LF: Feld-Hell on the 136kHz band

["Dick Rollema" <d.w.rollema@freeler.nl>]

To All from PA0SE,

Following my Feld-Hell transmissions on Saturday  22 June at 1300
UTC and Sunday 23 June at 0900 UTC I received reports by e-mail with
screenshots of my transmissions from Alan, G3NYK; Ko, NL9222; Wolf,
DL4YHF/DF0WD; Koos, PA0KDF; Geri, DK8KW, Mike, G3XDV and Jim, M0BMU. Many
thanks to you all!

My Saturday transmission was answered in Hell by Markus, DF6NM and Wolf,
DF0WD. Unfortunately the signal/noise ratio was too poor for readable
print on the paper tape. Using CW they reported good copy of my Hell
signals ("UFB"). Their CW was perfectly readable which shows
that Hell is not a weak signal system!
Good reception was also reported in CW by Jim, M0BMU. 

The Sunday transmission was answered in Hell by DF6NM, DF0WD and DK8KW.
Again their signals were too weak for a useable print. But then Wolf,
DF0WD, switched to a large font (a useful feature of the IZ8BLY
software!) and then I became readable text on the paper tape: see
attachment. I also attach a screenshot of my signal, as sent in by Ko,
NL9222. Geri also switched to the large font but it helped not enough for
readable print. Koos, PA0KDF, had readable text on the screen of Geri's
signal. But he lives near the German border in a rural area. So he is
much nearer to Geri than me and probably has a lower local noise level as
well.

Now for some more detail on the 1944 Hellschreiber I use. It 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. 

It is not possible to send a photograph of "my" Hellscheiber
via the Reflector. But I will send the picture by direct e-mail to those
who have reported my signal and to anybody else who likes to receive it.
Just drop me an e-mail.

I also wanted to send this report to Hell-promotor Murray Greenman,
ZL1BPU. But my server reports the message cannot be delivered. Perhaps
his e-mail address has been changed and it is not on his web site.
May I ask one of our New Zealand friends on the reflector to pass it on
to Murray? Many thanks!

73, Dick, PA0SE
JO22GD