TELEVISION TERMS [Video Handbook (1954)]

accelerating electrode. Otherwise known as the second anode of a cathode ray tube.

This electrode serves to increase the velocity of the electron beam so that when it strikes the screen, light is emitted.

active lines. Those lines, of the 525 possible lines in a television image, which appear on the screen. The inactive lines are blanked out during the time that the beam is returning from the bottom of the picture to start of the next frame.

adjacent sound carrier frequency. The sound carrier in the television channel on the low frequency side of the channel.

align. To adjust two or more tuned circuits in radio so that they respond to the same frequency.

alternating current. (abbr: ac). An electric current which reverses its direction of flow at regular intervals.

amplitude modulation (am). A method of conveying information by changing the amplitude of a radio frequency carrier.

amplitude separation. The process of separating the synchronizing signal from the video information in the composite television signal utilizing the difference in their amplitude levels.

antenna. (Abbr: ant.). The portion, usually wires or rods, of a radio or television station or receiving set, for radiating waves into space or receiving them from space. Also called aerial.

antenna array. An arrangement of two or more antennas (or reflectors) coupled together so as to improve transmission or reception in a given direction.

aspect ratio. The ratio of picture width to picture height. 4 to 3 in the present television system.

associated sound carrier frequency. The sound carrier in the television channel under consideration.

870 astigmatism. A condition of focus of the electron beam wherein the spot is not perfectly round, resulting in different trace widths when the beam is deflected from the center of the screen.

audio. The Latin word for "hear". Used synonymously with the word sound.

audio carrier. The frequency modulated RF signal which carries the sound information.

audio frequency (Abbr: an. A frequency corresponding to a normally audible sound wave-about 20 to 15,000 cycles a second.

automatic brightness control. A circuit which automatically controls the average brightness in the received image so that it corresponds with that being transmitted.

automatic frequency control (Abbr: afc). A circuit that keeps a radio receiver from "drifting" off the frequency to which 1t is tuned.

automatic volume control. A circuit which varies the amplification of a receiver so that its output remains constant despite changes in input signal strength.

average brightness. The average illumination in the television picture.

bandwidth. The number of continuous frequencies required to convey the information being transmitted, either visual or aural. The bandwidth of a television channel is 6 mhz.

band-pass filter. A filter which passes a group of continuous frequencies and rejects all others.

beam. The stream of electrons which travels from the electron gun toward the screen in a cathode ray tube.

beat frequency. A frequency resulting from a combination of two frequencies.

black level. The amplitude level of the television signal which corresponds to black in the picture. At this level the beam in the cathode ray tube is biased to cutoff.

blacker-than-black level. The portion of the television signal devoted to the synchronizing pulses. These synchronizing signals are transmitted at higher amplitudes than those representing the blackest part of the picture.

blanking. The process of cutting off the picture tube beam during the time it is not forming the picture. This occurs when the spot returns from the far right to begin the next line and from the bottom to the top of the next picture.

blanking pulse. The pulse used to blank out the electron beam in both the camera and picture tubes during the blanking interval.

blocking oscillator. A type of oscillator used for triggering horizontal and vertical sweep generators.

blooming. The defocusing of the white regions of the television picture when an excess of electrons increases the spot size.

brightness control. A receiver control used to regulate the overall brightness of the picture.

camera. The unit housing the optical system and light sensitive pick-up tube which converts the visual image into electrical impulses.

camera tube. A cathode-ray tube used to transform an image into electrical impulses.

carrier frequency. The frequency of the unmodulated radio signal produced by the transmitter.

cathode-ray tube. An electron tube in which a stream of electrons from a cathode are formed into a narrow beam and deflected by means of electrostatic or magnetic fields over a target, usually a mosaic or fluorescent screen which glows wherever the beam strikes. The iconoscope, kinescope, picture tube, etc. fall into this category.

centering controls. The controls which are used to move the image in the vertical and horizontal directions to properly center it on the screen.

center frequency. As applied to frequency modulation, it Is the frequency of the un modulated carrier. With modulation, the instantaneous frequency swings above and below the center frequency.

channel. A band of frequencies assigned to a station for the transmission of the television and sound signals.

clipper. A vacuum tube circuit which removes a portion of a signal above or below a fixed amplitude level. In television, it refers to the stage which separates the video and sync signals.

clipping level. The amplitude level of a signal, above or below which a clipper removes part of the signal.

co-axial cable. A type of conductor which transmits a wide range of frequencies efficiently. Such a cable in its simplest form consists of a hollow metallic conductor with a single wire accurately centered along the axis of the hollow conductor, and held in position by a suitable insulating material.

composite television signal. The television signal composed of the video information and the synchronizing and blanking pulses.

composite sync signal. The portion of the television signal consisting of the horizontal, vertical, and equalizing pulses.

contrast. The difference in brightness between black and white portions of a picture.

Pictures having high contrast have very deep blacks and brilliant whites, while a picture with low contrast has an overall gray appearance.

contrast control. The control which is used to vary the contrast of the picture by changing the gain of the video stages. It corresponds to the volume control in an aural receiver.

control electrode. The metal structure adjacent to the cathode in a cathode-ray tube to which a voltage is applied to regulate the electron flow. Sometimes called the grid, this electrode controls the light intensity of the image on the screen.

cross-over point. The point, between the grid and pre-accelerator, of a cathode-ray tube where the electrons emitted by the cathode converge.

damping tube. A vacuum tube used in horizontal sweep circuits to prevent transient oscillations.

d-c restorer. A circuit used to reinsert the d-c component of the video signal lost during amplification. The d-c component determines the average brightness of the received image.

d-c transmission. A system of transmission which retains the d-c component of the signal.

definition. The ability of a system to reproduce small details in an image.

deflection. The moving of the cathode ray beam by electrostatic or magnetic fields.

deflecting plates. Two pairs of metal plates used in an electrostatic cathode-ray tubes. Potentials applied to these plates cause the electron beam to move.

demodulation. The process of removing the modulating signal from a modulated radio frequency carrier.

diathermy interference. Interference which results from the signals generated by diathermy machines operated by doctors or hospitals in the vicinity of the television receiver.

differentiating circuit. A circuit used to separate the high frequency horizontal sync pulses from the low frequency vertical sync pulses.

dipole. A simple antenna whose total length is equal to one half the wavelength of the frequency for which it is tuned.

diplexer. A coupling unit which allows two transmitters to operate simultaneously or separately from the same antenna.

directional antenna. An antenna designed to receive radio signals better from some directions than from others.

director. A rod slightly shorter than a dipole, placed in front of it to provide greater directivity.

direct view receiver. A television receiver in which the image is viewed on the face director. A rod slightly shorter than a dipole, placed in front of it to provide greater directivity.

direct view receiver. A television receiver in which the image is viewed on the face of the picture tube.

discriminator. A circuit used in FM receivers to convert the frequency modulated signal into an audio frequency signal.

dissector tube. A pick-up tube containing a continuous photosensitive cathode on which an electron image is formed.

dissolve. A camera technique whereby two images from different cameras are momentarily overlapped and then one is gradually faded out.

discharge tube. A tube used in sawtooth generating circuits to discharge a capacitor.

double-sideband transmission. A system of transmission wherein the sum and difference frequencies of the modulating and carrier signals are transmitted.

electromagnetic deflection coil. A current carrying coil placed over the neck of a cathode-ray tube. The resulting magnetic field deflects the electron beam. Two sets of coils, the vertical and horizontal, are combined into one case, called a yoke.

electron beam. The stream of electrons in a cathode-ray tube. The stream is focused to a sharp point on the tube's fluorescent screen.

electron emission. The releasing of electrons by the surface of an electrode, usually due to heat.

electron gun. That part of a cathode-ray tube in which the electrons are emitted and focused into a beam.

electron lens. The electromagnetic or electrostatic fields in a cathode-ray tube which cause the electrons to converge into a narrow beam.

electronic scanning. The deflection of an electron beam by means of electromagnetic or electrostatic fields.

electrostatic focusing. The process by which electrons are confined into a thin stream by an electrostatic field.

equalizing pulses. A series of six pulses occurring at twice the horizontal frequency. The equalizing pulses precede and follow the vertical sync pulse and are used to maintain proper interlace.

fidelity. The ability of a circuit to reproduce faithfully signals impressed upon it.

field. One half of a television image. With present standards, pictures are transmitted in two fields of 2621 lines each, which are interlaced to form 30 complete frames or images per second.

field frequency. The repetition rate of the field which in present systems is 60 per second or twice the frame frequency.

field pick-up. The televising of remote events by mobile camera and transmitting equipment.

film pick-up. The televising of motion picture films.

flicker. Objectionable low frequency variation in intensity of illumination of a television picture.

fine tuning control. A control on the receiver which varies the frequency of the local oscillator over a small range so as to compensate for drift and permit fine adjustment to a station's carrier frequency.

fluorescent screen. The chemical coating on the inside face of a cathode-ray tube which emits light when struck by electrons.

flyback time. The period during which the electron beam is returning from the end of a scanning line to begin the next line.

flywheel synchronization. Another term for automatic frequency control of a scanning circuit. In such a system the sweep oscillator responds to the average timing of the sync pulses and not to each individual pulse.

focus. In a cathode-ray tube, this refers to the size the spot of light on the fluorescent screen. The tube is said to be focused when the spot is smallest. This term also refers to the optical focusing of camera lenses.

focusing control. The potentiometer control on the receiver which varies the first anode voltage of an electrostatic tube or the focus coil current of a magnetic tube and so focuses the electron beam.

focusing electrode. A metal cylinder in the electron gun, sometimes called the first anode. The electrostatic field produced by this electrode in combination with the control electrode and the accelerating electrode act to focus the electron beam to a small spot on the screen.

frame. One complete television image which consists of 525 lines or two interlaced fields.

frame frequency. The number of times per second the picture area is completely scanned. This frequency is 30 times per second in the present television system.

frequency modulation. A system for transmitting intelligence wherein the frequency of a radio signal is varied in proportion to the modulating signal.

ghost. A secondary picture formed on a television receiver by a signal from the transmitter which reaches the antenna by a longer path. Ghosts are usually caused by reflected signals.

O halation. The ring of illumination which surrounds the point at which the electron beam strikes the fluorescent screen.

height. The vertical dimension of the television image.

height control. The control which varies the vertical size of the picture.

heterodyne frequency. A frequency which is produced by combining two other frequencies and which is their numerical sum or difference.

high voltage. The accelerating potential used to increase the velocity of the electrons in a cathode-ray tube beam.

hold control. A potentiometer in either a vertical or horizontal sweep oscillator circuit which varies the natural frequency of the oscillator and enables it to synchronize with applied sync pulses.

horizontal. This term refers to the direction of sweep of the electron beam from left to right.

horizontal blanking. The blanking pulse which occurs at the end of each horizontal line and cuts off the electron beam while it is returning to the left side of the screen.

horizontal centering-control. The potentiometer used to move the picture in the horizontal direction.

horizontal hold control. A control used to vary the natural frequency of the horizontal sweep oscillator so that it locks with the applied sync pulses.

horizontal resolution. The ability of a television system to reproduce small objects in the horizontal plane.

horizontal retrace. A line on the screen which is formed by the electron beam during the time the spot is returning from the right to the left side of the screen.

CD iconoscope. A camera tube in which a high velocity electron beam scans a photosensitive mosaic which stores an electrical image.

image dissector. A television camera tube in which the photoelectrons are moved past a pickup aperture by deflection circuits. (See Dissector)

image orthicon. A highly sensitive camera tube which combines the principles of the image dissector, orthicon, and image multiplier.

integrating circuit. A circuit which combines the vertical pulses into a single composite pulse.

intensifier electrode. Otherwise known as the third anode. It imparts additional kinetic energy to the electron beam after it has been deflected.

interference. Spurious signals which enter a receiver and mar the picture or sound.

interlaced scanning. A system of scanning whereby the odd and even numbered lines of a picture are transmitted consecutively as two separate fields which are superimposed to create one frame or complete picture at the receiver. The effect is to double the apparent number of pictures and so reduce the amount of flicker.

intermediate frequency (abbr: i.f.). The frequency resulting from the combination of two frequencies in one circuit.

ion. A particle carrying an electric charge. Ions may be positive or negative.

ion spot. A discoloration at the center of the screen of a picture tube due to bombardment of the fluorescent material by negative ions.

ion trap. An electron gun structure and magnetic field which permits electrons to flow toward the screen but diverts negative ions thereby avoiding the formation of an ion spot.

O jitter. The tendency of either several lines or the entire picture to vibrate because of poor synchronization.

keystone effect. Distortion of a television image which results in a keystone shaped pattern.

kickback-supply. A high voltage power supply which derives its energy from the pulses occurring in the primary of the horizontal sweep output transformer when the magnetic field collapses during the retrace period.

lens turret. A part of a television camera on which several lenses are mounted for rapid selection.

limiter. The last 1-f stage in the FM audio circuits. This stage is so biased that it removes amplitude variations above a given level.

line. The path traced by the electron spot as it moves across the width of the screen.

The intensity of the spot is changed as it moves to create varying shades in the picture. In present systems, 525 lines make up a complete picture.

linearity. The relative spacing of picture elements in the television image.

linearity control. A potentiometer in a vertical or horizontal sweep circuit which is used to adjust the spacing and distribution of the picture elements.

line scanning frequency. The number of lines scanned each second. In any system it is equal to the number of scanning lines per frame, multiplied by the frame frequency. Under present standards this is 525 lines x 30 frames per second or 15,750 lines per second.

local oscillator. The heterodyne oscillator in a superheterodyne receiver.

lock-in. A term describing the condition which exists when a sweep oscillator is in synchronism with the applied sync pulses.

magnetic focus. The focusing of the electron beam by means of a magnetic field set up by a coil placed over the neck of the cathode-ray tube.

microsecond. One millionth of a second.

megacycle. One million cycles.

mixing amplifier. An amplifier which combines several signals of different amplitudes and waveshapes into a composite signal. Such an amplifier is used to mix the blanking and sync pulses in the sync generator.

modulation. The variation of the amplitude, phase, or frequency of a radio carrier frequency by a lower frequency signal.

modulation grid. An electrode interposed between the cathode and focusing electrodes in a cathode-ray tube to control the amount of emission and thereby the brilliance of the spot. This controlling effect is produced by altering the voltage of the grid with respect to the cathode.

monitor. A cathode-ray tube and associated circuits, used in a television station to check the transmitted picture.

monoscope. A cathode-ray tube which produces a stationary pattern for the testing and adjusting of television equipment.

mosaic. The photosensitive plate in the iconoscope which emits electrons when struck by light.

multipath reception. The condition in which the radio signal from the transmitter travels by more than one route to a receiver antenna, Usually because of reflections from obstacles, resulting in ghosts in the picture.

multivibrator. A type of oscillator, using R-C components, commonly used to generate the sawtooth voltages in television receiver circuits.

negative ghosts. Ghosts which appear on the screen with intensity variations opposite to those of the picture.

negative transmission. The modulation of the picture carrier by a picture signal whose polarity is such that the sync pulses occur in the blacker-than-black level.

noise. Spurious impulses which modulate the picture or sound signals.

non-linearity. The unequal distribution of picture elements in the vertical and/or horizontal direction.

odd-line interlace. A type of interlace system, such as is now used, in which there are an odd number of lines in each frame.

open-wire transmission line. A transmission line formed by two parallel spaced wires. The distance between the two wires and their diameters determine the surge impedance of the transmission line.

orthicon. A camera tube in which a low velocity electron beam scans a photosensitive mosaic.

oscillograph. An indicating instrument consisting of a cathode-ray tube and a sweep generator for plotting an alternating voltage against time.

over-coupled circuit. A tuned circuit in which the coupling is greater than critical coupling resulting in a broad-band response characteristic.

pairing. A condition of improper interlacing which exists when the lines in alternate fields are superimposed. The fields may "pair" intermittently or continuously.

panning. The movement of the camera head from right to left or up and down.

peaking resistor. A resistor placed in series with the charging capacitor of the vertical sawtooth generator in order to add a negative peaking pulse to the sawtooth voltage to create the waveform required to produce a linear sawtooth current in the yoke.

peaking coil. A small inductive coil placed in an amplifying circuit in order to increase its response at certain frequencies.

pedestal. The portion of the television video signal used to blank out the beam as it flies back from the right to the left side of the screen.

phosphor. A chemical compound which fluoresces when struck by electrons. The screen material of cathode-ray tubes.

photocell. A device containing a photosensitive cathode which emits electrons when exposed to light.

photoelectric emission. The discharge of electrons by a photosensitive material when exposed to light.

pick-up tube. A camera tube used to transform a light image into an equivalent electrical signal.

picture element. The smallest portion of an image that can be resolved by the electron beam.

picture tube. The receiving cathode-ray tube.

polarization. The direction of the electrostatic and electromagnetic fields surrounding an antenna.

pre-amplifier. An auxiliary amplifier, usually located near the camera in order to minimize effects of noise pickup.

pre-emphasis. The increasing of the relative amplitude of the higher audio frequencies in order to minimize the effects of noise during transmission.

projection receiver. A television receiver in which the image is optically enlarged and projected onto a screen.

projection television. A combination of lenses and mirrors which project an enlarged television picture onto a screen.

raster. The pattern obtained when the electron beam sweeps across the screen vertically and horizontally without being modulated.

R-C circuit. A circuit consisting of a combination of resistors and capacitors. The time constant of such a circuit is the product of the resistance and capacitance.

resolution. A measure of the ability of a system to reproduce small details.

resolution chart. A pattern of black and white lines used to determine the resolution capabilities of equipment.

return trace. Lines on the cathode-ray screen formed by the beam when it moves back to its starting position.

0 sawtooth. A voltage or current whose variation with time follows a sawtooth configuration.

sawtooth voltage. A voltage that varies between two values at regular intervals.

Since the voltage drops faster than it rises it gives a waveform pattern resembling the teeth of a saw. Used in television to help form the scanning raster.

scanning. The process of breaking down a picture into elements by means of a moving electron beam.

scanning line. A horizontal line, whose width is equal to the diameter of the scanning electron beam, composed of elements varying in intensity.

scanning raster. See raster.

Schmidt system. An optical system adapted for television projection receivers in which the light from the image is collected by a concave mirror and directed through a correcting lens onto a screen.

second anode. The positively charged electrode in the electron gun which accelerates the beam.

serrated vertical pulse. A vertical pulse broken up into shorter duration pulses so that the horizontal oscillator does not fall out of synchronization during the vertical sync interval.

shading. The process of correcting for distorted light distribution in the image by injecting a voltage into the signal.

side bands. The radio frequencies on each side of the carrier produced by modulation.

signal. An electrical wave.

spot. The point of light produced by the electron beam as it strikes the fluorescent screen.

stagger tuning. The tuning of amplifier stages to slightly different frequencies in order to obtain broad-band response.

sweep. The uniform motion of the electron beam across the face of the cathode-ray tube.

synchronization. The process of maintaining the frequency of one signal in step with that of another.

synchronizing generator. An electronic generator which supplies synchronizing pulses to television studio and transmitter equipment.

sync pulses. Pulses transmitted as part of the video signal for the purpose of synchronizing the sweep circuits in the receiver with those in the transmitter.

station selector. The switch or tuning element in the receiver which is used to select the desired television signal.

tearing. An effect observed on the screen when the horizontal synchronization is unstable.

television channel. The group of frequencies allotted to a television station for the transmission of the sound and picture signals.

test pattern. A geometric pattern containing a group of lines and circles, used for testing the performance of a receiver or transmitter.

turnstile antenna. One or more layers of crossed horizontal half-wave antennas arranged vertically on a mast, resembling an old-fashioned turnstile. Used in television and other ultrahigh-frequency systems where a symmetrical radiation pattern is desired.

vertical blanking pulse. A pulse transmitted at the end of each field to cut off the cathode-ray beam while it is returning to the top of the picture for the start of the next field.

vertical centering control. The potentiometer in the vertical positioning circuit which raises or lowers the entire image on the screen.

vertical hold control. A potentiometer which varies the natural frequency of the vertical sweep oscillator to enable it to synchronize with the applied sync pulses.

vertical resolution. A measure of the ability of a system to reproduce fine horizontal lines.

vertical scanning. The motion of the electron beam in the vertical direction.

vestigial side-band transmission. A type of transmission in which one side band is suppressed to limit the bandwidth required.

video. Latin meaning "I see". video amplifier. A wideband amplifier for the video frequencies. In a television receiver, this term generally refers to the amplifier located after the second detector and whose frequency response extends from approximately 30 cycles to about 4 megacycles.

video frequency. The frequency of the signal voltage containing the picture information which arises from the television scanning process. In the present television system, these frequencies are limited to 4 mhz.

view finder. A term applied to an attachment to a television camera to enable the cameraman to observe the area covered by the camera.

viewing screen. The face of a cathode-ray tube on which the image is produced.

video transmitter. The radio transmitter used for transmitting the picture signal.

width control. The control in the horizontal sweep circuit which varies the size of the picture in the horizontal direction.

yoke. A set of coils placed over the neck of a cathode-ray tube which produce horizontal and vertical deflection of the electron beam when suitable currents are passed through them.

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