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From: dmc@videovax.Tek.COM (Donald M. Craig)
Newsgroups: rec.video,comp.graphics
Subject: Re: The origins of frequencies in NTSC
Message-ID: <4149@videovax.Tek.COM>
Date: Wed, 14-Jan-87 01:23:53 EST
Article-I.D.: videovax.4149
Posted: Wed Jan 14 01:23:53 1987
Date-Received: Wed, 14-Jan-87 22:43:55 EST
References:  <4017@caip.RUTGERS.EDU> <15180@onfcanim.UUCP>
Reply-To: dmc@videovax.Tek.COM (Donald M. Craig)
Organization: Tektronix Television Systems, Beaverton, Oregon
Lines: 163
Keywords: NTSC video
Xref: mnetor rec.video:336 comp.graphics:145

I'm not sure how much people want to know about the origins of NTSC,
but there was a time when it didn't look like there would be a
compatible color system at all.   The following information is
excerpted from a paper by Walt Bundy, Chairman of the Specialist
Group on NTSC Specifications of the Advanced Television Systems
Committee.


Black and White TV and NTSC-1

The first National Television System Committee met during 1940 and
1941.  The group's work resulted in the submission of "transmission
standards for commercial television broadcasting" to the Federal
Communications Commision (FCC) at a hearing on March 20, 1941.  The
FCC made the NTSC-1 recommendations the standards for "monochromatic
transmission systems", in May 1941.  Commercial television broadcasting
began in the United States on July 1, 1941.


Color TV and FCC

During 1950, the FCC, after eight months of hearings and about 10,000
pages of testimony, selected the incompatible field sequential color
TV system.  The Commission's decision was challenged in the courts, with
the US Supreme Court upholding the validity of the FCC decision on May
28, 1951.

The challenges to the field sequential color tv system at both the
Commission and the court were based primarily on the fact that the
field sequential color tv system was incompatible with the then existing
black and white tv sets.  The commission apparently felt that the talk
about compatible color systems was just a way of delaying Commission
action.

On June 11, 1951, the FCC in Public Notice 656008 stated that it was
to be the field sequential color tv system until someone could come
up with a better (but not necessarily compatible) system.


NTSC-2

The second National Television System Committee (NTSC-2) was started
during 1950 by the Radio Television Manufacturers Association (RTMA)
in hopes that the committee would be as effective as was the committee
of 1940-1941.  This group (which is often referred to as the RTMA group)
did make comments to the FCC during the 1949-1950 color hearings,
suggesting a series of tests for color systems.

The NTSC/RTMA committee also set up and Ad Hoc group to study the then
state-of-the-art.  From this Ad Hoc group came the broad ideas of using
the 1941 B&W standard for the brightness information and adding color
(painting) information using a subcarrier.

With the release of the FCC Notice on June 11, 1951, the Chairman of
the committee recommended that NTSC2/RTMA be reorganized as a group
to achieve the optimum standard for commercial color television.  This
reorganized NTSC2 met 26 times between June 18, 1951 and September 1,
1953.  The committee's only real goal was a compatible color tv system.

NTSC2 had a main committee of about 40 members with 10 panels or
working groups.  The writing of the present US color tv system came
from the work of panel 13, which did the video, and panel 14 which
did the synchronizing pulses.  (Panel numbering started at 11.)


Sync and Burst

There were many suggestions to panel 14 on where to put the synchronizing
burst including:  tip of sync, after sync with pedestal, after sync
without pedestal, everywhere.  Panel 14 liked tip of sync until the
broadcasters explained that the operation of tv transmitters is not
linear in the sync region.  The next choice was after sync with a
pedestal and was recommended for the first field test.  The burst
frequency was 3.898125 MHz.

The burst after sync with pedestal caused problems for the then
state-of-art B&W tv sets.  The revised specifications for field
test called for burst after sync without pedestal and a burst
frequency of 3.579545 MHz.

Operating with burst after sync without pedestal caused "brightening
of the retrace" and was called for in the report of panel 15 Sub-Committee
on Test Procedures (4-21-1952) as necessary for compatibility  "...,
the the signal is compatible if, (1) the horizontal sync pulse is
widened to 8%, and (2) the burst pedestal is removed".


Color Video

To eliminate "brightening of the retrace", panel 13 then recommended
a 'setup' of seven and a half percent, which would raise the black
level of the picture above the burst and blanking levels.
Setup was already in use in 1953 by the B&W standard because any
video that went near or below the blanking level would cause some
then state-of-the-art tv sets problems.  (The elimination of setup
is currently under discussion in various standards committees, here
in 1987.)

Of the 27 B&W sets used for subcarrier compatibility testing at RCA
labs (October 23, 1952), 5 sets had separate carrier (IF) sound and
13 of the sets (all inter-carrier) used an IF frequency of 20 or 21
MHz.

When using the 3.898125 MHz. subcarrier the separate sound sets
and some intercarrier sets had a 608 KHz. beat signal in the video
(4.5 MHz. Sound - 3.89 MHz. Color = 608 KHz).  When using the 3.58
MHz. subcarrier the beat frequency became 920 KHz. which was a
finer pattern.  The early color signal specifications had "Color
Phase Alteration (CPA)", which was later dropped because of flicker
problems.


NTSC and FCC

On February 2, 1953, NTSC-2 had approved for publication a recommendation
for transmission standards for color television.

At the meeting on June 24, 1953, the full committee was aware that
RCA was planning to jump the gun and file a petition for rule making.
The next day, June 25, 1953, RCA and NBC did file a petition for rule
making.  The RCA-NBC color television system was in fact identical to
the NTSC-2 approved recommendation.

On July 8, 1953, Rosel Hyde, Chairman FCC, wrote to NTSC, asking for
field testing information.  At the full NTSC committee meeting of
July 21, 1953, the NTSC Petition was ready and a motion was passed
sending the petition to the FCC.  The NTSC petition was filed with
the FCC on July 23, 1953.


Final Report

The FCC issued a Notice of Rule Making (Docket 10637, Amendment
of the Commision's Rules Governing COlor Television Transmissions)
on August 7, 1953.  NTSC2 held its final meeting on September 1,
1953, and issued a final report.

From the RCA-NBC petition:
"4. The color standards proposed in this Petition are technical
signal specifications approved February 2, 1953, by outstanding
engineers and scientists of the radio and television industry,
including members of Petitioner's staff, through the National
Television System Committee (NTSC).  Petitioners know of no responsible
engineer or scientist in the radio or television field who proposes
adoption of any other color standards."

Well, as to the last part...
Dana Griffin of Communication Measurements Labs and Paul Raibourn
of station KTLA were in there to the last, fighting for a Line/Field
Sequential Color System.  The NTSC's answer was that line and field
sequential color systems were fixed systems whereas the NTSC specification
could grow.

As an example, from a report of A. V. Loughren, Chairman, Ad Hoc
Subcommittee of NTSC, 8-12-53:
"The committee concludes that a set of standards proposed for television
broadcasting sould have the expectation of long-term utility, thus
satisfying the optimists of 1953 and presumably also the pessimists of
1973; in brief, the basic consideration is `Don't sell the future short'".

-- 
Don Craig			dmc@videovax.Tek.COM
Tektronix Television Systems	... tektronix!videovax!dmc