Narrow-bandwidth television

The three predominant worldwide broadcast television standards use either 6 MHz wide channels (as in the Americas and Japan, as ATSC and ISDB-T both use those standards) or 8 MHz (as in most of Europe with DVB-T).

Narrow-bandwidth television refers to any method that reduces the bandwidth below that threshold.

When the scan rate is reduced, this is referred to as slow-scan TV or, in the most extreme cases when the scan rate is too slow to simulate motion, freeze frame television.

In the most extreme cases, the number of lines in an image may be reduced to just a few dozen, and bandwidth reduced to a few tens of kilohertz, within the bandwidth of an amateur radio voice channel.

The earliest mechanical television systems often used narrow channels for sending moving images.