What’s in this presentation?
• What you gain by using a Network Analyzer
• Learn the difference between a Network Analyzer and Scalar
• Look at the dynamics involved with antenna performance aka “Smith Chart Intro”
• Familiarization with the VIA Bravo’s display
• Preview Bravo PC VisionTM software
• Summarization Plus Question and Answer session
Why Use a Vector Impedance Analyzer?
Scalars provide SWR & Return Loss information, but not Vector Impedance. A high SWR reading doesn’t tell you what to fix or what to tune in an antenna system
The VIA Bravo’s information can be used to:Maximize an antenna system’s efficiencyDocument an installation with electronic or paper mediaDiagnose an Antenna System to effect timely repairs
The VIA Bravo can be used at the antenna base or at the feed line using the “Nulling Cable” feature
Optimize Your Antenna Systemto Enhance Range and Quality
Minimum Service Threshold
Range
Eff
ecti
ve R
adia
ted
Pow
er (
ER
P)
Un-Tuned Antenna
Tuned Antenna
EXAMPLE of a COMMUNICATIONS IMPROVEMENT
Un-Tuned Transmission Tuned Transmission
Proper tuning delivers more power and a higher quality oftransmission from the same equipment and antenna system
What Chokes an Antenna?
Resistance InductanceCapacitance
Impedance Reactance
Frequency
Resonance
Impedance Angle Reflection Coefficient
All the factors for antenna performance MUST balance or the result is Power Loss from out-of-phase current and voltage
and increased VSWR from impedance mismatches
Vector Impedance and the Right Hand Plane (RHP)
X = Reactance, Z = Total Impedance, R = Resistance, θ = Z Angle, and i or j = square root of -1
Above, the positive X values plot into one quadrant of a Cartesian graph’s RHP, negative X values plot in the other
quadrant directly below this one
Mapping the RHP to a unit circle – Smith Chart
Note where Zo plots – Dead Center is Antenna System Perfection
Inductive
ResistiveLow ZHigh Z
Capacitive
ELI the ICE ManFor best performance an antenna should be purely resistive and resonant near Zo at the center frequency (Fc)
Power loss factors include:
If the antenna is inductive, voltage will lead current (ELI)
If the antenna is capacitive, current will lead voltage (ICE)
Either of these conditions exceeding the manufacturer’s specifications require corrective action by tuning the antenna or adding a tuning stub
VIA Bravo
Vector Impedance Analyzer
Measures the impedance and resonant frequencies of antennas, coils, circuits & components
100 kHz – 200 MHz
Single & Two Port Versions
Bravo PC Vision Software
Left = Unit of measure for selected test on Left vertical axis
Right = Unit of measure for selected test on Right vertical axis
VIA Bravo LCD Display
VIA Bravo
R +++
L/C
L
Left Right
FCFL FH
00.0
00.0
00.0
FL>FC>FH = Frequency sweep range
FL = Lowest frequency of the sweep
FC = Center frequency of the sweep
FH = Highest frequency of the sweep
L/C = Numeric display of the inductive or capacitive component of the measurement. For SWR mode, L/C = the calculated “Q”
VIA Bravo
R +++
L/C
L
Left Right
FCFL FH
00.0
00.0
00.0
L = Numeric readout for Left Plot ( ) center frequency. In EXAM/PLOT the measurement at the cursor
frequency
R = Numeric readout for Right Plot (+++++) center frequency measurement or in EXAM/PLOT the measurement at
the cursor frequency
VIA Bravo
R +++
L/C
L 50.6
2.38
19.7LNH
200 OHMS
0
DEGREES90
90
+0-
FC = 21.000 MHZ-6.40M +6.40M
An antenna is resonant at the frequency(s) where the Impedance (Phase) Angle is equal to zero (0).
Center Frequency
Right plot (thick)
= ө Angle of 2.38o
Left plot (thin) = Z of 50.6Ώ at resonance
Positive ө Angle= inductive X at19.7 nH.[Note: Negative ө Anglewould = capacitive X]
Smith Chart
Frequency Sweep vs CW ModeFrequency Sweep
Normal ModeOne sweep about every second from FL to FHTuning requires a 1-2 seconds wait for change to post
Continuous Wave ModeUpdate rate is increased to about 5 times per secondCW operates at Center Frequency – no sweepTuning changes appear almost instantlyTuning by the numbers is fasterNo additional power drain on the batteries
VIA Bravo IITwo ports (S11 and S21) add measurement versatility:
Antenna-to-Antenna Isolation
Amplifier Gain
Group Delay
Gain Compression
Differential Amplifiers
AM to PM Distortion
VIA Bravo & PC Software
Impedance
Impedance Angle
Resistance
Reactance
Smith Chart*
VSWR
Return Loss
Reflection CoefficientMagnitude
Angle
Capacitance
Parallel
Series
Plot save capabilities
*In the Bravo PC Vision software which is included
Smith Chart from Antenna Sweep
As the frequency changes the antenna’s reactance moves from inductive to capacitive with some impedance change and is resonant slightly off the center of the swept frequency
Bravo PC Vision Software
Upload Current or Stored Plots from the VIA Bravo
Chart 8 Parameters at once
Save Charts on a PC or on CDs
Export Charts – (BMP, JPEG, GIF or TIFF)
Produce Smith Charts
Print Charts
Create a Records data base and provide documentation to customers
Weigh the Cost Against
the Gain Radio equipment - $$$$
Antenna site or tower - $$$$
Transmission lines - $$$
Installation and turn-up - $$$
Antenna Test & Tune - $
VIA Bravo BonusIt’s not just for measuring antennae
Tune ½ and ¼ wave transmission lines
Measuring inductors and capacitors
Tuning antenna traps
Determine resonant frequencies
Tuning cavity filters
Adjusting antenna tuners
Signal tracing
Determine Cable Characteristics
Use as a Signal Source
VIA Bravo II BonusIt’s not just for measuring antennae
Measuring Group Delay
Measuring Gain Compression
Measuring Differential Amplifiers
Measuring Amplifier Gain
Measuring AM to PM distortion
SummaryProper antenna tuning for clear long range communications
Scalars provide only SWR and Return Loss, but NOT resonance information. Proper antenna tuning or diagnostic work requires a network analyzer
The VIA Bravo is a 100KHz to 200MHz network analyzer for antennas, coils, circuits or components
The VIA Bravo displays any two parameters at once, but stores all eight parameters measured
Bravo PC Vision will display all eight parameters at once