Transcript Antenna Analyzer - Array Solutions

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.
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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 Infinity
SWR 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……..
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Agenda
Design considerations for the analyzer.
A bit of theory.
Measurement results.
Demonstration.
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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 channels
Special 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 Immunity
Patented 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
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Tower tuned to 1 MHz
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Tower tuned to 1 MHz – Averaging Added
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Tower tuned to 1 MHz – Trend Only
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Same Channel Interference
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Same Channel Interference– AVG and Trend On
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Same Channel Interference– DSP Overlaid
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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!!!
W5BIG