Radiofax, also known as Weatherfax and HF fax due to its common use in 

the HF bands (shortwave), is an analogue mode for transmitting images 

in grayscale. It was the predecessor to slow-scan television (SSTV).



Radiofax is transmitted in single sideband and uses frequency modulation. 

The signal shifts up or down a given amount to designate white or black 

pixels.



Numerous WEFAX transmissions can be found in the 19MHz to 21MHz band.