The Marconi Challenge      Originally web posted on www.arrl.org on March 14, 2001

On February 24, 2001, the College of Engineering at Temple University, Philadelphia, and its Amateur Radio club, The Temple University Amateur Radio Club, K3TU, celebrated Engineers' Week and the 100th anniversary of Guglielmo Marconi's transatlantic wireless transmission by sponsoring a technical competition for high school and Temple undergraduate students.

In 1901 Marconi succeeded in transmitting a radio signal across the Atlantic Ocean. The wavelength of the transmitted signal was approximately 1500 meters, and input power was measured in kilowatts. In contrast, the 2001 Temple University Marconi Challenge required contestants to transmit an infrared light signal at an approximate wavelength of 900 nanometers and power measured in milliwatts to a receiver at the greatest measurable indoor distance from the transmitter--likely in the same room as the transmitter!

The competition entry form prescribed a general configuration for the system and specifications for the components. Standard equipment for the Marconi Challenge was a single high-output LED as a transmitter, and a single phototransistor as a receiver. Contest rules limited the IR transmitter current to 75 mA dc or average. The entry form also suggested experiments--using Ohm's law and measurements--to set the transmitter current and, by varying the collector load resistor, adjusting the sensitivity of the phototransistor.

The rules allowed physically modifying the IR LED's half-intensity angle--nominally 45 degrees. Any method, except fiber optics, could be used at the receiver to focus and capture the optical transmission.

Focal lengths of standard physics lab one to four-inch convex lenses were measured and stable lens mounts were constructed. The performance of different IR LED-lens and lens-phototransistor configurations was compared. Adjusting the load resistor and applying novel optical biasing optimized the sensitivity of the phototransistor.

(L-R) Jason Voytilla, Anthony Matarazzo, Carl Waitz, and Patrick Dahl setup for the 2001 Marconi Challenge. Jason and Carl are Temple University ECE undergraduates. Patrick is a junior at Northeast High School, Philadelphia.

First place in the high school competition was awarded to Patrick Dahl, a junior at Northeast High School, Philadelphia. His winning distance was 34 feet for a minimum discernable signal change of 10%. Anthony Matarazzo, director of the Southern Pennsylvania Amateur Radio Club aerospace and medical magnet school program at Northeast High School, was Dahl's advisor. SPARC is home to W3YC, the oldest high school Amateur Radio station in the US.

"The Marconi Challenge gave our students a chance to see how electrical and optical systems could be combined to transmit a signal," said Matarazzo. "Ohm's law and focal length calculations made more sense to the students when the measurements they obtained could be applied directly in this competition."

Voytilla's first-place entry--for undergraduates. The AVR microprocessor pulse-modulates an IR LED. A laser-pointer rangefinder is used to align the system.

Jason Voytilla, a TU Senior, took first place in the more sophisticated college entry for TU undergraduates. His design employed pulse modulation, C-mount lens, and a laser-pointer rangefinder that made aligning the system very easy. His record transmission was 60 feet--the entire length of the lecture hall--and a measured 65% discernable signal change.

Contestants hard at work making final adjustments.

The Marconi Challenge competition could be a basis for including Amateur Radio in the high school science and technology curriculum. The activity demonstrates wireless transmission using electrical and optical principles. Junior and senior high school students will find that IR data transmission projects are much simpler to comprehend and less expensive to build than are robotics projects. IR data transmission projects can easily be expanded to include electronic circuits for pulse modulation and PC serial-port interfacing. Improved optics--telescopes and parabolic mirrors--can allow communication across the width of an entire campus or school ground.

Editor's note: Dennis Silage, K3DS, is a professor of electrical and computer engineering at Temple University, where he teaches digital communication and digital signal processing. An ARRL Life Member, he serves as an Assistant Director in the Atlantic Division. The author can be reached at silage@temple.edu.

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