SAQ Grimeton: the 1924 Alexanderson alternator on the air on 17.2 kHz

What you hear

Most of the year, 17.2 kHz is quiet, and that is as it should be. On a handful of announced days, after a warm-up during which a carrier appears and tuning is adjusted, the station sends a message in slow, clean Morse code, a greeting to the world, a few lines long, repeated so that listeners who missed the start can copy it. The sending is leisurely, and a CW decoder prints it as plain text. Then the carrier drops and the station is silent again, sometimes for months.

What makes those minutes remarkable is what produces them: there is no transistor and no valve in the transmitter. The signal comes from an alternator, a machine of the kind that generates mains electricity, spun fast enough that its output is 17,200 hertz instead of 50, and fed straight into the antenna. The Morse is keyed not by a switch but by shifting the machine's load with a magnetic amplifier. It was built in 1924 by the Swedish Telegraph Administration to carry telegrams to America, and it is the only Alexanderson alternator transmitter left in the world in working order.

Who transmits and why

The station is at Grimeton, near Varberg on the west coast of Sweden, and it is a UNESCO World Heritage site. In the 1920s and 1930s it carried transatlantic telegraph traffic; later it was kept as a reserve and, in the end, as a monument. Today an association of volunteers maintains the alternator and runs it on special days, each time with a short Morse message addressed to listeners everywhere, and each time asking those who heard it to send a reception report, which the station confirms.

The regular dates are Alexanderson Day, at the end of June or the beginning of July, named after the engineer who designed the machine; Christmas Eve, 24 December, around 08:00 UTC; and United Nations Day in October. Additional transmissions happen from time to time. The exact dates, times and any changes are announced in advance on the station's own site, alexander.n.se, which is the place to check before planning a session, because a machine from 1924 does occasionally refuse to start on the day.

There is no mystery about this station, except the sort that comes from hearing a hundred-year-old generator speak Morse across a continent.

When and where to listen

Be on 17.2 kHz early: the carrier is usually switched on well before the message for tuning, and that is when you find out whether the receiver you picked hears VLF. Receivers in Sweden, Denmark, Norway, Finland, Germany, the Netherlands and Britain hear SAQ well; reports come from much further, including North America, on quiet days. The receiver needs an antenna that works this low and a site away from mains harmonics and switching noise, so a rural receiver in Scandinavia or northern Germany is the safest choice.

The program tunes the station in CW with a passband of about a kilohertz, which puts the Morse as a tone in the middle of the audio. The frequency sits just above JXN at 16.4 kHz and well below the submarine transmitters, so the SAQ carrier stands alone on the waterfall and is easy to pick out.

In ShackDeck

Station catalogue → Mystery stations → SAQ Grimeton (17.2 kHz). The program picks a public receiver whose range reaches 17.2 kHz, tunes it and sets CW; no receiver, antenna or account of your own is needed. Switch on the CW decoder and the message prints as text while the alternator sends it; for a station this slow and clean, the decoder rarely misses a letter.