If the technology futurists
of the 1970s had been correct, by now we would be reading historical articles on the
early days of holographic television. I have read, though, that any day now a battery-powered
flying car with a holographic dashboard / instrument panel display is going on sale.
Not. The Sadly, the Ercoupe (pronounced "air coupe," as in automobile
coupe of the air) is
still the closest thing to "an airplane in every garage." But, I digress. This story
from a 1953 issue of Radio & Television News magazine reports on the roll-out
of the country's first color television system: The
sequential system (aka the CBS system). It was a fine system, but unfortunately the
modulated signal format was not backward compatible with the existing black and white
(B&W) system. That meant separate receivers for B&W and color televisions. Even
as CBS TV sets were being produced, the National Television System Committee (NTSC) was working on a replacement
system that permits co-existence of B&W and color signals. Note the mention of how
the DPA (Defense Production Administrator), in 1951, requested that color
TV manufacturers halt research and development on the CBS system in order to free engineers
for defense-related design and production hardware, it being the death knell of CBS and
clearing the way for NTSC (Korean War).
Color TV - Part 1: Clarifying the color TV situation with some predictions
on what to expect in color receivers.
Fig. 1. An experimental single-tube color TV camera, not much larger
than its black-and-white counterpart.
By William R. Feingold,
Emerson Radio & Phonograph Corporation
On October 11, 1950, the Federal Communications Commission approved the field sequential
system (popularly known as the CBS system) as the official color TV standard for the
United States. This system had been under development for approximately 10 years, and
gave a fairly presentable performance in comparison with competitive methods which were
more or less newly conceived. It was an unfortunate choice, however, because the field
sequential color system required a vertical field rate of 144 per second (as opposed
to the black and white of 60) and a line rate of 29,160 cycles-per-second (as against
the black and white of 15,750) to eliminate flicker, thereby making this system incompatible
with black and white transmission standards. Finally, when the DPA terminated all color
TV activity on November 20, 1951 in the interest of national defense, the CBS system,
as used in aerial TV transmissions, died a natural death. For strictly industrial television
use, the CBS system is still being employed in closed circuit applications.
In the meantime, the Radio-Electronics-Television Manufacturers Association set up
a committee to formulate an improved compatible color signal. The more than 200 engineers
and physicists of this National Television System Committee (NTSC) from 91 leading companies
in the television industry formulated and tested a color TV signal which could fit into
the present 6 mc. channel, and was compatible with the black and white transmission standards.
The NTSC does not own any equipment, neither transmitters nor receivers, and is not
interested in the detailed circuitry of either type of equipment. Its interest in equipment
stops at the point where it has been established that the signal specifications can be
met with readily available gear. The end goal is a set of signal specifications, proven
and practical, that can be presented to the FCC for approval. That this goal has been
met has been amply attested to by the fact that numerous organized field tests have been
arranged by the NTSC and attended by some 15 different manufacturers with their color
receivers. These receivers represent the varied outputs of the different engineers all
working from the same signal specifications and all receivers are producing excellent
The NTSC Signal
Although a detailed treatment of this new color signal will be made in the second
article of this series, a simplified treatment is in order.
From a welter of data pertaining to the physiological aspects of color vision and
a mass of theoretical data regarding the character of the television signal itself, the
following color signal has been formulated. To the present monochrome standards as they
now exist an additional color signal specification has been added. The resultant effect
is not unlike the conventional lithographic technique of printing in three colors plus
black to add the detail. In our case, the present monochrome information carries the
shades of black and white including all the fine detail, and the color information is
added on a color sub carrier to fill in the large areas of color (Fig. 2).
Tests have shown that the eye cannot perceive fine color detail, hence, there is no
need to burden the color circuits with wide-band information. The shaded area on Fig.
2 indicates that this color information in the lower sideband is restricted to a bandwidth
of 1.3 mc. Note, too, that the upper sideband cannot extend this far since the limits
of the channel restrict this area to approximately 0.4 mc. Although this unsymmetrical
distribution of sideband energy is not a desirable situation, it has been possible to
design the details of the system in such a manner that it causes no extra trouble.
Fig. 2. Color signal characteristics.
Because the lower sideband of the color information falls well within the monochrome
video channel it was necessary, in the interest of compatibility, that this color data
be made invisible on a standard black and white receiver. This was done (within the limitations
of the linearity of the system) by setting the color subcarrier at a frequency which
is an odd multiple of half the line repetition rate. The actual frequency selected by
the NTSC is 3.58 mc. This unique feature of adding narrow-band color information on a
special color subcarrier to a standard monochrome transmission is the essential characteristic
of the signal. When a color signal is transmitted, the conventional monochrome receiver
will present the picture in shades of black, gray, and white with a negligible trace
of the picture's color signal origin. An interesting point is that these black and white
pictures usually have better resolution than that obtained from conventional monochrome
reception. The reason for this improvement is simply that the transmitters have to be
more carefully adjusted to handle the color data on the 3.58 mc. subcarrier and, as a
result, the monochrome information is present in more detail.
The conversion of a good monochrome transmitter from black and white to color is simplicity
itself. (See Fig. 3.) If a color video signal is already available, either from a color
camera or a network link, no changes are required. To get this video information from
a network a minor investment in new terminal equipment will be required. Networks will
probably be the main source of nationwide color transmissions until a sufficient number
of color studios are constructed.
The color studio gear and the camera equipment are somewhat more complicated than
their monochrome counterparts. Present color cameras consist of three pickup tubes mounted
side by side with each one masked with a proper primary filter. By the use of properly
positioned dichroic mirrors (mirrors which reflect light of one color and pass all other
colors) the single viewed image of one lens is made to fall on each of the three photosensitive
camera surfaces. Since these images must pass through green, red, and blue filters respectively
before they strike these surfaces, the three resultant video outputs. represent the green,
red, and blue signals corresponding to these colors in the original scene.
Progress has already been made toward the development of a single camera pickup tube
that will put out three primary signals (Fig. 1). There is no doubt that technical advances
in studio equipment will be made towards simplification. In this connection it is interesting
to note that the compatible nature of the signal allows for testing transmitting and
receiving equipment by radiating color signals (with FCC approval) without public announcements
of the fact. One of the first such "sneak" transmissions took place late in June in New
York City on WNBT during a "Howdy Doody" program.
The Color Receiver
The color receiver is basically a monochrome receiver with additional circuitry. This
additional circuitry falls into two groups. The first group is that part required by
the color information alone. In Fig. 4 this area is covered by the chroma, decoding.
color sync, and matrix networks. This part produces as its end product the green, red,
and blue video signals. The second group is that area of circuitry dictated by the requirements
of the picture tube (or display device). Since Fig. 4 indicates an RCA tri-color tube,
a dynamic convergence network is used, as required by this tube.
Although the interior of the color receiver is somewhat more complex than its monochrome
brother, the user's controls are only complicated by the addition of one more knob. This
control is marked "Chroma." It allows a customer who takes issue with the mathematically
correct ratio of color to monochrome to vary this ratio. The picture color can thus be
varied from a light pastel shading to an intense lush overly-colored display.
With regard to the fine tuning control, the public will have to be reeducated. It
will be recalled that split-sound receivers of five years ago required a careful setting
of the fine tuning control or there was no sound. This careful setting of the tuner oscillator
made for optimum picture quality. However, the problem of oscillator drift gave way to
the use of intercarrier systems with the net result that sound was always present and
tuning the oscillator to obtain the best picture became a forgotten operation.
In order that the color receiver retain the benefits of intercarrier operation and
yet force the customer to adjust the tuner oscillator to its proper place to insure good
color quality, the designer is forced to use some sort of tuning indicator. In this case
what could be better than the face of the picture tube? The sound traps in the receiver
are made sharp and deep so that when the oscillator is properly tuned the picture is
clean. When the oscillator is mistuned the picture will show annoying sound patterns.
Color TV signal generating equipment used by Emerson for the design
and testing of color TV receivers. Included is a monoscope and flying-spot scanner.
The most publicized aspect of the color TV receiver has been the picture tube. All
color tubes presently used or being developed have three color phosphors deposited on
the front face of the picture tube in either a dot pattern array or a striped pattern,
horizontal or vertical. The RCA tri-color tube" utilizing three gun structures is typical
of the former type, while the Lawrence tubes as made by Chromatic Laboratories, containing
a single gun, is typical of the latter.
The RCA picture tube contains a phosphor dot pattern consisting of 195,000 dots in
each of three colors for a total of 585,000 dots. The three guns are so arranged that
each gun will excite only its particular phosphor color. As a consequence it is possible
and desirable to excite the three guns simultaneously with their respective color signals
and thereby have a simultaneous light output in red, green, and blue. This design does
not require any form of sequential color switching and provides a maximum light output
roughly three times that which would be available on any sequential system using this
tube. The use of three guns carries with it some severe mechanical and electronic circuit
requirements. The first is the specification that each gun strike its respective phosphor
without contamination from the other two. The second is the problem of registration of
the three colored pictures. Improvements in the production control of the picture tube
and in the electronic circuitry associated with the tube have reduced both problems to
an acceptable level.
The Lawrence tube contains a series of red, green, and blue stripes approximately
0.015 inch wide with a built-in switching grid to allow the single electron beam to scan
anyone color depending on the switching potential present. Because of the single gun
construction, a sequential display is essential. This means that this tube cannot suffer
from any registration problems. However, it does suffer from a light output loss of two-thirds
because only one phosphor is in use at one time. There is the additional requirement
of substantial switching energy to the switching electrodes.
The test receivers used by the various manufacturers during NTSC field trials have
utilized the RCA tri-color tube exclusively. Although limited numbers of the Lawrence
tube have been released to the industry, a comparative appraisal is not possible at this
time. It is probable that the first production color receivers will contain the RCA tube.
It should be quite obvious by now that the color receiver will be somewhat more complex
and considerably more expensive than the present monochrome receiver. The picture tube
alone is expected to cost from 150 to 200 dollars. The tube complement of the receiver
will fall between 40 and 50 tubes. These two factors alone make a cost estimate of the
first color receivers fall in the $750 to $1000 class. In addition, these receivers will
produce a small picture, judged by present-day standards. The most successful RCA tri-color
tube developed to date contains an exterior shell similar to the old 16AP4 and produces
a 12 1/2" pumpkin-type picture. Although intensive developmental work is now going on
toward a 16" picture there is no indication when this larger tube will be available or
how much it will cost.
Fig. 3. Simplified block diagram of a typical color television transmitter.
Fig. 4. Simplified block diagram of a typical color television receiver.
Obviously there will be no rush to buy the first color receivers. Very few prospective
customers will buy a 12 1/2" color picture at $800 in preference to a 21" monochrome
picture at $300. However, the novelty is expected to appeal to some, and first production
schedules will cater to this rather meager demand.
How soon manufacturers will put color receivers in the field, after FCC approval,
is entirely up to the manufacturer himself. There will probably not be a repeat of the
630TS experience where RCA released complete data on this black and white receiver to
their licensees, covering chassis layout, component specifications, alignment procedure,
troubleshooting, etc. It will be necessary for each manufacturer to build up a nucleus
of engineers familiar with the color TV problem. Fortunately, a number of companies have
already done this and have also accumulated a fair amount of specialized test and alignment
The next step, however, is actual production. The single bottleneck here is the test
and alignment equipment for line use. Delivery of this material, from only a few sources,
is quoted at from six months to a year. Realizing this, some manufacturers have already
placed orders for production test equipment prior to FCC approval. Assuming FCC approval
early in 1954, it is safe to say that the first color receiver will be released in the
late spring of 1954 with a number of manufacturers in the field by the fall.
The Service Technician
The conscientious service technician who understands the workings of a black and white
receiver will not fear the complexities of a color receiver. The transition is not as
dramatic as his previous transition from a 5-tube radio to a 25-tube TV receiver. The
additional 15 to 25 tubes required by a color receiver are, in some circuits, just more
of the same. However, in other circuits there are new concepts, an understanding of which
is essential to the proper diagnosis of trouble. At the present stage of color receiver
development, color adjustments are extremely critical, requiring a broad knowledge of
color circuitry. Service technicians will have to study such circuits conscientiously
to be successful in this field.
At this point the writer would like to utter a small prayer on the service technician's
behalf. Knowing that more service test and alignment equipment will be required in working
with a color receiver let us hope that the designers of this test gear (it has not yet
been designed) will keep down the size and weight. In the same breath let us pray that
the designers of these new color receivers allow for troubleshooting in the home and
in the cabinet. These larger chassis are considerably heavier than black and white chassis
with half their tube complement. A combination of lighter test gear and a chassis which
could be "troubleshot" in the cabinet will make for fewer ruptured service technicians,
fewer chassis dropped down the stairs, and what is not a negligible factor in service
technician-customer relations, smaller service bills.
This article has attempted to dispel the fog that has shrouded the color TV picture.
Considerable progress has been made in the formulation of an improved compatible color
signal. Two applications for a "Change of Rule" have been filed with the FCC. The first
was made on June 25, 1953 by RCA, and the second by the NTSC one month later on July
23, 1953. In each case a request was made to have the present monochrome standards amended
to provide for color TV transmissions in accordance with the new NTSC signal. FCC approval
is expected by the first of the year or shortly thereafter.
Receiver production should start slowly in the fall of 1954 with a price range of
$750 to $1000. This price range is expected to fall as developmental work continues.
One laboratory has already produced an experimental receiver which requires. only 34
Part 2 of this series will discuss the color signal in detail and examine a typical
1. Buchsbaum, Walter H.: "The RCA Tri-color Tube," Radio & Television News, November
2. Dressler, Robert,: "The PDF Chromatron - A Single or Multi-Gun Tri-Color Cathode-Ray
Tube," Proceedings of the IRE, July 1953.
(To be continued)
Color Television Articles
Posted December 3, 2018