Slow-Scan Television (SSTV)
SSTV is a mode that uses a computer and an amateur radio transceiver to send and receive still images over radio. SSTV was originally an analogue mode based on Frequency Modulation (FM). Digital SSTV has become possible with little trouble in recent times with the use of Digital Radio Mondiale (DRM). Despite the name "television", SSTV cannot send or receive moving pictures; it is more akin to sending a FAX.
For SSTV to work, an image is "broken" into lines, composed of dots of colour and light intensity known as pixels.
Each pixel is given a specific audio frequency ( that modulates the carrier) depending on its brightness. In a colour image, each of the primary colours, red green and blue are analysed for brightness.
The lines of a picture are scanned from left to right. The modulating frequency varies between 1500Hz and 2300 Hz. There are a number of modes used for SSTV
- see below for information. Computer software attaches a Vertical Interval Signaling (VIS) code at the start of a picture being sent. this enables receiving software to determine which mode is being used, and hence permits successful decoding of the signal.
The colour and brightness information modulates a carrier wave for transmission. A remote station picks up the signal and a computer is used to re-create the picture from the FM signal.
SSTV should not be confused with amateur Fast-Scan Television, often simply called Amateur Television or ATV
Source: Slow-Scan Television (SSTV) - Amateur Radio Wiki
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