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C/MT & S/MT Hellschreiber
Concurrent Multi Tone Hell
C/MT-Hell was first demonstrated in 1937. Peter G3PLX recently developed an FFT receiver to display the signal, and a few other programmers have followed suit. All rows of each character are transmitted at the same time using different tones. High resolution is possible allowing elaborate fonts to be used. The system is very interference immune.
But for my experiences it neither is a Sensitive mode
S/MT HELL
Sequential Multi tone Hell
A invention by Nino Porcino ZL1BPU , S/MT-Hell is a compromise between Feld-Hell and C/MT-Hell. Like Feld-Hell, the characters are transmitted in a matrix in same sequence, but different tones are used for each row of dots in the character. The font is restricted to 7 x 5 and the white dots can be left out of it , since the reception is in the frequency domain using an FFT receiver . S/MT-Hell is very effective on noisy bands and may provide better sensitivity that C/MT-Hell.