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Theory & Practice: 1917

Theory & Practice: 1917

New York, 1917. "Helen Campbell." A Hunter College student licensed as a wireless operator during World War I. Bain News Service. View full size.


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I'm fairly sure

that she's actually working on an early Dalek.

And now, the female viewpoint!

Her dress is very plain for 1917--it was a rather frilly fashion period compared to today--but I love the sheer sleeves! I just hope there are no moving parts to catch her skirt flounces.


As a tinkering kid I indeed discovered that not only was a relay turned into a buzzer by having the off circuit wired back to the power of the relay but that the coils inside the relay released high voltage magnetic field collapse spikes too, so wiring those to alternative rows of wire threaded around a margarine container with a mercury switch inside would shock victims told to turn it over so badly it was hard for them to even let go!

You guys can say what you want

but to me it looks like she's working under Robbie the Robot's hood.....


Assuming the mystery part is a capacitor (condenser before 1960), it's probably to provide an RF path around the coil.

I believe

it is a capacitor to absorb the "spark" caused when the relay makes & breaks. To keep the contacts from burning. It does the same job as the capacitor in old cars with points & condensor ignition. I'm a retired electronics tech but my ticket doesn't quite go back to 1917.

EMF can be a bear

Is that the symbol for a non solid state diode to suppress the back EMF from the coils as the field collapses?

Spark transmitter?

The circuit diagram seems to want to produce a more or less regular continuous sparking as the relay makes and breaks contact with the battery circuit, operating as a buzzer, and a component of that noise at radio frequencies as selected out by the tank circuit (coil and variable capacitor at right).

I believe

(R/L) should be (L/C)

In theory

I love the textbook excerpts up on the wall!

This really shows accurately the state of art for early radiotelegraphy. The transmitter circuit (albeit lacking a key) is a simple "buzzer" interrupter that feeds the (R/L) tuned output. The waveform in "Fic 9" shows the end of a transmitted burst, as the oscillations decay.

It would be nice to know the frequency they were working at...


Quite correct Papa Bear!
Should have been (L/C) in the tank circuit. And yes, a capacitor (perhaps that bank of Leyden Jars) to protect the relay contacts, and as also suggested, to provide a continuous RF path around the coil.

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