Trade Secrets of a Guy with a Network Analyzer

1
Trade Secrets of a Guy with a Network Analyzer

• Jeremy D. Ruck-Senior Engineer
• D.L. Markley Associates, Inc. Consulting
  Engineers
• Peoria, Illinois

2
Theory
3
Coordinate Systems

• Cartesian System.
• Polar System.
• Cartesian and Polar Provide Same Information but
  in a Different Format.
• Many Other Types are Possible, However, Other
  Systems are Beyond the Scope of This Presentation.

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The Cartesian Coordinate System

• Considering only 2-Dimensional Version.
• Represented in 2 Dimensions by a Plane with 2
  Axes.
• Axes are Perpendicular or Orthogonal.
• Axes are Typically Labeled X and Y.
• X is the Horizontal Axis.
• Y is the Vertical Axis.
• Locations are Represented by an Ordered Pair Such
  as (3,-5) or (4,8).
• First Number denotes X Axis Location.
• Second Number denotes Y Axis Location.

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Polar Coordinates

• Basis of System is Same Plane as in Cartesian
  System.
• Locations Also Defined by Two Numbers.
• Locations are Defined in Terms of a Distance or
  Radius from the Zero Point and an Angle Relative
  to the X Axis.
• Radius from Zero Point Denoted as r
• Angle from X-Axis Denoted as q
• Angles are Typically Measured in a
  Counterclockwise Direction.
• Conversion Between Cartesian and Polar is Simple,
  and Relies on Basic Trigonometry.

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Cartesian and Polar Coordinate Planes
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Cartesian vs. Polar Location Example 1
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Cartesian vs. Polar Location Example 2
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Right Triangles

• Obviously Three Sided Object which is Made up of
  Three Angles.
• Sum of all Three Angles Must Equal 180 Degrees.
• In a Right Triangle, One Angle Equals 90 Degrees
  Therefore Sum of Other Two Angles Must Equal 90
  Degrees.
• The Longest Side of a Right Triangle is Called
  the Hypotenuse and is Opposite the Right Angle.
• Pythagoras Theorem and Basic Trigonometry Give
  Us the Relationship Between the Angles and the
  Side Lengths.

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Right Triangles

• Six Parameters Define a Particular Right
  Triangle. Three are Side Lengths and Three are
  Angles.
• One Item is Fixed by Definition Since a Right
  Triangle ALWAYS Contains One Angle of 90 Degrees.
• If the Length of One Side and Any Other Side
  Length or Angle is Known, then the Other
  Parameters can be Easily Determined. SOH-CAH-TOA.

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Right Triangles
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Complex Numbers

• For Our Purposes a Complex Number is Defined as
  the Sum of a Real Number and an Imaginary Number.
• A Real Number is an Everyday Number such as 6,
  10, -7, etc.
• An Imaginary Number is a Real Number Multiplied
  by the Square Root of -1.
• The More Rigorous Definition of Complex and
  Imaginary Numbers is Beyond the Scope of this
  Presentation.
• Mathematicians use the operator i to Denote
  Imaginary Numbers. As Engineers We Use j.

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Complex Numbers - Examples

• A Mathematician Would Label a Particular Complex
  Number 34i. We Would Label the Same Number
  3j4.
• A Particular Complex Number We Would Label as
  8-j5 Would be Known to a Mathematician as 8-5i.
• How Else Can 50j0 be Represented?
• Is it Possible to Denote a Complex Number Using a
  Magnitude and an Angle?

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Complex Numbers

• A Complex Number May be Easily Represented Using
  our Previously Defined Coordinate Systems.
• The Real Component is Typically Defined in Terms
  of the X-axis.
• The Imaginary Component is Typically Defined in
  Terms of the Y-axis.
• It Follows that a Polar or Phasor Notation of a
  Particular Complex Number May Also be Utilized or
  Determined.

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Impedance

• Impedance is a Complex Quantity Consisting of the
  Sum of a Resistance and a Reactance.
• Resistance is the Real Quantity, While
  Reactance is the Imaginary Quantity.
• Although We are Using Imaginary with Regard to
  Reactance, it is Very Much a Real Quantity.
• Reactance Comes in Two Flavors, which are a
  Result of Inductance and Capacitance.
• Reactance is Frequency Dependent. For a DC
  Circuit, Reactance is Meaningless.

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Impedance

• A Pure Resistance is a Special Subset of
  Impedance Where the Reactance is Zero.
• The Converse is True for a Pure Reactance.
• Reactance May Be Thought of as Energy Storage.
• Energy is Stored in a Magnetic Field in an
  Inductor.
• Energy is Stored in an Electric Field in a
  Capacitor.
• Under Standard Conventions, Positive Reactance is
  Caused by Inductance while Negative Reactance is
  a Consequence of Capacitance.
• Resistance is Denoted by R while X or jX
  Denotes Reactance.

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Impedance - Graphical Representation

• The X-axis in our Cartesian Coordinate System
  Denotes the Resistance Component.
• The Y-axis in our Cartesian Coordinate System
  Denotes the Reactance Component.
• In Polar Coordinates an Impedance is Defined by a
  Magnitude and Phase Angle.
• The Phase Angle Typically Uses the Positive
  X-axis as the Reference with Angles Measured
  Counterclockwise.

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Impedance - Graphical Representation
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Phase Angles

• A Good Mnemonic for Remembering Sign of a Phase
  Angle is ELI the ICE man.
• In an Inductor, Voltage Leads Current or Current
  Lags Voltage. Your Choice.
• In a Capacitor, Current Leads Voltage or Voltage
  Lags Current. Also Your Choice.
• In an Inductor, the Voltage Leads the Current by
  90 Degrees. In a Capacitor, the Voltage Lags the
  Current by 90 Degrees.
• The Phase Angle is the Angle Between the Voltage
  and Current in a Circuit with the Voltage as the
  Reference.

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A Couple of Definitions Before Continuing

• Lets Define Two Quantities for a Simple System.
• What We Will Call the Nominal Impedance is the
  Impedance of the Transmitter, and We Will
  Denote it as Z0.
• The Load Impedance is the Impedance of the Load
  that the Transmitter Sees, and Will be Denoted as
  ZL.
• We Will Also, for the Sake of Simplicity, Make
  the Assumption that the Transmission Line is the
  Same Impedance as the Transmitter.

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Reflections

• Reflections in a System Occur When the Load
  Impedance Varies from the Transmitter Impedance.
• If a Load, such as an Antenna, is Perfectly
  Matched to the Transmitter, then there will be no
  Reflection. All Power is Transmitted to the
  Load.
• If there is a Mismatch, then Some of the Power
  will be Transferred and Some will be Reflected
  back to the Transmitter.
• In the Case of an Open or a Short, All of the
  Power is Reflected Back Towards the Transmitter.

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The Reflection Coefficient

• The Reflection Coefficient may be Used to
  Describe Reflections and is Defined as the Ratio
  of the Reflected Voltage to the Incident Voltage.
• The Value of this Quantity Varies from -1 to 0 to
  1.
• For a Short, the Value of the Coefficient is -1.
• For a Perfect Match, the Value is 0.
• For an Open, the Coefficient Value is 1.
• The Reflection Coefficient is Denoted by G.

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The Reflection Coefficient

• By Substitution, a General Form for the
  Reflection Coefficient in Terms of Impedance is
  as Follows

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The Reflection Coefficient - Example 1
Given a Transmitter Impedance of 50 Ohms, and a
Load Impedance of 25j0, what is the reflection
coefficient?
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The Reflection Coefficient

• Note that the Sign of the Reflection Coefficient
  is Negative. This is a Consequence of the Load
  Impedance being Less than the Nominal System
  Impedance.
• Examples Showing a Complex Impedance Require More
  Time than We Have Today to Explain, Therefore,
  Ill Put a Couple of Examples on
  www.dlmarkley.com. Feel Free to Call Me with Any
  Questions Over These Other Examples.

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VSWR - Voltage Standing Wave Ratio

• Similar to Reflection Coefficient, but is the
  Ratio of the Maximum to Minimum Voltage.
• VSWR is Typically Denoted by S.
• VSWR is Easily Related to the Reflection
  Coefficient.
• High VSWR Can Degrade Transmitted Signal, De-Rate
  Transmission Line, and Cause Excessive Heating.

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Relationship of VSWR to the Reflection Coefficient

• The Reflection Coefficient and VSWR are Related
  by the Following

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Return Loss

• Return Loss in Laymens Terms is the Logarithmic
  Difference Between the Incident Signal and the
  Reflected Signal.
• A Return Loss of 0 dB Would Indicate an Open or
  Short.
• An Infinite Return Loss Would Indicate a Perfect
  Match.

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Relationship of Return Loss to S and G

• We Can Relate Return Loss to the Other Quantities
  as Follows

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S, RL, and G Key Values

• VSWR of 1.0532.36 dB Return Loss
• VSWR of 1.0828.30 dB Return Loss
• VSWR of 1.1026.44 dB Return Loss
• VSWR of 1.1523.13 dB Return Loss
• 3 ReflectionVSWR of 1.06

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The Smith Chart

• The Smith Chart is a Graphical Calculator.
• The Chart Shown in its Current Orientation Would
  be Used for Impedance.
• Mirror Image is Used for Admittance.
• Three Families of Circles are on the Chart
  Constant Resistance, Constant Reactance, and
  Constant VSWR.

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The Smith Chart

• There are Many Design Uses for the Smith Chart.
• Our Use of the Chart with the Network Analyzer is
  Primarily for the Illustration of Issues with a
  Particular System.
• We Typically Look at the Impedance Version of the
  Chart.
• The Polar Format on the Network Analyzer Shows a
  Smith Chart, but Uses the Constant VSWR Circles.

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The Smith Chart

• An Ideal Match on the Chart Would be Indicated by
  a Dot at the Center.
• Near End Mismatches are Indicated by the
  Spirals Being Slid Off-Center.
• Distant Mismatches are Indicated by the Relative
  Radius of the Spirals about the Center Point.
• Both a Near End and Distant Mismatch Would be
  Indicated by a Large Radius Spiral Slid
  Off-Center.

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The Smith Chart
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The Smith Chart
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Practical Stuff
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Practical Stuff

• Desired System Specifications - A Revisit of a
  Portion of my 2001 Presentation on Antenna
  Maintenance.
• What to Look For When Somebody Sweeps Your
  Antenna System.
• Additional Considerations.

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Desired System Specifications

• In 2001 We Discussed Desired System
  Specifications.
• NTSC Visual Carrier VSWR 1.05 or Less.
• NTSC Aural Carrier VSWR 1.08 or Less.
• NTSC Color Carrier VSWR 1.10 or Less.
• Maximum in Channel VSWR NTSC or DTV 1.10 or Less.
• Far End Reflection 3.0 Percent or Less.
• FM VSWR 1.10 or Less in Channel.

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Desired System Specifications

• The Specifications Listed Implicitly Also Require
  No Issues with the Transmission Line.
• Most of the Specifications Listed Pertain to the
  Frequency Domain.
• Time Domain Specifications Will be Discussed
  Later.

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What to Look for When Your System is Swept
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What to Look for When Your System is Swept

• Network Analyzer is Vector Type.
• Network Analyzer has Time Domain Option.
• User Properly Calibrates Network Analyzer.
• Tuned or Wideband Test Adapters are Utilized.
• Narrowband and Wideband Measurements are
  Performed.
• Location of Test Adapter.

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What to Look for When Your System is Swept

• Vector Type Network Analyzer is Crucial.
• Scalar Analyzers do not Measure Phase. Only
  Magnitude is Considered.
• Vector Type is Necessary in order to Have Time
  Domain Option.

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What to Look for When Your System is Swept

• Time Domain Option is Crucial for Identifying
  Fault Locations.
• Without Time Domain Option, it is not Possible to
  Accurately Identify if an Issue with the System
  is in the Antenna, Transmission Line, or Both.

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What to Look for When Your System is Swept

• Network Analyzer Must Be Calibrated on Site for
  Frequency Ranges of Interest after Equipment
  Warm-Up.
• Calibration of Analyzer Should be Performed with
  Open, Short, and Load for Each Frequency Range
  Under Consideration.
• Measurements with 8753 Series Should have COR
  on Left Side of Screen. Reject Measurements with
  C? or CD.
• Measurements with 8712 Series Should have C at
  Top of Screen. Reject Measurements with C?.

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What to Look for When Your System is Swept

• Tuned or Wideband Adapters Should be Used at all
  Frequency Ranges, Especially UHF Channels.
• Top-Hats, Quick-Step, or Other Non-Optimized
  Adapters May be Used Only for FM, TV 2-6, and TV
  7-13.
• Tuned or Optimized Adapters Are Easy to Identify.
  They Typically Will Have One or More Bolts
  Which Optimize the Adapter for the Frequency
  Range of Interest.

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What to Look For When Your System is Swept

• For Television a 6 MHz Frequency Domain Sweep
  Centered on the Midpoint of the Channel of
  Operation.
• For FM a 1 MHz Frequency Domain Sweep Centered on
  the Carrier Frequency.
• For Both Types of Systems a 100 and 350 MHz Time
  Domain Sweep.

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What to Look for When Your System is Swept

• Location of Test Adapter is Important.
• As Many Components as Possible Beyond the RF
  System Should be Included.
• Wideband Measurements Need to be Taken at the
  Input to the Transmission Line and not Through
  the RF System. (Coax Systems)
• Narrowband Measurements Should be Taken at the
  Waveguide Switch so it can be Optimized for
  Channel of Operation.

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Case Studies
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UHF Antenna System Installation of Fine Matcher

• Station Complained of Increased Reflected Power.
• Problem Determined to be Mis-Calibrated Power
  Meter.
• Un-Optimized Elbow Complexes.
• Fine Matcher Installed to Correct Far End
  Reflection.

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UHF Antenna System Installation of Fine Matcher

• Installation and Optimization of Fine Matcher
  Reduced System VSWR and Far End Reflection.
• Additional System VSWR Reduction Could be
  Performed by Modification of Near End Elbow
  Complex.
• System VSWR does Slightly Exceed 1.10 at and Near
  the Aural Carrier.
• Far End Reflection Reduced from 5.78 (1.12 VSWR)
  to 0.62 (1.01 VSWR).

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VHF Antenna System Damage and Repair

• Station Complained of Increased VSWR and Degraded
  Coverage in Certain Directions.
• Antenna was Known to Have Taken Significant
  Lightning Strikes.

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VHF Antenna System Damage and Repair

• Indicated VSWR Consistent with Element Failure.
• Each Element was Shorted Out in Order to Identify
  Characteristic Change in VSWR or Lack Thereof.
• Special Transmission Line Consideration due to
  Location of Facility.

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VHF Antenna System Damage and Repair

• Damage Occurred to One Port on Power Divider and
  Associated Cable.
• These Components Replaced Along With Inner Bay
  Transformers.
• System Re-Optimized.

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VHF Antenna System Damage and Repair

• System VSWR Reduced Through Repairs.

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UHF Antenna System System Comissioning
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Transmission Line Phasing

• Jeremy Ruck and Richard Wood Developed a
  Technique for Phasing Dual Input Antenna Systems.
• This Technique Has Been Repeated on Multiple
  Systems with Excellent Results.
• The Technique is Ideal for Multiple Channel
  Antenna Systems, but is Also Very Useful for
  Single Channel Systems Such as Super Turnstile
  Type Antennas.

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Transmission Line Phasing

• Identify a Location at Tower Top Which is
  Identical Between Both Lines and Short Both
  Lines.
• Measure One Line and Save the Data to the
  Analyzer Memory.
• Measure the Second Line in Data-Mem Mode.
  Analyzer Depicts Phase Differential Between the
  Two Lines.
• Add or Subtract Electrical Delay Until Desired
  Phase Shift is Indicated.
• Construct Temporary Trombone Section and Trim as
  Necessary.
• Confirm Phase Measurements.

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Transmission Line Phasing
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Preparation Work as a Chief Engineer
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Preparation Work as a Chief Engineer

• Have any and All Previous Data on Hand for
  Reference.
• Document and Provide Documentation of any
  Anomalies You Have Observed.
• Provide your Consultant with Information
  Concerning your System Layout Including Line Size
  and Impedance, Presence and Lack of Transformers,
  Elbows, Fine Matchers, etc.
• Know the Approximate Length of your Transmission
  Line.

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Preparation Work as a Chief Engineer

• In Order to Conserve Station Resources, Eliminate
  What You Can as the Source of a Problem Before
  the Consultant Arrives.
• Plan on Being There as the Chief. You are
  Ultimately Responsible for Technical Operations.
  Have Your Transmitter Supervisor Present as Well.
• Discuss the Situation With Your Consultant Ahead
  of Time. Have a Tower Crew Available if You and
  the Consultant Agree it May be Necessary.

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Looking Over the Shoulder of the Consultant
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Looking Over the Shoulder of the Consultant

• Look over Their Shoulder. If They are Offended
  by You Doing This, Then They Have Forgotten Who
  Their Client Is.
• Ask Questions. You are Paying for the Service.
  You Have a Right to Know How, What, and Why Your
  System is Being Swept.
• Verify Their Measurements. We Are All Human and
  Can Make Mistakes.

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Looking Over the Shoulder of the Consultant

• Get an Idea of What the Analyzer is Showing You
  and Your Consultant.
• The Measurement Format Will Typically be
  Indicated in the Upper Left Hand Corner of the
  Display.
• The Scale and Reference Level Will be Indicated
  in the Upper Middle of the Display.
• The Reference Line Will be Indicated by a Carat.
• Data Smoothing Should NOT be Used.

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A Typical Display Frequency Domain
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A Typical Display Time Domain
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Some of the Tricks of the Trade

• Create Plots on Sensible Scales. Obscure Scales,
  While Perhaps Meaningful to the Consultant, Can
  Confuse the Client.
• Setup all Frequency Sweeps, Calibrate, and Then
  Store to Memory. This Makes it Easy to Switch
  Between Desired Spans.
• Save Analyzer State Files. If a Disk is Damaged,
  then Plots Can be Rebuilt from Memories.

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Some of the Tricks of the Trade

• Time to Fault in nS Divided By 2 is a Good
  Approximation in Feet to the Location of the
  Fault.
• When Locating a Fault, Find a Reference
  Component, then Count the Flanges as Displayed on
  Wideband Sweeps.
• Use of Averaging is Fine. Smoothing is Not.
• Turn Up the Averaging Sample to Compensate for
  Interference.

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The Final Word

• Always Examine System in Frequency Domain over
  Applicable Spans.
• Always Examine System in Time Domain over
  Narrowband and Wideband Spans for TV and Wideband
  for FM.
• TV Antenna Far End Reflection Should be 3 Percent
  or Less (VSWR of 1.06).
• Flange and Insulator Reflections Should be
  Uniform and Have VSWR of 1.006 or Less.
• Systematically Identify and Visually Examine any
  Anomalies. Replace Components as Necessary.

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And Most Importantly..
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• Have Your System Swept Regularly. Once Every Two
  to Three Years Will Usually Ensure Problems Are
  Caught Before they Become Catastrophic.

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Thank You For Your Attention

• Please Feel Free to Contact Me With Any
  Questions.
• Jeremy D. Ruck
• D.L. Markley Associates, Inc.
• 2104 West Moss
• Peoria, IL 61604
• 309-673-7511
• jdr_at_dlmarkley.com