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| Cat Whisker Detector |
The Cat Whisker played an important role in the development
and evolution of the radio receiver.
Hertz’s first detector [1888] was but a circular ring with an air gap.
Later, Marconi [1896] and others developed the coherer using metal filings. The next progression was Deforest developing
the first vacuum tube, the audion, in 1906.
Although the audion was an improvement, it didn’t get widespread use
until Armstrong improved upon it. The
quest to develop a sensitive receiver that would work better than the coherer was
always in the forefront.
Enter the Cat Whisker. The cat whisker was the first
sensitive and stable wireless detector, an improvement that ultimately became the
replacement for the coherer until the development of Armstrong’s regenerative
circuits that ultimately expanded wireless and broadcast technology.
The crystal set was simple construction, made up of the cat
whisker and a headphone.
The central component of the Cat Whisker is a crystal used as
a detector, a point contact rectifier - a diode. It allows the current to flow only in one
direction, acting as a detector converting radio signals into varying amplitude
pulses in the audio range that can be heard in a headset. Simple and very
effective. The crystal [cat whisker]
detector was actually the first type of semiconductor diode.
A fragment of crystal mineral is placed in a small cup or
clamp with an attached wire. A springy, or coiled piece of wire or a piece of
graphite [pencil lead] was used to probe the surface of the crystal.
The final resting spot would then be secured to prevent movement. Some
of the popular crystals used were galena, silicon, iron pyrites, and carborundum
– ultimately around 250 minerals were experimented with.
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| Galena Crystal |
The Galena crystal, although effective, did have problems as
the light contact pressure could knock the device off adjustment and the user
would have to re-adjust the contact. Galena was popular as it is a cubic crystal;
that is, it occurs in square shape and breaking it into smaller pieces always
left a flat surface that made it easy to find the correct placement on the
crystal.
The Cat Whisker set allowed the general public to build or
purchase receivers very easily and inexpensively. Radio receivers using the cat
whisker detector were called crystal sets and were instrumental in the upsurge
of broadcast radio in the 1920s. This was the most popular type of receiver in
the early 1920s as it was 30% - 40% less in cost of tube sets. Due to the enormous growth of broadcasting,
better tube sets were built and competition lowered the cost. By 1928 the cat
whisker crystal set was a thing of the past.
Greenleaf Whittier Pickard is one of the most successful
early experimenters of crystal minerals used as radio detectors. If fact, it was Greenleaf that was
responsible for naming the crystal detector the “cat whisker”. His device is significant for two historical generations
of wireless advancement. The first generation
was in the early days of wireless development, and later in the early days of broadcast
radio.
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| Greenleaf Whittier Pickard |
The crystal set was so simple, inexpensive, and it worked
exceptionally well that it was easy for the general public to embrace it. Although not given credit, the crystal can be
considered a major contributor in wireless growth from the experimental period to
early commercial broadcast.
Greenleaf Whittier Pickard was born in Portland, ME in
1877. Pickard’s father, Samuel Pickard,
was publisher of the Portland Transcript newspaper. His mother Elizabeth
Whittier was the niece of the famed American poet John Greenleaf Whittier. Thus
the namesake Greenleaf Whittier Pickard.
Young Pickard started his technical work at an early age, as
he installed telephones to communicate between his friend’s houses. He also
installed a warning bell circuit for patrons of a Portland speakeasy. He was smart but some considered him a
troubled adolescent.
Pickard went to Lawrence Scientific at Harvard University.
He never graduated but eventually took classes at MIT. He also was aware of the
Marconi’s early wireless experiments.
He soon took a position at the Blue Hill Observatory in
Milton, MA. The Blue Hill Meteorological
Observatory was founded in 1884, and is the oldest weather observatory in the
US. The Blue Hill Observatory conducted
early kite experiments and directed the first atmospheric soundings in
1898. Pickard participated in these
experiments and when the Smithsonian Institute asked the Blue Hill Observatory
to conduct wireless experiments, he was assigned to the project. The
Smithsonian was interested in how heights affected radio wave transmissions. This
was Pickard’s exposure and entry point into wireless research.
Later in 1902, while working for the first US wireless company,
the American Wireless Tel & Tel, Pickard worked on setting up wireless
station in Cape May, NJ.
While in Cape May and working as a research engineer, he was
experimenting on microphone detectors. One day he unintentionally left some
sewing needles lying across a carbon block and observed that he was able to
receive a signal from one of the company’s ship transmitters.
Thus, this coincidence led him to work on the crystal detector
design [essentially a modified microphone circuit] consisting of carbon against
steel in series with three batteries and a headphone. The signal was audible
but there was static in the background that sounded like frying noise. The story is Pickard was annoyed with this
noise and wanted to eliminate it. This was done by removing one of the
batteries, which lowered the noise but also the audio. Ultimately, and to his amazement, he found he
could remove all the batteries and still receive a radio signal.
Reception of the radio wave was solely from the energy received
from the antenna, no one believed that such a thing was possible. From this point, and for the next three
years, Pickard continued to experiment with the crystal detector.
As a result, in 1906, he was able to obtain fused silicon
and found this to be the best crystal material for the cat whisker detector. He
applied for a patent that same year – the silicon crystal detector.
With more experimentation, he developed and patented the
Perikon detector [Perfect Pickard Contact]. He continued
experimentation at his great uncle home in Amesbury, MA – the home of John
Greenleaf Whittier. Note that Pickard had one of the first beach cottages in
Seabrook, NH – named “Perikon Cottage”.
The Perikon Detector was very much favored by experimenters,
as it was exceedingly sensitive and easy to adjust, however it needed constant
adjustment. This detector uses two types of crystals making contact with each
other, and is adjusted by a spring and screw arrangement.
In 1908, along with two partners, Pickard founded the
Wireless Specialty Apparatus Company [WSA].
This company became the major supplier to the US Navy for crystal
receivers until about 1914. Their
equipment was considered the highest quality. WSA also became the conduit that
sold transmitters manufactured by the National Electric Signaling Co.
In 1926, Pickard received his first wireless award, a Medal
of Honor from the Institute of Radio Engineers:
“to that person who has made public the greatest advance in the science
or art of radio communication, regardless of the time of performance or
publication of the work on which the award is based.”
Greenleaf Whittier Pickard died in 1956 in Newton, MA – he
was 78 years old.
Throughout his career Pickard was involved in many other
technical research, working on military projects through WWII. In 1946 with a
new partner, the Pickard & Burns Company continued to conduct research. The
company manufactured submarine antennas, antenna coupling equipment, and nuclear
reactor temperature monitors. Other products included the Humistor, the
Bolometer amplifier rotary waveguide, and IF strips for airborne radar
receivers. His legacy continues as
Pickard and Burns were acquired by other companies and continue to provide
component to the aerospace industry.
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| Family listening to the crystal set |
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