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


Special signal-tracing probes

Special signal-tracing probes

Special probes are often needed in land mobile radio servicing for signal tracing in radio transmitters and receivers. The main problem to overcome is
  • Written by Urgent Communications Administrator
  • 1st July 2000

Special probes are often needed in land mobile radio servicing for signal tracing in radio transmitters and receivers. The main problem to overcome is the loading effect many probes cause in high-impedance circuits. Certain probes can be used with instrumentation to minimize these loading errors when you are signal tracing.

Circuit loading Resistive and capacitive effects can cause circuit loading when a test probe is applied to a circuit. Generally, the impedance of the probe should be at least 10 times the impedance of the circuit under test. The stray probe capacitance should be a small percentage of the capacitance of the circuit under test. In Figure 1 below, the circuit to the right of the test point is an RLC-tuned circuit. For example, suppose that the impedance of the tuned circuit is 500V. Suppose that: (1) a direct probe were to be touched to the test point (TP1), (2) the input to the instrument (spectrum analyzer) is 50V and (3) the shunt capacitance of the probe is 50% of the capacitance of the tuned circuit under test. Obviously, the loading effect of the probe would be severe, and useful measurements would be impossible.

By using an isolation probe such as shown in Figure 1, the loading effect of the probe can be reduced. Suppose the isolation resistor (Rp) is 450V and the instrument impedance (RI) is 50V. This would represent a probe impedance of 500V as seen by the circuit under test. If the impedance of the circuit under test were 500V, the 500V probe would load the circuit such that the measurement would be useless. In some cases, the circuit under test might even cease to function. If the resistance is placed near the probe tip, it will have the added benefit of reducing the probe’s stray capacitance as seen by the circuit under test. Because this forms a simple 10:1 voltage divider network, the voltage appearing across the input to the instrument will be 10% of the actual voltage at the probe tip. This represents a 20dB isolation, and the instrument should have enough reserve sensitivity to overcome the probe loss. Otherwise, the probe will be of little value.

Similarly, a 100:1 voltage divider could be used to provide even more isolation. This would require a 4,950V isolating resistor, making the probe 5,000V impedance (as seen by the circuit under test). This would provide an isolation of 40dB-barely meeting the 10:1 rule of thumb when connected across the 500V impedance of the circuit previously discussed. The spectrum analyzer or other instrument would have to have high sensitivity to overcome the loss of such a probe.

The previous discussion pertained to resistive loading. The other part of the problem is capacitive loading. Because capacitive reactance is frequency-dependent, the probe input impedance will drop as the frequency increases. Thus, the loading effect increases dramatically as the frequency increases.

Active probes One way to reduce probe loading is to place an amplifier in the probe near the tip. The amplifier would have high input impedance-and an output impedance to match the input impedance of the instrument with which it is used. Low-power, high-impedance FET devices are usually used for such applications. Power to the preamplifier is supplied from the instrument-or externally for generic devices.Many spectrum analyzer manufacturers provide special connections, designed specifically for their instruments, for powering an active probe.

Photo 1 above shows an instrument that can be used in conjunction with a spectrum analyzer to signal trace or to examine signals in high-impedance circuits. This particular device is the preamplified probe, model PP-1, made by Ramsey Electronics of Victor, NY. Figure 2 on page 30 is a block diagram of a typical use for the active probe. Although Figure 2 shows the probe used with a spectrum analyzer, it can be used with a frequency counter, oscilloscope or other instrumentation as well. The specifications are listed in Table 1 at the top of page 30.

Grounding hints The PP-1 preamplifier probe comes with various probe attachments: two grounding adapters-a gold wire spring clip and a clip-on alligator clip, plus a BNC probe tip adapter. The following information is from the instruction manual for the PP-1 probe.

When probing on a PC board, use the gold spring clip. At higher frequencies, it is important to keep the probe’s ground connection short. Errors will be introduced by a long ground wire draping over the circuit board under test. The best technique is to touch the probe tip to the desired measuring point while simultaneously touching the ground spring wire to a nearby ground point. This technique provides a short path to ground, but it does require some manual dexterity.

Low-frequency measurements allow the use of the standard alligator clip ground. Simply slip the alligator clip wire on the probe body and clip the alligator to a convenient ground point. Above about 10MHz, the gold spring clip ground should be used for best results.

You can even use your body as a ground when measuring some high-frequency signals. Simply hold your finger firmly against the metal ground sleeve near the probe tip. Sometimes this technique works well when measuring frequencies in the 50MHz-150MHz range.

Ramsey Electronics also makes a special RF detector probe (model RF-1), which it calls the “Sniff-it.” It is very broadband (100kHz to over 1GHz) and can be used to measure low-level signals in conjunction with any multimeter. The probe uses microwave low-barrier Schottky diodes to provide a sensitive detector reaching 1GHz with a logarithmic output. See Photo 2 above.

The current price of the preamplified probe (PP-1), fully wired and tested, is $195.95. The price of the model RF-1 “Sniff-it” detector probe is $22.95, wired and tested. Contact Ramsey Electronics, 793 Canning Parkway, Victor, NY 14564; 716-924-4560. Web site: www.ramseyelectronics.com. Until next time-stay tuned! n

Tags: content

Most Recent


  • Special signal-tracing probes
    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.
  • Special signal-tracing probes
    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."
  • Special signal-tracing probes
    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.
  • Special signal-tracing probes
    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
  • Special signal-tracing probes
    Top 5 Stories - Week of Sept. 22
  • Special signal-tracing probes
    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

Airbus U.S.: Rebecca Purcell, Bob Baumann discuss MCX, Agnet offerings dlvr.it/SlJNqW

22nd March 2023
UrgentComm

Microsoft Outlook vulnerability could be 2023’s ‘It’ bug dlvr.it/SlC3Hh

20th March 2023
UrgentComm

Getting to know the how–and why–of the telecom cloud dlvr.it/SlBbD1

20th March 2023
UrgentComm

Zipline delivery drone docks, charges by itself dlvr.it/SlBNWy

20th March 2023
UrgentComm

State and local leaders can alleviate the burden on public-safety personnel by tackling three workforce trends dlvr.it/SlBH89

20th March 2023
UrgentComm

6G is shaping up to disappoint, and the industry can blame itself dlvr.it/Sl918J

20th March 2023
UrgentComm

Change is coming to the network detection and response (NDR) market dlvr.it/Sl4cts

18th March 2023
UrgentComm

Telcos need to build businesses, as well as networks dlvr.it/Sl4cRR

18th 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.