Television systems before 1940

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A number of experimental and broadcast pre World War II television systems were tested. The first ones were mechanical based (mechanical TV) and of very low resolution, sometimes with no sound. Later TV systems were electronic (electronic TV).

Contents

[edit] France

  • France 1932 (mechanical): 60 lines, 12.5 frame/s, 3:7 vertical aspect ratio, vertical scanning ~35x60 pixels per frame, sound, live images
  • France 1935: 375 lines, abandoned 1936
  • France 1935 (electronic): 441 lines, 25 frame/s, line frequency 11025 Hz, discontinued in 1956. (Monitored in the UK during WWII to gather intelligence information from occupied France) Vision 46.0 MHz Sound 42.0 MHz.
  • France 1937 (electronic): 455 lines, abandoned 1940
  • France 1939 (electronic): 405 lines, abandoned 1940

[edit] Belgium

  • Belgium 1932 (mechanical): 30 lines, 12.5 & 16.6 frame/s, 4:3 horizontal aspect ratio, ~40x30 pixels per frame, sound, talking movies

[edit] Germany

  • Paul Gottlieb Nipkow 1884: 24 lines.
  • Nipkow was granted a patent, but no practical TV transmissions came out of Nipkow's work.
  • The Nipkow system may be the first system for transmitting television.

(Note that Nipkow was a German of Kashubian origin; the town in which he was born is now in Poland).

  • Germany 1928: 96 lines (city experimented in not found)
  • Berlin 1932 (mechanical): 30 lines, 12.5 frame/s, 4:3 horizontal aspect ratio, ~40x30 pixels per frame, test movies and live images
  • Koningswusterhausen 1932 (mechanical): 39 lines, 12.5 frame/s, 4:3 horizontal aspect ratio, ~31x30 pixels per frame, movies
  • Doberitz 1932 (mechanical): 48 lines, 25 frame/s, 4:3 horizontal aspect ratio, ~64x48 pixels per frame, sound, talking movies
  • Berlin R.P.Z. 1932 (mechanical): 60 lines, 25 frame/s, 4:3 horizontal aspect ratio, ~83x60 pixels per frame, test movies and live images
  • Germany 1932: 90 lines
  • Germany 1935: 180 lines
  • Germany 1939 (Einheitsempfänger E 1): 441 lines, 25 frame/s, line frequency 11025 Hz. Vision 46.0 MHz Sound 43.2 MHz.

[edit] Netherlands

  • Netherlands 1930's: 441 lines, 25 frame/s, line frequency 11025 Hz

[edit] Poland

  • Warsaw 1937 (mechanical): 120 lines, test movies and live images from a studio
  • Electronic TV (343 lines) was under development and was publicly demonstrated during the Radio Exhibition in Warsaw in August 1939, regular operations planned to start at the beginning of 1940, work stopped due to outbreak of WW2

[edit] Switzerland

  • Switzerland 1932 (mechanical): 30 lines, 16.6 frame/s, 4:3 horizontal aspect ratio, ~40x30 pixels per frame, test movies and live images

[edit] Italy

During the 1930s there were also experimental transmissions from the Vatican - further details unknown

  • Italy 1932 (mechanical): 60 lines, 20 frame/s, 4:3 horizontal aspect ratio, ~45x60 pixels per frame, test movies and live images
  • Italy 1939 (electronic): 441 lines, 21 frame/s, 4:3 horizontal aspect ratio, regular service from Rome and Milan. 2 kW transmission power on VHF 50 MHz

[edit] UK

[edit] Mechanical
  • England 1926 (Baird mechanical): 30 lines, 5 frame/s, black-and-white experimental transmissions
  • England 1928 (Baird mechanical): 30 lines, 5 frame/s, first experimental color TV transmissions
  • London 1932 (Baird mechanical) : 30 lines, 12.5 frame/s, 3:7 vertical aspect ratio, vertical scanning, ~70x30 pixels per frame, sound, live TV from studio
  • England 1936 (Baird): 240 lines, 25 frame/s, line frequency 6000 Hz, used from November 1936 to February 1937

[edit] Electronic
  • UK (1936, EMI): 405 lines / 50 Hz. Used from November 1936 to 1985.
    • The EMI 405 lines system (1938-1939) was the first to have an ITU System Letter Designation.
    • The EMI system is officially known as System-A. As the EMI system predates PAL, there is no PAL designator in the ITU television system table.

[edit] USSR

  • USSR 1932 (mechanical): 30 lines, 12.5 frame/s, 4:3 horizontal aspect ratio, ~40x30 pixels per frame, test movies and live images

[edit] North America

  • USA 1933: 240 lines
  • USA 1936: 343 lines; limited public demonstrations in New York City (RCA) and Philadelphia (Philco). Field tests in Los Angeles used various line systems, but adopted RCA's 441-line system by 1938.
  • USA 1938-9: First TV receivers sold on a very limited basis, mostly in New York. Manufactures included RCA, GE, DuMont, and Andrea.
  • USA 1937-1941: 441 lines @ 30 f.p.s.(RCA) and 605 lines (Proposed by Philco), both replaced by 525 line System-M on July 1, 1941 when the FCC issued the first commercial licenses.

[edit] How and why particular line rates were chosen

Because an interlaced system requires accurate positioning of scanning lines it is important to make sure that the horizontal and vertical timebases are in a precise ratio. This is accomplished by passing the one through a series of electronic divider circuits to produce the other. Each division is by a prime number. Therefore there has to be a straightforward mathematical relationship between the line and field frequencies, the latter being derived by dividing down from the former. Technology constraints of the 1930s meant that this division process could only be done using small integers, preferably no greater than 7, for good stability. The number of lines was odd because of 2:1 interlace. The British 405 line system for example used a vertical frequency of 50 Hz (Standard AC mains supply frequency in Britain) and a horizontal one of 10,125Hz (50 × 405 ÷ 2)

  • 2 × 3 × 3 × 5 Gives 90 (not interlaced)
  • 2 × 2 × 2 × 2 × 2 × 3 Gives 96 (not interlaced)
  • 2 × 2 × 3 × 3 × 5 Gives 180 (not interlaced)
  • 2 × 2 × 2 × 2 × 3 × 5 Gives 240 (Used for the experimental Baird transmissions in England -not interlaced)
  • 3 × 3 × 3 × 3 × 3 Gives 243
  • 7 × 7 × 7 Gives 343 (Early North American system also used in Poland before WW2)
  • 3 × 5 × 5 × 5 Gives 375
  • 3 × 3 × 3 × 3 × 5 Gives 405 (Used in Britain Ireland and Hong Kong before 1985)
  • 2 × 2 × 2 × 5 × 11 Gives 440 (not interlaced)
  • 3 × 3 × 7 × 7 Gives 441 (Used by RCA in North America America before the 525 standard was adopted and widely used before WW2 in Continental Europe with different frame rates )
  • 2 × 3 × 3 × 5 × 5 Gives 450
  • 5 × 7 × 13 Gives 455 (Used in France before WW2)
  • 3 × 5 × 5 × 7 Gives 525 (A compromise between the RCA and Philco systems Still used today In America and parts of Asia)
  • 3 × 3 × 3 × 3 × 7 produces 567 (used for a while after WW2 in the Netherlands)
  • 5 × 11 × 11 Gives 605 (Used experimentally by Philco in North America before the 525 standard was adopted)
  • 5 × 5 × 5 × 5 gives 625 (Still used today in most parts of the world)
  • 3 × 3 × 7 × 13 Gives 819 (Used in France from the 1950’s till the 1980's)

Even some digital TV line rates (i.e. 480 and 576) are based on the number of active lines in the 525 and 625 analogue video standards which preceded them.

[edit] How and why particular frame/field rates were chosen

Since the mid-1930s it has been standard practice to use a field frequency equal to or a submultiple of the AC mains electric supply frequency 50 Hz in most countries (60 Hz in others) because studio lighting generally uses alternating current lamps and if these were not synchronized with the field frequency, an unwelcome strobe effect could appear on TV pictures. Secondly the smoothing (filtering) of power supply circuits in early TV receivers was rather poor and ripple superimposed on the DC could cause visual interference. If the picture was locked to the mains frequency, this interference would at least be static on the screen and thus less obtrusive. By the 1930s most countries had standardized their public electricity supplies on either 50 Hz or 60 Hz and this heavily influenced the choice of frame rate (12.5 25 or 30 frame/s)

[edit] Other considerations

The bandwidth required to transmit a television signal increases as the field rate and particularly as the line rate increases. In the interests of economic use of the available radio frequency spectrum, it is important that the bandwidth of the TV signals does not become too large; a more pressing consideration in the 1930s was that given the limits of the technology of the day, wide-bandwidth signals were very difficult to handle within transmitter, receiver and antenna circuitry. Thus while it may have been desirable to maximize picture quality by using very high line and frame rates, in practice there were limits to what could be used.

The THEORETICAL bandwidth requirements of the different standards are as follows

  • (number of lines * frame rate) * (number of lines * aspect ratio) /2
  • 405 line (405 * 25) * (405 * 4/3) /2 = 2733750 Hz or 2.75 MHz (5:4 aspect ratio pre-1950)
  • 525 line (525 * 30) * (525 * 4/3) /2 = 5512500 Hz or 5.52 MHz (29.98 Hz field rate with Colour NTSC)
  • 625 line (625 * 25) * (625 * 4/3) /2 = 6510417 Hz or 6.51 MHz
  • 819 line (819 * 25) * (819 * 4/3) /2 = 11179350 Hz or 11.2 MHz

In practice most broadcast TV systems use slightly less video bandwidth sacrificing some horizontal resolution in the process. This was based on the work of Ray Kell at RCA in the late 1930s who asked groups of viewers to judge when the horizontal resolution equalled the vertical resolution as he displayed signals with different bandwidths. He concluded that for progressive scanning the practical bandwidth could be reduced to two thirds of the theoretical bandwidth. Later work in the 1950s concluded that for interlaced standards it could be halved for signals with a lot of movement. The amount by which the theoretical bandwidth is reduced in a given standard is called the Kell Factor.

[edit] See also

[edit] Individual television stations

[edit] Broadcast television systems

[edit] Specific Television Articles