Introduction to Hellschreiber Modes

Feld-Hell     PSK- & FM-Hell     MT-Hell     Fuzzy Philosophy      Mode Summary


Radio communications, like most things in this world, would appear to come in two forms, analogue and digital. Analogue refers to things that have smoothly varying properties that are not easily expressed in numbers; for example human speech, time read from a clock with moving hands, and almost all natural processes. Digital refers to things that can be defined in steps - on and off, pass and fail, stop and go, up and down, day and night, integer numbers.

The radio spectrum is filled with analogue and digital signals. AM and FM broadcast radio, standard TV, SSB transmissions and noise, both man-made and natural, are analog transmissions; while radio teletype (RTTY), PSK31, DRM, satellite and terrestrial HDTV broadcasting, cellular phones and a whole range of data communication, radio control and telemetry applications involve digital transmissions. (By the time the signals are passed through the atmosphere and received, they may be more analogue than digital, but that's another story!)

These days digital is considered trendy - computers, HDTV, CD and MP3 music, telephones, clocks - but humans are not digital animals. All our senses - feel, sight, smell, taste and sound - are analogue in nature. Consequently we do not relate easily to the digital world. We relate best to information presented in an analogue manner. So welcome to the world of Fuzzy modes! 'Fuzzy' is a term I coined back in 1998 to describe radio modes which use digital transmissions but employ human-readable reception.

These Fuzzy modes have unusual characteristics, and some very real benefits. See the Philosophy of Fuzzy Modes page for further information. Hellschreiber, and related modes, to which these pages are dedicated,are generally digitally transmitted, but are analogue, human readable, uncoded, direct viewing or printing modes, and so are truly 'Fuzzy'.

By the way - Morse may be considered a Fuzzy mode. To experts it is not coded, rather it is a natural language. The signal is read from the receiver without any change to time of arrival of data or content of data. Computer reception of Morse, which requires electronic decisions, must always perform worse than a human expert, and also worse than some modes especially designed to be machine readable.


Most digital communications modes are intended to be read by a mechanical or electronic machine. There are however a few machine generated communication modes intended to be human readable. These include Morse, FAX, SSTV and NBTV. These pages are dedicated to the least known of visual human readable modes, the Hell family.

Hellschreiber describes a method of sending text by radio or telephone line, that involves dividing each text character into little pieces, then sending these digitally. Hellschreiber is a German name, meaning "bright writing", or "clear writing", and may be a pun on the name of the inventor, Rudolf Hell, who patented Hellschreiber in 1929.

The first major application of Hellschreiber was transmission of text for newspapers by telephone line in the years before World War II. Hell's invention was thus the world's first widely used and practical facsimile machine. War-time machines were more portable, and intended for use with field telephones and radio equipment.Later, Hell page printers were developed.

Print from a wartime mechanical Hellschreiber
Print from a wartime mechanical Hellschreiber

The traditional method of sending Hellschreiber by radio is to key a Morse-type (CW) transmitter ON for every black spot in a text character,and OFF for every white place. Different parts of each character are sent at different times. The technique is still in use by interested Amateurs, communicating world-wide. This mode is now called Feld-Hell (Field-Hell), since the pre-war format still used was originally used for field communications by the German Army. Feld-Hell offered good immunity to interference and provided a clandestine transmission capability, because nothing was transmitted until a key was pressed. Commercial variations of Feld-Hell could still be heard occasionally on HF up until the 1980s, transmitting Chinese and Korean characters.

G3PLX working PA3BQS in Feld-Hell

After Radio teletype took over on HF, Hellschreiber was almost completely lost and forgotten, but for a group of dedicated German and Dutch Amateurs who restored and used war-time equipment, and ultimately it was popularized by significant software developments in the 1980s and 1990s.


It is also possible to transmit text information by sending the dots using some other property of the transmitter carrier, for example phase (PSK-Hell) or frequency (FSK-Hell and FM-Hell). Alternatively, different parts of each character can be sent on different frequencies. This latter technique uses the frequency domain, as opposed to the more conventional time domain. This type of transmission is known as Multi-Tone or MT-Hell. Until recently, it was thought that MT-Hell was a 1990's invention, but we now know it was described in 1937!

Feld-Hell, PSK-Hell, FM-Hell and MT-Hell are all in use on the amateur bands. With all these modes long distance DX is practical, and has a similar 'feel' to Morse QSOs.

Feld-Hell is especially useful in poor conditions when other modes are ineffective - especially just after a magnetic storm when the ionosphere is lively but unstable. FM-Hell is best for very weak signal DX, and is not seriously affected by the Doppler problems that limit PSK31. MT-Hell lacks sensitivity unless very slow, but is excellent on LF, MF and low HF where atmospheric noise is the limiting factor. Very slow sequential-tone MT-Hell (one dot per second!) is popular for low power propagation tests.

MOSAIC II (Sequential MT-Hell), 20 Hz row spacing, full duration white pixels, received 15 dB above the noise on 3.5 MHz at 18 pixels/second
Sequential MT-Hell on 80m at 18 pixels/sec

Most of the known Hell modes are described in the Mode Summary.


The technical specifications of Feld-Hell and MT-Hell are not especially complicated. The PDF document (133kb) does not include specifications for PSK-Hell or FM-Hell.


  • ZL/VK: 3550 kHz or 3560 kHz LSB (SSB, Hell and you name it!) at 8:30 pm, most nights, especially Fridays
  • Europe: 3579 kHz at 2130 UTC Tuesdays, 7037 kHz Sundays at 1200 UTC, and 3579 kHz Sundays at 1530 UTC.
  • DX Hell: 14.071 - 14.075 MHz, 18.104 - 18.107 MHz or 21.063 - 21.070 MHz, 24 hours/day! Calling frequency 14.073 MHz carrier. USB operation is conventional (affects FM-Hell, MT-Hell and Duplo-Hell).
    DX contacts can also be arranged by email, via the Hell Reflector, or by commandeering PSK31 stations!
  • A Feld-Hell Contest is hosted by the DARC each October.

You too can enjoy 10,000 km Hell contacts as good as this!

Copyright Murray Greenman 1997-2009. All rights reserved. Contact the author before using any of this material.