|
|
|
|
W6XAO, A Pioneering Television Station, by F. Alton Everest |
||
|
Several decades before commercial television 'rounded the corner', the Don Lee Broadcasting System was actively broadcasting television images. This work started in 1930 and by November 1931, the television transmitter W6XAO was on the air from the Don Lee Building, 7th and Bixel Streets, Los Angeles [1062 West 7th to be exact]. On May 21st. 1932, the first television motion picture was reproduced on a cathode-ray receiver in an airplane. [Lubcke subsequently wrote this up in a paper reproduced in the IRE Journal] On May 14, 1933 [sic] filmed scenes of the Long Beach Earthquake were broadcast a few hours after the event [actually, the LB Temblor was on March 10, 1933]. The year 1936 marked my arrival on Harry R. Lubcke's television research and development staff in the Don Lee Building. The display of Cadillac and LaSalle motor cars on the first floor gave no hint of what was going on upstairs. The KHJ transmitter and television activity of 3 or 4 workers shared the eighth floor. [at the time, KHJ was on 900 kc utilizing a horizontal antenna strung between two self-supporting towers anchored to the roof. KHJ later moved to a two tower DA site on Venice Blvd.] As my graduate work at Stanford was drawing to a close, Dr. Frederick E. Terman, my close professor mentioned an opening at the Don Lee television laboratory and asked if I was interested. A recommendation by Terman to Harry Lubcke sealed the job for me. My first job was the design and construction of a sine-wave oscillator covering 50 to 1000 kHz with 400 volt peak-to-peak amplitude primarily for transmitter testing. Other jobs covered receiver and transmitter design, adjustment and testing. My work with Lubcke lasted only four months because of an opportunity to join the Electrical Engineering faculty at Oregon State University. Lubcke (1905-1991) received his degree in electrical engineering from the University of California in 1929. Even before his graduation, he worked in Philo T. Farnsworth's television laboratory in San Francisco. While there, he built, operated and patented the first all-electric synchronizing, scanning and blanking-pulse generator. He joined the Don Lee system on December 31st 1931 [1930 ?]. During his later years he was a prominent patent attorney in Los Angeles. Don Lee television in 1936 was built around a disc scanning system for motion picture film, the sole program source. Figure 1 is a photograph of the film scanning equipment and Figure 2 is a schematic of the system. The film traveling at a constant rate of speed is sequentially scanned by light through the holes of the scanning disc. The video signal from the photo electric cell is amplified and passed on to the transmitter. The holes in the disc (#80 drill) were not in a spiral but at a constant distance from the center. The effect of the spiral was achieved by constant film motion which provided the movement from line to line. The light from the arc lamp fell on the disc at an angle, reduced the effective spot size and giving a modest improvement in image quality. The demotionizing lens directed at the spot of light from a single spot on the photo-sensitive surface of the photo cell to minimize the effect of irregularities over the emission surface.
Fig 1
Fig 2 It took 5-7 minutes to being the sync motor up to 3600 rpm speed upon application of standard voltage. When hunting began, double voltage was briefly applied to pull it into step, after which the standard voltage was applied. When the motor was turned off, it took about 18 minutes for it to come to rest. I remember turning the equipment off after an evening broadcast, going down the elevator and walking [east] to Figueroa Street before the motor whine became inaudible. The pulses for synchronization were modulated upon the carrier along with the video signal. During the frame interval a synchronizing pulse is transmitted to stabilize the 24hz sawtooth generator of the receiver. This pulse was obtained by the arrangement of Figure 3.
Fig 3 The slotted drum was driven from the film drive train so that the two slots lined up with the light beam every time a frame line passed. The line synch pulses were obtained by directing a beam of light onto holes a short distance from the point where the picture light falls. The over-all composite video signal (the rectified carrier) looked something like the idealized sketch of Figure 4. The frame pulses were 24/sec and the line synch pulses were 7,200/sec (300 lines x 24 frames).
Fig 4 A photograph of the 1936 television transmitter is shown in Figure 5. It was grid modulated with an output power of 150 watts and operated on a frequency of 45 mHz. The image was transmitted as negative for greater linearity. Modest distortion of the synch pulses by the saturated bend of the grid-modulation characteristic had negligible effect. By adjusting the number of stages in the receiver the negative picture was made positive... [description of amateurs, Don Lee TV set plans, etc. omitted]
Fig 5 A well-publicized demonstration for the general public was held in June 1936, shortly before my departure. Long lines of people patiently waited to view the wonder of 'pictures by radio' [several years later, off air TV reception would be demonstrated at the Griffith Planetarium].
Fig 7 Figure 7 shows people straining to get a good view of the 9-inch cathode-ray image (about 5x7 inch picture). The transmitting antenna outside the eighth floor window which sent the picture signal to the first-floor demonstration is shown in Figure 8.
Fig 8 In the waiting lines, I spotted William S. Klein, a fellow EE graduate of Oregon State. Bill applied for my job and was hired. After the television work faded he became a KHJ network and transmitter engineer until retirement. Many other demonstrations were conducted on an invitational basis from Lubcke's home in the Silver Lake District, 3-1/2 miles from the transmitter. Old newsreels provided much of the programming for W6XAO because the motion picture industry was extremely wary about the future legal implications. I remember one historical film, 'The Train Wreck' which always lost frame hold as the train went in and out of a tunnel.
Screen shots of 300 line image During 1939, grandiose plans were presented at the Los Angeles Planning Commission for a Mutual-Don Lee Television Center on a hill to the rear of and above the Hollywood sign overlooking the heart of Hollywood. This project was later abandoned. Au contraire relative to the site atop Mt. Lee. |
