Monoscope

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The widely used Indian Head test pattern was generated by a monoscope. RCA Indian Head test pattern.JPG
The widely used Indian Head test pattern was generated by a monoscope.
A monoscope Monoscope.jpg
A monoscope
Early Cinema Television (UK) monoscope advertisement Cintel monoscope.jpg
Early Cinema Television (UK) monoscope advertisement

A monoscope was a special form of video camera tube which displayed a single still video image. The image was built into the tube, hence the name. The tube resembled a small cathode ray tube (CRT). Monoscopes were used beginning in the 1950s to generate TV test patterns and station logos. This type of test card generation system was technologically obsolete by the 1980s.

Video camera tube

Video camera tubes were devices based on the cathode ray tube that were used to capture television images prior to the introduction of charge-coupled devices (CCDs) in the 1980s. Several different types of tubes were in use from the early 1930s to the 1980s.

Contents

Design

The monoscope was similar in construction to a CRT, with an electron gun at one end and at the other, a metal target screen with an image formed on it. This was in the position where a CRT would have its phosphor-coated display screen. As the electron beam scanned the target, varying numbers of electrons were reflected from the different areas of the image. The reflected electrons were picked up by an internal electrode ring, producing a varying electrical signal which was amplified to become the video output of the tube.

Phosphor substance exhibiting luminescence

A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness, and fluorescent materials, where the emission decay takes place over tens of nanoseconds. Phosphorescent materials are known for their use in radar screens and glow-in-the-dark materials, whereas fluorescent materials are common in cathode ray tube (CRT) and plasma video display screens, fluorescent lights, sensors, and white LEDs.

This signal reproduced an accurate still image of the target, so the monoscope was used to produce still images such as test patterns and station logo cards. For example, the classic Indian Head test card used by NBC, shown on the right was often produced using a monoscope.

Usage

The target is Test Card G in this example MonoscopeCU.jpg
The target is Test Card G in this example

Monoscopes were available with a wide variety of standard patterns and messages, and could be ordered with a custom image such as a station logo. Monoscope "cameras" were widely used to produce test cards, station logos, special signals for test purposes and standard announcements like "Please stand by" and "normal service will be resumed....". They had many advantages over using a live camera pointed at a card; an expensive camera was not tied up, they were always ready, and were never misframed or out of focus. Indeed, monoscopes were often used to calibrate the live cameras, by comparing the monoscope image and the live camera image of the same test pattern.

Part of a character generator target with numbers and symbols Anodo de monoscopio CK1414F10C.JPG
Part of a character generator target with numbers and symbols

Pointing an electronic camera at the same stationary monochrome caption for a long period of time could result in the image becoming burnt onto the camera tube's target — and even onto the phosphor of a monitor displaying it in extreme cases.

Monoscopes were used as character generators for text mode video rendering in computer displays for a short time in the 1960s. [1] [2] [3] [4] The monoscope declined in popularity during the 1960s due to its inability to generate a colour test card, and the development of solid state TV test pattern signal generators.

Character generator

A character generator, often abbreviated as CG, is a device or software that produces static or animated text for keying into a video stream. Modern character generators are computer-based, and can generate graphics as well as text.

Text mode is a computer display mode in which content is internally represented on a computer screen in terms of characters rather than individual pixels. Typically, the screen consists of a uniform rectangular grid of character cells, each of which contains one of the characters of a character set. Text mode is contrasted to all points addressable (APA) mode or other kinds of computer graphics modes.

See also

Test card Signal test used in television broadcasting.

A test card, also known as a test pattern or start-up/closedown test, is a television test signal, typically broadcast at times when the transmitter is active but no program is being broadcast. Used since the earliest TV broadcasts, test cards were originally physical cards at which a television camera was pointed, and such cards are still often used for calibration, alignment, and matching of cameras and camcorders. Test patterns used for calibrating or troubleshooting the downstream signal path are these days generated by test signal generators, which do not depend on the correct configuration of a camera. Digitally generated cards allow vendors, viewers and television stations to adjust their equipment for optimal functionality. The audio broadcast while test cards are shown is typically a sine wave tone, radio or music.

Related Research Articles

Cathode-ray tube vacuum tube that can show moving pictures, vector graphics, or lines

The cathode-ray tube (CRT) is a vacuum tube that contains one or more electron guns and a phosphorescent screen, and is used to display images. It modulates, accelerates, and deflects electron beam(s) onto the screen to create the images. The images may represent electrical waveforms (oscilloscope), pictures, radar targets, or other phenomena. CRTs have also been used as memory devices, in which case the visible light emitted from the fluorescent material is not intended to have significant meaning to a visual observer.

Williams tube elektronka

The Williams tube, or the Williams–Kilburn tube after inventors Freddie Williams and Tom Kilburn, is an early form of computer memory. It was the first random-access digital storage device, and was used successfully in several early computers.

Selectron tube trademark

The Selectron was an early form of digital computer memory developed by Jan A. Rajchman and his group at the Radio Corporation of America (RCA) under the direction of Vladimir K. Zworykin. It was a vacuum tube that stored digital data as electrostatic charges using technology similar to the Williams tube storage device. The team was never able to produce a commercially viable form of Selectron before magnetic-core memory became almost universal, and it remains practically unknown today.

Electron gun

An electron gun is an electrical component in some vacuum tubes that produces a narrow, collimated electron beam that has a precise kinetic energy. The largest use is in cathode ray tubes (CRTs), used in nearly all television sets, computer displays and oscilloscopes that are not flat-panel displays. They are also used in field emission displays (FEDs), which are essentially flat-panel displays made out of rows of extremely small cathode ray tubes. They are also used in microwave linear beam vacuum tubes such as klystrons, inductive output tubes, travelling wave tubes, and gyrotrons, as well as in scientific instruments such as electron microscopes and particle accelerators. Electron guns may be classified by the type of electric field generation, by emission mechanism, by focusing, or by the number of electrodes.

Storage tube

Storage tubes are a class of cathode-ray tubes (CRTs) that are designed to hold an image for a long period of time, typically as long as power is supplied to the tube.

An output device is any piece of computer hardware equipment which converts information into human-readable form.

Direct-view bistable storage tube

Direct-view bistable storage tube (DVBST) was an acronym used by Tektronix to describe their line of storage tubes. These were cathode ray tubes (CRT) that stored information written to them using an analog technique inherent in the CRT and based upon the secondary emission of electrons from the phosphor screen itself. The resulting image was visible in the continuously glowing patterns on the face of the CRT.

Indian-head test pattern

The Indian-head test pattern is a black-and-white television test pattern which was introduced in 1939 by RCA of Harrison, New Jersey as a part of the RCA TK-1 monoscope. Its name comes from the original art of a Native American featured on the card. It was widely used by television stations worldwide during the black-and-white TV broadcasting era.

Charactron

Charactron was a U.S. registered trademark of Consolidated Vultee Aircraft Corporation (Convair) for its shaped electron beam cathode ray tube. Charactron CRTs performed functions of both a display device and a read-only memory storing multiple characters and fonts. The similar Typotron was a U.S. registered trademark of Hughes Aircraft Corporation for its type of shaped electron beam storage tube with a direct-view bistable storage screen.

7JP4

The 7JP4 is an early black and white or monochrome cathode ray tube. It was a popular type used in late 1940s low cost and small table model televisions. The 7JP4 has a 7" diameter round screen which was often partially masked. Unlike later electromagnetically deflected TV tubes, the 7JP4 is electrostatically deflected like an oscilloscope tube.

Monochrome monitor CRT computer display

A monochrome monitor is a type of CRT computer monitor which was very common in the early days of computing, from the 1960s through the 1980s, before color monitors became popular. They are still widely used in applications such as computerized cash register systems, owing to the age of many registers. Green screen was the common name for a monochrome monitor using a green "P1" phosphor screen.

The beam-index tube is a color television cathode ray tube (CRT) design, using phosphor stripes and active-feedback timing, rather than phosphor dots and a beam-shadowing mask as developed by RCA. Beam indexing offered much brighter pictures than shadow-mask CRTs, reducing power consumption, and as they used a single a electron gun rather than three, they were easier to build and keep in alignment.

This is a subdivision of the Oscilloscope article, discussing the various types and models of oscilloscopes in greater detail.

This article discusses the history and development of oscilloscope technology. The modern day digital oscilloscope grew out of multiple developments of analog oscilloscopes, which in turn grew out of the older oscillograph. The oscillograph started as a hand drawn chart which was later slightly automated. This then grew into galvanometer driven recorders and photographic recorders. Eventually, the cathode ray tube came along and displaced the oscillograph, eventually taking over the majority of the market when advancements such as triggers were added to them. With the lowering costs of digital circuitry, the digital oscilloscope has taken over the majority of the modern oscilloscope sales, with almost no makers offering analog cathode ray tube oscilloscopes. However, the oscillograph lives on to a degree in pen chart recorders for electrical signals.

Beam deflection tube

Beam deflection tubes, sometimes known as sheet beam tubes, are vacuum tubes with an electron gun, a beam intensity control grid, a screen grid, sometimes a suppressor grid, and two electrostatic deflection electrodes on opposite sides of the electron beam, that can direct the rectangular beam to either of two anodes in the same plane. They can be used as two-quadrant, single-balanced mixers or (de)modulators with very linear qualities, their mode of operation similar to one-half of a Gilbert Cell, by applying an unbalanced signal f1 to the control grid and a balanced signal f2 to the deflection electrodes, then extracting the balanced mixing products f1f2 and f1 + f2 from the two anodes. Similar to a pentagrid converter, the cathode and the first two grids can be made into an oscillator. Two beam deflection tubes can be combined to form a double-balanced mixer.

A time base generators, or timebase, is a special type of function generator, an electronic circuit that generates a varying voltage to produce a particular waveform. Time base generators produce very high frequency sawtooth waves specifically designed to deflect the beam in cathode ray tube (CRT) smoothly across the face of the tube and then return it to its starting position.

Deflection yoke kind of magnetic lens, used in cathode ray tubes (CRT) to scan the electron beam both vertically and horizontally over the whole screen

A deflection yoke is a kind of magnetic lens, used in cathode ray tubes to scan the electron beam both vertically and horizontally over the whole screen.

References

  1. "4560 Custom-built, 2" diameter, Electrostatic-Focus, Electrostatic-Deflection Monoscope Tubes For Use As Alphanumeric Character Generators data sheet" (PDF). RCA Electronic Components. May 1969. Retrieved 27 September 2017.
  2. "CK1414 Symbolray character generating cathode ray tube data sheet" (PDF). Raytheon Company components division, industrial components operation. 15 April 1966. Retrieved 29 July 2017.
  3. "Symbolray™ application note" (PDF). Raytheon Company components division, industrial components operation. Retrieved 27 September 2017.
  4. "TH9503 Character generating cathode ray tube data sheet" (PDF). Compagnie Française Thomson-Houston division tubes electroniques, Paris (France). January 1968. Retrieved 27 September 2017.