Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!lll-lcc!ames!ucbcad!ucbvax!decvax!tektronix!tekcrl!vice!tekfdi!videovax!dmc 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