June 10, 2004
Intriguing the Physicists, Radio Buff Shrinks an Antenna
By IAN AUSTEN
NY Times
WHILE a lifetime in ham radio played a role, it was love that ultimately
led Rob Vincent to develop what he says is a way to make antennas
significantly smaller but still efficient.
"About 1995 I had met a sweetheart and we fell in love," Mr. Vincent, now
60, recalled. "I went to live with her, but the only problem was that she
lived on this postage stamp of a yard in a congested neighborhood."
The real estate owned by Carolyn Hardie, the woman Mr. Vincent later
married, was an issue because his amateur radio interests had turned toward
frequencies in the 160-meter band. That band is close to broadcast AM
radio. And, like an AM station, operating on it requires a tall antenna -
in Mr. Vincent's case, one that is 140 feet high. Aesthetic and zoning
questions aside, the 50-by-100 foot lot was not big enough to accommodate
the guy wires needed to stabilize a tower that high.
So Mr. Vincent, a technician with the University of Rhode Island's physics
department, began thinking about ways to make antennas smaller. The end
result is a system that he claims can produce antennas that are one-third
to one-ninth as high as normally required. He has spoken to other ham
operators in over 80 countries on the 160-meter band through his relatively
new, self-supported backyard tower, which is one-third of the conventional
minimum size.
Mr. Vincent said his improvements were not just applicable to ham radio
towers. They could be used to either further shrink the tiny antennas in
cellphones, he said, or boost their efficiency.
Small yet efficient antennas have long been a goal for radio researchers,
said R. Dean Straw, the senior assistant technical editor for the American
Radio Relay League, an association of amateur operators. "The holy grail is
an antenna the size of a grain of salt that produces big signals," he said.
Generally the size of antennas increases with the wavelength of the
frequencies they are transmitting or receiving. While there are several
formulas for determining optimum height, the height of most antennas is
one-quarter to one-half the wavelength. At 140 feet, for instance, Mr.
Vincent's ham tower would have been slightly higher than one-quarter of the
wavelength of 160 meters, which is equal to 525 feet.
Smaller antennas can be used, but with a trade-off. "When you get below a
quarter-wavelength, efficiency drops off dramatically," Mr. Vincent said.
Before arriving at the university in the early 1990's in a
still-unfulfilled quest to complete his undergraduate degree, Mr. Vincent
spent about 30 years in radio-related engineering jobs, mostly with a radar
division of Raytheon. But his tinkering with antennas dates back to when he
obtained his first amateur radio license at the age of 14.
"I've always had a natural understanding of radio - maybe it's from a prior
life," Mr. Vincent said. "But in those early days I could not fathom how an
antenna worked."
The relationship between antenna height and efficiency was so well
established that he initially kept his antenna-shrinking work a secret. Mr.
Vincent also acknowledged that he had relatively little idea of what might
work when he began the project.
"When I started out to do this it was 10 percent theory and 90 percent
black magic," he said. After reviewing much of the literature, Mr. Vincent
started designing antennas with special simulation software on a personal
computer.
From the most promising of those virtual designs, he ran tests using
antennas that were about 18 inches high and fashioned from copper-covered
Plexiglas rods. One model seemed particularly successful until it lost its
signal during a high-powered broadcast test. When Mr. Vincent went outside,
he found only a lump of molten metal and plastic.
Gradually, he said, potential areas of improvement became apparent. He
began confiding in some friends from the ham radio world and faculty
members in the physics department. One friend allowed Mr. Vincent to build
a 46-foot-high experimental antenna at his country home, which includes a
salt marsh.
Saltwater is an antenna builder's dream. By providing a highly conductive
base for the antenna, the water improves reception.
The big prototype improved upon conventional designs in many ways. But one
crucial one involved the placement of devices known as load coils along its
length. Load coils are commonly used in cellphone antennas to alter their
current patterns.
Conventional broadcast antennas, Mr. Vincent said, generally have a lot of
current at the bottom and very little if any at the top. With his design,
current is more evenly distributed.
To avoid suggestions that saltwater, not his design, was the magic, another
46-foot prototype followed, built on rock. It offered 80 to 100 percent of
the efficiency of an antenna three times its size.
About three years ago, the University of Rhode Island became interested
enough in Mr. Vincent's work that it gave him office space. After a review
by engineering and physics professors, it began the process of patenting
and selling the technology. Mr. Vincent has turned over all his rights to
the university.
"We've seen test data from Rob Vincent and it sure is attractive," said
Quentin Turtle, the director of industry research and technology transfer
for the university.
Mr. Straw of the radio relay league said he was impressed with Mr.
Vincent's work ethic. "But I remain somewhat skeptical,'' he said. "I'd
like to see some validated field test measurements."
Mr. Vincent said he was aware that would-be buyers of his technology would
demand better test results, although measuring the efficiency of antennas
is difficult. But given the scrutiny his project has received to date, he
said he was confident that his antennas would pass muster.
"I'm part of the technical staff to a whole bunch of Ph.D's," he said. "You
can't fool these people."
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