At
the very beginning
The NBS manually operated system for making microwave measurements
is a maze of rectangular waveguide and associated equipment.
Although unexcelled for accuracy, it is expensive to operate
and has been virtually supplanted by the new, compact dual 6-port
automated systems. |
NIST's
work in radio research traces back almost to its founding in 1901.
The first researcher in radio was Dr. Louis W. Austin who, in 1904,
began to investigate the practical application of radiotelegraphy
for the Navy. He headed the U.S. Naval Radiotelegraphic Laboratory
at NIST from 1908 to 1932. In 1907, J. Howard Dellinger came to
NIST as the agency's wireless expert, heading a section in the Electrical
Division called Radio Measurements. One of his first measurements,
in 1911, was the calibration of a frequency meter. Frederick A.
Kolster, a radio engineer, came to NIST in 1911 and developed a
portable instrument to measure wavelengths and other properties
of radio transmissions. NIST received its first special appropriation
from Congress for radio research in 1915--$10,000 "for the
investigation and standardization of methods and instruments employed
in radio communication."
Training
the troops
During World
War I, NIST trained thousands of soldiers in radio communication
for the Army Signal Corps. It developed a reference book for radio
instructors for use in the Army, Navy and universities. Frequent
updates and reprints made this reference book a bible for radio
engineers and amateurs for two decades. Kolster also developed a
radio direction finder for locating enemy submarines. This direction
finder was later adapted as a crude aid in airplane navigation.
Also during the war, NIST developed methods for measuring the characteristics
of the new vacuum tube that was beginning to be adopted by radio
manufacturers.
A tiny microwave horn is being mounted on a very solid base
surrounded by carbon-loaded foam-rubber absorbing material
in a NIST antenna range. Setups like this are used in the
measurement of the performance and characteristics of microwave
antennas.
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Radiating
through the Jazz and Swing Ages
The early days
of radio broadcasting in the 1920s were somewhat messy. Commercial
stations did not always stay on their assigned frequencies and tended
to drift, causing interference with other stations' signals. In
1923, NIST began broadcasting precise frequency signals over its
laboratory transmitter WWV in Washington, D.C. Commercial stations
could use WWV's frequencies as calibration standards to keep their
own frequencies constant. The early NIST station also transmitted
music and market and crop reports; but these were only done experimentally
and soon disappeared. Precise frequency information is still available
on WWV, now located near Fort Collins, Colo. Time information was
added to the WWV format in 1945. In addition to WWV, NIST operates
two other time and frequency radio stations - WWVB near Fort Collins,
and WWVH in Hawaii. Today's customers still include radio (and television)
stations but also include electrical power and telecommunications
companies, the financial community, scientists and engineers, computer
networks, and navigators.
NIST also helped
the fledgling radio industry in other ways in the 1920's. It issued
a handbook that showed thousands of Americans how to build their
own radio sets. And, it built the first alternating-current radio
set in 1922, years before commercial firms offered ac-powered radios
for the home (earlier models were battery operated). It helped train
radio technicians, published early reference works, and coordinated
the writing of an academic textbook that was admired by Thomas Edison
as "the greatest book on this subject that I have ever read."
A
beacon during the Depression
In the 1930's,
NIST was perhaps best known for developing radio aids for the airplane
industry. Much of the work started when Harry Diamond came to NIST
in 1927. He developed the first visual-type radio beacon that enabled
a pilot to keep on course and know his approximate position at all
times while in flight. Later, Diamond added a unit to the radio
beacon that enabled the first blind landing of an airplane entirely
by radio guidance. Diamond operated the radio himself in the first
series of blind landing tests between College Park, Md., and Newark,
N.J. Because of the Great Depression, radio research at NIST was
curtailed in the 1930's and centered on audio frequency standards,
radio wave propagation phenomena, and measurements of the ionosphere
for long-distance radio transmission. Working for the Weather Bureau,
NIST scientists developed radiosondes--balloon-borne instruments
which transmitted weather data to the ground from altitudes up to
20 miles. By 1940, some 35,000 radiosonde units were being built
and sent aloft.
These structures are mounted on precision rails so that the
distance between them can be varied in a controlled manner while
the antennas mounted on them are tested. Their nonconductive
materials and outdoor setting reduces the reflections that would
complicate the analysis of the tests. |
World
War II brings bats and fuzes
During World
War II, NIST's radio research programs were perhaps best known for
developing the radio proximity fuze that enabled shells or bombs
to be more effective. The radio proximity fuze is essentially a
tiny radio sending and receiving device about the size of an ordinary
light bulb. It continuously sends out radio waves; when these waves
approach a sizable object, they reflect back to the fuze. As the
waves intensify, they trigger an electronic switch that detonates
the fuze and the weapon. In another project, NIST helped to develop
a radio-operated guided missile called the Bat; it was used by the
Navy late in the Pacific campaign. The radio direction finder, first
designed by Kolster in 1915, was updated in World War II to detect
German submarines. NIST's work on the characteristics of radio wave
propagation led to the formation of the Interservice Radio Propagation
Laboratory (IRPL) at NIST in 1942. In another radio-related project,
NIST developed a quartz crystal inspection and testing laboratory
to determine the best quartz to be used in military radio and electronic
equipment.
Post-war
frequencies become clocks
After the war,
the IRPL evolved into the Central Radio Propagation Lab (CRPL).
A significant part of the ionospheric and propagation studies depended
on having accurate frequency standards in the high frequency range.
These were based on special quartz crystal oscillators which constituted
the national primary standard of frequency. Before long, the expansion
of radio technology into higher frequencies involved the CRPL in
developing measurement techniques for microwaves, and in 1949, this
expertise was employed in developing the world's first atomic clock.
Based on using the absorption of microwaves in ammonia gas to stabilize
the frequency, this clock was only slightly more accurate than the
spinning earth, but it quickly led to other clocks based on a resonance
in cesium atoms, and which far exceeded the accuracy of any previous
timekeeping system. The latest version (the eighth generation, called
NIST
F-1,) of these cesium clocks attains an uncertainty of better
than 2 parts in a million billion (comparable to 1 second in 20
million years).
A
move to Colorado in the '50s
The CRPL, which
moved to Boulder, Colorado, when the NIST laboratories there were
opened in the early 1950s, was later divided and part became the
National Oceanic and Atmospheric Administration's Environmental
Research Laboratory and the National Telecommunications and Information
Administration's Institute for Telecommunication Sciences. The part
that stayed with NIST became the Electromagnetics Division of NIST
(now the Radio
Frequency Technology, Electromagnetic
Technology, Optoelectronics,
Magnetic Technology
and Time and
Frequency Divisions).
A small probe on the right scans the near field of the microwave
horn on the left; this series of measurements can then be
transformed mathematically to produce a predicted map of the
far-field pattern of the horn.
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These have
continued their research efforts in support of industry, with the
development of advanced measurement techniques for microwave parameters,
antenna performance, lasers, optical fibers, magnetic data storage,
time transfer, and numerous other technologies.
Taking
measurements in the near-field
Of
crucial importance to many radar and microwave communications manufacturers
is the near-field/far-field microwave antenna measurement technique
invented and developed by NIST. It permits the accurate evaluation
of antenna performance at far less cost than previous methods. Until
this development, the radiation and gain patterns of antennas were
difficult and expensive to characterize, as they required measurements
at large distances. Often it was necessary to fly a planeload of
instruments through the far-field pattern many times in many directions
before an adequate picture of the pattern emerged. Engineers, physicists
and mathematicians of the Electromagnetics Division developed techniques
to calculate complete three-dimensional far-field patterns from
measurements made close to the antenna or electronically steerable
array. This means the measurements can be made conveniently in the
laboratory for many antennas, and eliminates the problem of transporting
instruments over large areas. The near-field data are fed to a computer,
which uses a new and rigorous mathematical approach to transform
them into far-field predictions. The results can then be machine-plotted
in the form of maps, graphs, or tables of values. The technique
permits economical solutions to problems that sometimes couldn't
even be attacked before, and is often more accurate than actually
making the measurements at a large distance. Near-field measurement
ranges based on NIST's technology have been built at dozens of manufacturers
and defense installations.
A large phased array radar antenna, similar to those used
on airborne warning and control system (AWACS) aircraft, undergoes
evaluation at NIST's near-field scanning range.
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Other microwave
innovations based on NIST's work are the automatic network analyzer
and 6-port. They enable rapid, accurate measurements of a suite
of important parameters in microwave equipment and components.
Laser
measurements lead into new century
Laser performance
measurements have been made at NIST almost as long as lasers have
been around. Beginning in the early 1960's, NIST developed techniques
for measuring the output power and energy of lasers. Research on
measurements and standards to support the development and application
of lasers continues. Research related to optical communications
was begun in the 1970's, expanded in the 1980's, and continues at
a substantial effort today.
In the still-young
field of optical fibers, standards of performance and dimensions
are still evolving. NIST's work in this area includes methods for
determining the core and cladding diameters of fiber, the intensity
profile across the face of the fiber, and chromatic dispersion.
The Optoelectronics Division conducts over 200 calibrations annually
and provides industry with standard reference materials that can
be used to calibrate a customer's own instruments.
An experimental television-time-code system developed at NBS
in the '70s offered time signals that could be transmitted
over national networks. Once the code was received and recognized,
it was displayed as small numerals on the screen. The numbers
changed in exact step with the master clock at the broadcast
station or network origin.
This
TV-Time system was the basis for the development of today's
"closed captioning" system, for which NIST received
an Emmy in 1980.
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TV
time system leads to an Emmy
In the '70s,
NIST developed an experimental television-time-code system to provide
inexpensive coarse- and fine-time signals to a great number of users.
The code carried information designating the hour, minute, and second,
and displayed it on the bottom of the screen. This "TV-Time"
technology was the basis for the development of today's "Closed
Captioning" system, for which NIST received an Emmy in 1980.
Closed captions provide the capability to display the text of television
dialog and narration, in any language. This has been a development
of great benefit to the hearing impaired and to the patrons of sports
bars.
Date created: 9/17/01
Last updated:
Contact: inquiries@nist.gov
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