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VIA Bravo
Network Analyzer
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 efficiency
Document an installation with electronic or paper media
Diagnose 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
Effective Radiated Power (ERP)
Optimize Your Antenna System
to Enhance Range and Quality
Tuned Antenna
Un-Tuned Antenna
Minimum Service Threshold
Range
EXAMPLE of a
COMMUNICATIONS IMPROVEMENT
Un-Tuned Transmission
Tuned Transmission
Proper tuning delivers more power and a higher quality of
transmission from the same equipment and antenna system
What Chokes an Antenna?
Reflection Coefficient
Reactance
Capacitance
Inductance
Impedance Angle
Impedance
Resonance
Resistance
Frequency
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
Inductive
Low Z
Resistive
High Z
Capacitive
Note where Zo plots – Dead Center is Antenna System Perfection
ELI the ICE Man
For 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
VIA Bravo
Left
L
Right
00.0
VIA Bravo
00.0
LCD Display
R +++
L/C
00.0
FL
FC
FH
Left = Unit of measure for selected test on Left vertical axis
Right = Unit of measure for selected test on Right vertical axis
FL>FC>FH = Frequency sweep range
FL = Lowest frequency of the sweep
FC = Center frequency of the sweep
FH = Highest frequency of the sweep
VIA Bravo
Left
L
00.0
R +++
00.0
L/C
00.0
FL
Right
FC
FH
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
L/C = Numeric display of the inductive or capacitive
component of the measurement. For SWR mode,
L/C = the calculated “Q”
An antenna is resonant at the frequency(s) where
the Impedance (Phase) Angle is equal to zero (0).
Left plot (thin)
= Z of 50.6Ώ at
resonance
Right plot (thick)
= ө Angle of
VIA Bravo
200 OHMS
L
R +++
2.38o
50.6
2.38
DEGREES
90
+
0
-
0
90
Positive ө Angle L/C 19.7
LNH
-6.40M
FC = 21.000 MHZ +6.40M
= inductive X at
19.7 nH.
[Note: Negative ө Angle
Center Frequency
would = capacitive X]
Smith Chart
Frequency Sweep vs CW Mode
Frequency Sweep
Normal Mode
One sweep about every second from FL to FH
Tuning requires a 1-2 seconds wait for change to post
Continuous Wave Mode
Update rate is increased to about 5 times per second
CW operates at Center Frequency – no sweep
Tuning changes appear almost instantly
Tuning by the numbers is faster
No additional power drain on the batteries
VIA Bravo II
Two 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 Coefficient
Magnitude
Angle
Capacitance
Parallel
Series
Plot save capabilities
*In the Bravo PC Vision software which is included
Bravo PC Vision
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 Bonus
It’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 Bonus
It’s not just for measuring antennae
Measuring Group Delay
Measuring Gain Compression
Measuring Differential Amplifiers
Measuring Amplifier Gain
Measuring AM to PM distortion
Summary
Proper 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