A Glossary of Television Terms & Definitions – Spouting Off!
Have you ever tried to listen to your television repairman tell you about your television? I bet you’ve marvelled at the strange words coming out of his mouth. It sounds like a completely different language, doesn’t it? Well, you don’t have to worry about that problem anymore. Take a moment to look over these common terms of the television world and the next time your repairman starts spouting off things like “progressive scan” and “cathode ray tube”, you’ll know exactly what he (or she!) is talking about.
An Analog transmission is a continuously variable transmission. This means that the signal bounces around on its bandwidth as opposed to being rounded up or down numerically to fit a specific design. A good example of this is in colour television systems, where an analog signal can produce virtually any shade of colour. In contrast, a non-analog system in a colour television would have a set variance of colours that it had to choose from, and anything that didn’t exactly fit its predetermined frequencies would have to be rounded up or down in order to fit the system.
An Anode is the opposite of a cathode, and makes up part of a Cathode Ray Tube. The positively charged anode attracts the stream of negatively charged electrons and compacts them into a compressed beam. A second anode then accelerates them, and the electron beam is then ready to be projected at the phosphor display screen.
A cathode is the opposite of an anode. A cathode in a television is essentially a filament coated in a substance that gives off negative electrons when heated. In many ways, the filament is like the filament on a light bulb.
- Cathode Ray Tube
The Cathode Ray tube is the heart, soul, and guts of any standard television set. The CRT is the picture tube used in all television and monitor sets that require a scanning tube. In a CRT, “Cathode” is the device used for creating negative charged electrons, “Ray” is the beam of electrons shot toward the display screen, and “Tube” is the glass vacuum that houses the device.
- Chrominance Signal
The Chrominance signal is the colour information broadcast to televisions in order to display the proper colours on the screen. The chrominance signal is created by adding a 3.579545 MHz sine wave to a monochrome television signal. The signal is ignored by monochrome television receivers, but is picked up and decoded by a colour set as part of the broadcast. The colours are shifted by degrees, and usually come in pairs to graph the full colour spectrum.
The F.C.C. stands for the Federal Communications Commission. The F.C.C. is the final authority on North American broadcasting, and handles rulings on how television (among other things) is to be packaged to the public. It also acts as a mediator in cases where disputes arise between broadcasting companies.
- Frame Rate
The frame rate is the rate at which still images are shown on a screen in order to achieve a full-motion effect. A slow frame rate makes for a flickering, stuttering image. A fast frame rate improves the image quality of a motion sequence. Generally, 15 frames per second is the minimum amount for avoiding motion problems. Any less, and the motion sequence begins to flicker. Standard televisions these days display between 30 (interlacing) and 60 (progressive) images per second.
HDTV stands for High Definition Television. HDTV is essentially a high-resolution digital image with Dolby Digital Surround Sound. The broadcast and reception of pure digital broadcasts (DTV) are being pushed heavily by people in the television industry today, and it is possible that in the near future all broadcasts will be a digital format resulting in no loss of signal or quality. Where a standard television in the United States has around 525 lines of resolution refreshed 30 times a second, HDTV could provide amazing clarity with 700 or even 1000 lines of clarity refreshed 60 times a second.
- Horizontal Retrace
The term Horizontal Retrace is used to describe the movement of the scanning electron beam in a cathode ray tube as it travels from the right to the left. The scanning beam begins on the left side of the screen, and when it is finished with the line it switches off, drops down, and moves back to the left side of the screen to start another line.
- Horizontal Retrace Signal
The Horizontal Retrace Signal is part of a television broadcast signal that tells the receiving television where to stop scanning (at the end of a line) as well as where to re-align itself on the left side. In a television broadcast signal this is one of several parts used by the television to display the images being sent.
The Iconoscope is one of the first television “cameras” developed by Russian inventor Vladimir Zworykin in the early days of television. This early camera tube was equipped for rapid scanning and information storing of the photoactive mosaic that was to become the television broadcast. Equipped with the iconoscope and a cathode ray tube, Zworykin and RCA officially launched the television industry in 1931.
- Image Dissector
The Image Dissector was invented by Philo Farnsworth in the early days of television development. Essentially, based on the charge it collected, the device was able to recreate an image placed in front if it. It was an important step in the development of signal transfer for television devices, but was a poor conductor and needed very high light levels to work properly.
- Intensity Information
Intensity information is part of a television broad cast signal. The intensity information sent to televisions tells the electron beam how bright or dim a group of phosphors need to be for the image to be viewed properly. This is essential for proper reconstruction, and also helps with colour construction as it tells the electron beams the proper intensity for each colour. Without intensity information, all the blues on a screen would be the same colour and intensity, as would all the reds, etc.
Interlacing refers to the scanning format of standard television screens. In an interlace format, the entire screen is painted with the electron beam, but in alternating lines. On the first pass the odd-numbered lines are painted, and then the beam makes a second pass to paint the even–numbered lines. In the United States, standard televisions have 525 lines of resolution and the screen is refreshed 30 times a second. This means an interlacing beam paints over 15,000 lines a second.
The Kinescope was inventor Vladimir Zworykin’s version of a cathode ray tube. Armed with a kinescope and his patented iconoscope camera tube, Zworykin and RCA spawned the birth of the television industry.
The Klystron is an electron tube that makes use of velocity modulation in order to amplify or create ultra high frequency waves. As well as being instrumental in the advent of Doppler radar (which was, in fact, the invention that lead to the defeat of the Axis powers in World War Two) the Klystron was instrumental in the development of high frequency broadcasting, which made large-scale broadcast television possible.
Monochrome is a term used to describe black and white televisions. It can be broken down into “mono” meaning one and “chromatic” which means colour. It is literally “one colour”. This is because black and white cathode ray tubes are painted with white phosphors only. Painting the white phosphors with the electron beam makes them give off white light, and by switching off the beam a black effect is achieved. Black and white is a bit of a misnomer then as there is really only one colour differential on a monochrome screen. A better name than “black and white” would be “light and dark”.
Mpeg-2 is a compression format for digital information that is used by broadcasters and DVD manufacturers to compress the additional picture detail and digital surround sound into the standard 6 MHz bandwidth used by analog televisions. In each image, mpeg-2 compression records just enough detail to keep the image from breaking up, while in subsequent images only the changes are recorded. Mpeg-2 layering allows the information to be compressed at a ratio of 55 to 1.
NTSC stands for the National Television System Committee. The National Television System Committee set the broadcast standards for the 525 line 60-frame standard for television broadcasting in early 1950s. The NTSC format, used almost exclusively in North America and Japan, breaks the 525 lines down into 480 lines of image and the remaining 45 lines contain synchronizing information, closed caption text, and a time delay sequencer that allows the electron beam time to refresh back to the top-left side of the screen when it has completed a full sweep of the screen.
PAL stands for Phase Alternate Line. PAL is the standard broadcast protocol for televisions outside of North America and much of Japan. PAL is comprised of a 625 line 50-interlaced fields per second format that is used to reduce artifacts on screen (left over pixels that form objects that interfere with the picture). Phase Alternate Line is so-called because of how the chrominance signal is phase reversed on every other line, in between the spaces on an interlacing signal.
- Progressive Scan
A Progressive Scan is an improved scanning format for television systems. Where a standard television uses an interlacing format (alternating lines 60 times a second, creating a full image 30 times a second) higher market televisions and digital television systems use progressive scanning in which the television scans all the lines on the television in succession, and does a full screen 60 times a second. The result is a doubling of the frame rate and drastically improved picture quality.
- Shadow Mask
A Shadow Mask is a metal plate filled with holes that perfectly match the phosphor groupings in a colour television. The shadow mask, or aperture grill as it’s sometimes known, is used to keep the electron beams from straying into other phosphor groupings in a colour cathode ray tube. Often the shadow mask is installed as part of the phosphor addition process because the tiny holes need to be perfectly aligned. A slight variance in the position of the shadow mask can greatly affect screen performance.
- Steering Coil
A Steering Coil in a television is simply a large bind of copper wire that is hooked up to the power supply, effectively creating an electromagnet. There are 2 steering coils in a television: the first one is used to control horizontal direction of the electron beam and the second is used for vertical control. Since the electron beam in the cathode ray tube carries a negative charge, it can be directed by manipulating the magnetic fields that the steering coils produce. Using this vertical and horizontal directional system the electron beam can be pointed at any space on the television screen.
UHF stands for Ultra High Frequency. The F.C.C. sliced three bands of radio spectrum into television frequencies, and they broke down as follows:
- 54 to 88 MHz for channels 2 to 6
- 174 to 216 MHz for channels 7 to 13
- 470 to 890 MHz in UHF for channels 14-83
These UHF frequencies have been widely abandoned by television broadcasters and television sets are no longer required to pick them up. UHF is now mainly the domain of devices such as cell phones, which tend to broadcast in the 316 MHz to 3.16 GHz range.
- Vertical Retrace
The term Vertical Retrace is used to describe the movement of the electron beam as it makes its way from the bottom right part of the television screen back up to the top of the screen on the left side. The painting beam always finishes in the bottom right corner and always starts again in the top left corner, whether the television is using an interlacing scan or a progressive scan to show the image.
- Vertical Retrace Signal
The Vertical Retrace Signal is the part of a television broadcast signal that tells the electron beam to return to the top left corner of the screen to begin painting again. This is an important part of the television broadcast as it tells the television basically when the new image needs to be started, about 30 times a second.
The language of television can be complicated and frustrating to get a handle on. Who knew that something as technically complex as the television industry would also be hard to understand? For most people, it is simply enough that you push a button and your favourite show comes on. But dealing with television experts can be a confusing hassle when you have no idea what they’re talking about.
Hopefully, these terms help you understand a little more, and get you back to watching your favourite shows in no time flat!
About The Author
Bill Schnarr is a successful freelance writer providing valuable tips and advice for consumers purchasing digital video recorders as well as audio receivers, speakers, magazines & reviews and big screen home theater projectors. His numerous articles offer moneysaving tips and valuable insight on typically confusing topics.
This "Glossary of Television Terms & Definitions" reprinted with permission.
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