Thursday, March 31, 2016

Cat Whisker

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.
Galena Crystal
The tip of the wire is moved over the crystal to find the most effective spot for it to receive. Placing the wire pressure on the crystal does this. The amount of pressure depended upon the type of crystal used. Galena crystal only needed light pressure to make the electrical contact.

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.
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.

Family listening to the crystal set