W5BIG

Antenna Analyzer

By Bob Clunn – W5BIG&

Jay Terleski – WX0B

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Agenda

Design considerations for the analyzer.

A bit of theory.

Measurement results.

Demonstration.

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Basic Approach

Apply an RF voltage to the transmission line input.

Measure the applied voltage and the current.

Calculate the input impedance: magnitude & phase.

Calculate various parameters, including:

SWR

Equivalent series/parallel circuit.

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Zin Measurement Method

Frequency range is 0.1 to 170 MHz.Digital Synthesizers for Source and LO (AD9859)Heterodyne V and I to 1 KHz.

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Block Diagram

+LPF

+LPF

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Signal Processing

Low frequency (1KHz) V and I signals are amplified and filtered.

ADC in the Microprocessor samples each signal 16 times per cycle.

Microprocessor sends raw data to PC via RS232.

PC performs calculations and plots data.

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Advantages of This Method

Circuit is linear (no diode detectors).

Wide dynamic range with a 12 bit ADC.

True phase shift is determined.

Signal applied to the load is very small.

Narrow bandpass filter rejects stray inputs.

No internal adjustments for calibration.

Good long term accuracy.

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Inside View

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Agenda

Design considerations for the analyzer.A bit of theory.

Measurement results.

Demonstration.

W5BIG

Impedance

Impedance = Z = R + jX

R = Resistance (real)

X = Reactance (imaginary)

j = square root of –1.

Inductive Reactance is positive.

Capacitive Reactance is negative.

Magnitude = SquareRoot(R*R + X*X)

Phase Angle = ArcTan(X/R)

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Reflection Coefficient

Ratio of voltage reflected by the antenna to the voltage arriving at the antenna, Er/Ei.

Caused by difference between transmission line impedance and antenna impedance.

Rho = 0 for a perfect match, no reflection.

Rho = +1 for an open circuit.

Rho = -1 for a short circuit.

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Reflection Coefficient

ZL= load impedance.

ZO = transmission line impedance.

The impedances are complex numbers.

Magnitude of Rho ranges from 0 to 1.

Measure ZL and calculate Rho.

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What Is SWR ?

Ratio of Maximum Voltage to Minimum Voltage on the transmission line.

SWR is in the range of +1 to infinity.

SWR is the same at all points along a (lossless) transmission line.

Loss in a long transmission line reduces the SWR read at the transmitter.

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SWR Determination

SWR ranges from +1 to InfinitySWR is not a complex number.For example: Rho = 0.1 SWR = 1.2 Rho = 0.5 SWR = 3.0

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So what does the math allow?

SWR referenced to any impedance Resistance and reactance at the cable input Resistance and reactance at the antenna terminals Resistance and reactance of discrete components Return loss Reflection coefficient Cable length Cable impedance Cable loss Distance to fault (open or short) Smith chart display Band scan for interfering signals Quartz crystal parameters And more……..

W5BIG

Agenda

Design considerations for the analyzer.

A bit of theory.Measurement results.

Demonstration.

W5BIG

Cable Length

Find the frequency where theta = 0

This corresponds to ¼ wavelength.

5.813 MHz =>51.6meters.

51.6m*3.28ft/m=169.2ft

(169.2/4)*0.66=27.9ft

(velocity factor=0.66)

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Smith Chart

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Effect of Interference 1

No interference. Load=186 ohms at end of 28ft of RG58

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Effect of Interference 2

Interference level approx 63db over S9

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Expanded View

Without interference With interference

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Comparisons 4170 – As measured by the ARRL Lab

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The Next Generation of Analyzers

Professional Broadcast AM, MW,SW, FM, TV need very accurate instruments to tune up antenna systems.New HD Radio requires special tuning of the Antenna system to produce the HD signals without distortion or interference products to adjacent channelsSpecial Software is needed to quickly allow the BC Engineer to do his adjustments and documentation for the FCC

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PowerAIM is here

Higher output power to overcome nearby and skywave RF overload

Increased filtering and protection circuitry

Huge software tool set added to the basic AIM 4170 tools

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PowerAIM

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PowerAIM Replaces • Signal generator $3k

• Linear Power Amp $5K

• Calibrated directional couplers and attenuators $5k

• Vector Network Analyzer $50K

• Cables, misc. probes $2k

Total $65,000 of equipment plus engineering time and documentation time savings

PowerAIM approx. $3,000

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PowerAIM

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PowerAIM • Can measure all parameters of RF measurement at UUT and translated to the end of a cable, component values, and networks.

• Plots can be linear, rotated and multiple Smith Charts

• Line lengths, and phase of lines and networks. Calculation tools available for simulated lines and phase delays.

• Can operate up to 50 volts peak-to-peak of RF overload on the antenna system, and it will protect itself if exceeded.

• Calibrates easily, fast, and to NIST standards. Eliminating expensive Lab certification.

• Huge software tools to make the job easy and self documenting

•Outputs can be saved, printed, and imported into spreadsheets

• Many more functions for the broadcast professional

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PowerAIM

Package includes• Power Aim

• Calibration Loads

• Software and Manual

• Battery and Charger

• Brief Case with room for your PC

• Free 1 year software upgrades

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Strong Signal ImmunityPatented signal processing circuitry

Heterodyning measurement and Band Pass filters

Higher power output

Averaging tools

Trend Tools

Smoothing tools

DSP filtering tools

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Strong Signal Immunity

+LPF

+LPF

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Strong Signal Immunity

Before DSP filter 1 After DSP filter 1

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Strong Signal Immunity

Before DSP filter 2 After DSP filter 2

W5BIG Tower tuned to 1 MHz

W5BIGTower tuned to 1 MHz – Averaging Added

W5BIGTower tuned to 1 MHz – Trend Only

W5BIG Same Channel Interference

W5BIG Same Channel Interference– AVG and Trend On

W5BIG Same Channel Interference– DSP Overlaid

W5BIG Same Channel Interference– DSP 2 ONLY

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AIM4170 and PowerAIM

Distributed by Array Solutions: www.arraysolutions.com/pricelist.htm

W5BIG

Agenda

Design considerations for the analyzer.

A bit of theory.

Measurement results.Demonstration - At our Booth

Thank You!!!