Hellschreiber

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Hellschreiber
Feld Hellthmb.jpg
Frequencies 3 MHz,30 MHz
Frequency Range 3 MHz - 30 MHz
Mode USB
Modulation OOK,FSK,MSK
ACF
Bandwidth 350 Hz,800 Hz
Location Worldwide
Short Description Hellschreiber (Also known as Feld Hell or just Hell) is a teleprinter system developed in the late 1920's by Rudolf Hell, a German inventor.
I/Q Raw Recording
Audio Sample

Hellschreiber (Also known as Feld Hell or just Hell) is a teleprinter system developed in the late 1920's by Rudolf Hell, a German inventor. Hell physically prints characters onto the screen, unlike other modern teletype modes which encode and decode signals.

Feld Hell (and it's immediate variants) and Slow Hell use On-Off Keying, where Feld Hell 80 (Rudolf Hell's last original Hell mode, designed in the 1970's) uses 2-FSKFrequency-Shift Keying modulation and the FSKFrequency-Shift Keying Hell modes use 2-DMSK (Differential Minimum Key Shifting).

Mode Symbol Rate Typing Speed Duty Cycle Modulation Bandwidth ITU Designation
Feld-Hell 122.5 baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. ~2.5 cps(25 wpm) ~22% OOKOn-Off Keying Modulation ASKAmplitude-Shift Keying 350Hz 350HA1B
Slow Hell 14 baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. ~0.28 cps(2.8 wpm) ~22% OOKOn-Off Keying Modulation ASKAmplitude-Shift Keying 40Hz 40H0A1B
Feld-Hell X5 612.5 baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. ~12.5 cps(125 wpm) ~22% OOKOn-Off Keying Modulation ASKAmplitude-Shift Keying 1750Hz 1K75A1B
Feld-Hell X9 1102.5 baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. ~22.5 cps(225 wpm) ~22% OOKOn-Off Keying Modulation ASKAmplitude-Shift Keying 3150Hz 3K15A1B
FSKFrequency-Shift Keying-Hell 245 baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. ~2.5 cps(25 wpm) ~80% 2-MSKMinimum-Shift Keying (When Shift/Bd = 0.5. It is impossible to get this ratio to be lower than 0.5, hence it is called the 'Minimum' shift.) 490Hz 490HF1B
FSKFrequency-Shift Keying-Hell 105 105 baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. ~2.5 cps(25 wpm) ~80% 2-MSKMinimum-Shift Keying (When Shift/Bd = 0.5. It is impossible to get this ratio to be lower than 0.5, hence it is called the 'Minimum' shift.) 210Hz 210HF1B
Hell 80 245 baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. ~5.0 cps(50 wpm) 100% 2-MSKMinimum-Shift Keying (When Shift/Bd = 0.5. It is impossible to get this ratio to be lower than 0.5, hence it is called the 'Minimum' shift.)(480Hz) 800Hz 800HF1B

Modulation details[edit]

The signal is transmitted in columns. The receiver generally displays each column twice, one below the other. This is done to mitigate the skew that can be cause by timing errors.

Each column is sent on equal time slices, and the time it takes to send one column depends on the variant. Here’s a small table that shows this.

Mode Column time (seconds)
Feld-hell 1 / 17.5
Slow hell 1 / 17.5 * 8
Feld-hell X5 1 / 17.5 / 5
Feld-hell X9 1 / 17.5 / 9

It can be seen from this table that the default method transmits 17.5 columns in one seconds, the faster modes are 5 and 9 times faster, and the slower mode is 8 times slower. A small disclaimer is that I have only tested these values by using software decoders made by other people, since I don’t have a real machine.

The faster variants use more bandwidth and are less resistant to noise, while the slower variants become narrow signals that can be decoded with plenty of noise. If you know the conditions beforehand, you can make a good tradeoff in order to transmit your signal as fast as possible without making it unintelligible.

If the signal is being generated as sound, it needs to be put on a carrier frequency. 1500 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). can be a good default.

Samples[edit]

Feld Hell Feld Hell 80 Slow Hell
Feld Hell.jpg
HELL 80.jpg
Slow Hell.jpg

FSKFrequency-Shift Keying Hell 245 FSKFrequency-Shift Keying Hell 105 FMFrequency Modulation Hell
FSK HELL.jpg
FSK HELL 105.jpg
FM HELL.png

Feld Hell x5 Feld Hell X9
Feld Hell X5.jpg
Feld Hell X9.jpg

Decoding Software[edit]

Hobby Level Software

Additional Links[edit]

Additional Images[edit]