ARRL

Image Modes

Overview

Before the advent of digital transmission modes, several analog schemes were developed to transmit images or image-like information on the Amateur Radio bands.

  • ATV (Amateur Television) refers to "fast-scan" television transmitted in real time using wideband modulation methods, generally compatible with consumer TV standards.  Originally that was NTSC in the U.S., but some hams are now working on communications with the latest digital TV standards. For further information, see the ATV page.
  • Hellschreiber and variants were an early text transmission mode.  A line of "printed" text would be scanned into a series of lines, much as a TV picture or FAX image is scanned.  The picture data is sent as a series of white and black pixels, line by line.  At the receiving end, the process is reversed, and the result is presented to the recipient as a simple image of a line of text.
  • SSTV (Slow Scan Television) is a method of sending good quality photographic images, monochrome or color, using a voice channel, typically an SSB transmitter on the HF bands. The visual data is used to frequency modulate an audio carrier.  For further information, see the SSTV page.
  • WEFAX (Weather Facsimile) is a system for broadcasting weather images from satellites or other stations.  WEFAX uses a modulation scheme similar to SSTV.  Hams use it to receive weather information, but it is not a standard Amateur transmission method.

Web Links

Hellschreiber

WEFAX