Simple Student-Built IQ Modulator/Demodulators for Wireless Communication Laboratory Digital Communication Link Demonstrations

Dennis Derickson

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Conference: 2018 ASEE Zone IV Conference
Location: Boulder, Colorado
Publication Date: March 25, 2018
Start Date: March 25, 2018
End Date: March 27, 2018
Page Count: 9
DOI: 10.18260/1-2--29625
Permanent URL: https://peer.asee.org/29625
Download Count: 4993

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Dennis Derickson California Polytechnic State University, San Luis Obispo

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Dennis Derickson is the department chair of Electrical Engineering at California Polytechnic State University. He received his Ph.D. , MS, and BS in electrical engineering from the University of California at Santa Barbara, the University of Wisconsin and South Dakota State respectively. He got his start in Electrical Engineering by getting his amateur radio license in 1975.

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Abstract

TITLE Simple Student-Built IQ Modulator/Demodulators for Wireless Communication Laboratory Digital Communication Link Demonstrations

ABSTRACT Instrumentation Vector Signal Generators (VSG) and Vector Signal Analyzers (VSA) are great tools to demonstrate wireless communication link characteristics but are often too expensive for equipping every station in a digital communications laboratory. Software Defined Radios (SDR) equipment are also great tools for demonstrating wireless links as there are models now that are relatively inexpensive and have great performance.

The laboratory exercise discussed in this contribution provides many of the learning outcomes possible with VSA/VSG equipment with additional insights at the hardware level that might not be evident using SDRs. The laboratory exercise in this contribution centers on having students build IQ modulators/demodulators that can be used to demonstrate digital communication links. The required construction parts include semi-rigid coaxial cable, surface mount frequency mixers, and surface mount resistors that cost $12. A pre-lab handout and introductory laboratory lecture illustrate how IQ modulators are used to generate arbitrary digital modulation constellations in the I-Q plane. An example completed IQ modulator is shown to students demonstrating the basics of high frequency signal routing with short lead lengths and good grounding. Each student then individually solders together the IQ modulator assembly in a process that can be done in about 2 hours. A wireless communication link is then demonstrated by having one student using their assembly as an IQ modulator and a student partner using their assembly as an IQ demodulator. The IQ modulator uses a function generator input and the IQ demodulator uses an oscilloscope as the receiver. Students can directly witness the importance of having the local oscillator of the transmitter phase locked to the local oscillator of the receiver in order for the digital communication link to be successful. Students also compare Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK) and higher order constellations as part of the characterization of the digital links.

Student feedback on the IQ Modulator/Demodulator laboratory project centers on how the soldering and high frequency layout of the project are eye-opening compared to early laboratory activities in the curriculum. Students also report a much more in-depth understanding of I-Q modulation techniques as they use more capable VSA/VSG and SDR equipment in future laboratory sessions.

The intent is to present this as a poster paper and the author would give some live demonstrations of the laboratory exercise.

Citation
Format

Derickson, D. (2018, March), Simple Student-Built IQ Modulator/Demodulators for Wireless Communication Laboratory Digital Communication Link Demonstrations Paper presented at 2018 ASEE Zone IV Conference, Boulder, Colorado. 10.18260/1-2--29625

TY  - CPAPER
AB  - TITLE
Simple Student-Built IQ Modulator/Demodulators for Wireless Communication Laboratory Digital Communication Link Demonstrations

ABSTRACT
Instrumentation Vector Signal Generators (VSG) and Vector Signal Analyzers (VSA) are great tools to demonstrate wireless communication link characteristics but are often too expensive for equipping every station in a digital communications laboratory.  Software Defined Radios (SDR) equipment are also great tools for demonstrating wireless links as there are models now that are relatively inexpensive and have great performance.  

The laboratory exercise discussed in this contribution provides many of the learning outcomes possible with VSA/VSG equipment with additional insights at the hardware level that might not be evident using SDRs.
The laboratory exercise in this contribution centers on having students build IQ modulators/demodulators that can be used to demonstrate digital communication links.  The required construction parts include semi-rigid coaxial cable, surface mount frequency mixers, and surface mount resistors that cost $12.   A pre-lab handout and introductory laboratory lecture illustrate how IQ modulators are used to generate arbitrary digital modulation constellations in the I-Q plane.   An example completed IQ modulator is shown to students demonstrating the basics of high frequency signal routing with short lead lengths and good grounding. Each student then individually solders together the IQ modulator assembly in a process that can be done in about 2 hours.   
 
A wireless communication link is then demonstrated by having one student using their assembly as an IQ modulator and a student partner using their assembly as an IQ demodulator.    The IQ modulator uses a function generator input and the IQ demodulator uses an oscilloscope as the receiver.   Students can directly witness the importance of having the local oscillator of the transmitter phase locked to the local oscillator of the receiver in order for the digital communication link to be successful.   Students also compare Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK) and higher order constellations as part of the characterization of the digital links.

Student feedback on the IQ Modulator/Demodulator laboratory project centers on how the soldering and high frequency layout of the project are eye-opening compared to early laboratory activities in the curriculum.  Students also report a much more in-depth understanding of I-Q modulation techniques as they use more capable VSA/VSG and SDR equipment in future laboratory sessions.

The intent is to present this as a poster paper and the author would give some live demonstrations of the laboratory exercise.
AU  - Dennis Derickson
CY  - Boulder, Colorado
DA  - 2018/03/25
PB  - ASEE Conferences
TI  - Simple Student-Built IQ Modulator/Demodulators for Wireless Communication Laboratory Digital Communication Link Demonstrations
UR  - https://peer.asee.org/29625
DO  - 10.18260/1-2--29625
ER  -