Editing Slow-scan television (section)

===Progression===
Commercial systems started appearing in the United States in 1970, after the [[Federal Communications Commission|FCC]] had legalized the use of SSTV for [[Amateur radio licensing in the United States|advanced level]] amateur radio operators in 1968.

SSTV originally required quite a bit of specialized equipment. Usually there was a scanner or camera, a modem to create and receive the characteristic [[sound reproduction|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 about ten seconds.

The [[modem]] would generate audio tones between 1,200 and 2,300&nbsp;Hz from picture signals, and picture signals from received audio tones. The audio would be attached to a radio [[receiver (radio)|receiver]] and [[transmitter]].