A machine from 1924 still transmits every Christmas Eve
2026-06-16 · EA5IYR
Most radio transmitters are electronic. This one has moving parts.
SAQ Grimeton, on the Swedish west coast, entered commercial service on 1 December 1924 carrying telegrams to the United States. Its transmitter is an Alexanderson alternator: a 200 kilowatt rotating machine that generates radio the way a power station generates mains electricity, by spinning a rotor very fast in a magnetic field.
Every other one was scrapped decades ago. This is the last working example on Earth, and it is a UNESCO World Heritage site. Why the antenna is the size it is
SAQ transmits on 17.2 kHz, and a wavelength at 17.2 kHz is about 17.4 kilometres.
You cannot build an antenna a wavelength long at those frequencies. Nobody can. So Grimeton does the only thing available: 2.2 km of horizontal wire strung between six towers, each 127 metres tall, tuned to behave electrically like something far bigger than it is.
The result is a structure visible from a long way off, built to radiate a signal you cannot hear and that carries a few words a minute.
Compare it with a normal amateur antenna at 14 MHz: about twenty metres of wire. The same physics that pushes a submarine broadcast down to 24 kHz is what forces this. Why it survives
Because somebody decided not to scrap it, and because a machine that is run occasionally stays alive in a way a mothballed one does not.
The Alexander association keeps it in working condition and starts it up a handful of times a year — Alexanderson Day in the summer, and Christmas Eve morning, when it sends a seasonal message in Morse on 17.2 kHz.
Listeners worldwide report reception. Sending a few sentences at 17.2 kHz across a continent, in 2026, using a machine older than television. Hearing it yourself
You need a receiver that goes down to 17.2 kHz, which rules out most conventional radios and rules in a computer sound card with a long wire — the same setup that picks up natural VLF.
Or use one of the public web receivers on the day; there are always several pointed at 17.2 kHz when SAQ is due.
The transmission times are announced in advance. It is worth an alarm clock. There is nothing else like it left, and one day there will be nobody who knows how to run it.
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Sources: The Alexander association — SAQ Grimeton, Grimeton — 100 years of communication, Signal Identification Wiki — Grimeton Radio (SAQ)), Wikipedia — Alexanderson Day.