Mechanical television

NBTVA test image, taken by Klaas Robers from a television set he built with a Nipkow disc

Mechanical television is a comprehensive term, a generic term for the first existing television process. It encompassed the technical processes involved in the functioning of the studio and transmission systems through to the receivers. The later system, which replaced this first television of the 1920s to 1940s, was fully electronic television , which has existed to the present day.

The term mechanical television has not yet been updated, although it is a television process that works with

• mechanical ,
• optical ,
• electrical and
• electronic

Components works. In the field of amateur television, the principle of this original television is still used today.

history

Recording and playback principle according to J. L. Baird

Numerous steps are necessary to transfer a picture from the studio to the home screen. Mechanical television included the first attempts at image transmission. The basis for this was laid by the pioneers of picture telegraphy (historically: copy- telegraphy ) with their work to transmit immobile pictures. As early as the first half of the 19th century a. a. Frederick Collier Bakewell a rotating drum wrapped in a foil made of metal and an electrical contact that spirally scans an image attached to it. The further development of this drum principle for moving pictures was an important path of mechanical television, which at that time was called "electrical television".

Of pendulums, drums and discs

Drawing of a 30-hole optical image-splitting disk in a spiral shape

The first useful realization of the important step in the television process, image decomposition, was invented by Paul Nipkow in 1883 . Before that, he set himself three tasks:

1. want to replace the image drawn with non-conductive ink with a light image such as is drawn directly from an object by means of a lens or a concave mirror on its screen;
2. one might want to transmit an image drawn with non-conductive ink in such a way that the receiving apparatus projects a copy of the original in the form of a light image onto a screen;
3. or at last one might want to apply the two improvements mentioned to the same apparatus.

He describes the initial situation as follows: “Apparatuses that did something like this were already in the copy telegraph; In fact, with the help of it, a picture drawn under certain circumstances could be transferred into the distance. ”On the way to his own invention, the Telectroscope from 1877, which was also based on a turntable (and later developed several times), and Constantin Selencq's d ' Ardres and Shelford Bidwell ’s 1881 “Tele-Photography” with a cylinder as a rotating component are the most important inventions.

Nipkow's rotating disk , named after him, is the heart of his “electric telescope”. Strictly speaking, however, this is no longer a mechanical component, but an optical one. However, real “remote viewing” was out of the question, because the rotating image-splitting disk of the transmitter and the image-composing disk of the receiver are still on one and the same axis. A synchronization of both panes was not yet possible with this device at a distance, but the revolutionary thing about it was that an image, converted into electrical current with the help of technology, “flowed” through a wire in order to reappear as an image. Paul Nipkow registered his patent with the Imperial Patent Office in 1884 under the name "Electric Telescope", which was then granted on January 15, 1885. Due to a lack of money, however, the patent expired a year later and was therefore able to serve numerous television pioneers as a basis for their own developments.

Bust in L. Baird's hometown Helensburgh

Pioneers

The Soviet mechanical television set B-2 (Б-2) from the Leningrad N. G. Kosinzkowo plant. The television picture was behind the round glass.

The development of "electrical television" is based on the experiments of several technology pioneers. The work of Dénes by Mihálys and John Logie Bairds deserves particular mention. The Scottish inventor J. L. Baird relied on an image splitting disk, while the Hungarian engineer D. von Mihály initially developed a completely different process without a Nipkow disk, in which a mirror oscillated quickly between a horseshoe magnet. In an improved method, a mirror was attached to wire strings, which were set into rapid oscillation after current was passed through. After only minor successes, Dénes von Mihály also used Nipkow disks; the first commercial ones were built around 1929 in collaboration with John Logie Baird. Another method was developed by August Karolus at Telefunken , where fast rotating mirrors were used. Karolus also combined both systems with one another; i.e. the mirror wheel for horizontal scanning and the oscillating mirror for vertical scanning.

John Logie Baird deserves the credit for introducing the first fully functioning television (with matching camera) based on a Nipkow disk in 1926. Baird's "Television Development Company" also managed the first transatlantic transmission of a television image from London to Hartsdale ( NY ) in 1928.

Other pioneers of mechanical television were René Barthélemy for France and Charles Francis Jenkins for the USA .

Establishment as a medium

Transmitters

Mechanical television broadcasters were mainly used in Europe, America and Australia. Experimental programs were broadcast from 1927 onwards. The first broadcasts were followed by regular broadcasts in several US cities in 1929, in London in the UK and Melbourne, Australia, and in Moscow in the Soviet Union in 1931. From 1932 onwards there were broadcasts in Paris, Brussels, Rome and four German locations, Berlin-Witzleben , Döberitz and Königs Wusterhausen near and in Berlin.

receiver

Drawing of a Model B Televizor by Logie Baird

With the commercialization of mechanical television, the Nipkow disk prevailed for image splitting and for the receiving devices, which was used on the transmitter side for image splitting of films until the early 1940s.

On the recipient side, televisions with Nipkow discs were sold until around 1935. Logie Baird sold his Model B Televisor from 1928 . Since the signals were transmitted over the frequency or wave ranges of the long , medium or short wave , considerable ranges were possible, which the fully electronic television could not achieve until today.

The recipient's equipment varied. There were total recipients as well as additional recipients. The latter were, for example, the Soviet B-2 devices, which only reproduced the picture and had to be connected to a short or medium wave radio in order to receive the picture from the transmitter. The sound could be received with a second radio. Due to their simple design, the receivers could be made by amateurs themselves. Therefore, the devices enjoyed great popularity among hobbyists. Construction kits and instructions were sold, almost exclusively with Nipkow discs. In addition to Great Britain, these self-made devices were also particularly successful in the USA, where, however, after a brief boom due to the numerous different standards and the further development towards high-definition television, mechanical television quickly lost its importance again by 1933.

The BBC television service broadcast in London with 30 lines until 1935. The same was true in the Netherlands, here even in the British standard until September 1939. Practically all receivers in both countries worked with the mechanical method. All salable first generation receivers with Nipkow disks in Great Britain, France, the Netherlands, the USSR and the USA had the same number of picture lines of a television picture of 30 lines. In Germany, too, until the later standard with 180 lines was introduced (used until 1938), many mechanical receivers were in use, but television in Germany was hardly widespread for private people. On the transmitter side, there were refined further developments of mechanical image decomposition in the 1940s, in which mirror-drum systems were used again, making image-improving line numbers over 400 possible. But there was no equivalent further development on the receiver side in the 1940s.

Televisor

Logie Baird marketed his televisions under the made-up word "Televisor", which was a common expression for a television receiver itself in the UK until the 1950s. This word also found its way into other languages, for example in Russian , like in Spanish, Televis or is a word for television. No distinction is made between mechanical and electronic image decomposition.

Aspect ratio

While low-definition television with mechanical image splitters predominantly had an aspect ratio of 1: 1 or 4: 3 (even with fully electronic television, the 4: 3 (12: 9) format was adhered to worldwide for over 60 years, through all quality levels and later color television systems until the 16: 9 ratio was introduced in the mid-1990s) and horizontal lines were used, Baird used vertical scanning with pictures in portrait formats 2: 3 and 3: 7, i.e. upright pictures in "portrait format". His consideration was that television does not offer the necessary performance for the transmission of films and landscape shots anyway, but that it is ideally suited for the transmission of close-ups, i.e. usually people. The fact that the Bairds standard was able to assert itself longer than other low-resolution systems and is still widely used today in a modified form in Narrow Bandwidth Television speaks for the correctness of this consideration.

Station table

area	transmission beginning	frequency	Send deadline	Note / operator / founder
USA , over 25 cities	1929	Various	1939
London I	1929	MW 752 kHz	1932	Longacre
Melbourne	1929	?	?
Moscow	1931	LW 271 kHz, MW 1304 kHz	1941	WZSPS
Brussels	1932	MW 589 kHz and 1172 kHz	?
Paris	1932	MW 671 kHz	?	"Postes, Télégraphes et Téléphones" (PTT)
Southwest from Paris , Montrouge	1932	MW 1.5 MHz	?
King Wusterhausen	1932	LW 183.5 kHz	?
Berlin joke life	1932	MW 716 kHz	?
Doberitz	1932	MW 2.1 MHz	?
Berlin	1932	KW 44.476 MHz	?	Reichspost
London II	1932	MW 1147 kHz	1935	Brookmans Park
Rome	1932	KW 3.75 MHz	?
Netherlands	1932	?	1939

Terms

The term “mechanical television” is used internationally in many countries and has established itself, although hardly any mechanical processes are used. The only mechanical element that appears is the visibly rotating Nipkow disk . Whether the term developed on the basis of the visual perception that this rotating essential functional element was assessed as a mechanical component cannot be proven. Nipkow himself described his apparatus in the patent specification as an "electric telescope".

Electrical and electronic parts

The Nipkow device consists largely of electrically operated components, of which at least one - the selenium cell - is an early electronic component. Furthermore, the transmission from the transmitter to the receiver takes place electrically via a cable. Even the speed of the motor that drives the Nipkow disk has to be synchronized with an electronic circuit, usually with an electron tube.

Optical parts

On the receiver side, in the Nipkow design, a polarized light beam is rotated by the magnetic field of a coil depending on the signal from the transmitter selenium cell and filtered by subsequent lenses that the same impression of brightness is produced for the eye as it is the sender side exists. This polarized light beam was generated with the help of a special optical glass, the so-called "Nicol's prism". Alternatively, a tube filled with carbon disulfide or neon (a " glow lamp ") was used to make the fluctuations in brightness visible . A picture tube was therefore not required. With the introduction of this and other optical television processes, sometimes with the first optoelectronic components , the term mechanical television was no longer sufficient as early as 1929.

Term assignment

This shows that the term “mechanical television” is too brief. At most, the term “mechanical image decomposition” would be correct. The term mechanical television, which is customary internationally, is more of a historical delimiting term for all other methods of television and its technology

• from recording or scanning,
• Sound and image decomposition,
• Transfer,
• Send and receive
• up to preparation for the end device,

which are not based on the techniques of fully electronic television .

The term is thus - ultimately - only to be understood as a generic term for delimitation. However, since the term is not clear and has not yet been updated, a correct assignment of technologies developed since then is often problematic.

Real mechanical television

In principle, fully mechanical television is definitely conceivable. The dismantling would take place in the manner described using a Nipkow disk or a mirror system, but the image point would not be transmitted electrically, but by means of fiber optic cables . This would not require a single electrical component. B. spring mechanisms or steam engines are used, daylight, candlelight or gas light is used as the light source. Several members of the Narrow Bandwidth Television Association are currently working on such a project, which should prove that at least in principle television would have been possible as early as the 19th century.

present

Image generation with light-emitting diode strips: The improved model of the television picture machine from 1989 works with four strips.

Procedure with components of mechanical television

Even today, mechanical television is not insignificant. The Nipkow disk and mirror systems are used again today in the construction of confocal microscopes or video projectors . There was a special application of mechanical television on the American space probe Pioneer 11 : Since the probe rotates on its own axis, a single light-sensitive cell was attached to the outside, which scans a line by rotating the probe. Since the probe itself also moves, complete images can be scanned. In terms of the functional principle, this type of image scanning can therefore be compared with the Nipkow disk. The Virtual Boy from Nintendo used only one picture line, composed of 240 LEDs ; a rotating mirror creates the impression of a complete picture. A device developed by Peter Schmalenbach can be regarded as a forerunner of modern advertising panels. Four rotating light-emitting diodes, each with 232 light-emitting diodes, write all 625 lines of today's television standard in the air. This creates a complete television picture. The machine shows z. B. the fed current television program or videos on a virtual image drum. Almost 122,000 pixels result in a remarkable resolution.

Continued as "electric television"

Experimental self-made color televisor with Nipkow disk, built by the user G1MFG of the English Wikipedia. Here the TV picture is created behind the magnifying glass on the right.

Projects of amateur television as NBTV.org, one from today's perspective, the extremely narrow-band version ( English narrow-bandwidth television ) television with a bandwidth of 2.5 kHz, for example, Baird, finished replicas dealt in the present with the inventions as well as complete new designs with Nipkow image splitting disks. Due to the considerable improvement and miniaturization of components since the times of Nipkow and Baird, this has led to astonishing success again and again. Color image transmissions, on which JL Baird already experimented, are also possible.

In Great Britain a kit for a televisor based on historical models has been sold for many years.

Web links

• Mechanical television: circuits, mode of operation
• The beginnings of television: basic technical decisions
• Beginnings and basics with animation
• TV with 4 rotating LED strips

Individual evidence

1. ^ Franz Pichler: Telegraphy and telephone systems of the 19th century . In: Edith Decker, Peter Weibel (eds.): From Disappearance of Distance , exhibition catalog German Post Museum Frankfurt. Du Mont Buchverlag, Cologne 1991
2. ^ Raphael Eduard Liesegang: Contributions to the problem of electrical television . Ed.-Liesegang-Verlag, Düsseldorf 1891
3. ^ Paul Nipkow: The telephotograph and the electric telescope . In: Elektrotechnische Zeitschrift , October 1885, pp. 419-425
4. ↑ Patent DE30105 : Electric telescope. Registered January 6, 1884 , published January 15, 1885 , applicant: Paul Nipkow. ‌
5. ^ Transatlantic Television in 1928 . Bairdtelevision of the Baird family according to a New York Times report on February 9, 1928
6. ^ First transatlantic TV broadcast .  ( Page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. Guinness book  
7. ^ European Mechanical TV Stations , Early Television Foundation
8. ^ Exhibit in the Bradford National Media Museum
9. ^ Narrow-bandwidth Television Association. Retrieved January 27, 2013 . 
10. ↑ Patent DE3529072 : TV image generation by rotating rows of LEDs. Registered on August 14, 1985 , published on May 28, 1986 , applicant: Peter Schmalenbach. ‌
11. ↑ The new Guinness Book of Records 1990 . Ullstein Verlag, Frankfurt am Main / Berlin 1990, ISBN 3-550-07747-5 , pp. 285 .
12. ↑ Steve Ostler "Mechanical Television". Radiocraft