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Dead medium: Early/Mechanical Television Systems
From: kadrey@well.com Richard Kadrey
Source(s): These are excerpts from the catalog from the exhibition at the Royal Ontario Museum, "Watching TV". The exhibition runs through September 15, 1996.

The catalogue is available from Royal Ontario Museum shops, CityStore 299 Queen Street, West, Ontario, Canada or from MZTV Museum. Cost - $11.50 Cdn., $10.00 US, plus shipping. Send email orders to mztv@bravo.ca

Credits: An excerpt from "Watching TV: Opening the Doors of Reception" by Liss Jeffrey, Acting Director, MZTV Museum. Technical research by Gary Borton, Consulting Curator, and Iain Baird, Researcher, MZTV Museum.

"Mechanical TV: Baird Television"

The ROM's Institute of Contemporary Culture in

association with the MZTV Museum invites you to join us

for an historic demonstration of BAIRD TELEVISION, live at

the Royal Ontario Museum, Sunday April 14th, 1996, 1:00pm.

John Logie Baird is the Scottish inventor who

obtained the world's first real television picture in his

laboratory in October, 1925, and demonstrated it to the

British public on January 26, 1926. The image

obtained was a small 30-line vertically-scanned red and

black image, but it was television. Mechanical television

based on Baird's systems dominated international

television for the next few years into the early 30's.

The first live public demonstration of a Baird

Television system in North America since 1932 will take

place in Toronto on Sunday, April 14th. John Logie Baird's

son, Professor Malcolm Baird, will give a short speech to

commemorate the 70th anniversary of the first public

demonstration of television; grandson Iain Baird, who

presently works at MZTV, will be in attendance to operate

the Televisor.

Mechanical systems of this period are not

compatible with today's TV signals. When the MZTV Museum

decided to restore this televisor to full operation, the

first obstacle was to feed a signal to it that it could

receive. We requested the assistance of Peter Yanczer, a

modern-day mechanical television enthusiast, author, and

technician. He built a mechanical camera that would work

on a 30-line system, and connected this camera to the

television with cables. The televisor itself needed only

minor repairs and lubrication, and has remained workable.

By 1930, a British or West European television

enthusiast could buy this televisor for home reception for

about 18 pounds. The Baird company was licensed to provide

intermittent broadcasts from the BBC transmitters, and at

least 3,000 enthusiasts "looked in" to see as well as hear

some of Britain's most popular singers and comedians.

Mechanical TV: How it works

The scanning and reproducing discs are similar. Both are

mounted on driving motors, and each is punched with a

spiral of small holes along the outer edge. The number of

holes matches the number of lines of picture definition.

At the transmitter in this mechanical system, the

studio is in total darkness. A light emanates from a lamp

behind the disc and, projected through the holes set in

the spiral on the outer edge, scans the features of the

subject's face. The photocell converts these variations

in the reflected light into the electric impulses, which,

once amplified, can be transmitted by radio waves.

At the receiver, the signal is converted into a

sequence of bright flashes by the neon tube. The

reproducing disc rotates rapidly in front of this tube,

and converts each flash of the lamp into a small element

of the image. The rapid speed of the disc makes

"persistence of vision" possible for the looker-in.

"Persistence of vision" means that the brain retains

an image for one tenth of a second after it is perceived

by the eye. The rapid repetition of moving images (in film

or television) tricks the brain into perceiving continuous

images.

Richard Kadrey (kadrey@well.com)