FLDIGI Users Manual  3.21
Hellschreiber

Table of Contents

Hellschreiber modem

All Hellschreiber modes are based on character scanning, reproducing characters in a similar way to a dot-matrix printer. This technique uses a digital transmission, yet allows the received result to be interpreted by eye, a similar concept to the reception of Morse by ear. The character is scanned upwards, then left to right. There are typically 14 pixels (transmitted dot elements) per column (although single pixels are never transmitted) and up to seven columns per character including inter-character space.

These remarkably simple modes are easy to use, easy to tune, and although not especially sensitive, are entirely suited to HF/VHF since they use no sync and the eye can discern the text even in high levels of noise. fldigi can operate in the following :

Hellschreiber modes

Mode Symbol Rate Typing Speed Duty Cycle Bandwidth
Feld-Hell 122.5 baud ~ 2.5 cps (25 wpm) ~ 22% 350 Hz
Slow Hell 14 baud ~ 0.28 cps (2.8 wpm) ~ 22% 40 Hz
Feld-Hell X5 612.5 baud ~ 12.5 cps (125 wpm) ~ 22% 1750 Hz
Feld-Hell X9 1102.5 baud ~ 22.5 cps (225 wpm) ~ 22% 3150 Hz
FSK-Hell 245 baud ~ 2.5 cps (25 wpm) ~ 80% 490 Hz
FSK-Hell 105 105 baud ~ 2.5 cps (25 wpm) ~ 80% 210 Hz
Hell 80 245 baud ~ 5.0 cps (50 wpm) 100% 800 Hz

Hellschreiber Waterfall

Feld-Hell look like this when being received by fldigi:

feld-hell.png
Feld-Hell, Slow Hell, Feld-Hell X5, and Feld-Hell X9 are all pulse

Feld-Hell seems to be the most commonly used and use can usually be found on 80 and 40 meters at the high end of the digital sub bands. Extreme linearity is required in the transmit path in order to control the bandwidth of the transmitted signal. Feld-Hell X5, Feld-Hell X9 and Hell 80 should probably not be used on HF in the US. They can be used on VHF and UHF.


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