Sferics
What the hell are Sferics?
A radio atmospheric signal or sferic (sometimes also spelled “spheric”) is a broadband electromagnetic impulse that occurs as a result of natural atmospheric lightning discharges. Sferics may propagate from their lightning source without major attenuation in the Earth–ionosphere waveguide, and can be received thousands of kilometres from their source.
Why catch them?
Microsferics is a nice reference Project, which is a network of Sferics antennas, which are used to detect lightning strikes. Through triangulation not unlike the Maths happening in GPS, the (more or less) exact location of the strike can be determined. This is useful for weather prediction, but also for the detection of forest fires, which are often caused by lightning strikes.
Because the Frequency of the Sferics is, when converted to audio, still in the audible range, it is possible to listen to the strikes. This usually sounds a bit like a crackling noise, but can also be quite melodic. I was a bit reminded by a Geiger Counter.
Sferics are in the VLF (Very Low Frequency) range, sitting roughly at 10kHz, which is a bit of a problem for most radios, as they are not designed to pick up such low frequencies. This is why we built our own antenna. At 10kHz, we are talking about insanely large waves. a single wavelength there is roughly 30 Kilometers. This is why the antenna needs to be quite large. A special property of waves this large is, that they get easily reflected by the Ionosphere and the Earth’s surface. Effectively, a wave like this can bounce around the globe several times before it is absorbed by the ground. This is why we can pick up Sferics from all over the world and even listen to Australian Lightning strikes. Of course, without the maths, we cannot attribute directions, but the so called “Tweeks” we picked up, usually come from at least 2000km distance.
The Build
We built several so-called “Long-Loop” antennas, which are essentially a coil of wire with a capacitor at the end. Further, a specific balun is needed, depending on the length of the wire. this can then directly output an electric signal on an XLR cable.
Loosely based on instructions from Calvin R. Graf, We built a 26m long antenna, looped several times around a wooden frame.
The Result
We have several hour-long recordings of the Sferics, which we are currently investigating for further potential.
Have a listen to a recording of the Sferics here:
As you can hear, there is quite a bit of 60 hz ground buzz in the recording. This is either due to the fact that the antenna was not properly grounded or we simply were still too close to the bustling city. I think it is already surprising that we got such a clear impression so close to Berlin. Let’s see what we can get in the countryside!
