The Alexanderson Transmitter: Very-low Frequency Radio Rides Again!

Is your ham radio rig made of iron and steel? Is it mechanically driven? Classified as a World Heritage Site? We didn’t think so. But if you’d like to tune in one that is, or if you’re just a ham radio geek in need of a bizarre challenge, don’t miss Alexanderson Day 2015 tomorrow, Sunday, June 28th

The Alexanderson Transmitter design dates back to around 1910, before any of the newfangled tube technology had been invented. Weighing in at around 50 tons, the monster powering the Varberg Radio Station is essentially a high-speed alternator — a generator that puts out 17.2 kHz instead of the 50-60 Hz  that the electric companies give us today.

Most of the challenge in receiving the Alexanderson transmitter broadcasts are due to this very low broadcast frequency; your antenna is not long enough. If you’re in Europe, it’s a lot easier because the station, SAQ, is located in Sweden. But given that the original purpose of these behemoths was transcontinental Morse code transmission, it only seems sporting to try to pick it up in the USA. East Coasters are well situated to give it a shot.

And of course, there’s an app for that. The original SAQrx VLF Receiver and the extended version both use your computer’s sound card and FFTs to extract the probably weak signal from the noise.

We scouted around the net for an antenna design and didn’t come up with anything more concrete than “few hundred turns of wire in a coil” plugged into the mic input.  If anyone has an optimized antenna design for this frequency, post up in the comments?

Thanks [Martin] for the tip!

41 thoughts on “The Alexanderson Transmitter: Very-low Frequency Radio Rides Again!

      1. Not if there are wooden poles to hold the wire. Even if it is a real fence and it touches the ground it’s unlikely to drain much into dry surface ground.
        It’s actually done more often than you might think where people use the oddest objects including fences/barbed wires for antennas in the lower frequencies. With plenty of stories about it on the internet.

  1. The wavelength of 17.2 Khz would be over 17 Kilometers. That’s going to require one hell of a loading coil. The US navy uses this frequiency range to transmit to submerged submarines. I have read that they use a series of telephone poles cross country at 2 sites, east coast and west coast, to transmit.

    1. I live near, and my father worked at, the Cutler Naval Base (https://en.wikipedia.org/wiki/VLF_Transmitter_Cutler) and I’m not entirely sure what is meant by a series of telephone poles… but if you look at the wiki you can see a couple diagrams of the arrays they use. Something along the same lines except in the reverse is an also nearby Over The Horizon radar (https://en.wikipedia.org/wiki/Over-the-horizon_radar) which sounds closer to what you’re describing.

  2. Varberg Radio Station had twin, bigger sister in Poland called Transatlantic Radiostation. After Hitler’s invasion on Poland was used by Germans for communication with Kriegsmarine submarines. In 1945 big sister’s antennas was demolished by fleeing German’s soldiers.

  3. How long before someone makes one out of a dremel with multiple offset blades to increase the tooth count per rotation or better still a bandsaw. Say 32 teeth per inch at 1200 rpm for example.

    1. Interesting idea…
      Two bandsaw blades with the teeth facing each other rotating in opposite directions. Each passing through a strong static magnetic field before thier crossing point.
      They are synchronised so that teeth pass out of phase with each other. A coil in the middle reads the net alternating feild across the gap.
      Better than simply applying several kv to the blade and measuring the ac generated by the arc then having to quench it and smooth it into a nicer wave.

      1. Of course a warn out blade would be better, as the wave form would take the shape of the teeth. Rounding all those might not be an easy task. Maybe run it forward then backwards. Or use electrolysis and carefully adjust the depth.

  4. Interesting idea…
    Two bandsaw blades with the teeth facing each other rotating in opposite directions. Each passing through a strong static magnetic field before thier crossing point.
    They are synchronised so that teeth pass out of phase with each other. A coil in the middle reads the net alternating feild across the gap.
    Better than simply applying several kv to the blade and measuring the ac generated by the arc then having to quench it and smooth it into a nicer wave.

      1. I’m 33, and my hearing stops at 16 KHz. That, or the capability of my stereo set. I’d bet hearing, because my kid told me he can still hear the sound. Youtube is full of sine waves, so it’s easy to test yourself.

          1. Except the link is talking about low frequency sound, not high frequency sound, and the rest of the article is going on about stuff that is definitely *below* our hearing range. So I stand by my comment.

  5. Wavelength = (Speed of light in vacuum/ Frequency). Wavelength = (300 Km/s/17.2 Khz). Wavelength ~= 17441.86 meters. Although, if you use a dipole antenna you can get away with using half wave length of 8720.93M of wire, or a quarter wave-length for your ground connection, and a quarter wave-length for your (+). Which makes a combined total of 1/2 wavelength. Still very long, but…yeah!

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