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The Hellschreiber machine

vintage Hellschreiber machine

Here is a picture of the Hellschreiber machine used by PA0SE to have QSOs on the 136kHz band.

The Hell tarnsmission

This is PA0SE's transmission as received by Ko, NL9222.

DF0WD as received on the machine

And here is the printout of the machine when receiving DF0WD.

Dick says: "The machine belongs to collector Arthur Bauer, PA0AOB and I have it on "permanent loan" since 1977, having used it for numerous QSO's on 20, 40 and 80 metres and now 2km. As you can see in the screenshots the machine produces the line of text twice, one above the other. That is done to avoid the requirement of perfect synchronous running of the sending and receiving machine. When their speed differs the lines of text become slanting on the paper tape (can be seen in the screenshot of NL9222) . But when the upper line disappears over the top the lower one is already coming up from the bottom. It took a genius like Dr. Rudolf Hell to devise such a simple way of avoiding the need of synchronism! The Hellschreiber has a speed control. In practice one simply turns the control until the lines of text become horizontal. The motor speed is controlled by a centrifugal speed regulator, like the one invented by James Watt for the steam engine. But in the Hellschreiber the rotating mass does not work against gravity but against a spring. When the motor speed exceeds the wanted value the mass moves outwards against the force of the spring and closes a contact. This causes an increase of the current through the field coils of the motor and the speed decreases until the contact opens again. The speed settles down at a value at which the contact periodically closes and opens. The small variations in speed are not noticeable. With the speed control knob the tension of the spring can be varied and with it the motor speed. The speed is controlled within very tight limits. The current through the field coils is not directly controlled by the regulator contact but via a thermionic valve so the contact is not loaded by the current and does not spark. The motor also is also a dynamotor producing130V HT for the valves from the 12V DC supply."