Several communication modes allow amateurs to exchange still or moving images over the air. Advances in technology have brought the price of image transmission equipment within reach of the average ham’s budget. This has caused a surge of interest in image communication.
Amateur TV (ATV) is full-motion video over the air, sometimes called “fast-scan TV.” Amateur Radio communication takes on an exciting, new dimension when you can actually see the person you’re communicating with. In addition, ATV has proved to be very useful in emergency and disaster communication situations.
Amateur groups in some areas have set up ATV repeaters, allowing lowerpower stations to communicate over a fairly wide area. Since this is a wide-bandwidth mode, operation is limited to the UHF bands (70 cm and higher). Digital ATV folds nicely into a recent Amateur Radio technological initiative called high-speed multimedia (HSMM) radio.
The ham bands above 50 MHz can support computer-to-computer communication at speeds high enough to support multimedia applications — voice, data and image. One approach adapts IEEE 802 technologies, particularly 802.11b, operating on specific Amateur Radio frequencies in the 2400- 2450 MHz band.
SSTV or “slow-scan TV” is a narrow-bandwidth image mode that has remained popular for many years in Amateur Radio. Instead of full-motion video, SSTV is for the exchange of photographs and other images. Individual SSTV pictures take anywhere from 8 seconds to about 2 minutes to send depending on the transmission method. These days most SSTV operation is done in color using computers and soundcards. Images are converted into a series of audio tones representing brightness level and colors. Since SSTV is a narrowband mode, it is popular on HF on the same frequencies used for voice operation.