Swr

SWR/WattmeterSWR/WattmeterECE 4532: Design 1 Group 04ECE 4532: Design 1 Group 04

What is an SWR/Wattmeter?What is an SWR/Wattmeter?

An SWR/Wattmeter is an electronic testing An SWR/Wattmeter is an electronic testing device used by ham radio operators to device used by ham radio operators to measure the strength and quality of measure the strength and quality of transmissions. An SWR/Wattmeter is used to transmissions. An SWR/Wattmeter is used to measure the following values:measure the following values:

• Forward PowerForward Power• Reflected PowerReflected Power• Standing Wave Ratio (SWR)Standing Wave Ratio (SWR)

Block DiagramBlock Diagram

Directional Coupler Transmitter

Microprocessor

Power Meter SWR Meter LCD

Display Unit Voltage

Regulator

User InterfaceUser Interface

Power MeterDisplays the forward and reflected power calculated by the microprocessor

SWR MeterDisplays the SWR calculated by the microprocessor

LCD Display (3 Modes)2. Forward power, reflected

power, and SWR numerical readings

3. SWR numerical reading and bar graph

4. Forward power and reflected power numerical values and bar graph

Forward/Reflected SwitchSwitches the power meter between forward and reflective power readings

Mode SwitchSwitches the LCD between the three modes

Sensor SwitchSwitches between the two sensor input ports

Lamp SwitchActivates the power and SWR meter lamps

Hardware Design: Directional CouplerHardware Design: Directional Coupler

Description and ConstraintsDescription and Constraints

Connects in-line between the radio and the Connects in-line between the radio and the antenna antenna

Samples forward and reflected powerSamples forward and reflected power Several different designsSeveral different designs

Constraint 1: Must measure forward and reflected Constraint 1: Must measure forward and reflected power within 10% of full-scale (SWR also)power within 10% of full-scale (SWR also)

Constraint 2: Must maintain accuracy at all Constraint 2: Must maintain accuracy at all frequencies between 1.8 MHz and 30 MHzfrequencies between 1.8 MHz and 30 MHz

Constraint 3: Must maintain accuracy at all power Constraint 3: Must maintain accuracy at all power levels up to the legal limit (1500W)levels up to the legal limit (1500W)


Choosing the Right DesignChoosing the Right Design

noyesnoThruline Principle

yesnoyesStripline

yesnonoResistive Bridge

yesyesnoReflectometer

Low Cost?Handles High Power?

Frequency Sensitive?Model


SchematicSchematic


TestingTesting

0

20

40

60

80

100

120

1 2 3 4 5 6 7 8 9

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

FWDPWR

REFPWR

SWR

Tested at 9 different bands in the HF range from 1.8-28.4 MHz

Power values were within constraints for all frequencies at all tested power levels

SWR values were accurate for all power values

Hardware Design: Voltage RegulationHardware Design: Voltage Regulation

Description and Design ConstraintsDescription and Design Constraints

Need to regulate 12-18V DC supply to 5V DC for Need to regulate 12-18V DC supply to 5V DC for the microprocessor circuit and LCDthe microprocessor circuit and LCD

Constraint 1: Must accept 12-18V DC power Constraint 1: Must accept 12-18V DC power source and use less than 1Asource and use less than 1A

Constraint 2: Voltage regulation must be accurate Constraint 2: Voltage regulation must be accurate within 10% of 5Vwithin 10% of 5V


Choice and SchematicChoice and Schematic

78M05 regulator is the best option78M05 regulator is the best option• Output current in excess of 0.5AOutput current in excess of 0.5A• Output voltage between 4.75V and 5.25VOutput voltage between 4.75V and 5.25V• Internal thermal overload protectionInternal thermal overload protection• Cheap ($.30)Cheap ($.30)


TestingTesting

78M05 rated from 7.25-35V78M05 rated from 7.25-35V Tested from 6-20VTested from 6-20V Output voltages were well Output voltages were well

within tolerances (-1%)within tolerances (-1%)

3.226

4.9120

4.9319

4.9518

4.9617

4.9716

4.9715

4.9814

4.9813

4.9912

4.9911

4.9910

4.999

5.008

4.677

Avg. Output VoltageInput Voltage

0

1

2

3

4

5

6

0 5 10 15 20 25

Input Voltage

Ou

tpu

t V

olt

ag

e

Hardware Design: Cost of PartsHardware Design: Cost of Parts

Description and Design ConstraintDescription and Design Constraint

SWR/Wattmeters typically cost between $30 and SWR/Wattmeters typically cost between $30 and $300$300• Projected retail price for our meter: $300Projected retail price for our meter: $300

Typical MFJ retail price: 2X cost of partsTypical MFJ retail price: 2X cost of parts• Cost of parts should be less than $150 for MFJ to make Cost of parts should be less than $150 for MFJ to make

a profita profit

Constraint: Cost of parts must be Constraint: Cost of parts must be ≤ ≤ $125$125

• Cost of parts should be ¼ retail price = $75Cost of parts should be ¼ retail price = $75

Hardware Design: Cost of PartsHardware Design: Cost of Parts

$2.50$0.505Variable Resistor

$20.00$10.002Board

$2.50$0.505Switch

$10.00$5.002Analog Meter

$6.00$6.001Microprocessor

$15.00$15.001LCD

$10.00$10.001Case

$75.90X1TOTAL COST

$0.15$0.151Processor Socket

$5.00$5.001Speaker

$0.30$0.301Voltage Regulator

$0.10$0.052Ferrite Bead

$0.50$0.501Toroid

$0.80$0.402Variable Capacitor

$0.05$0.015Diode

$2.00$0.1020Capacitor

$1.00$0.0520Resistor

Total CostUnit Cost per

thousandQuantityMaterials

Software Design: MicroprocessorSoftware Design: Microprocessor

Comparison and ChoiceComparison and Choice

13333322I/O Pins

08858-bit A/D Channels

10 MHz20 MHz20 MHz20 MHzMax. Clock Speed

64 B192 B368 B368 BData Memory

512 B4 KB8 KB8 KBProgram Memory

16F8316C7416C7716C76

Software Design: MicroprocessorSoftware Design: Microprocessor

16C76 Pinout and Usage16C76 Pinout and Usage

• 2 A/D channels used to measure sampled power values

• 3 PWM channels used to control the meters

• 6 pins to control the LCD

Software Design: CodeSoftware Design: Code

Calculations and ControlCalculations and Control

Calculate forward and reflected power using a Calculate forward and reflected power using a look-up table (LUT).look-up table (LUT).

Calculate SWR using forward and reflected power Calculate SWR using forward and reflected power valuesvalues• Used a LUT to measure square root of powerUsed a LUT to measure square root of power

Control meters using PWM value read from LUTControl meters using PWM value read from LUT• Calibrated LUT for the meter (non-linear)Calibrated LUT for the meter (non-linear)

Control LCDControl LCD• Average readings to minimize flickerAverage readings to minimize flicker• Control LCD modesControl LCD modes• Convert binary values to ascii numbersConvert binary values to ascii numbers• Display labels, values, and bar graph on LCDDisplay labels, values, and bar graph on LCD

Software Design: CodeSoftware Design: Code

TestingTesting

Tested using a voltage Tested using a voltage source vs. directional source vs. directional couplercoupler

Values were correct for Values were correct for the LCD and meter, the LCD and meter, demonstrating demonstrating accuracy of the LUT for accuracy of the LUT for power measurement power measurement and meter control and meter control

Calculated SWR values Calculated SWR values by hand to verify SWR by hand to verify SWR calculation algorithmcalculation algorithm

109.59.5/0.5

160163163/3.5

260264262/4.5

151616/1.0

333433/1.5

555655/2.0

5.0

4.0

3.0

2.5

0.2

Input Voltage

310320*320/

200209207/

120122120/

858585/

11.21.2/

Meter Values

LCD Values

LUT Fwd/Ref

SummarySummary

Working Features on PrototypeWorking Features on Prototype• Accurately measures forward power, reflected power Accurately measures forward power, reflected power

and SWRand SWR• Correctly displays forward and reflected power on a Correctly displays forward and reflected power on a

cross-needle metercross-needle meter• Correctly displays power and SWR measurements to an Correctly displays power and SWR measurements to an

LCDLCD

Improvements for Packaged ProductImprovements for Packaged Product• Accurately measure high-power levelsAccurately measure high-power levels• Implement auto-range functionalityImplement auto-range functionality• Use separate meters for power and SWR Use separate meters for power and SWR • Choose and implement SWR alarmChoose and implement SWR alarm• Move hardware to PCBMove hardware to PCB• Design aluminum caseDesign aluminum case

AcknowledgementsAcknowledgements

We would like to thank the following people for We would like to thank the following people for their support:their support:

Mr. Martin F. Jue, President of MFJ EnterprisesMr. Martin F. Jue, President of MFJ Enterprises Harry Wong, project engineer for MFJ EnterprisesHarry Wong, project engineer for MFJ Enterprises Dr. J. Patrick Donohoe, faculty advisorDr. J. Patrick Donohoe, faculty advisor Dr. PiconeDr. Picone Jordan GoulderJordan Goulder

QuestionsQuestions

??

ReferencesReferences

[1] Kelson, Francis, “Calibration and Repair for Bird [1] Kelson, Francis, “Calibration and Repair for Bird Wattmeter Elements,” Amateur Radio, pp.48, April Wattmeter Elements,” Amateur Radio, pp.48, April 1980. 1980. [2] McCoy, Lewis G, “Meet the SWR Bridge,” QST, March [2] McCoy, Lewis G, “Meet the SWR Bridge,” QST, March

1955.1955.[3] Gray, John J, “How to Build a Simple SWR Bridge,” CQ, [3] Gray, John J, “How to Build a Simple SWR Bridge,” CQ,

pp.36-39, Sept. 1987.pp.36-39, Sept. 1987.[4] Bruene, Warren, “An Inside Picture of Directional [4] Bruene, Warren, “An Inside Picture of Directional Wattmeters,” QST, pp.24-28, April 1959.Wattmeters,” QST, pp.24-28, April 1959.[5] Kemper, John Greben, “The Tandem Match - An [5] Kemper, John Greben, “The Tandem Match - An Accurate Directional Wattmeter,” QST, pp.Accurate Directional Wattmeter,” QST, pp. 18-26, Jan. 18-26, Jan.

1987.1987.

Swr

Engineering