How a Television Works
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How a Television Works
First, a video camera is used to record the image and a sound recording system, which may be built into the camera, records the sound. The light in the setting bounces off the actor or object being recorded and into the video camera. The image goes through the lens and onto a wire-meshed target plate where an electron gun scans the image in lines. In color cameras, the scanned image then hits color-filtering mirrors of the three primaries.The way a television works is actually quite simple. Below is a summary of how an image shows up on your television set.
Next, the scanned image in all three colors is transmitted to an encoder, which may be separate from the camera. The encoder combines the three primary color information into one signal, which is then transferred to a transmitter, joining this signal with that of the recorded sound, which has been amplified.
The signal then is broadcast from an antenna. Although satellites may be used to transfer it, the combined color and sound signal will eventually reach the receiving antenna on your home.
From here, the signal goes down into your living room and goes through a tuner. The tuner splits the sound and color signals apart. The sound, or audio signal is then amplified and comes out your speaker. Simultaneously, the color signals are fed into a decoder and then into the tube of your television set.
Here, electron guns of the three primaries fire electron beams through a shadow mask onto a phosphorous-coated screen. The shadow mask is what makes the television image appear to be made of spots when closely examined. The electron guns rapidly change the position and color of the dots, creating the illusion of a moving picture.
IMAGES FROM: Microsoft Encarta '96 Encyclopedia CD-ROM
Camera Tubes
Although this page is about television, the video cameras have much to do with how the television processes images. Many different camera systems have been developed over the years. However, there are only five main ones which were or are popular. Below is a chart of these camera tubes and a description of how they work.
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The iconoscope was invented by Viadimir Zworykin in 1929. It consists of a mica plate, which has one metal-plated side and the other a mosaic. This mosaic is made of metal, which releases electrons when exposed to light. It makes up a series of mini condensers, which are bombarded by the electron beam. |
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The super iconoscope was invented in 1939. The image falls onto a transparent, photoelectric surface, producing an electron beam. This beam then hits the mosaic, scanning it. |
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The orthicon was invented in 1939. Its target also used a mica sheet between a conducting surface and a photoemissive surface. The beam is perpendicular t the mosaic and hits it at a slow speed. |
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The image orthicon was invented in 1946. Under light, the photosensitive coating releases electrons, which hit two more targets and are scanned. |
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The Vidicon was created in 1951 and has a photoconductive target, which measures illumination better. It contacts a metallic coating which produces the signal and will or won't let electrons through depending on the amount of lighting. All camera tubes used today are based on the Vidicon model. |