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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.
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.
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 as used by many television stations in North America, was often produced using a monoscope.
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....". [1] 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.
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. [2] [3] [4] [5] The monoscope declined in popularity after the 1960s due to its inability to generate a colour test card, and the development of solid state TV test pattern signal generators.
Analog television is the original television technology that uses analog signals to transmit video and audio. In an analog television broadcast, the brightness, colors and sound are represented by amplitude, phase and frequency of an analog signal.
A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms on an oscilloscope, a frame of video on an analog television set (TV), digital raster graphics on a computer monitor, or other phenomena like radar targets. A CRT in a TV is commonly called a picture tube. CRTs have also been used as memory devices, in which case the screen is not intended to be visible to an observer. The term cathode ray was used to describe electron beams when they were first discovered, before it was understood that what was emitted from the cathode was a beam of electrons.
The Williams tube, or the Williams–Kilburn tube named 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.
A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or visible light, and cathodoluminescent substances which glow when struck by an electron beam in a cathode-ray tube.
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.
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.
An electron gun is an electrical component in some vacuum tubes that produces a narrow, collimated electron beam that has a precise kinetic energy.
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 that converts information or data into a human-perceptible form or, historically, into a physical machine-readable form for use with other non-computerized equipment. It can be text, graphics, tactile, audio, or video. Examples include monitors, printers and sound cards.
The Indian-head test pattern is a test card that gained widespread adoption during the black-and-white television broadcasting era as an aid in the calibration of television equipment. It features a drawing of a Native American wearing a headdress surrounded by numerous graphic elements designed to test different aspects of broadcast display. The card was created by RCA to be the standard image for their TK-1 monoscope, a simple video camera capable of producing only the image embedded within it. The pattern was introduced in 1939 and over the following two decades became a fixture of television broadcast across North America in 525-line resolution and abroad in 525- and 625-line resolution until it was made obsolete by the rise of color television in the 1960s.
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 they can generate graphics as well as text.
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.
A vector monitor, vector display, or calligraphic display is a display device used for computer graphics up through the 1970s. It is a type of CRT, similar to that of an early oscilloscope. In a vector display, the image is composed of drawn lines rather than a grid of glowing pixels as in raster graphics. The electron beam follows an arbitrary path, tracing the connected sloped lines rather than following the same horizontal raster path for all images. The beam skips over dark areas of the image without visiting their points.
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.
This is a subdivision of the Oscilloscope article, discussing the various types and models of oscilloscopes in greater detail.
The history of the oscilloscope was fundamental to science because an oscilloscope is a device for viewing waveform oscillations, as of electrical voltage or current, in order to measure frequency and other wave characteristics. This was important in developing electromagnetic theory. The first recordings of waveforms were with a galvanometer coupled to a mechanical drawing system dating from the second decade of the 19th century. The modern day digital oscilloscope is a consequence of multiple generations of development of the oscillograph, cathode-ray tubes, analog oscilloscopes, and digital electronics.
Laser-powered phosphor display (LPD) is a large-format display technology similar to the cathode-ray tube (CRT). Prysm, Inc., a video wall designer and manufacturer in Silicon Valley, California, invented and patented the LPD technology. The key components of the LPD technology are its TD2 tiles, its image processor, and its backing frame that supports LPD tile arrays. The company unveiled the LPD in January 2010.
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.
A time base generator 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 of a cathode ray tube (CRT) smoothly across the face of the tube and then return it to its starting position.
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.
