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[My Hell-printer]   [Other homebuilt printers]   [Hell/CW filters]

My Hell-printer. I built a mechanical Hellschreiber (receive/print only) in 1983. Most of the structure was made from double-sided PCB, precision-cut with a CNC machine during a summer job at the Dutch public telephone company (PTT) in 1982. The the printer spindle and the paper transport rolls were machined during a university internship at Philips Research Labs in Eindhoven in 1983.

My Hell-printer measures 15x8x12cm (lxhxd)


Click on photo for original without labels

My home-built Hell printer in 3D
(you will need red/green glasses to get the stereoscopic effect)

The circuitry for the tone detector, solenoid driver, and motor speed control (paper transport and spindle) is rather straightforward. The schematics below show the circuits that I used. A solid-state implementation of the driver circuit typically needs a diode (installed with reversed polarity) across the magnet solenoid, to avoid damage due to the inductive voltage spike upon de-energizing the solenoid. This is referred to as a flyback, snubber, freewheeling, catch, or suppressor diode.

Detector and solenoid driver circuitry
(from Bastiaan, PA3FFZ)

Speed regulator for the spindle motor
(H.S. Malvar, from Wireless World, August 1980)

                  Detector and solenoid driver                Speed regulator for the paper transport motor
(from Martien, PAØMJS)

Alternate detector designs are described here:

	"Radiomodem voor Hell, Morse en RTTY", Koos Fockens (PAØKDF), Electron, 10-12/1986  [in Dutch].
	"CW/Hell-skrift demodulator", Jan-Martin Nøding (LA8AK), Amatørradio, 1987, nr. 41, February, Nr. 41, pp. 41-43, Nr. 42, March, pp. 66-69

If the relay is a bit slow when energized, you may try to speed it up with one of the simple circuits described here. They basically briefly apply almost twice the supply voltage to the relay coil when energizing. The capacitor in the circuit will have to be adapted to the desired speed and relay (decay time).

Paper transport speed calibration is easy: all you need is a stopwatch and a ruler or tape measure. Simply adjust the motor rpm to obtain about 47 cm per minute. Unlike the spindle in a Feld-Hell machine, my spindle is a single-thread (1-start) worm. It needs to turn at 7 columns per character x 2½ characters per sec x 60 sec/min = 1050 rpm. The Feld-Hell machine has a double-thread (2-start) spindle: it has two intertwined windings. Note that the number of threads is not related to the number of turns of each thread!  Both the Feld-Hell and my homebuilt spindle have two turns. The Feld-Hell spindle only needs to turn at ½ x 1050 = 525 rpm,  to get the same effect as a single-thread spindle at 1050 rpm.

Adjusting the spindle speed to 1050 rpm can be done several ways: 1) first get the electro-magnet to work properly (which you have to do anyway, hi), then feed the printer with "known-good" Hell-audio and adjust the rpm until the print becomes legible and the text lines are horizontal; or 2) use a tachometer.

I used method nr. 2 by building a very simple optical sensor (4 cheap components), attaching a strobe disk to the spindle shaft with a dab of glue, and measuring the sensor output signal with an oscilloscope. You can make a crude strobe card with a black felt marker, but such markers are really not black at all, and the ink does not have good reflectivity. Best is to print one on regular paper with a laser printer. Here is a file with strobe disks that have 1, 2, and 4 black segments and ±5 cm (2") diameter.

Small strobe disk attached to the spindle shaft

The sensor simply consists of an infrared LED and a phototransistor. No specific types (you can also use an IR diode + transistor in a single package, e.g., an SY-CR102). I shielded them with shrink tube (black on the 5 mm LED, blue on the 3 mm phototransistor in the photo below). As you can see in the photo, I bent the leads such that the diode and transistor are not parallel, but are trained at a point just in front of them (about 2-3 cm, 1").

      
My very fancy tachometer sensor

The largest swing in the sensor output signal (5 Vpp) was observed at a distance of 0.8-1 cm (±3/8") from the strobe disk. The scope image below indicates that the spindle is turning at 1500 rpm, and needs adjustment. A period of 10 msec (100 Hz) = 100 cycles per second, and 4 black segments on the strobe card means 100/4=25 rps which is 25x60=1500 rpm. The scope is set to AC-coupling.

The scope indicates 1500 rpm
 

The ink-roller is made of several round felt pads that I stacked, glued together, and drilled a hole through the center. The pads are simply felt bumper-feet for furniture (the ones with adhesive backing are the easiest), available in several forms at your local Do It Yourself store. An other option is a felt polishing wheel  (or tip) from a Dremel^® type rotary tool.

I use Pelikan-brand endorsing ink. It is thick and comes in a tube. The label says that it is intended for felt pads. Just what I need. You just may want to use gloves when handling this type of ink! And don't use water-based ink; not only will it cause the spindle to rust, the capillary properties of the paper will cause the ink to be dispersed and make the print fuzzy.

Some other options are Pelikan dark violet "Stempelfarbe ohne Öl" (endorsing ink without oil). This is liquid ink that comes in a small bottle. Another (slightly) thicker liquid ink is Edding T25 (e.g., black); this is basically professional drafters ink.

Here are the descriptions of some other homebuilt Hell-printers and Hellschreibers:

	Ref. 1: "PAØMJS maakte zelf een mechanische hellontvanger", Dick Rollema (PA0SE), Electron, nr. 10, October 1980, pp. 557-559 (courtesy Gerard Wolthuis, PA3BCB)
	Ref. 2: "Selbstbau eines Feld-Hellschreibers", Eckhard, DG9JO, RTTY, No. 2, 1981
	Ref. 3: "Schrijftoestel voor ontvangst van hell- of morsesignalen", Martien, PAØMJS, Electron, 5/1982
	Ref. 4: “Mode HELL, zelfbouw (deel 1-2)”,  Bastiaan Edelman (PA3FFZ), CQ-PA, 10/1997, pp.  348-349 and 11/1997, pp.  385-387 some more details are described here by PA3FFZ; personal communication, June 2008, in Dutch
	Ref. 5: "Hellschrijver voor zelfbouw (deel 1-5)", (description of home-built Feld-Hell of Martinus Rooth (PA0MPR) and A. Rooth-Beems (PA0ARB)), Bastiaan Edelman (PA3FFZ), CQ-PA, 2/1994, pp. 32-34, 3/1994, pp. 63-64, 4/1994, pp.  97-98. 5/1994 , pp. 121-122, 12/1994, pp. 322-325
	Ref. 6: "A home - built, direct printing telegraph system. *The Feld-Hellschreiber*", Dale Hughes (VK2DSH), Amateur Radio Magazine (WIA),  Vol. 68, No. 11, November 2000
	Ref. 7: "De XYLCD - Deel 1 & 2", 128x256 LCD with micro-controller that can be programmed to be a hardware Feld-Hell receiver, see photo below), by Wim, PAØWV, CQ-PA, 2008, nr. 11 & 12 [in Dutch]. See photo further below.
	Ref. 8: "Zelfbouw HELLschrijver met nonstop Helix" & "Gereedschap voor HELL80 in startsop bedrijf", Arie van Oijen (PE1AQB), 2011, 10 pp.
	Ref. 9: "Hellschrijven wint terrein", Dick Rollema (PA0SE), Electron, nr. 2, February 1983, pp. 73-76  (courtesy Gerard Wolthuis, PA3BCB)

[Bastiaan, PA3FFZ]     [PA0ARB & PA0MPR (3x)]    [ON4IB]    [PE1DXH]    [Jan, ON4ASZ/ex-EA3DPB (2x)]    [Dale, VK1DSH/VK2DSH]     [Wim, PAØWV]     [Arie, PE1AQB (3x)]     [Bronzi, IZ6HPJ]

The Hellschreiber printer of Bastiaan, PA3FZZ
(home-built spindle is etched from brass rod; motors are tape transport motors from a VCR (high torque and easy to control speed, unlike VCR video-head motors)
 

Homebuilt printers by PAØARB and PAØMPR (SK)

(on display during the 2003 annual Hell-meeting hosted by Cor, PAØVYL,

at the Jan Corver Amateur Radio Museum in Budel; original photo courtesy Gerard, PA3BCB)

Homebuilt Feld-Hell by PAØARB and PAØMPR (SK)
(modified typewriter keyboard; instead of character drum: single stationary character-disk with 7x14=98 contacts + diode matrix (±800 diodes) + rotating contact; printer helix made of 2 turns of heavy-gauge steel spring (5 mm ID), stretched to 10 mm (for 10 mm wide paper); ECF80 triode/pentode)

Beautiful compact Hell-printer, home-built by OM Geerinck, ON4IB

(source: ref. 9 )

A Hell-printer, home-built by OM Crijns, PE1DXH

(source: ref. 9 )

Jan Smeets (ON4ASZ/ex-EA3DPB) has built two Hell-printers. The second one was completed in August of 2010.

The first Hellschreiber printer of Jan Smeets
(paper transport motor is a 220 Vac squirrel-cage motor; printer helix is driven by a 24 Vdc motor, with (coarse) speed control via a rheostat/potmeter); the printer's electro-magnet came from an electro-mechanical pulse counter (mfr: Hengstler); prints on standard 11/16 inch wide Telex punch tape)

Fragments of some QSOs printed with Jan's first machine
 

The second Hellschreiber printer of Jan Smeets
(completed August 2010; the helix and the printer's electro-magnet are also homebuilt!)

Details of the printing and paper transport mechanisms
 

A side view of the two motors; the die-cast box above the motors contains an LC-filter, pre-amp, and driver circuitry for the printer's electro-magnet
 

The Hellschreiber sender/printer of Dale, VK1DSH/VK2DSH - built 1999
 

(ACSII keyboard from a TTY terminal, a Single Board Computer (SBC) with a 65C02 processor (source-code is available from Dale), spindle motor (with optical encoder) from a DEC line printer, paper transport stepper-motor from a 5¼" floppy disk drive, electromagnet from a telephone relay, 16-char LCD, electronics for motor speed control, tone generation, and tone detection/magnet driver; prints onto standard 11/16" telex paper tape. All details are in Dale's article referenced above)

Close-up of the printer mechanism

The XYLCD project of Wim, PAØWV
(the LCD measures approximately 12½x7 cm / 5x2¾", including the rim)

Arie van Ooijen, PE1AQB, has built has built a very nice modular Hellschreiber printer system. He demonstrated the system at the 33rd annual Hell Meeting (9 Oct 2010). It includes his latest addition: two printer heads for the start-stop Hell-80 mode - most likely a "world's first"! One printer head uses a continuously spinning spindle, the other uses a 7-pin needle printer-head and ribbon cassette from a PC-printer. The paper transport module uses a stepper motor. The electronics are implemented on several cards in a rack.

The modular Hellschreiber printer system of Arie, PE1AQB

(here shown with  needle printer head for start-stop Hell-80)

The Hell-80 character set, printed by Arie's needle printer head.

The paper transport module and the start-stop Hell-80 printer head

Close-up of the start-stop Hell-80 printer head - in operation

Close-up of the start-stop Hell-80 printer head

(note the the pin sticking up from the brass hub of the helix/spindle; as the shaft turns, the pin passes through the (black) optical sensor below the shaft. This is part of the start-stop mechanism)

Making a start-stop Hell printer (or more precisely: a printer that is compatible with the start-stop Hell-system) is tricky. The original Hell start-stop equipment (Hell-72, Hell-80) uses a continuously turning motor and a complicated clutch mechanism - not suitable for home-building! Arie has kept the continuously turning motor, but does not use a clutch. His ingenious solution detects the start position of the spinning spindle, with a pin that protrudes radially from the spindle shaft. The pin passes through an optical detector. The detector's output signal signal is sampled, and shifted through a FIFO-register. The depth of the register is equivalent to a single column of the Hell-characters. Upon detection of the start-pulse of a character (5 pixels in the first column of the Hell-80 font; effectively at least ≈ 3 msec of the "mark" tone), the FIFO buffering is used to delay the received pixels until the pixel stream is properly aligned with the position of the spindle. See ref. 8 (above).

The latest creation of Arie is another Hell-80 start-stop printer. The paper transport motor and spindle motor with optical detector are as described above. The helix shaft, printer magnet, and chassis parts are from a salvaged Hell-72 machine. The original printer spindle was damaged; the damaged spindle thread was removed and replaced with a 2-turn steel spring (i.e., with intent to use it as a Feld-Hell printer). The photos below show operation with 9.5 mm wide paper tape, whereas the modified 2-turn spindle was dimensioned  for 1/2 inch wide paper tape.

Another start-stop Hell-80 printer head

Bronzi Luca, IZ6HPJ, has built a Feld-Hell mode printer mid-2010. The helix is a steel spring. The ink roller is a wooden piece that he turned on a lathe, and covered with felt. The motors are from an old printer and copier. The speed of the spindle motor is controlled with pulse-width modulation (duty cycle), based on a 555 timer IC. The paper transport speed is adjusted via the motor voltage. The pinch roller is also wooden, with two rubber O-rings. He uses rolls of cash-register paper tape, cut back to 15 mm width, and Rexel-brand ink. He also wound the 400 mH solenoid of the electromagnet. You can see this printer in action here on YouTube.

Hell/CW filters. At some point, I built a very sharp AF filter for my printer (-3  dB bandwidth is 150 Hz, -60 dB is 680 Hz!). The filter output impedance is that of land-line POTS: 600 ohm. This matches the audio input impedance of Hellschreibers, as they were also intended for use over telephone land-lines. The design is from Klaas, PA0KLS (ref. 1).  It uses five standard 88 mH toroids, surplus from telephone companies; 88 mH loading coils (in various forms, sizes, materials) have been used extensively on long telephone lines worldwide since the early 1900s, when the famous Serbian-born scientist Mihajlo Idvorsky Pupin postulated and proved their effectiveness. In 1951, the 135 mH value was introduced (in addition to 22, 44, 88, and 115 mH). In phone systems, these (series) loading coils do not permit data communication (POTS-modem, (A)DSL, etc.) beyond voice bandwidth.

The 88 mH telephone toroids have become rather hard to find. There is a very good alternative: the Toko 10RB series. I bought two sets of five at a very reasonable price at JAB Electronic Components in the UK, for use in a filter per ref. 9 below. Note that that you can find inductors of the same value for considerably less money elsewhere. However, you will find that they do not work in these filter applications: their DC resistance is much too high - at least five times that of the Toko inductors!

Articles about this and other passive narrow AF-filters:

	Ref. 1: "Laagfrequent filter voor Hell en CW", in "Reflecties door PA0SE", Electron, 6/1981
	Ref. 2: "CW-Filter mit 200 Hz Bandbreite", E. Kantz, Funkamateur, Nr. 8, August 1981, pp. 402-403
	Ref. 3: "Die Frequenztrennung", Funktechnische Monatshefte (FTM), Heft 5, May 1942, pp. 66-68
	Ref. 4: "Laagfrequentfilter van ON4ASZ voor telegrafie en hellschrijven”, in "Reflecties door PA0SE", Electron, January 1992, pp. 5-6
	Ref. 5: "Audiofilter - realisiert nur mit L und C" [ON4ASZ/EA3DPB filter], Frank Sichla (DL7VFS), CQ-DL, 3/1999, p. 223
	Ref. 6: "CW-Signalregenerierung ganz einfach" [ON4ASZ/EA3DPB filter], CQ/DL, 9/1999, p. 735
	Ref. 7: "Audiofilter - einfach, aber gut" [ON4ASZ/EA3DPB filter], CQ-DL, 12/1999, p. 984
	Ref. 8: “Passive (LC) narrow band AF filters” [with ON4ASZ filter], Pat Walker (G3VA), in “Technical Topics”, Radio Communications (RadCom), March 1998, pp. 62-63
	Ref. 9: “Een passief laagfrequentfilter voor de ontvangst van telegrafie”, Roelof Bakker (PA0RDT), Electron, January 1997, pp. 15-20 (incl. PA0KLS CW/Hell filter). Here is a small Excel spreadsheet that I made for calculating the filter component values.

A razor-sharp passive CW/Hell filter
(additional circuitry on the right is an LM386 AF amplifier (bottom) and a TL082 input buffer amp)

CW/Hell filter design by Klaas, PAØKLS
 

Interfacing the CW/Hell filter to an RX and Feld-Hell
 

Band-pass characteristics of my filter
(spec curve in red, measured curve of the bandpass filter in my Feld-Hell is shown as reference (curve shifted from 900Hz to 1000 Hz))

©2005-2010 F. Dörenberg N4SPP

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