UNESCO World Heritage Site Grimeton Radio

The Antenna

The Software Defined Receiver: SAQrx

First Steps Preparing for Reception


Listen to World Heritage Grimeton Radio (SAQ)

Grimeton Radio is the last transmitter in the world generating rf power without any electronic parts. No tubes, no semiconductors, only an engine driving an AC generator. Receiving Grimeton Radio (SAQ) on 17.2 kHz is as easy as the sketch below depicts:


Fig. 1:   Receiving Grimeton Radio with the aid of the computer’s sound card

You only need to connect an active antenna or some aerial wire to the sound card of your PC and to install SAQrx, a software defined VLF receiver by SM6LKM for the VLF band.

UNESCO World Heritage Site Grimeton Radio (SAQ)

Grimeton Radio (SAQ) is the last transmitter in the world preserved that generates VLF radio frequencies with an alternating current generator (alternator), i. e. a machine that nowadays is only known to produce AC current with frequencies below 100 Hz – electric power. After its inventor, a Swedish engineer, this type of transmitter is called Alexanderson Alternator (see Fig. 2 below).


Fig. 2:  The Alexanderson Alternator of Grimeton Radio
(photo: Gunther Tschuch;  Wikimedia Commons)

From the late 1860s to 1930 about 1.2 million unemployed people left Sweden to seek good fortune in the big cities of America. Grimeton Radio with the call sign SAQ was built in the 1920s to maintain communication between the Swedish emigrants and their home country. For years the transmitter was operated as a transatlantic telegraphy link to the RCA transmitter Radio Central in Long Island, New York, USA.

With the advent of tube transmitters and rising knowledge of worldwide propagation of short waves, VLF transmitters became less important. Grimeton Radio was adopted by the Swedish navy to communicate with submarines for the next decades and so could survive until the end of the 20th century. It was finally put out of service in the year 1995 – fully operative with 200 kW output and the last of its kind in the world.

As early as 1996, Grimeton Radio was declared to be a national heritage of Sweden and in the year 2004 it became a UNESCO World Heritage Site.



Fig. 3:  Lars Kålland, SM6NM, at the key at Grimeton
(photo: Mats Gunnarsson; courtesy Alexanderson Society)

Grimeton Radio (SAQ) is activated in cw transmission by the Alexanderson Society at least two times a year, at the beginning of July around the Alexanderson Day and on christmas eve (look out for skeds).

These are the rare moments, when US swls and hams have the opportunity to prove that the old lady in Sweden still can be copied at the east coast of the USA. Reports (from everybody, not only US hams!) are rewarded by qsl cards.

Have a look at some videos on this site and decide for yourself if it might be an exciting experience to listen to Grimeton Radio on 17.2 kHz.


The Antenna

Don’t waste much thought on creating a resonant antenna – the half wave length at 17.2 kHz is 8700 meters, much too long for your garden. And don’t think your antenna  is meant to last forever with a King Kong approved fastening and measures for lightning protection.

You just need the antenna for half an hour two times a year, so clamp a wooden holder for an active antenna into your shack window (see Fig. 1). Try the PA0RDT mini whip – it comes ready to use from a friendly Dutch radio amateur and is very tiny.

If you want to build a simple antenna by your own, try this example for a homebrew active antenna. Maybe you want to try a ferrite rod antenna. Our ancestors used it with great effort for long wave reception.

Antennas successfully used by US stations reach from a 4 foot loop portable on Port Mahon Beach (Dover, Delaware) to a 100 meter long zepp at 22 meters height at Marietta, Ohio. Find your own solution and don’t give up after the first try!

The Software Defined Receiver: SAQrx

SAQrx is a sound card based receiver software by Johan Bodin, SM6LKM, originally covering the frequency band from 0-22 kHz and running under Microsoft Windows. It requires a sound card capable of full duplex at 44 kHz sampling rate (satisfied by most of the onboard PC sound cards).

Roland Fröhlich, a mathematician and active long-/shortwave listener, extended the capabilities of SAQrx with lots of convenient features. You can now use sound cards up to 192 kHz sampling rate, change between modes (CW, SSB, AM), store and play soundfiles and much more. Please read his introduction to SAQrx to learn what options are included.

Once you have unzipped the zip file and started SAQrx*.exe, you will have a panoramic view of the frequency band decoded by your sound card (see screenshot below). Press [Help] to learn how to tune the receiver and change the bandwidth.

You can download the files needed from Roland’s web site (version 0.94) or from here: latest version 0.98.


screenshot v09


Fig. 4:   Screenshot of SM6LKM’s SAQrx, enhanced by Roland Fröhlich

First Steps Preparing for Reception of SAQ

For a first test, you should try to find a military transmission somewhere in the band pass of SAQrx. In Europe, there are several navy stations between 18 kHz and 22 kHz transmitting a constant MFSK signal. On weekdays, you may find them transmitting information using a two-tone or multi-tone FSK mode. Even at parts of the spectrum being quiet on other days, you may discover data transmissions. From time to time, there is a RTTY signal (? 45 baud) on 18.1 kHz, maybe transmitted by RDL, a Russian navy station.