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Twenty-eight
The INTERNATIONAL PHOTOGRAPHER
Television
How to Receive Don Lee Television Images
March, 1934
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HE Don Lee television transmitter, W6XS, transmits television images on a carrier frequency of 2800 kilocycles (107 meters) nightly, except Sunday, from 7 to 9 P. M., and Monday, Wednesday and Friday mornings from 9 to 11 A. M. Pacific Standard Time; and W6XAO on 44,500 kilocycles (6-_>4 meters) nightly, except Sunday, from 7 to 9 P. M. and Monday morning from 9 to 11 A. M.; on 66,750 kilocycles (4*/> meters) on Wednesday morning from 9 to 11 A. M.; and on 49,400 kilocycles (6 meters) on Friday morning from 9 to 1 1 A. M. RECEIVER The receiver for tuning in W6XS or W6XAO should tune hroadly. It should pass a band 100 kilocycles wide. This can be accomplished by the use of closely coupled radio-frequency transformers ; both primary and secondary wound on the same form and separated by only 1/32 of an inch. The audio amplifier should be resistance coupled and capable of passing frequencies up to 50,000 kilocycles. "Positive" images are transmitted ; high light intensity in the image corresponding to a high radio frequency output of the transmitters. They are correctly received by a receiver with "C" bias
detector and two stages of resistance coupled audio amplification, with a neon lamp directly in the last tube plate circuit; or with "C" bias detector and one state of amplification for a cathode ray tube.
SCANNING DISK
The Don Lee television transmitters, W6XS and W6XAO, operate simultaneously, and transmit 80 line single spiral images, repeated 15 times per second, scanned from left to right and top to bottom. An inexpensive scanning disk for reproducing these images can be made as follows:
On a disk of cardboard or aluminum two feet in diameter, a circle of exactly 11^4 inches radius is drawn, and divided around its circumference into eighty equal parts. This corresponds to each Al/2 degrees. Radial lines are drawn from each of these divisions to the center of the disk. A small hole, fifteen thousandths of an inch in diameter, is punched or drilled at the intersection of the circle and any one of the radial lines. With cardboard, the hole can be made by pushing a common pin through the disk until one-sixteenth of an inch of the point projects on the further side. The next hole is punched on the next radial line in a counter-clockwise
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