commercial mobile radio services, or CMRS, providers operating systems on channels in close proximity to those utilized by public-safety entities. Given the homeland security obligations of the nation’s public-safety agencies, it is imperative that their communications are robust, highly reliable and free from harmful interference.

The FCC has adopted a plan designed to address the harmful interference to public-safety communications systems operating in the 800 MHz band (see news story on page 6). The plan has both long- and short-term objectives. Over the long term, the FCC’s plan calls for separating generally incompatible technologies. In the short term, the FCC has implemented objective technical standards — called “enhanced best practices” — for defining unacceptable interference to public-safety systems operating in the 800 MHz band and procedures detailing the responsibilities and expectations regarding abatement of such interference.

The FCC’s plan will result in an additional 4.5 MHz in the 800 MHz spectrum — the equivalent of 90 additional two-way channels — becoming available to public safety, critical infrastructure and private wireless users, including 10 channels for public-safety/critical infrastructure interoperability.

Even with the spectrum changes adopted by the FCC, interference will remain a concern. Accurately measuring interference will go a long way toward ensuring the performance of public-safety networks. However, there is more to it than simply measuring interference. Locating the source of interference so that it can be corrected quickly is equally important.

There are two basic types of interference: in-channel signals and noise, and out-of-channel signals. Each applies to both licensed and unlicensed systems.

In most licensed systems, the frequency allocation process — as well as antenna positioning applications and approvals — prevents overlapping signal paths and unexpected interference. No two systems are deliberately licensed to use identical channels and physically interfering signal paths. So, in-channel interference from other systems generally is not expected, although unintended antenna misalignment can put signals where they don’t belong. Typically, when licensed systems interact, the likely cause is out-of-channel signal effects.

Out-of-channel signals that cause problems for an affected receiver are generally found in areas close to high-power transmitters. These conditions are not unusual when the affected communications system shares common real estate with high-power transmitters, such as the highest points in an urban area, which are prized for the large signal footprint they afford broadcast stations. The two primary interference mechanisms are desensitization and intermodulation.

Desensitization occurs when a legal high-power transmitted signal enters the typical affected receiver and overpowers the designed rejection capability of the front-end RF filter. As the high-power signal comes in, the automatic gain control, or AGC, of the affected receiver cuts back its own amplification. In that action, the amount of gain required for proper signal-to-noise processing of the needed data is reduced. Interference also can clip off the crest factor peaks of digitally modulated signals, including bit errors.

Intermodulation occurs when high-power, out-of-channel transmitters interact to create new signals that appear in the passband of the affected receiver. In order for such signals to intermodulate, there must be an external electrical non-linear element present.

In crowded real estate with many high-power transmitters, non-linear detection can cause the re-generation of multiple intermodulation cross products. If any fall within the affected receiver passband, they reduce the carrier-to-noise (C/N) ratio of the system.

Because the interfering process usually involves overlapping frequencies, a hand-held spectrum analyzer is the test instrument of choice because it conveniently captures and displays such signal overlaps. To ensure accuracy and measurement confidence, the spectrum analyzer should have powerful measurement functions and control key routines that can enhance the technician’s time and skills. Some of the critical functions are markers, preamplifier, demodulation, field-strength parameters and occupied bandwidth/channel power.

Field technicians can use marker controls to identify the frequency of the interfering signal. Marker controls also highlight the simplicity of today’s hand-held spectrum analyzers. If the interfering signal is higher than the intended affected channel signal, the technician simply has to press a key on the spectrum analyzer. An annotation on the display will indicate the frequency and power level of the signal at the appropriate marker position. If the interfering signal is smaller in amplitude than the affected channel signal but still overlaps the signal, the technician can move the marker key to the center of the display. The technician then can reduce the span containing the interfering signal to make it easier measure or identify.

When received signals are weak, which often is the case for field measurements, the preamplifier function becomes important. A preamplifier can add as much as 20 dB of gain at the front-end input. It isn’t permanently wired into the spectrum analyzer because it will be saturated when larger signals are measured. Therefore, it should be used judiciously and with knowledge of the signal environment.

The demodulator function is important if there is AM or FM modulation in the interfering signal. This is common if there is a powerful AM or FM station tower nearby. The demodulator function allows the field technician to select either AM or FM, which is determined by the RF frequency characteristics. Once that is selected, the technician can actually hear the audio on either an internal speaker or plug-in headset.

Identifying interfering signals often requires relative quantities, such as affected signal versus interfering signal, and can be measured in dB ratios. There are occasions, however, when the absolute field strength units need to be measured. One example is when technicians must determine field strength at the affected signals.

Occupied bandwidth, or OBW, allows technicians to define the band edges of an occupied band by defining the RF power points. After the measurement is conducted, the markers are displayed as annotated frequencies on the display and define the band edges where the signal is 20 dB below the carrier. Complementing OBW is channel power, which arithmetically computes the integrated power contained within its defined bandwidth. This mode integrates the power contained within defined OBW.

All of these measurements can be made easily with today’s hand-held spectrum analyzers. Many of the control settings and common measurements can be pre-set by engineering management, stored in the spectrum analyzer’s memory and recalled by technicians in the field. This is especially useful when the site under test is routine and repetitive or if the spectrum analyzer is being used when measure standardized frequencies and bandwidths.

There are two configurations in which a hand-held spectrum analyzer can be used to measure interference. One is to directly connect the instrument to the affected system’s antenna, and the second is to use a portable antenna with the spectrum analyzer.

A spectrum analyzer exhibits approximately the same sensitivity as a typical affected system receiver and can be connected into the communications system antenna in place of the affected system receiver. Also, the spectrum analyzer can be easily connected to the system combiner/splitter by unscrewing the signal cable and connecting it to the spectrum analyzer input.

When not connected to the communications system antenna, the spectrum analyzer still can conduct interference measurements via an independent antenna that utilizes a “whip” design. A whip antenna is a linear conductor connected to the coaxial input connector on the spectrum analyzer.

Each antenna is sized for one-quarter wavelength at the specified center frequency. Some whip antennas are also “inductive-loaded,” i.e., their physical length is not equal to the one-quarter electrical wavelength. Whip antenna designs are omnidirectional so they are insensitive to directional efforts.

For additional diagnostic power in certain interference measurement situations, the operator must use a directional antenna. In those cases, a directional antenna attached to the spectrum analyzer can help determine the direction from which an interfering signal is arriving. Obviously, this makes it easier to find the location of the interfering signal’s source.


Donn Mulder is the field solutions business unit manager for Anritsu Co. He earned a bachelor’s degree in electrical engineering from Iowa State University and has been involved in the test and measurement market for 25 years.

Interpreting dB power displays on a spectrum analyzer

When using a spectrum analyzer in its logarithmic display mode, typically 10 dB per division, adding the displayed signal powers from several sources is not immediately obvious. In the figure, the main affected Signal A is shown flat at -50 dBm. An interfering Signal B is shown having the same -50 dBm power level.

The sum of two different signal traces is not the added physical heights of the two displayed traces. Decibels are logarithmic values so they add in non-linear fashion. When Signals A and B add together to form a single trace — though they create a combined linear power that is twice the amount of either — the displayed logarithmic power is just +3 dB higher.

Likewise, when Signal A combines with Signal C, since Signal C is 10 dB lower than Signal A — meaning only one-tenth the power — the combined power of A and C is 10% higher, or 1.1 times the power of Signal A. This logarithmically adds to only +0.42 dB higher than Signal A, as shown.

Tags: Regulation content Operations Policy Wireless Networks

Most Recent


  • Public-safety coalition renews efforts to secure federal NG911 funding
    A coalition of public-safety associations today reiterated its support for federal legislation that would provide the funding needed to pay for 911 centers to migrate from legacy technologies to an IP-based next-generation 911 (NG911) platform that is designed to support multimedia communications, as well as traditional voice calls. Representatives of the Public Safety Next Generation […]
  • Measuring 800 MHz interference
    Newscan: Cyberattacks on DoE national labs draw lawmaker scrutiny
    Web Roundup Items from other news organizations Cyberattacks on DoE national labs draw lawmaker scrutiny Blinken postpones trip to Beijing after Chinese spy balloon spotted over U.S., officials say To protect satellites, secure your networks, chief of space ops says Ransomware offlines Arizona’s largest school district Mending the fabric: FCC says to file broadband-location challenges […]
  • The shine begins to wear off 5G private wireless
    Verizon had high hopes for private wireless networking. The company had predicted that by now it would be well on its way to making billions of dollars from the sale of custom 4G and 5G networks dedicated exclusively to its enterprise customers. Indeed, during 2021 Verizon execs pegged the total addressable market for private wireless at around […]
  • Phishers trick Microsoft into granting them 'verified' Cloud Partner status
    Late last year, a group of threat actors managed to obtain “verified publisher” status through the Microsoft Cloud Partner Program (MCPP). This allowed them to surpass levels of brand impersonation ordinarily seen in phishing campaigns, as they distributed malicious applications bolstered by a verified blue badge only ever given to trusted vendors and service providers in […]

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

  • L3Harris unveils P25-LTE device that is designed to meet stringent new fire standard
  • Open-source tools for the IoT ecosystem
  • New Orleans-area 911 center inks multiyear APEX deal with Carbyne to replace call-handling system
  • Measuring 800 MHz interference
    Newscan: Feds recover millions from pipeline ransom hackers, hint at U.S. Internet tactic

Commentary


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

26th January 2023

3GPP moves Release 18 freeze date to March 2024

18th January 2023

Do smart cities make safer cities?

  • 1
6th January 2023
view all

Events


UC Ezines


IWCE 2019 Wrap Up

13th May 2019
view all

Twitter


UrgentComm

Public-safety coalition renews efforts to secure federal NG911 funding dlvr.it/ShwGfn

4th February 2023
UrgentComm

Newscan: Cyberattacks on DoE national labs draw lawmaker scrutiny dlvr.it/Shvpw3

3rd February 2023
UrgentComm

The shine begins to wear off 5G private wireless dlvr.it/Shth0P

3rd February 2023
UrgentComm

Phishers trick Microsoft into granting them ‘verified’ Cloud Partner status dlvr.it/Shqngn

2nd February 2023
UrgentComm

Shapeshifting robot can morph from a liquid to a solid dlvr.it/Shqk9K

2nd February 2023
UrgentComm

Automakers against stampede to BEV dominance dlvr.it/ShpX08

2nd February 2023
UrgentComm

FCC nominee Gigi Sohn headed for third Senate hearing dlvr.it/ShpDcZ

1st February 2023
UrgentComm

Sign up to learn how to successfully manage your Motorola ASTRO® 25 System: spr.ly/60143j8fp https://t.co/XcxiUwzN27

1st February 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.