Thursday, December 10, 2009

Receiving SAQ on VLF

Roger G3XBM has posted a reminder in his blog that the Swedish station SAQ will be making a special Morse transmission today on 17.2KHz VLF to celebrate the 100th anniversary of the Nobel Prize award to Guglielmo Marconi and Karl Ferdinand Braun.

As 17.2KHz is in the audio spectrum it should be possible to receive this transmission with nothing more than a computer sound card. And Johan SM6LKM has written a software defined radio (SDR) program that will do just that. All you have to do is download the program from his web page, unzip it to a suitable folder (it's tiny, and there is no installer) and run it.

You need to connect an antenna to the left channel of the sound card microphone input (the program uses the Windows default sound card.) I don't have a long wire or any other VLF antenna so I have just used the outer (screen) of the feeder to my attic multiband dipole. Check that you have enabled the microphone input and increase the volume slider to maximum. The program will tell you if the input level is too high. You should see signals appear that disappear when you disconnect the antenna.

You can then increase the output gain in the program itself until you can hear the background noise. I can hear a few warbly carriers near the top part of the spectrum, as you can see in the screenshot above, and the occasional burst of static, so I'm definitely receiving something off-air and not just locally generated noise. There's a button that will set the correct frequency for the SAQ transmission.

It's too late for the transmission that was sent at 0800UTC today, but another is scheduled for 1600UTC. I have no idea if it will be possible to receive it with such a simple setup and poor antenna but it will be fun to try. If you read this too late for that, then there will be another transmission at 0800UTC on Christmas Eve, December 24th. I'd be interested to hear if anyone manages to receive it using this program, and with what antenna.
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