SWR/Wattmeter ECE 4542: Design II Group 04

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SWR/WattmeterECE 4542 Design II Group 04
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Design Team Members
Faculty Advisor Dr. John P. Donohoe MSU ECE
Professor
Industrial Advisor Martin F. Jue President
of MFJ Enterprises Starkville, MS
Team Member Chad Butler Email
ceb9_at_msstate.edu
Team Member Timothy Garton Email
twg2_at_msstate.edu
Team Member Corey Amis Email
hca6_at_msstate.edu
Team Leader John Kennedy Email
jwk7_at_msstate.edu
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Abstract

• Design a radio frequency wattmeter that
• operates at 1.8 30 MHz
• measures and displays forward and reflected power
• calculates and displays standing wave ratio
• auto-ranges at 30/300/3000 watts forward power
  and 6/60/600 watts reflected power

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Block Diagram
Directional Coupler
Transmitter
Display Unit
Microprocessor
Voltage Regulator
Power Meter
SWR Meter
LCD
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Directional Coupler Design Constraints
Constraint Performance Pass/Fail
Frequency Range Operational at 1.8 30 MHz ?
Forward/Reflected Power Accuracy Accurate within 10 ?
Power Range Handles 30/300/3000W fwd and 6/60/600W ref ?
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Directional Coupler PCB and Enclosure

• 2.25 x 2.5
• Variable capacitor used to increase accuracy
• Current transformer samples incoming current from
  transmission line

• Compact, external sensor for flexibility
• Connects to main unit using lightweight telephone
  wire
• Standard SO-239 cable connectors

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Directional Coupler Prototype vs. Packaged
Testing(100W w/50 ohm dummy load)
Frequency (MHz) Forward (V) Reflected (V)
Prototype Packaged Prototype Packaged
1.83 3.91 3.90 0.03 0.02
3.53 3.86 3.93 0.03 0.05
7.25 3.87 3.95 0.08 0.07
10.11 3.90 3.99 0.12 0.10
14.20 3.95 4.01 0.19 0.15
18.12 3.98 4.02 0.25 0.21
21.01 3.99 4.02 0.29 0.26
24.94 4.11 4.10 0.33 0.29
28.00 4.13 4.12 0.37 0.34
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Directional Coupler Performance Analysis
Constraint Performance Pass/Fail
Frequency Range Operational at 1.8 30 MHz Pass
Forward/Reflected Power and SWR Accuracy Accurate within 10 Pass
Power Range Handles 30/300/3000W fwd and 6/60/600W ref Pass
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Display Unit Design Constraints
Constraint Performance Pass/Fail
Frequency Range Operational at 1.8 30 MHz ?
Forward/Reflected Power Accurate within 10 ?
SWR Accuracy Accurate within 10 ?
Power Range Auto Range _at_ 30/300/3000W fwd 6/60/600W ref ?
Voltage Regulation 12-18V DC to 5V DC within 10 ?
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Display Unit PCB and Enclosure

• Working together with MFJ to design a display
  unit that will
• meet the design specifications set forth by our
  design team
• Meet the design specifications set forth by MFJ
  design team
• Fabrication of PCB complete, software changes
  still underway
• Enclosure being designed using AutoCAD software

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Display Unit Prototype vs. Expected Packaged
Testing(100W w/50 ohm dummy load)
Frequency (MHz) Forward (W) Reflected (W)
Prototype Expected Packaged Packaged Prototype Expected Packaged Packaged
1.83 100.1 100.0 0.0 0.0
3.53 100.1 100.0 0.0 0.0
7.25 100.1 100.0 0.0 0.0
10.11 100.0 100.0 0.0 0.0
14.20 99.9 100.0 0.1 0.0
18.12 99.8 100.0 0.1 0.0
21.01 99.7 100.0 0.1 0.0
24.94 99.6 100.0 0.2 0.0
28.00 99.5 100.0 0.2 0.0
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Display Unit Expected Performance

• Once the software changes are complete the
  display unit will
• Provide correct functionality of LCD display
• SWR, forward power, and reflected power digital
  readings
• SWR, forward power, and reflected power bar graph
  readings
• Provide correct display of two analog meters
• SWR meter
• Forward/reflected power meter
• Provide correct functionality of mode buttons
• Provide an audible and visible SWR alert for high
  SWR readings

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Display Unit Performance Analysis
Constraint Performance Pass/Fail
Frequency Range Operational at 1.8 30 MHz ?
Forward/Reflected Power Accurate within 10 ?
SWR Accuracy Accurate within 10 ?
Power Range Auto Range _at_ 30/300/3000W fwd 6/60/600W ref ?
Voltage Regulation 12-18V DC to 5V DC within 10 ?
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Packaged Design Cost of Parts
Materials Quantity Unit Cost per thousand Total Cost
Resistor 20 0.05 1.00
Capacitor 20 0.10 2.00
Diode 5 0.01 0.05
Variable Resistor 5 0.50 2.50
Variable Capacitor 2 0.40 0.80
Toroid 1 0.50 0.50
Ferrite Bead 2 0.05 0.10
Voltage Regulator 1 0.30 0.30
Speaker 1 5.00 5.00
Switch 5 0.50 2.50
Processor Socket 1 0.15 0.15
Microprocessor 1 6.00 6.00
LCD 1 15.00 15.00
Board 2 10.00 20.00
Case 1 10.00 10.00
Analog Meter 2 5.00 10.00
TOTAL COST 1 X 75.90
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Software Design Code

• Software functionality was completed during the
  first semester (i.e. calculations and LCD control
  functions)
• Some software changes are needed to provide
  additional functions and control the new analog
  meters
• Implement a high SWR alarm on the LCD
• Control a buzzer and amplifier shut-off relay
• Modify the look-up table values used to generate
  the PWM voltages to the new analog meters
• Software changes are still being worked out

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Software Design MicroprocessorResource Usage
Available Resources Resources Used
Program Memory 8K instructions 2K instructions
Data Memory 368 bytes 80 bytes
Clock Speed 20 MHz (max) 4 MHz
8-bit A/D Channels 5 2
PWM Channels 2 2
I/O Pins 22 17
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Interaction with MFJ Design Team

• PCB Layout
• Tips for minimizing PCB area
• Tips for laying out the PCB
• Help with double sided PCB trace routing
• Help implementing MFJ design changes
• Package
• Tips for AutoCAD and creating a CNC file for the
  metal punch machine
• Tips for minimizing metal usage
• Operating punch and bend machines

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Summary

• Completed work
• Directional coupler PCB design
• Directional coupler packaging
• Directional coupler testing
• Display unit PCB design
• Display unit packaging design
• Tasks remaining
• Software tweaking and final testing
• Final product testing

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Acknowledgements

• We would like to thank the following people for
  their support
• Dr. J. Patrick Donohoe, Faculty Advisor
• Mr. Martin F. Jue, President of MFJ
• Harry Wong, Project Engineer for MFJ
• Carlous Perry, Associate Engineer for MFJ
• Dr. Picone
• Nishant Chandra

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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.