Summary

8 to 300 kHz is the target frequency range for this Very Low Frequency (VLF) radio astronomy instrument.

Very Low Frequency or VLF extends from 30 kHz to 300 kHz. One can think of this as being from the high end of the audio frequency range to nearly the bottom of the AM radio band. Many natural processes have been found to emit radio frequency energy in this range. Fluctuations in the Earth's magnetic field and ionosphere create many spooky sounds (click on picture below for a wav file example). Meteors burning up in the atmosphere, and even earthquake energy is thought to manifest itself in VLF energy at times. With names like "dawn chorous", "spherics", "sudden ionospheric disturbances (SIDs)", and Schuman resonances, these phenomena make up the low end of radio astronomy.

PARI has a 12 ft x 12 ft 24 turn loop antenna for listening to VLF signals. The balanced loop configuration was chosen to improve our immunity to lightning static noise by concentrating on receiving the magnetic component of the VLF signals. PARI Volunteers: Tor Liholt, Tom Crowley, Andy Perry, David Jones, Dexter McIntyre, Chris Waldrup, and others helped with the construction or offered guidance in doing the system.

Click the image for an audio recording of some spooky natural VLF radio signals

A recent development involves connecting the system to our main control building over fiber optic cable. This allows us to only use an: antenna tuner, preamplifier, and fiber transceiver powered by battery/solar power. This greatly reduced the spurious signals the system was seeing from PCs and their video monitors. In effect the PC and receiver is a mile away over fiber optic cable.

A new receiver is being tried. Its a VLF-3 receiver kit designed for a NASA project called INSPIRE ( http://image.gsfc.nasa.gov/poetry/inspire/ ).

VLF is primarily a winter project in North America. Summer thunderstorm interference disturbs the readings even when received from thousands of miles away. Our system should be online from October thru March. Depending on atmospheric noise, it may be placed online at other times as well. SkyPipe ( http://radiosky.com ) is our primary data logging/sharing software for this system.

      Natural Radio Signals
      LF and VLF radio monitoring