VIA BravoNetwork 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 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

ectiv

e R

adia

ted

Pow

er (E

RP)

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 BravoVector Impedance AnalyzerMeasures the impedance and resonant frequencies of antennas, coils, circuits & components 100 kHz – 200 MHzSingle & Two Port VersionsBravo 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

LLeft 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

LLeft 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

DEGREES 90

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

ImpedanceImpedance AngleResistanceReactanceSmith Chart*VSWRReturn Loss

Reflection CoefficientMagnitudeAngle

CapacitanceParallelSeriesPlot 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 BravoChart 8 Parameters at onceSave Charts on a PC or on CDs Export Charts – (BMP, JPEG, GIF or TIFF) Produce Smith ChartsPrint ChartsCreate 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 linesMeasuring inductors and capacitorsTuning antenna trapsDetermine resonant frequenciesTuning cavity filtersAdjusting antenna tunersSignal tracingDetermine Cable CharacteristicsUse as a Signal Source

VIA Bravo II BonusIt’s not just for measuring antennae

Measuring Group DelayMeasuring Gain CompressionMeasuring Differential AmplifiersMeasuring Amplifier GainMeasuring 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