|My thanks to George Willeman for the digging up this article and scanning it. At first I attempted to simply post the full scans, but they were barely legible and took up an enormous amount of web space. I think it is a better compromise that I transcribe the text and retain only the pictures. All content in this article is, of course, copyrighted to Popular Science magazine and its publishers.|
|“Here at last – Video disc players”
Two disc machines that let you program your own shows will be introduced in ’77.
By John Free
One of them, RCA, is already field-testing a few hundred of its capacitance-sensing SelectaVision disc players. N.V. Philips, the Dutch firm that brought us the standard audio cassette, and MCA Inc., an American entertainment-oriented firm, also plan to offer an optical video-disc system this year.
The latest price estimates: about $500 for the player, and $10 to $18 for a disc or set of discs.
There’s even a possibility that a Japanese licensee of a British and German disc venture, the grooved-disc TED system [PS, Nov. ‘74], could be marketing disc players, too. Players for 10-minute TED discs have been available in Germany since 1975, although only for European TV-signal standards. Sales have been poor. A TED changer that handles 12 discs was recently shown. Spinning on the sidelines are other disc systems still under development [see box: “In the labs: machines that record and play discs”].
Both the RCA and Philips/MCA players will appear in stores just when new home video-cassette recorders [PS, Dec. ‘75], video games [PS, Nov. ‘76], and pay-cable programming are teaching viewers that their TV receivers can easily display something other than fixed-time broadcast fare.
What’s different about the new disc hardware and programming? After operating both the RCA and Philips/MCA players, trying some amazing manipulations of TV images, and listening to stereo hi-fi TV sound I found that the new machines offer spectacular gains in performance compared with other home program sources.
Stamping out tons of discs at low cost is the biggest advantage of the new medium. Both Philips/MCA and RCA expect to offer a broad selection of discs when their players appear. MCA, which will manufacture most U.S. discs for the Magnavox-built player, plans 1000 albums initially.
MCA discs will include new and old films, ballet,
opera, theater, sports, how-to and children’s programs, and documentaries.
MCA can also make a thin flexible disc that might be inserted in periodicals.
Discs may also be distributed as entire magazines, catalogs, or talking
Together, the disc and metal-tipped stylus form an electrical circuit. As the slots spin past the stylus, tiny abrupt changes in circuit capacitance occur. These changes detune an oscillator circuit to produce the TV signal.
To compensate for small changes in rotational speed, a tiny transducer, which functions somewhat like a loudspeaker coil and cone, stretches the stylus arm back and forth parallel to the groove. Errors in speed are detected by monitoring the recorded color-burst signal.
A close look at a SelectaVision player confirms RCA’s disc-system design philosophy. Components are housed in a simple, inexpensive cabinet with a minimum number of controls. Internal circuit boards and components, prominently displayed on a pegboard in RCA’s New York demonstration room, remind you of a Heathkit spread out for assembly. RCA deliberately designed a player that could be easily mass-produced with relatively standard parts.
Care is necessary when loading discs in the machine, since fingerprints or smudges can create interference. Playing discs repeatedly through can remove contaminants from the grooves, but since the $15 stylus must be replaced after 200 to 300 hours of use, it’s wiser to take good care of records. Each disc an be played about 500 times.
Pictures I’ve seen at several demonstrations were excellent. You can rapidly move the tangential stylus arm forward or backward to selected disc areas by pushing buttons; a lighted index on the panel becomes larger or smaller. A pause button breaks stylus contact. The player has two audio channels for stereo or bilingual programming, and audio output jacks for optional connection to a hi-fi amplifier.
This concept differs radically from SelectaVision. Only the center spindle touches Philips/MCA discs as they spin at 1800 rpm. An air bearing that develops at that speed aids stabilization. A low-power laser beam, focused to a one-micron spot, strikes the bottom surface of the aluminum disc [see diagram]. This highly reflective layer has a clear-plastic protective coating. The beam falls on a spiral track that consists of oblong bumps of varying lengths, with flat areas between them. The encoded picture information varies the distance between bumps. Part of the laser light is reflected from the flat area between bumps back through the optics to a light-sensitive diode that detects the TV signal. Only one side of a disc is programmed, with 30 minutes of material.
By shifting the beam spot slightly on the spinning disc, three sophisticated servo circuits maintain focus, tracking, and proper speed. The servos sense deviations by monitoring auxiliary beams reflected from the disc. Corrections are made with electronic signals that can shift the focusing lens up or down; or, to compensate for radial (sideway) and speed errors, two mirrors positioned at right angles to each other can be pivoted to shift the beam spot.
Jolting a player
Despite the extraordinarily small tolerances involved, the servos do their jobs remarkably well. Even a sharp rap on the Philips/MCA layer case – enough to jolt an audio-cartridge stylus from its groove – does nothing, or produces only a brief flicker on the picture.
Philips/MCA discs can be handled easily without concern for smudges or dust. The thick protective coating keeps blemishes out of focus, which prevents picture interference. Discs should last indefinitely, since there’s no wear from playback. The helium-neon laser “stylus” lasts a minimum of 10,000 hours before replacement may become necessary.
There’s a distinct look and feel of compact precision to the Philips/MCA player. The front panel is packed with controls that capitalize on the contactless readout and the fact that each revolution of the disc produces one TV picture.
One button lets you indefinitely freeze any one of 54,000 picture frames for in-depth viewing on the screen. Other controls enable you to advance the picture sequences manually, frame by frame, forward or backward. A variable-speed control does the same thing automatically.
In the fast-scan mode, pictures become a blur; however, every few seconds one is frozen for an instant to help pinpoint a location. All Philips/MCA discs will be encoded with signals that serve to identify each frame. Tap another button and the frame numbers appear in a corner of the TV screen. The player has stereo hi-fi output jacks and a video-output jack (a non-RF signal).
Both RCA and Philips/MCA have invested perhaps several hundred million dollars without knowing whether consumers will buy the players and discs to program their own shows. If the spectacular climb in sales of video-cassette recorders, TV-game, and pay-cable systems are any indication, the video-disc manufacturers have made a shrewd investment.
In the labs: machines that record and play discs
As the big contenders (RCA, N.V. Philips, and MCA Inc.) gear up production lines to produce capacitance and optical video-disc systems (diagrams above), other companies and institutions are busy refining other ingenious disc systems in laboratories. Although developers of new players frequently say they plan to market them, the huge expense of manufacturing and distributing a major new product today may prevent you from ever seeing most new systems in stores. Some of these disc systems are intriguing because they can record TV programs as well as play prerecorded discs:
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