| Slow-scan Television |
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EARLY ORIGINS SSTV was used extensively during the early years of the NASA Apollo program to transmit images to Earth, and the first images from '' Apollo 11 '' on the Moon were SSTV. NARROW BANDWIDTH Broadcast Television requires huge 5, 6 or 8 MHz wide channels, because it transmits 25 or 30 pictures per second (in the NTSC , PAL or SECAM systems).
HARDWARE ORIGINS SSTV originally required quite a bit of specialized equipment. Usually there was a scanner or camera, a modem to create and receive the characteristic Audio howl, and a Cathode Ray Tube from a surplus Radar set. The special cathode ray tube would have "long persistence" Phosphor s that would keep a picture visible for a minute or so. The Modem would generate audio from pictures, and pictures from audio. The audio would be attached to a radio Receiver and Transmitter . The modern system uses a Personal Computer and special Software in place of much of the custom equipment. The audio system of a PC, with special processing software, acts as a modem. The Computer Screen provides the output. A small Digital Camera or digital photos provide the input. Since SSTV produces and generates audio, amateurs use it on Shortwave , VHF and UHF radio. REFERENCES
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