The Bridge - Issue 2, 2019 - 21

Feature

GREAT IMPEDANCE MATCH FOR KNOWLEDGE TRANSFER:
Amateur Radio as Part of Electrical and Computer Engineering Education

cost and simple test and measurement equipment
(examples include the QST and QEX Magazines
from ARRL (http://www.arrl.org/qst and http://www.
arrl.org/qex). University faculty in the electrical and
computer engineering discipline are interested in
finding practical construction projects that can be
incorporated into their laboratory curriculum. These
amateur radio community-created projects provide
a large pool of ideas freely available for inclusion in
the ECE laboratory curriculum. Students are often
inspired when they are able to design and construct
a useful project in the limited time available for their
laboratory meetings. Figures 3-6 illustrate examples
of the authors' use of amateur radio projects
in the
Filter Adjustment
Copper
Pipe
Screw
ECE laboratory curriculum.
End-Cap
Figure 3 shows an example microwave oscillator
design used in a high-frequency electronics
Double
laboratory.
SidedThe design uses a microwave frequency
BipolarPC
Junction Transistor in a negative-resistance
amplifier
configuration to provide gain. The
Board
adjustable quarter wave transmission line resonator
is used to provide frequency selective reflective
.085
inch resonator provides
feedback. The
High-Q
for a stable
Output
Semi-rigid coax Input
oscillator with low phase noise. The design article
Waveguide
Filter
at 5.8 GHz Band
from Ham Circular
Radio Magazine
also
demonstrates
how
to lock this microwave frequency resonator to a low
frequency 10 MHz crystal reference oscillator using
a simple phase-locked loop addition. Construction
materials include double-sided PC board material,
adjustable length brass hobby tubing and "dead bug"
construction techniques.
Figure 4 illustrates two high-frequency filter
designs used in a filter design course. (a) This is a
5.8 GHz amateur radio band bandpass filter using a
copper pipe end cap and two 0.085-inch semi-rigid
coaxial cable probes. (b) This is a 902 MHz band
interdigitated bandpass filter made from brass hobby
store tubing and double-sided PC board material.
A senior project student also used the microwave
CAD electromagnetic simulation program EM-Pro
to compare the experimental performance to the
simulated performance of the filters.

Filter Adjustment
Screw

Copper Pipe
End-Cap
Double
Sided
PC
Board
.085 inch
Semi-rigid coax Input

Output

Circular Waveguide Filter at 5.8 GHz Band
Resonator Adjustments

Brass Coupled Resonators
Filter Input

PC board material

Interdigital Filter for 902 MHz Band
Fig. 4: Here are two examples of passive filter designs made from
hardware-store equipment and semi-rigid 0.085-inch-diameter
coax assemblies. Top, circular waveguide bandpass filter for
5.8 GHz, and bottom, an interdigitated coupled-resonator filter
for the 902 MHz amateur band. Both designs are adapted from
the ARRL UHF/Microwave Projects Manual -- Volume 1
by Kent Britain (WA5VJB).

Figure 5 shows two implementations of digital
communication modulators used as part of a digital
communication laboratory experiment set. These I-Q
modulators create flexible combinations of amplitude
modulation and phase modulation depending
on the input waveforms at the in-phase "I-Input"
and quadrature phase "Q-Input" connectors. Both
traditional PC board construction (a) and "DeadBug" construction (b) are used to fabricate these
modulators. Sets of IQ modulator/demodulators
along with student built antennas, power amplifiers,
and pre-amplifiers are combined to demonstrate
wireless digital communication links.
HKN.ORG

https://www.hamstudy.org/ http://www.arrl.org/qst http://www.arrl.org/qex http://www.ncvec.org/ https://www.hamstudy.org/ http://www.arrl.org/qex https://hkn.ieee.org/ https://hkn.ieee.org/

The Bridge - Issue 2, 2019

Table of Contents for the Digital Edition of The Bridge - Issue 2, 2019