Category Archives: the 19-teens

Reblogged from the ARRL: NPR’s “All Things Considered” Segment to Include Spark Gap Morse


Here is a lovely note from the American Radio Relay League’s blogsite yesterday, to which I was alerted by Twitter.  I’m reproducing it verbatim here.  ‘NPR’, for you Europeans, is ‘National Public Radio’, the listener-funded network for Americans who, if they lived in the UK, would be Guardian readers.  Listener-funding means people donate through period on-air appeals.  There is no government underwriting, and there are no adverts.  Anyway, this is a demonstration of spark transmission for the lay public.  I’ve shown spark before on our blog here, but let’s do it again.  Picture and text all copyright 2014 by the ARRL.


As part of its series of vignettes exploring a “counterfactual” history, “What if World War I had never happened?” NPR afternoon news magazine All Things Considered” will air a segment, to explore “What if the assassination of Archduke Franz Ferdinand was not successful?”

“They needed a sound of a telegraph relaying the message of the failed assassination attempt,” said ARRL Media and Public Relations Manager Sean Kutzko, KX9X. “They wanted it to be as authentic as possible, so we explained that in 1914, it would have been relayed via spark.”

The ARRL Lab has a working spark transmitter, so Kutzko got the desired text from NPR, which he sent by hand (yes, he’s a lefty) and recorded. “They said it was ‘perfect,’” he reported. “It was a real thrill being able to help NPR; I used to work at NPR affiliates in Illinois and Indiana in the 1990s, so being able to help the network was exciting.”

NPR’s “All Things Considered” typically airs at 4 PM Eastern Time (2000 UTC). ARRL Maryland-DC Section Manager Jim Cross, WI3N, believes the segment will air 35 minutes into the first hour of the show. The program segments are subsequently available on the NPR website. — Thanks to Maryland-DC Section Manager Jim Cross, WI3N, and Sean Kutzko, KX9X’

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loose coupling

This is a ‘loose coupler,’ or a ‘receiving transformer.’  It’s a modular component from the early ‘teens, whose function was to be the tuned circuit at the heart of a receiver.  It worked by sliding a primary and secondary coil past each other; you could add variable condensers for more precision.  A little telephone condenser filtered out RF noise.  The larger Loose Couplers were sometimes called “Arlington” types, because they could tune to the very long wavelengths for time signal reception, broadcast from Virginia.

This picture, with a lot better informed commentary than mine, comes from Henry Rogers’ absolutely magnificent online Western Historic Radio Museum.  If you’re serious about ham radio history, you should go start learning this site by heart.

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the ‘quenched’ gap — a refinement of spark

The rotary spark gap manufacturers RF energy more smoothly than a static gap does, does not turn cantankerous when air temperature varies, and handles much, much higher power.  An efficiency limitation is the speed at which each spark dies.  One way of managing this was to conceive of a ‘synchronous’ rotary, about which more in a different post.  Another was to dispense with wheels, and quench the spark quickly across a series of stationary plates.  Here is a picture of such an apparatus, and an explanation of its operation as it was understood in 1916.  I’ve always thought it’s what I would have used as an Edwardian operator.  Those high-speed rotaries are alarming.  The ones they used on ships were the size of dinner plates — and as loud as automobiles.

This very fine video is the work of Anton Pankratov, at ‘CJSC Chip & Dip’, an electronics supplier in Moscow.

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spark gap transmitter in action

This breathtaking replica project — I’m too Youtube-primitive to figure out its creator’s name, or I’d give him well-deserved credit — shows what a ham station sounded like to its operator in about 1910.  This is ‘spark gap’ transmission.  Don’t confuse it with rotary spark transmission.  That was an innovation on this, a mechanical way to manufacture RF (‘radio frequency’) energy.  This is nothing more than a Tesla coil, whose arc causes radio noise, exactly the way lightning does.  Because their signals splattered across huge sections of the radio band, they were regulated out of existence quickly.

‘MESCO’ was an early supplier of amateur radio equipment, principally coils.  The condenser stack is small here.  Marconi’s transoceanic ones were the size of a small building.  There is a picture of this, in a superb paper, here, by Jack Belrose, VE2CV, explaining the physics that made spark work.  Marconi wasn’t sure what frequency (well, frequencies) he was transmitting on.  Nobody was very sure about their frequency, but it didn’t matter much.  The antennas were so out-of-tune, and often so overpowered, that they buzzed.  Kids could sit on your lawn of a quiet evening and copy your code from the arcing overhead.

Oh, the code here translates like this:


This is around 15 words per minute, slightly faster than average speed in 1910.

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