w5big antenna analyzer by bob clunn – w5big & jay terleski – wx0b
TRANSCRIPT
W5BIG
Antenna Analyzer
By Bob Clunn – W5BIG&
Jay Terleski – WX0B
W5BIG
Agenda
Design considerations for the analyzer.
A bit of theory.
Measurement results.
Demonstration.
W5BIG
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.
W5BIG
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.
W5BIG
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.
W5BIG
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.
W5BIG
Inside View
W5BIG
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)
W5BIG
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.
W5BIG
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
W5BIG
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
W5BIG
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
W5BIG
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
W5BIG
PowerAIM
W5BIG
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
W5BIG
PowerAIM
W5BIG
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
W5BIG
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
W5BIG
Strong Signal ImmunityPatented signal processing circuitry
Heterodyning measurement and Band Pass filters
Higher power output
Averaging tools
Trend Tools
Smoothing tools
DSP filtering tools
W5BIG
Strong Signal Immunity
+LPF
+LPF
W5BIG
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
W5BIG
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!!!