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

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

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.

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.

Block Diagram +LPF +LPF

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.

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.

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.

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

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.

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)

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.

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.

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.

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

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.

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……..

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

Dipole Antenna

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.

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.

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

Effect of Interference 2 Interference level approx 63db over S9

Expanded View Without interference With interference

Market Survey of Amateur Antenna Analyzers AEA Wireless: VIA-Bravo: 0.1-200MHz $2000 VIA-Analyzer: 0.1-54MHz $600 CIA-HF: 0.1-54MHz $400 TZ-900 AntennaSmith 0.2-55 MHz. $1400 AIM4170 0.1-170MHz true phase $490.00 MFJ269 : 1.8-170MHz,420MHz no phase $375 MFJ259B: 1.8-170 MHz, no phase $275

Comparisons 4170 – As measured by the ARRL Lab

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

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

PowerAIM

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

PowerAIM

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

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

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

Strong Signal Immunity +LPF +LPF

Strong Signal Immunity Before DSP filter 1 After DSP filter 1

Strong Signal Immunity Before DSP filter 2 After DSP filter 2

Tower tuned to 1 MHz

Tower tuned to 1 MHz – Averaging Added

Tower tuned to 1 MHz – Trend Only

Same Channel Interference

Same Channel Interference– AVG and Trend On

Same Channel Interference– DSP Overlaid

Same Channel Interference– DSP 2 ONLY

AIM4170 and PowerAIM Distributed by Array Solutions: www.arraysolutions.com/pricelist.htm

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