https://urgentcomm.com/wp-content/themes/ucm_child/assets/images/logo/footer-new-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
    • 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
    • Omdia Crit Comms Circle Podcast
    • Galleries
    • IWCE’s Video 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
    • 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

Test & Measurement


Why isn’t my walkie working?

Why isn’t my walkie working?

The answer often is simple - and usually involves the antenna
  • Written by Urgent Communications Administrator
  • 1st November 2007

Have you ever used a walkie-talkie and felt there was something wrong with the particular radio you were using, or with the system, because the range was reduced? Have you ever wondered why some walkie-talkies seem to have much farther range than other portable radios on the same system?

Case in point: A new VHF radio system recently installed for a public-safety agency worked sometimes, and sometimes not. Specifically, it had poor range with some of the walkie-talkies but great range with others. Why did some of the units work with a range of better than 20 miles, while others exhibited a range of less than 2 miles?

The range of a radio system is influenced by the aggregate of several factors, including the following: transmitter power; receiver sensitivity; transmission line losses; antenna gain, efficiency and height; line of sight; obstructions; terrain; noise floor; and RF interference. But the items dealing with the antenna have the greatest effect on the range.

Because the fixed part of the system, often referred to as the system infrastructure, is constant for all users, the system’s base station and mobile and portable radios have the same operating parameters. The main difference is that the external environment in which a portable handset operates can change simply by the user turning around. Reception also can be affected by where the radio is worn or where the user’s hand is placed in relation to the walkie-talkie antenna.

Even though antenna efficiency has the greatest influence on both the transmitting and receiving paths, it is rarely tested. While it is easy to measure a radio’s transmitter and receiver parameters, it is quite difficult to measure the antenna parameters.

When testing antennas for walkie-talkies, especially for VHF radios, it is very important that the antenna always be at least 1 to 2 inches away from the body if the radio is worn on the belt, as close proximity of the body to the entire length of the antenna seriously detunes the antenna. In fact, it is not uncommon for the range to shrink to 1% of normal should the antenna come in contact with a person’s body. Most of the radios on the market today have the antenna mounted to the case in a manner that creates suitable distance from the body, or they have leather or canvas cases that provide adequate separation. Those of us who have “extra handles” at our midsections must use the external cases or pouches, even on the radios that have the distances built into them.

The best way to determine how well an antenna performs standing in free space compared with sitting just above a belt is to use one of the antenna analyzers — such as Anritsu’s Site Master or Bird Technologies’ Site Analyzer — with a phase-stable cable, along with the proper adapter to match the end of the phase-stable cable to the antenna.

An antenna analyzer will give a graphical representation of the antenna performance, which is better than just looking at the reflected power on a specific frequency using a wattmeter.

Under normal circumstances, a standing wave ratio (SWR) of under 1.5:1, which is equivalent to -14 dB return loss, indicates a good match at the operating frequency. A SWR of 2.0:1, which is equivalent to a -9.0 dB return loss, is the worst case that would be tolerated. At 2.0:1 SWR, the antenna is operating only at 90% efficiency, which is the bare minimum.

Field tests show that many antennas operate only within a 5 MHz window where the SWR is less than 2.0:1, and the antenna manufacturers normally label such limits on the antenna or by the model designation.

In further testing, when an antenna that is tuned correctly and has a good SWR on the normal operating frequency is placed directly next to a body — as would occur when a walkie-talkie is mounted on a person’s belt and the antenna is touching the body — the SWR goes from acceptable to terrible. In the case of the public-safety agency installation mentioned earlier, the antenna was detuned to the point that it was operating at less than 1% efficiency.

Using an antenna analyzer, it was shown that just moving the antenna away from the body by at least 1 inch caused the antenna to behave as designed and the SWR returned to the acceptable range. Some manufacturers, such as Motorola and Kenwood, have addressed this problem with antennas that are mounted so that they are moved away from the body even when there is no holster case and only the belt clip is used.

Radios manufactured by other companies that were outfitted with the recommended holster cases — resulting in the antennas moving away from the body at the recommended distance of 2 inches or more — worked as designed. (See Figure 1 on page 34.)

Should someone want to leave the radio on the belt and use a lapel microphone, then the antenna must be away from the body by more than 1 inch — preferably by 2 inches — for the radio to work properly in the VHF band. As the frequency goes up, the distance between the body and the antenna can be reduced. Although VHF antennas need the most separation distance, it can be reduced to less than an inch for UHF and higher frequencies and the antenna will continue to work properly.

The ultimate way to determine whether a radio and antenna combination is working properly is to test the field intensity to see whether it matches the predicted value for the power at a controlled distance.

Field intensity is a quantitative measurement that indicates how much signal is radiated from a radio transmitter. One of the laws of physics that prevails here is that as you increase the distance between the transmitter and the receiver, the field intensity drops by the square of the distance. In simple terms, if you double the distance, you quarter the field intensity. If you triple the distance, the field intensity will drop by a factor of 1/9 the original value. If you quadruple the distance, the signal will be 1/16 the original value. A second factor is the free space attenuation of radio signals, which is expressed in Equation 1 above.

This formula works for line-of-sight signals. Any obstructions such as trees, buildings, vehicles or people will attenuate the signal to some extent. In this case, the body could block the antenna signal path to and from the base station site. Also, if line-of-sight conditions do not exist due to terrain obstructions, there will be severe losses between the transmitter and the receiver. Finally, it should be noted that the curvature of the earth prevents a signal from being line-of-sight over very great distances.

When a walkie-talkie radio is used without a lapel microphone, the radio is brought up to the face of the user, and the antenna is usually above the user’s head so that it does not matter which direction the user is from the base station or repeater with which they are communicating. When a lapel microphone is used with a portable radio, the handset is directional in such a way that when the body of the user blocks the radio and antenna from the other user or repeater, the signal will be attenuated to some extent.

This condition also is present with VHF radio systems, but not to the extent that most users need to worry about it. On UHF and higher frequencies, such as 700 MHz, 800 MHz and 900 MHz systems, the manufacturers of the radio systems put the antennas on the lapel microphones to lessen these directional effects. It was through field intensity tests that the manufacturers determined lapel microphone antennas were needed for these higher frequencies. Many of the UHF and higher frequency systems use multiple receivers and a voting system so that users in the field do not need to worry about which direction they are facing when using their radios.

A walkie-talkie still is the preferred mode of communications for many companies and agencies. Over the years, such radios have become very small, reliable and user-friendly. The one component that has not changed across the decades of use is the antennas. Due to the laws of physics, the antennas must be a certain length that corresponds to the frequency being used. When the antennas are placed so that they touch the body of the user, they will be detuned and no longer perform properly. Just an inch or two away from the body will ensure the antenna works as designed for VHF radios, and less for the higher frequencies. When your radio system fails to work as designed or expected, do not forget to look at the antennas of the walkie-talkies as the problem.


Ira Wiesenfeld, P.E., CETsr, is a licensed engineer in the state of Texas who holds an advanced class license (WA5GXP) as well as a GROL. He has been involved with commercial radio systems since 1966 and has a BS degree in electrical engineering. Wiesenfeld is the author of Wiring for Wireless Sites and can be reached at [email protected].

Tags: Antennas Test & Measurement Tower & Site

Most Recent


  • Humanoid robot explores shipwrecks
    Stanford University researchers created a humanoid diving robot that can access deeply-sunk vessels and objects, and features a haptic feedback system that simulates the feeling of items encountered so operators can experience what the robot does. The robot, known as OceanOneK, also comes fitted with 3D vision and eight multidirectional thrusters to help it navigate […]
  • Building open data systems to benefit road networks
    The proliferation of connected vehicles and sensors embedded into road infrastructure offer manifold possibilities to collect and analyze data to improve road safety, direct maintenance efforts and guide equitable mobility programs. Creating of open data systems, where the gathered information can be safely and affordably stored, analyzed and shared, could help better transportation networks on […]
  • Police adopt license-plate readers at an accelerating pace
    Without a doubt, more law enforcement agencies are acquiring automated license plate reader cameras and technology (ALPR). Study producer Transparency Market Research (TMR) expects the global ALPR market to expand at a compound annual growth rate of 9 percent during the forecast period, 2020 to 2030. Much of the growth is linked to a rise in usage […]
  • Why isn’t my walkie working?
    Newscan: FBI investigation determined Chinese-made Huawei equipment could disrupt U.S. nuclear-arsenal communications
    Web Roundup Items from other news organizations FBI investigation determined Chinese-made Huawei equipment could disrupt U.S. nuclear-arsenal communications Google, like Amazon, will let police see your video without a warrant TSA revises cyber rules for pipelines NIST revises cybersecurity guidelines specifically for HIPAA Police license-plate tech gets green light in Dayton, Ohio US-UK Data Access […]

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

  • New Orleans-area 911 center inks multiyear APEX deal with Carbyne to replace call-handling system
  • Cyber is the new Cold War, and AI is the arms race
  • Microsoft patches 6 zero-day vulnerabilities under active attack
  • AI energizes remote monitoring of patients, fuels bidirectional health care

Commentary


LTE and liability: Why the fire service must move forward with digital incident command

  • 2
6th May 2022

Partnership and collaboration must be the foundation for emergency communications

18th April 2022

FirstNet success means no hypothetical ‘shots’ need to be fired, Swenson says

22nd February 2022
view all

Events


UC Ezines


IWCE 2019 Wrap Up

13th May 2019
view all

Twitter


UrgentComm

Newscan: Verizon counts 5.1 million first-responder subs; AT&T has 3.7 million dlvr.it/SW84Gv

6th August 2022
UrgentComm

Taiwan crisis another blow to the supply chain dlvr.it/SW7GSs

5th August 2022
UrgentComm

Motorola Solutions seeks contempt finding, global injunction against Hytera for not paying royalty dlvr.it/SW6Ldm

5th August 2022
UrgentComm

Humanoid robot explores shipwrecks dlvr.it/SW36fy

4th August 2022
UrgentComm

How IT teams can use ‘harm reduction’ for better cybersecurity outcomes dlvr.it/SW32rd

4th August 2022
UrgentComm

Increase in emergency-response time caused by insufficient staffing, traffic congestion dlvr.it/SW16zp

3rd August 2022
UrgentComm

Tepid demand, taxation fears drag at 2.5GHz spectrum auction for 5G dlvr.it/SW15Yt

3rd August 2022
UrgentComm

Newscan: Cyberattacks against critical infrastructure quietly increase dlvr.it/SVxr3P

2nd August 2022

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”
  • Cookies Policy
  • Terms
Copyright © 2022 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