Radio News Magazine Aug. 1928
The cover of the August, 1928 issue of Radio News magazine
shows a young couple viewing "radio movies" at home. In terminology
coined by publisher Hugo Gernsback, a "radio movie" meant the broadcast of a
pre-recorded movie image, whereas true "television" meant broadcasting a live image.
The feature article describes a scheme that uses scanning-disk
technology to broadcast image from a strip of conventional movie film.
On the broadcasting end, a strong
light is shined at a scanning disk with 48 lenses. A "pinhead" of
light passes through the holes in the disk, traveling through the frames
of a movie film. The image is thus scanned into 48 separate horizontal
"strips" during each fifteenth of a second. Each scanned image is received by
a photocell and then transmitted.
On the receiving side, the signal is decoded with a complicated
apparatus, including a four-segment ring with contact brushes, which
turns off and on the four elements of a special cylindrical neon tube.
The tube sits inside a large rotating cylinder that uses 48 quartz rods
to conduct the light from the neon tube out through the large cylinder
to a mirror set at a 45-degree angle.
The image reflected from the mirror
passes through a magnifying lens about ten inches in diameter.
In the cover illustration, you can see the top of the rotating cylinder underneath
the small mirror on the top of the receiving device.
It's interesting to compare this device with the scanning-disk TV illustrated in the
November, 1928 Radio News issue. Both schemes use a scanning disk on the broadcast
end to slice the image into horizontal strips. They differ in the means by which
they reconstruct the image on the receiver side.
The November, 1928 scheme uses
a single neon tube placed behind a scanning disk which must be synchronized with
the transmitting disk. The "radio movie" device described in this issue uses a
four-element neon tube, which shines through a cylinder pierced with holes instead
of shining through a disk pierced with holes.
Synchronism, as well as mechanical complexity, was the bugaboo of scanning-disk schemes.
If the receiver is not synch with the transmitter, then the image is garbled, of course.
The article somewhat glosses over this crucial point, noting that synchronism was
easily obtained during the demonstration, since both the transmitter and receiver were
on the same power line. From that, we can infer that the devices were timed using
the pulses of their A.C. power supplies, although no means of doing so appears in
the illustrations.
Other articles in this issue include:
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What to Expect of Television, by Hugo Gernsback
-
Getting the Vote to Radio
-
Rain, Rays, and Radio (fiction)
-
Why the Weather Affects Radio Reception
-
Some Odd Uses for Vacuum Tubes
-
Radio Novelties From Abroad and Home (pictorial)
-
What Is a Good Loud Speaker?
-
A Two-Tube Reflex Receiver of Simple Construction (construction)
-
A Booster Unit for the Browning-Drake (construction)
-
A Screen-Grid Short-Wave Receiver (construction)
-
Better Direct-Coupled A.F. Amplifiers
-
The Capacity of a Condenser Combination Arrangement
-
The Zero-Reactance Plate Circuit
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