SWRWattmeter ECE 4532: Design 1 Group 04

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SWR/WattmeterECE 4532 Design 1 Group 04
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What is an SWR/Wattmeter?

• An SWR/Wattmeter is an electronic testing device
  used by ham radio operators to measure the
  strength and quality of transmissions. An
  SWR/Wattmeter is used to measure the following
  values
• Forward Power
• Reflected Power
• Standing Wave Ratio (SWR)

3
Block Diagram
Directional Coupler
Transmitter
Display Unit
Microprocessor
Voltage Regulator
Power Meter
SWR Meter
LCD
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User Interface

• LCD Display (3 Modes)
• Forward power, reflected power, and SWR numerical
  readings
• SWR numerical reading and bar graph
• Forward power and reflected power numerical
  values and bar graph

Power Meter Displays the forward and reflected
power calculated by the microprocessor
SWR Meter Displays the SWR calculated by the
microprocessor
Forward/Reflected Switch Switches the power meter
between forward and reflective power readings
Mode Switch Switches the LCD between the three
modes
Sensor Switch Switches between the two sensor
input ports
Lamp Switch Activates the power and SWR meter
lamps
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Hardware Design Directional CouplerDescription
and Constraints

• Connects in-line between the radio and the
  antenna
• Samples forward and reflected power
• Several different designs
• Constraint 1 Must measure forward and reflected
  power within 10 of full-scale (SWR also)
• Constraint 2 Must maintain accuracy at all
  frequencies between 1.8 MHz and 30 MHz
• Constraint 3 Must maintain accuracy at all power
  levels up to the legal limit (1500W)

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Hardware Design Directional CouplerChoosing
the Right Design
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Hardware Design Directional CouplerSchematic
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Hardware Design Directional CouplerTesting

• 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

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Hardware Design Voltage RegulationDescription
and Design Constraints

• Need to regulate 12-18V DC supply to 5V DC for
  the microprocessor circuit and LCD
• Constraint 1 Must accept 12-18V DC power source
  and use less than 1A
• Constraint 2 Voltage regulation must be accurate
  within 10 of 5V

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Hardware Design Voltage RegulationChoice and
Schematic

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

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Hardware Design Voltage RegulationTesting

• 78M05 rated from 7.25-35V
• Tested from 6-20V
• Output voltages were well within tolerances (-1)

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Hardware Design Cost of PartsDescription and
Design Constraint

• SWR/Wattmeters typically cost between 30 and
  300
• Projected retail price for our meter 300
• Typical MFJ retail price 2X cost of parts
• Cost of parts should be less than 150 for MFJ to
  make a profit
• Constraint Cost of parts must be 125
• Cost of parts should be ¼ retail price 75

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Hardware Design Cost of Parts
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Software Design MicroprocessorComparison and
Choice
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Software Design Microprocessor16C76 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

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Software Design CodeCalculations and Control

• Calculate forward and reflected power using a
  look-up table (LUT).
• Calculate SWR using forward and reflected power
  values
• Used a LUT to measure square root of power
• Control meters using PWM value read from LUT
• Calibrated LUT for the meter (non-linear)
• Control LCD
• Average readings to minimize flicker
• Control LCD modes
• Convert binary values to ascii numbers
• Display labels, values, and bar graph on LCD

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Software Design CodeTesting

• Tested using a voltage source vs. directional
  coupler
• Values were correct for the LCD and meter,
  demonstrating accuracy of the LUT for power
  measurement and meter control
• Calculated SWR values by hand to verify SWR
  calculation algorithm

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Summary

• Working Features on Prototype
• Accurately measures forward power, reflected
  power and SWR
• Correctly displays forward and reflected power on
  a cross-needle meter
• Correctly displays power and SWR measurements to
  an LCD
• Improvements for Packaged Product
• Accurately measure high-power levels
• Implement auto-range functionality
• Use separate meters for power and SWR
• Choose and implement SWR alarm
• Move hardware to PCB
• Design aluminum case

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Acknowledgements

• We would like to thank the following people for
  their support
• Mr. Martin F. Jue, President of MFJ Enterprises
• Harry Wong, project engineer for MFJ Enterprises
• Dr. J. Patrick Donohoe, faculty advisor
• Dr. Picone
• Jordan Goulder

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Questions

• ?

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References

• 1 Kelson, Francis, Calibration and Repair
  for Bird Wattmeter Elements, Amateur Radio,
  pp.48, April 1980.
• 2 McCoy, Lewis G, Meet the SWR Bridge, QST,
  March 1955.
• 3 Gray, John J, How to Build a Simple SWR
  Bridge, CQ, pp.36-39, Sept. 1987.
• 4 Bruene, Warren, An Inside Picture of
  Directional Wattmeters, QST, pp.24-28, April
  1959.
• 5 Kemper, John Greben, The Tandem Match - An
  Accurate Directional Wattmeter, QST, pp. 18-26,
  Jan. 1987.