This project detects solar flares by their effect on the ionosphere.  When the X-rays from a solar flare hit the rarified upper atmosphere, they ionize air molecules and temporarily increase the electron density.  This causes a sudden improvement in the propagation of VLF radio waves on the day side of the Earth.  Depending on the geometry of the propagation paths between transmitter and receiver, this results a sudden increase or decrease in the received signal strength.  By continuously monitoring the signal strength of multiple VLF transmitters, solar flares can be identified.

Several navies around the world operate high-power VLF transmitters in order to communicate with their submarines at depth.  The transmissions comprise a continuous encrypted data stream.  We don't care about the content of the data, but only the received signal strength. 

The system includes:

• 4ft x 4ft square loop antenna of 19AWG magnet wire.

• Two-stage preamplifier circuit.  (Variation of the Ideal Loop amplifier).

• Raspberry Pi with FE-PI AUDIO V1 codec hat (SGTL5000) using 96 KHz sample rate. 

The software implements a 19 - 25 KHz VLF receiver with FFT processing and continuous recording of multiple stations.  

Up to six stations are detectable from this site, in order of decreasing signal strength: