Abbreviation for Concurrent Multi-tone Hell.
An amateur radio facsimile mode, which is a variant of Hellschreiber.
Instead of the original 7 pixels per column, the text is transmitted in a grid 5
pixels high. Whereas the original Hellschreiber transmit all information
on the same frequency, and sends each pixel sequentially from low to
high, C-MT Hell sends each pixel with different frequencies, ranging
from a low frequency for the lowest pixel, to a high frequency for the
highest pixel. All pixels in one row are transmitted simultaneously.
Although C-MT Hell is sent and received with special software, it has
the amusing property of being able to be read directly from a standard
waterfall display.