1. Impedance Measurements
David Conn VE3KL
Ottawa Amateur Radio Club, Nov 2007
I have conducted a study to address the problem of noise in urban environments and will share my results with you tonight.
I will give you two graphs that you can use at home to evaluate signals and noise using a simple S meter
A method that you can use easily to evaluate your own noise environment
A method that you can use to evaluate the quality of the ionosphere at any give time.
Some methods to control received noise
The Shannon Hartley limits
11/15/2018

2. Acknowledgments Greg Danylchenko VE3YTZ Henry Hall General Radio
Bryan Campbell VE3ZRK
Croft for sponsoring me for QCWA membership
Gus for the invitation
Doug for reviewing the presentation and providing the lap top for power point
Ernie for taking measurements at his site to check my work.
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3. 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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4. What is Impedance Use A Dual Beam Oscilloscope
Time
Keep antenna far away from the house. Use good ground stakes
Two noise types
Graph from W5BIG
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5. Impedance Children SWR Cable Loss Cable Length Transformations
Reflection Coefficient
Magnitude and Phase Z
Velocity Factor
Return Loss
Receiving Antenna described by its effective area
Cable Zo
Smith Chart
Z: Impedance
And Much More
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6. History Time Line Euler’s Theorem (Essential for Smith Chart)
Ohm’s Law 1826
Christie Invents the Diamond Shaped Bridge
Fourier & Gauss (Fast Fourier Transform)
Wheatstone Bridge (same a Christie’s)
Maxwell Transient Bridge
Wien AC Bridge
General Radio 1650-A AC Bridge
Introduce a few terms such as effective area.
Literature uses area and field strength as a pair: must know idea about effective area.
Cooley Tuckey FFT
Digital and PC era
1748
1826
1833
1855
1843
1865
1891
1959
1965
1970
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7. 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
We need to use four terms
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8. Maxwell Bridge ..Type 1 Measures L and Q All Pass Network
(DC or AC or Transient Operation)
Two Variable Resistors
Resistors Interact
We need to use four terms
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9. 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
We need to use four terms
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10. The Aim 4170 Impedance Meter Lindenblad 2 Metre Antenna
We need to use four terms
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11. 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
We need to use four terms
Coupler
Main Unit
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12. Telepost LP-100 Digital Vector Wattmeter
We need to use four terms
Polar Plot Mode
Impedance Mode
Reprinted with Permission from Telepost
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13. 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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14. 73 David
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