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Feld Hell hints
Hellschreiber means 'Hell's writer'. The technique was developed by Rudolf Hell in 1927, and was used as a successful radio mode first in 1937, well before RTTY. All Hellschreiber or Feld Hell (FH) 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 since they use no sync and the eye can discern the text even in high levels of noise. One unique aspect of the FH modes is that the video font is determined by the sending station. You can clearly see the different fonts in the screen capture.
fldigi supports several different FH submodes:
| Mode | Symbol Rate | Typing Speed | Duty Cycle | Modulation | Bandwidth | Sideband Sensitive | ITU Designation |
|---|---|---|---|---|---|---|---|
| Feld-Hell | 122.5 baud | ~ 2.5 cps (25 wpm) | ~ 22% | OOK ASK | 350 Hz | no | 350HA1B |
| Slow Hell | 14 baud | ~ 0.28 cps (2.8 wpm) | ~ 22% | OOK ASK | 40 Hz | no | 40H0A1B |
| Feld-Hell X5 | 612.5 baud | ~ 12.5 cps (125 wpm) | ~ 22% | OOK ASK | 1750 Hz | no | 1K75A1B |
| Feld-Hell X9 | 1102.5 baud | ~ 22.5 cps (225 wpm) | ~ 22% | OOK ASK | 3150 Hz | no | 3K15A1B |
| FSK-Hell 245 | 245 baud | ~ 2.5 cps (25 wpm) | ~ 80% | 2-MSK6 | 490 Hz | yes | 490HF1B |
| FSK-Hell 105 | 105 baud | ~ 2.5 cps (25 wpm) | ~ 80% | 2-MSK6 | 210 Hz | yes | 210HF1B |
| Hell 80 | 245 baud | ~ 5.0 cps (50 wpm) | 100% | 2-FSK (480Hz) | 800 Hz | yes | 800HF1B |
FH video is normally black pixels on a white background. The FH modes that are sideband sensitive have the effect of reversing the image, white on black background if the sending and receiving stations are on opposite sidebands. Tuning the signal is not as critical as in some digital modes, but the mistuned signal will suffer a loss in signal-to-noise ratio. This is especially noticeable if you are participating in a FH net.
You will find FH activity on most bands. There is a Feld Hell Club with more than 6500 members, some of whom meet for a weekly schedule on 40 meters.
- submode: FH-105
- 7089.0 USB transceiver frequency
- 1500 Hz waterfall sub-carrier
- Thursday evenings, 2100 EST
- check-in sending CALL 3 times
- recommended font: fat 14, gives best visual s/n
- disable transceiver RIT, or CLARIFIER
- disable transceiver XIT
- the net control will transmit an RsID signal; other stations should enable RsID decoding; disable RsID transmission.
- fldigi users: make sure the Rev is disabled, refer to fldigi Feld Hell Help for configuration and operating help.
There are usually some early check-ins starting at 2030 EST.
The FH Club also has an active membership group on groups.io.
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