Hellschreiber

Hellschreiber
Frequencies	3 MHz,30 MHz
Frequency Range	3 MHz - 30 MHz
Mode	USB
Modulation	OOK,FSK,MSK
ACF	—
Emission Designator	—
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.