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

content


Using crystal filters at VHF high band

Using crystal filters at VHF high band

One of the principal drawbacks of crystal filters is their inherently high insertion loss. This column examines how such filters can be used and how to
  • Written by Urgent Communications Administrator
  • 1st June 1998

One of the principal drawbacks of crystal filters is their inherently high insertion loss. This column examines how such filters can be used and how to minimize the impact of the high insertion loss. Several examples will be shown, with comparisons of the various aspects of each.

Example 1 Figure 1 below shows a simple arrangement with an antenna, transmission line and receiver. In this example, and those that follow, the transmission line loss is 2dB and the receiver has a noise figure of 9.2dB (0.25mV sinad sensitivity). In each example, the effect of antenna noise figure (noise temperature) on system noise figure will be shown at antenna noise figures of 3dB, 10dB and 15dB. Such figures aid in analyzing the overall system noise figure under various site noise conditions.

Notice in Figure 1 that as the noise figure of the antenna increases, the overall system noise figure approaches the antenna noise figure. This is because the noise figure of the first device in a receiving chain has a dominant effect on the overall system noise figure. This is the reason for using low-noise, tower-top amplifiers. A low noise figure, along with gain, has a more pronounced effect on lowering the overall system noise figure.

Example 2 Figure 2 below shows a highly selective, four-pole crystal filter, with an insertion loss of 8dB, inserted in the receiving chain just ahead of the receiver. Compare the overall noise figures at various antenna noise figures with the example in Figure 1. Note that the overall noise figures (even with low antenna noise figure) are significantly higher due to the insertion loss of the crystal filter. An amplifier can be used to compensate for the insertion loss of the crystal filter. The next two examples study the effects of placing the amplifier before and after the crystal filter.

Example 3 In Figure 3 on page 46, a low-noise amplifier is placed between the crystal filter and the receiver input. The amplifier has a noise figure of 1.5dB, a gain of 15dB (and a third-order intercept point of 30dB). Compare the overall system noise figure of this arrangement with the system noise figures shown in Figures 1 and 2. There is a significant improvement over the arrangement in Figure 2. Note that the overall system noise figures are not significantly worse than those shown in Figure 1-especially at the higher antenna noise figures. Thus, the amplifier has practically negated the negative effect of the crystal filter’s insertion loss on overall system noise figure.

Example 4 In Figure 4 on page 46, the amplifier has been placed in front of the crystal filter in an effort to further improve the system noise figure. Compare the system noise figures with those in the previous examples. The effect is significant. At an antenna noise figure of 3dB, the overall system noise figure is now 7.64dB. This is almost 5dB better than in Figure 3 and almost 4dB better than in Figure 1. However, as the antenna noise figure increases, the differences in system noise figures are less significant.

Amplifier placement As shown, the placement of the amplifier in the receiving chain may or may not make a significant difference, depending on the antenna noise figure or site noise level. At low antenna noise figures, the amplifier makes a greater improvement as it is placed closer to the antenna. In such cases, a tower-top amplifier would yield maximum benefit. However, as the site noise increases, causing the antenna noise figure to rise, the relative position of the amplifier in the receiver chain is less important.

If the amplifier is placed ahead of the crystal filter, the susceptibility to interference will be increased. Strong, off-channel signals could be increased to the point of causing receiver desense; intermod becomes a greater possibility.

In Figure 5 on page 48, the amplifier is placed before the crystal filter. Assume that the frequency relationship between two signals (A and B) and the receiver frequency is such that 2A 2 B is equal to the receiver frequency. Again, the amplifier has a gain of 15dB and a third-order intercept point of 130dBm. If signal A is at 0dBm and signal B is at 220dBm at the amplifier input, then the third-order intermod signal (2A 2 B) at the amplifier output will be 280dBm. The insertion loss of the crystal filter (8dB) would put the intermod signal at 288dBm at the receiver input. This would certainly cause destructive interference.

In Figure 6 on page 48 the position of the amplifier and crystal filter has been reversed. Now, with the filter preceding the amplifier, the levels of signals A and B are much reduced by the selectivity of the filter. Assuming a 60dB reduction, signal A is now at 260dBm and signal B is at 280dBm at the amplifier input. Now, the intermod signal (2A 2 B) is at 2260dBm at the receiver input.

Obviously, such a low-level intermod signal could do no harm.

Summary >From this discussion, it is apparent that noise and interference levels must be taken into account when designing the receiver system chain. The arrangement that will produce the best system noise figure may not be practical in the presence of certain interfering signals. Usually, when a crystal filter is needed, the site is already heavily laden with noise and interfering signals. If this is the case, there are fewer choices in the design of the receiver chain.

Although the crystal filter referenced here had an insertion loss of 8dB, there are crystal filters available with less insertion loss. Generally speaking, the lower the insertion loss, the fewer the number of poles in the filter. And, the fewer the number of poles, the poorer the selectivity. Do not rule out a crystal filter based simply on the insertion loss. Study the entire receiver chain on the basis of system noise figure, taking into account the ambient site noise or antenna noise figure.

Until next time-stay tuned!

Tags: content

Most Recent


  • Using crystal filters at VHF high band
    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.
  • Using crystal filters at VHF high band
    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."
  • Using crystal filters at VHF high band
    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.
  • Using crystal filters at VHF high band
    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
  • Using crystal filters at VHF high band
    Top 5 Stories - Week of Sept. 22
  • Using crystal filters at VHF high band
    RCA plans to expand this year's Technical Symposium

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

Southern Linc official discusses MCPTT migration, interoperability with new partner Catalyst dlvr.it/SSr8VD

25th June 2022
UrgentComm

Newscan: NYPD’s bomb-sniffing dogs get a high-tech upgrade to keep city safe dlvr.it/SSpSD1

25th June 2022
UrgentComm

Chinese APT group likely using ransomware attacks as cover for IP theft dlvr.it/SSmJNm

24th June 2022
UrgentComm

AT&T, Verizon, T-Mobile tout Z-axis support for 911 dlvr.it/SSkGxK

23rd June 2022
UrgentComm

California grants first permit to test AVs using only Lidar sensing dlvr.it/SSkG7x

23rd June 2022
UrgentComm

Buying smart solutions: Technology is now part of (almost) every government purchase dlvr.it/SSk77q

23rd June 2022
UrgentComm

France preparing to launch public-safety broadband network, official says dlvr.it/SSh12p

23rd June 2022
UrgentComm

Newscan: Law-enforcement radios failed during Uvalde school mass shooting, Texas official says dlvr.it/SSf9vM

22nd June 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
  • 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 © 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