Analog high-definition television system: Wikis

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Historically the term high-definition television was first used to refer to television standards developed in the 1930s to replace early experimental systems with as few as 12 lines. Not long afterwards John Logie Baird, Philo T. Farnsworth and Vladimir Zworykin had each developed competing TV systems, but resolution was not the issue that separated their substantially different technologies, it was patent interference lawsuits and deployment issues given the tumultuous financial climate of the late '20s and '30s.

The British 405-line system was the first to advertise itself as high definition and see widespread use. Most patents were expiring by the end of World War II leaving the market wide open and no worldwide standard for television agreed upon. The standards introduced in the early 1950s stayed for over half a century.

Contents

French 819-line (737i) system

When Europe resumed TV transmissions after WWII, i.e., in the late 1940s and early 1950s, most countries standardized on a 625-line television system. The two exceptions were the British 405-line system, which had already been introduced in 1936, and the French 819-line system developed by René Barthélemy. During the 1940s Barthélemy reached 1015 and even 1042 lines. On November 20, 1948, future French president François Mitterrand decreed a broadcast standard of 819 lines; broadcasting began at the end of 1949 in this definition.

The French TV system was arguably the world's first HDTV system, and, by today's standards, it could be called 737i (as it had 737 active lines [1]) with a maximum theoretical resolution of 408 x 368 line pairs (which in digital terms can be expressed as equivalent to 816x737 pixels) with a 4:3 aspect ratio. It was used only in France by TF1, along with Tele Monte Carlo in Monaco. However, the theoretical picture quality far exceeded the capabilities of the equipment of its time, and each 819-line channel occupied a wide 14 MHz of VHF bandwidth.

To have an idea of the quality :
the modern 720p standard is 1280x720 pixels , of which the 4:3 portion would be 960x720 pixels.
A DVD is encoded 720*576 pixels.


Channels were arranged as follows:

Ch picture (MHz) sound (MHz)
F2 52.40 41.25
F4 65.55 54.40
F5 164.00 175.15
F6 173.40 162.25
F7 177.15 188.30
F8 186.55 175.40
F8a 185.25 174.10
F9 190.30 201.45
F10 199.70 188.55
F11 203.45 214.60
F12 212.85 201.70

Technical specifications of the broadcast television systems used with 819 lines.

Field frequency Active picture Field blanking No. of broad pulses Broad pulse width Line frequency Front porch Line sync Back porch Active line time Video/syncs ratio
50 Hz 737 lines 41 lines 1 per field 20.0 µs 20475 Hz 0.5 µs 2.5 µs 5.0 µs 40.8 µs 70/30
System Lines Frame rate Channel bandwidth (in MHz) Visual bandwidth (in MHz) Sound offset Vestigial sideband Vision mod. Sound mod.
System E 819 25 14 10 ±11.15 (Sound carrier separation +11.15 MHz on odd numbered channels, -11.15 MHz on even numbered channels.) 2.00 Pos. AM
System F 819 25 7 5 +5.5 0.75 Pos. AM

System E implementation provided very good (near HDTV) picture quality but with an uneconomical use of bandwidth.

In addition, an adapted 819-line system known as System F was used in Belgium and Luxembourg. It allowed French 819-line programming to be broadcast on the 7 MHz VHF channels used in those countries, with a substantial cost in horizontal resolution (408*737). It was discontinued in Belgium in February 1968, and in Luxembourg in September 1971.

Despite some attempts to create a color SECAM version of the 819-line system, France abandoned it in favor of the Europe-wide standard of 625 lines (576i50), with the final 819-line transmissions from Paris in 1984. TMC in Monaco were the last broadcasters to transmit 819-line television, closing down their System E transmitter in 1985.

From the French government's point of view, the 819 line TV system had the great advantage that it prevented French citizens from being able to receive 'inappropriate' broadcasts from foreign countries. The switch to the accepted European wide 625 line standard looked to undermine that advantage, but this was sidestepped by adopting positive video modulation when the rest of the world had switched to negative modulation with all its advantages.

Multiple sub-nyquist sampling Encoding system (MUSE)

Japan had the earliest working HDTV system, with design efforts going back to 1979. The country began broadcasting analog HDTV signals in the late 1980s using an interlaced resolution of 1035 or 1080 active lines (1035i) or 1125 total lines.

The Japanese system, developed by NHK Science and Technical Research Laboratories (STRL) in the 1980s, employed filtering tricks to reduce the original source signal to decrease bandwidth utilization. MUSE was marketed as "Hi-Vision" by NHK.

  • Japanese broadcast engineers immediately rejected conventional vestigial sideband broadcasting for well-founded technical reasons.
  • It was decided early on that MUSE would be a satellite broadcast format as Japan economically supports satellite broadcasting.

In the typical setup, three picture elements on a line were actually derived from three separate scans. Stationary images were transmitted at full resolution.However, as MUSE lowers the horizontal and vertical resolution of material that varies greatly from frame to frame, moving images were blurred in a manner similar to using 16 mm movie film for HDTV projection. In fact, whole-camera pans would result in a loss of 50% of horizontal resolution.

MUSE's "1125 lines" are an analog measurement, which includes non-video "scan lines" during which a CRT's electron beam returns to the top of the screen to begin scanning the next field. Only 1035 lines have picture information. Digital signals count only the lines (rows of pixels) of the picture makeup as there are no other scanning lines (though conversion to an analogue format will introduce them), so NTSC's 525 lines become 480i, and MUSE would be 1035i (or 1080i, hence the origin of less than ideal 1080 for digital HDTV. 960p60 for USA and 1152i25 for Europe and 1152p48 worldwide would be better).

Shadows and multipath still plague this analog frequency modulated transmission mode.

Considering the technological limitations of the time, MUSE was a very cleverly-designed analog system. Though Japan has since switched to a digital HDTV system based on ISDB, the original MUSE-based BS Satellite channel 9 (NHK BS Hi-vision) was still being broadcast as of 2007. It broadcast the same programs as BS-digital channel 103, but transmission ended on November 30, 2007[2].

HD-MAC

HD-MAC was a proposed television standard by the European Commission in 1986 (MAC standard) . It was an early attempt by the EEC to provide HDTV in Europe. It was a complex mix of analog signal (Multiplexed Analog Components) multiplexed with digital sound. The video signal (1250 (1152 visible) lines/50 frames in 16:9 aspect ratio) was encoded with a modified D2-MAC encoder.

HD-MAC test pattern more or less visually indistinguishable from B-MAC test pattern

In the 1992 Summer Olympics experimental HD-MAC broadcasting took place. 100 HD-MAC receivers (in that time, retroprojectors) in Europe were used to test the capabilities of the standard. This project was financed by the European Union (EU). The PAL-converted signal was used by mainstream broadcasters such as SWR, BR and 3Sat.

The HD-MAC standard was abandoned in 1993, and since then all EU and EBU efforts have focused on the DVB system (Digital Video Broadcasting), which allows both SDTV and HDTV.

See also

The analog TV systems these systems were meant to replace

Related standards

References

  1. ^ Report 308-2 of the XIIth Pleniary Asssembly of the CCIR - Characteristics of Monochrome Television Systems
  2. ^ MIC(Press Release-Telecom)

External links

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