Impedance Measurements

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Impedance Measurements

• David Conn VE3KL
• Ottawa Amateur Radio Club, Nov 2007

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Acknowledgments

• Greg Danylchenko VE3YTZ
• Henry Hall General Radio
• Bryan Campbell VE3ZRK

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Introduction

• Basics.What is Impedance
• A Short History of Impedance measurements
• The General Radio 1650-A Bridge
• AIM4170 Vector Impedance Meter
• Telepost L-100 Vector Wattmeter
• Demonstrations

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What is Impedance Use A Dual Beam Oscilloscope

Time
Graph from W5BIG
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Impedance Children
SWR
Cable Loss
Cable Length Transformations
Reflection Coefficient Magnitude and Phase
Z
Velocity Factor
Return Loss
Cable Zo
Smith Chart
Z Impedance
And Much More
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History Time Line
Eulers Theorem (Essential for Smith Chart)
Ohms Law 1826
Christie Invents the Diamond Shaped Bridge
Fourier Gauss (Fast Fourier Transform)
Wheatstone Bridge (same a Christies)
Maxwell Transient Bridge
Wien AC Bridge
General Radio 1650-A AC Bridge
Cooley Tuckey FFT
Digital and PC era
1748
1826
1833
1843
1865
1891
1959
1965
1970
1855
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General Radio 1650-A Bridge

• Five Bridges in one instrument (R, L, C, Q, D)
• Manual point-by-point data collection
• Voltage and Current not measured
• Includes a novel OrthoNull Mechanical
• computing device
• Two logarithmic coupled dials
• First Bridge to use Transistors

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Maxwell Bridge ..Type 1

• Measures L and Q
• All Pass Network
• (DC or AC or Transient Operation)
• Two Variable Resistors
• Resistors Interact

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The Aim 4170 Impedance Meter

• Measures load voltage and current
• Uses two DDS synthesizers as RF source
• Passes IF digital signals to PC
• PC performs FFT to compute magnitude and Phase of
  Z
• Many charts from 1 to 170 MHz produced

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The Aim 4170 Impedance MeterLindenblad 2 Metre
Antenna
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Telepost LP-100 Digital Vector Wattmeter

• Measures RF load voltage and current through a
  coupler
• Most calculations done with a PIC microcontroller
• Measures and displays power up to 3000 W
• Measures Magnitude/Phase electronically. No FFT
• Many charts from 1 to 170 MHz produced

Coupler
Main Unit
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Telepost LP-100 Digital Vector Wattmeter
Polar Plot Mode
Impedance Mode
Reprinted with Permission from Telepost
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Summary

• Older Bridges collect data one point at a time
• New Instruments measure voltage and current
• Aim4170 Measures Impedance
• Telepost LP-100 is a multi-purpose Digital Vector
  Wattmeter

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73 David