1. By Bob Clunn – W5BIG & Jay Terleski – WX0B
Antenna Analyzer
By Bob Clunn – W5BIG
&
Jay Terleski – WX0B

2. Agenda A bit of theory. Measurement results. Demonstration.
Design considerations for the analyzer.
A bit of theory.
Measurement results.
Demonstration.

3. 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.

4. 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.

5. Block Diagram
+LPF
+LPF

6. 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.

7. 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.

8. Inside View The RF board is 3.8 x 2.5 inches.
The two mixers are side by side in 8 pin DIP packages.
The second DDS chip is on the far side of the oscillator (barely visible in this picture).
The Zilog CPU board is on the bottom of the assembly. It’s about 4 inches square.

9. Agenda Design considerations for the analyzer. Measurement results.
A bit of theory.
Measurement results.
Demonstration.

10. Complex Numbers
Came into use about 500 years ago in solving algebraic equations: ax^2 + bx + c = 0
They are the sum of two parts:
Real part – like numbers in the everyday world.
Imaginary part – a number multiplied by sqrt(-1)
Resistance is a Real Number.
Reactance of a coil or capacitor is an Imaginary Number.
Impedance = Resistance + Reactance.

11. 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)

12. 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.

13. 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.

14. 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.

15. SWR Determination SWR ranges from +1 to Infinity
SWR is not a complex number.
For example:
Rho = SWR = 1.2
Rho = SWR = 3.0

16. Phase Is Preserved in Mixing
Stimulus frequency = X (0.1 to 170MHz)
Local Osc Freq = Y = X + 1 KHz
Phase difference between voltage and current = A
Voltage: Current:
sin(X) sin(X+A)
Mix both signals with Y=X+1KHz:
sin(X)*sin(Y) sin(X+A)*sin(Y)
Results after filtering out the sum of the two frequencies:
cos(X-Y) cos(X-Y+A)
= cos(1KHz) = cos(1KHz +A)
Phase is the same before and after mixing
By doing the analysis at 2KHz, it is much easier to get accurate phase information. Even a change of 0.1 degree makes a noticeable difference in the final impedance values.

17. 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……..

18. Agenda Design considerations for the analyzer. A bit of theory.
Measurement results.
Demonstration.

19. Dipole Antenna

20. 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)
Note how fast the phase passes through zero. This makes it possible to determine the resonance points with high accuracy.

21. Smith Chart
The resistance and reactance at the input end of 15 ft of RG59B terminated in a 243 ohm 1% metal film resistor. Green trace is data from “Transmission Line Details” which uses the exact equations for a lossy transmission line.
The difference between the measured data and the ideal data above 20 MHz results in a value for the impedance magnitude that is in error by only 2 percent. The phase shift is probably due to a variation in the velocity of propagation.
The plot is a spiral instead of a circle because of loss in the cable.

22. Effect of Interference 1
No interference. Load=186 ohms at end of 28ft of RG58

23. Effect of Interference 2
Interference level approx 63db over S9

24. Expanded View
Without interference With interference

25. Market Survey of Amateur Antenna Analyzers
AEA Wireless:
VIA-Bravo: MHz $2000
VIA-Analyzer: MHz $600
CIA-HF: MHz $400
TZ-900 AntennaSmith MHz. $1400
AIM MHz true phase $490.00
MFJ269 : MHz,420MHz no phase $375
MFJ259B: MHz, no phase $275

26. Comparisons 4170 – As measured by the ARRL Lab

27. 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

28. 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

29. PowerAIM

30. 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

31. PowerAIM

32. 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

33. 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

34. 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

35. Strong Signal Immunity
+LPF
+LPF

36. Strong Signal Immunity
Before DSP filter After DSP filter 1

37. Strong Signal Immunity
Before DSP filter After DSP filter 2

38. Tower tuned to 1 MHz

39. Tower tuned to 1 MHz – Averaging Added

40. Tower tuned to 1 MHz – Trend Only

41. Same Channel Interference

42. Same Channel Interference– AVG and Trend On

43. Same Channel Interference– DSP Overlaid

44. Same Channel Interference– DSP 2 ONLY

45. AIM4170 and PowerAIM
Distributed by Array Solutions:

46. Agenda Design considerations for the analyzer. A bit of theory.
Measurement results.
Demonstration - At our Booth
Thank You!!!