Earth’s ionosphere reacts strongly to the intense x-ray and ultraviolet radiation released by the Sun during a solar event. By using a receiver to monitor the signal strength from distant VLF (very low frequency) transmitters you can indirectly monitor solar activity by tracking SID (Solar Ionospheric Disturbance) events. The easiest way to do this is using loop antenna which is connected to PC soundcard. My setup consist of the loop antenna that is connected to amplifier and filter to reduce noise. The filter is bandpass with low cuttoff at around 15kHz and high cuttoff at around 50kHz. Output of the filter is then connected to the computer soundcard. It has sample rate of 44kHz so I can monitor stations up to 22kHz. With better/newer card you have sample rate up to 192kHz, and you can monitor larger portion of radio spectrum. ScpetrumLab
software is used to collect data. With this software I can monitor multiple stations at the same time.
Here are two sample plot pictures that I get with my receiver, you can even see today’s plots
and plots for previous days
. The first one is taken on a quiet day without any solar activity. On both pictures I marked typical shapes of Sid, sunset, sunrise.
Professional measurement of solar activity are made by GOES, SOHO, SDO satellites. Images and plots made by them can be seen on this page under Astro and weather forecast -> Space weather.
The monitoring station is located in the Kranj, Slovenia. It has the AAVSO observer code A129. Five stations between 19kHz and 24kHz are monitored and two with most SID events are used for reporting data to AAVSO Solar Section.
Read more about SID detectors: