Merry Christmas from 1924

Take a look at this photograph. What do you think this thing is? Since you're reading this magazine, you are probably technology-oriented. But unless you are 98-years old, you might not recognize that this device played a major role in the early days of radio and audio technology. Let me explain.

I hope you receive many Christmas greetings this year! Maybe some Christmas cards (man, a nice card is expensive these days). Maybe a shout-out from a Salvation Army volunteer (hey, toss a dollar in that kettle). At least some carols as your stroll through Walmart (no, don't buy all your presents there). But there's one Christmas greeting that unfortunately you won't receive (unless you have some specialized equipment tucked away in your radio shack).

The radiotelegraphy station in Grimeton, Sweden was constructed in 1922-1924. It was built with the highest tech of the day, which although super cool, was pre-electronic. Instead of using semiconductors or even vacuum tubes to transmit a radio signal, it uses a kind of electric motor. From the 1920s through the 1940s, it transmitted telegram traffic by Morse code throughout the world and even served a vital role during World War II. The station is the only remaining working example of this early radio technology and has been preserved as a UNESCO World Heritage site.

The heart of the radio station is the Alexanderson alternator. How do I describe the workings of this 50-ton beast? The photo shows that it has a definite steampunk vibe. It looks more like a power generator than a modern radio transmitter because it is in fact a generator that creates radio waves. The generator (or alternator) is constructed with a large number of rotor poles; by running the generator at a high rotational speed, a continuous signal is produced in the radio band.

As noted, the Alexanderson alternator in Grimeton is used for radiotelegraphy, in other words, the station transmits Morse code. By slightly altering the motor speed, and hence the frequency, the output signal strength of the narrow-band antenna is similarly altered. This acts as frequency-shift keying (FSK) modulation. Hook up a Morse key to vary the motor speed and you're in business. Other Alexanderson alternators were used for AM broadcasting. On Christmas Eve, 1906, an Alexanderson alternator was used to make an experimental broadcast of Christmas music. This is considered the first AM radio entertainment broadcast.

Oh, I forgot to describe the antenna, a copper wire 1.2 miles in length and supported on six 380-foot steel towers with a vertical conductor on each tower. Incidentally, it was quite tricky to develop a generator that could rotate at the necessary high speed and the inventor, Ernst Alexanderson, tested his prototypes from behind sandbags. Today, radio engineers are seldom injured by flying rotors.

Firing up and running this thing is no easy feat. For starters, the high-speed generator has to be precisely lubricated and cooled otherwise bad things happen. But when it runs, it has the power and majesty of a steam locomotive barreling down the railroad track. But, you reasonably ask, what does all this have to do with my Christmas greetings? Well, on Christmas Eve morning, December 24, the Alexander Grimeton Friendship Association will crank up this 98-year-old fellow and go on-air to send out a Christmas message to the world.

Here's the pertinent info:

The event will begin at 08:30 CET (07:30 UTC) with the startup and tuning of the 200 kW Alexanderson alternator transmitter through the Grimeton Radio Station, call sign SAQ. The transmission will begin at 09:00 CET (08:00 UTC) on 17.2 kHz CW. Grimeton Radio Station, SK6SAQ, will be QRV (ready) on the following frequencies: 3.535 MHz CW, 7.035 MHz CW 14.035 MHz CW, 3.755 MHz SSB, and 7.140 MHz SSB. QSL reports can be sent to SK6SAQ via email at

If you're like me, you are a little fuzzy on call signs and QSL reports, and in any case lack the equipment to receive the greeting. Fortunately, the event will also be live streamed on the Alexander SAQ Grimeton Friendship Association YouTube channel. More information about the Christmas Eve event and the transmitter can be found at the Grimeton Radio Station website.

And so, boys and girls, that's the story of the cranky old Swedish transmitter and how he sent out his warm signals on that cold winter morning.

Finally, I guess there's only one thing left to say:

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jeff-henning's picture

Very cool bit of kit, but I'd think that a generator with a big solenoid switch might be simpler and cheaper even in 1922. Whether that could work have a decent service life is another story.

Regardless, it is very steam punk. And that it wi still work 100 years later is a testament to how things use to be made and, for the most part, aren't made today.

samui's picture

Agree Its cool.

syrax's picture

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