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©2007-2010 F. Dörenberg. All rights reserved worldwide. No part of this publication may be used without permission from the author. It has taken considerable effort to create these pages. If you "borrow" content from them, at least reference the source.

[overview]       [character set (font)]      [technology]      [characteristics]       [literature]

This Hellschreiber, a.k.a. "T typ 80", "T App 80", or simply "Hell-80", is the most modern Hellschreiber produced. It is also the world's first fully electronic teleprinter. The initial model (T. typ. 80a, Hell-80a) was intended for both the West-German military (the Bundeswehr) and commercial customers. Its development started in 1958, and a first batch of 15 units was produced early 1961 (ref. 12).

The Hell-80a

(source: ref. 12)

Model T. typ. 80 (Hell-80) was developed only for the Bundeswehr (Bw). After a three-year development period, production started in 1965 at Siemens in Munich. It was used by the Bundeswehr until around 1985. Some 225 units entered service between 1965 and 1975 (ref. 13).

The Hell-80 can be operated in two modes:

	synchronous (like the Feld-Hell, but at twice the number of characters per second: 5 cps instead of 2½), and
	asynchronous (start-stop, like Hell 72 "GL" and 73 "AGL").

Both modes are selectable when operating from the built-in punch tape reader. For keyboard operation, only the start-stop mode is available. As Hell-80 can operate in synchronous mode, its printer has a two-turn spindle and uses 15 mm wide paper tape (like the Feld-Hell); it also uses the same felt ink roller as the Feld-Hell and Hell "GL". As the Hell-80 was designed for military field operations, it is referred to as a "Feldfernschreiber" (field-teleprinter), just like the Feld-Hell from the 1930s-1945.

The Hell-80 - front view

The Hell-80 - opened, showing its modular design

Inside of the cover - spare paper rolls and a compartment for spares/accessories

The list of spares/accessories (110/220 Vac power cable, 24 Vdc power cable, transceiver patch cable, soft cotton cloth, dust brush (goat hair!), ink roller set, fuses, rolls of paper tape)

The spares and accessories
 

A small weak point in the design is the choice of the timing belt (a.k.a toothed, notch, cog, timing, or synchronous belt; D: Zahnriemen, F: courroie dentée) between the speed control knob on the front panel, and the speed regulator module in the back of the machine.

The original belts have a joint that is glued, instead of fused. Sooner or later, such glued joints become undone, as the glue creeps and dries out, and the belt is flexed. The belt has a standard T-profile, a pitch of 5 mm, has 100 "teeth" (hence, 500 mm overall length), and a width of 6 mm. So it is a regular "T5 500 6" belt, and modern replacements either have a fused joint or no joint. I have replaced my broken belt with an  Optibelt ALPHA "T5 500 6". These new belts are not very expensive (€5.50, late 2011 pricing).

The broken joint of the original timing belt

The Hell-80 uses a font raster that is slightly different from the one used by the Feld-Hell and the Hell 72/73. The Hell-80 raster is 7x9, rather than 7x14. For start-stop operation, the first column contains a start-pulse, as for the "GL". The binary form of the Hell-80 font is here.

7x9 font of the Hell-80
(the 5-pixel start-pulse in the first column is only used in start-stop mode)

Print-out of the Hell-80 character set

	Click here for a recording of a real Hell-80 transmissions (both start-stop and asynchronous mode). Recorded 1 March 2010 around 7050 kHz. File size: 13 MB.
	Click here for ca. 4 minutes Hell-80 QSO, start-stop mode, 24-Jan-2011 - Part 1 Click here for a scan of the associated paper tape print-out
	Click here for ca. 4 minutes Hell-80 QSO, start-stop mode, 24-Jan-2011 - Final

Start of the first audio file above - printed with a Hell-80 machine in Start-Stop mode
 

Start of the first audio file above - printed with Multipsk software in synchronous mode

(in synchronous mode, start-pulses are also printed, but the "tape" does not stop after each character; the current version of Multipsk can transmit in start-stop mode; hopefully a future release can also print start-stop...)
 

As indicated above, Hell-80 operates at exactly twice the speed of the traditional Feld-Hell. So if you print Hell-80 signals with a Feld-Hell machine (or software), you will see four lines of text instead of two!

Hell-80 signals printed with Feld-Hell - tuned to the "mark" tone
(sent with Multipsk, printed with IZ8BLY Hellschreiber running on the same PC)

As Hell-80 is FSK, you can actually select between printing white-on-black and black-on-white ("reverse video"), by tuning to the "black" tone or to the "white" tone (300 Hz shift).
 

Hell-80 signals printed with Feld-Hell - tuned to the "space" tone
 

Arie, PE1AQB, has constructed several Hell-80 printers (start-stop). I have posted pictures and info on the Homebuilt Hell-printers page. Alie, PD2ALW, shows his Hell-80 in action in this YouTube video.

HELL-80 START-STOP MODE. The documentation of the Hell-80 does not reveal parameters of the start-pulse detection, nor when (and for how long) the printer is enabled upon detection of a start pulse. Some time after detection of the start-pulse, the shaft of the printer spindle is engaged via an electro-magnetic clutch mechanism, and the printer is enabled via a notch and associated contacts. After 6 revolutions, this shaft is halted. Clearly, the speed of the printer shaft depends on the speed of the local motor. However, the speed at which pixels are transmitted, is entirely independent of the motor speed! Instead, it is driven by a very accurate and stable crystal-clock time-base. This means that the slant of the printed text can be adjusted locally, without receiving text from an other machine!

Arie, PE1AQB, and I decided to run a number of tests, to characterize the timing of the start-pulse detection and printer of the Hell-80 machines. From his other Hell-80 experiments, Arie has a programmable Hell-80 character generator and FSK generator. We defined several dozen very specific test characters, and Arie programmed the character generator and made audio files (zipped and downloadable here; 15 MB). He also added a 360º protractor disk to the shaft of the printer spindle, to be able to accurately measure shaft rotation versus opening & closing of notch-driven contacts.

The aim was to determine four parameters:

1. time to detect the start-pulse

2. time between detection of the start-pulse, and enabling of the printer

3. time during which the printer remains enabled

4. time between detection of the start-pulse and re-enabling detection of the next start-pulse.

Obviously, the start-stop mechanism must still work, even when sending and the receiving machines have motor speeds that are at the maximum allowed difference. The nominal start-pulse has a duration of 5 pixels, that is: 15.87 msec. The start-pulse detection must trigger significantly faster than that. Our tests determined that the detection time is only 4.4 - 4.8 msec. That is, about 1.5 out of the 5 start-pulse pixels! The detection is done by analog circuitry (an other electronic Hell detection method is described in ref. 16). The measured variation in the detection time is equivalent to a mere 1/8 of the nominal pixel duration. It is partly driven by the cycle time of the 1625 Hz pixel-tone frequency (0.6 msec) and the fact that pulse transmission does not start at a zero-crossing of the tone. The pulse detection is disabled upon that detection, and remains disabled for 53.5 pixels. This effectively means that detection of the next start-pulse is enabled just before the printer is disabled. The printer is enabled 3.5 pixels after start-pulse detection, and remains enabled for about 52 pixels. That is, the printer is enabled 3 pixels before the first font-pixel is expected (2nd pixel from the bottom of the 2nd column), and remains enabled for 6 pixels after the last "official" pixel (1 pixel before the top of the 6th column). The timing diagram below captures the conclusions of our tests. The diagram can be downloaded in pdf format here (English) and here (French).

Experimentally derived timing diagram of the Hell-80 start-pulse detection and printer timing

(click on diagram or here to get full-resolution image)
 

Timing diagram - transposed to the nominal Hell-80 font matrix
 

Like the Feld-Hell and Hell-72, the Hell-80 font is stored in non-volatile memory: without power, the memory contents is retained indefinitely. However, the Hell-80 memory is not a mechanical character-drum, but consists of magnetic core memory - a technology dating back to the early 1950s. It uses 35 pairs of small ceramic magnetic rings (the "cores", "Ringkerne"). Several wires are treaded through each of the cores, to provide read/write access. Addressing signals are provided by the decoder-card shown further below.

Magnetic cores, used in a character generator memory

(source: Figure 2 in Rudolf Hell's patents 1086738 (Germany, ref. 14) and 3255313 (US, ref. 15))
 

The Hell-80 "Bildpunktregisterkarte" - the pixel-memory card
(also shown in 3D on the "3D stereoscopic photos" page)

The pixel-memory card has 80 magnetic cores, 56 glass-encapsulated germanium diodes of type OA5 (Siemens; datasheet is here), and 3 germanium PNP transistors of type ASY11-1 (Siemens) in TO-1 package.

Schematic of the "Bildpunktregisterkarte"
(click on image for full scale)

The photos below show the decoder card of a Hell-80. It generates a pulse sequence, based on the selected key of the keyboard or the 5-bit code received from the punch tape reader. It contains 16 magnetic cores, and as many switching transistors. The latter are of type OC123, made by Valvo Radioröhrenfabrik GmbH (Philips) in Hamburg. Mullard (UK) also made this type. The OC123 is a germanium bipolar PNP junction transistor, with a max power dissipation of 300 mW, max Ic of 500 mA, a typical static gain h(FE) of 160, max Uce of 50 V, f(T) of 1.5 MHz, and a TO-7 metal case package (h=9 mm, Ø = 8 mm, ≈ 0.3x0.3"). Official equivalents are the ACY24, ASY48, ASY77, and BFX87. The AC128 has been used successfully as replacement.

The decoder card ("Decodierer") of the Hell-80 - 16 ceramic magnetic rings
(photo courtesy Remmelt-Jan, PAØRJW)

Close-up of the decoder card
(photo courtesy Remmelt-Jan, PAØRJW)

My 3D/stereoscopic photos of the Hell-80 are here.

Here is a summary of the characteristics of the Hell-80: 

	Technology: fully transistorized / solid-state (a "world's first"); modular design magnetic core memory for the character font.
	Modulation: two-tone FSK with 300 Hz shift: 1625 Hz (white pixel / no pixel, "space"). When no characters are transmitted for a certain amount of time, the amplitude of the 1625 Hz tone is reduced. 1925 Hz (black pixels, "mark") equivalent: FM with center frequency of 1775 Hz and a deviation of 150 Hz.
	Signaling: 1260 Hz, for remote control of (or by) the machine at the opposite station.
	Keyboard: same character set as Hell "GL", with additional characters Ñ Á Ä Ö
	Modes: asynchronous (start-stop; uses start-pulse in first column of character matrix, like Hell-72/73): from built-in punch-tape reader or from keyboard synchronous (no start-pulse, like Feld-Hell): from punch-tape reader. It is technically possible to use this mode from the keyboard, but few operators achieve sustained 5 cps typing speed. As the paper tape moves fast and continuously, this causes large spaces to appear between printed characters, which is impractical.
	Font raster: 7x9 (vs 7x14 for Feld-Hell and Hell "GL")
	Data rate: 315 baud (3.175 msec minimum pulse width)
	Transmission rate: 5 characters per sec (2x Feld-Hell)
	Telegraphy speed: 50 WPM.
	Channel bandwidth: 2000 Hz recommended (1100 Hz minimum); "necessary bandwidth" per ITU: 945Hz. However, the "Schrittfrequenz" ("Bildpunkfrequenz" = pixel rate = 1 / time required for one white+ 1 black pixel) is 157.5 Hz. This implies a necessary bandwidth of 3 x 157.5 = 475 Hz.
	Duty cycle: 100 % (in both asynchronous and in start-stop mode)
	Line interface: 2- and 4-wire
	Allowed signal path attenuation: 35 dB / 4 neper (same as Hell "GL")
	Punch tape reader: built-in. Uses International Telegraphy Alphabet No. 2 (ITA2) standard (5-bit, superseding the 1901 Murray-code and 1874 Baudot-code). Uses standard 11/16 inch wide punch tape.
	Remote control: remote (de-)activation via the 1260 Hz signaling tone. Automatically reverts to standby mode if no signals are received for more than 40 sec. the receiving machine can also remote control the sending station, e.g., to stop transmission from punch tape while in start-stop mode. However remote control in this direction requires full duplex operation (4-wire), and is not available during normal communication via radio (unless full duplex via split-frequency operation).
	Power: 21-30 Vdc (24 Vdc nominal. 1.6 Amp nominal) or 110/127/220/240 Vac (±10%), 40-60 Hz. Reduced dissipation when in standby mode (remote activation via tone signaling).
	Weight: 30 kg (≈ 66 lbs)
	Dimensions: 47x51x29 cm (WxDxH)  (≈ 18½ x 20 x 11½ in)

The easiest way to hook up a Hell-80 machine to a transceiver or to the soundcard of a PC is to select "4 Draht-Betrieb" (4-wire operation) on the machines interconnect panel. This configures the interface as a 2-wire audio input plus a separate 2-wire audio output. The interfaces are transformer-coupled, so no issues with DC offsets. I checked the input and output with my scope, just to be safe. No signal on the input, and 1.8 Vpp on the output ("Sendepegel" (output level) selected to -1 Neper, next to the 2 vs. 4 wire selector button). Obviously this output level needs to be reduced via a simple voltage divider (e.g., a potmeter), before connecting it to the microphone input of a transceiver or PC soundcard (though it is OK for the line-input of a soundcard).

A transceiver can also be hooked up via the round receptacle marked "Funkgerät" - transceiver. It has 10 spring-loaded contacts, and is located at the top left of the front panel. This is a type U-79/U chassis-mount receptacle. It mates with the standard NATO (MIL-C-10544) audio connectors U-77/U and  U-127/U (90º angled connector). U-78/U is the connector equivalent of the U-79/U receptacle. Surplus U-77/U connectors are still readily available (e.g., here).

The interface block of the Hell-80 front panel
 

Left-to-right: U-79/U, U-77/U, U-127/U, and U-78/U

This connector provides access to the 4-wire interface, plus PTT. There are two PTT pins. They are floating (interconnected via two relay contacts in series), so they can be used with any type of PTT input (pull up, pull down,..). Note that the PTT is not accessible via any of the other connectors.

Pin allocation of the U-79/U receptacle per schematic L80-N1-8

(front view)

	Ref. 1: "Siemens-Hell-Schreiber 80 – Betriebsanleitung Teileliste“, Siemens AG, Bereich Fernschreib- und Datenverkehr, document A22232-A80-A1-1-30, SuW 55097 UN, 270.0,1,  7/1968, 175 pp.; also: Technische Dienstvorschrift TDv 5815/018-13; (Operating manual; 49 MB; low-res file (39 MB) is here).
	Ref. 2: “Siemens Hell Schreiber 80 – Beschreibung“, Siemens AG, document A22232-A80-A1-1-18, SuW 54232 1268.0,5, 11/1968, 31 pp. (Description; 15 MB)
	Ref. 3: “Siemens-Hell-Schreiber 80 - Bedienungsanleitung“, Siemens AG, Wernerwerk für Telegrafen- und Signaltechnik, Werksabteilung für Fernschreibgeräte, document A22232-A80-A1-1-19, SuW 54658 UN, 769.0,4, 5/1969, also: technische Dienstvorschrift TDv 5815/018-13; (Operating manual; 39 MB; low-res file (29 MB) is here).
	Ref. 4: "Siemens Hell Schreiber 80 schematics A1-0-12, A1-6-12, F1-6, L80-N1-8, L80-F21-3-11 [very large format originals (size A0, A1), each scanned as multiple A3 sheets].
	Ref. 5: "Siemens-Hell-Schreiber 80 Bedienungsanleitung", Siemens AG, April 1967, transcribed by Andrew, SM6MOJ. The Hellschreiber pages of Andrew's website are here
	Ref. 6: "The Siemens Hell 80", by Murray Greenman, ZL1BPU (used with permission)
	Ref. 7: "Telegrafía Hell: El teletipo Siemens-Hell 80", Jan Smeets (EA3DPB/ ON4ASZ), Radioaficionados (revista de URE), Vol XXXV, April 1984, pp. 232-234 (courtesy Juan Martin/URE)
	Ref. 8: ”Feldhell op de Hell80”, Arie van Ooijen (PE1AQB), Electron, April 2006, p. 185
	Ref. 9: “Siemens-Hell-Schreiber 80” [description & characteristics], Siemens & Halske AG, Wernerwerk für Telegrafen- und Signaltechnik, SH 9651, 6 pp., 1960? (courtesy Arie van Oijen, PE1AQB)
	Ref. 10: “Feldfernschreiber (Siemens-Hell-Schreiber 80) Bedienungsvorschrift Wa T App 80” [operating instructions summary], Siemens & Halske AG, SuW 54656 UN, 769.0.1, 3/68, 2 pp. (1968) (courtesy Arie van Oijen, PE1AQB)
	Ref. 11: “Hellschrijven”, Reflecties door PA0SE, Dick Rollema (PA0SE), Electron, nr. 8, August 1982, pp. 404-405 (courtesy Gerard Wolthuis, PA3BCB)
	Ref. 12: "Siemens Hellgeräte", Siemens, ca. August 1965 [6 pp. but incomplete; includes Hell-80 and Hell-80A)
	Ref. 13: "Fs Apparate Sammlung 1945 - Ein neuer Anfang 1975, dem großen Strukturwandel in der Technologie", 1960s ? [2 pp. but incomplete; Hell-80]
	Ref. 14: "Verfahren und elektronischer Vorrichting zur Aussendung von Schriftzeichen im Hell-Code oder einem ähnlichen Code für Blattschreiberempfang (Faksimileverfahren)" [Method and electronic device for transmittal of characters in Hell-code or similar code, for sheet-printers (facsimile method)], Rudolf Hell, Deutsches Patentamt, Patentschrift 1086738, filed 27-Dec-1958, awarded 11-Aug-1960
	Ref. 15: "Electronic method of and apparatus for transmitting characters for facsimile sheet printing reception", Rudolf Hell, US Patent 3255313, filed 24-Dec-1959, awarded 7-Jun-1966
	Ref. 16: "Electronische HELL-schrijver met weergave van half-tinten" [electronic Hellschreiber with half-tone display on CRT/TV], E.H. Leefsma (PA0KTV), graduation report, June 1980, 127 pp. (courtesy Arie, PE1AQB)

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