VLF Emissions are Natural Radio signals that are thought to originate in the magnetosphere on the sunward side of the earth near the geomagnetic equator and then propagate toward the poles along the field lines where they exit the ionosphere and propagate along the surface of the earth where they may be heard. While the mechanism is understood in the general sense, much still remains to be learned. VLF emissions include chorus, risers, hiss, and a variety of other signals. They are often heard during times of high geomagnetic activity.
Finding a quiet listening location is usually the biggest challenge facing the Natural Radio listener. Power lines emit signals that are in the same frequency range of the signals that we want to hear, so the obvious solution is to get away from power lines. For good listening, you should be at least a couple of miles from high-voltage transmissions lines (These are the lines with big insulators that are usually on metal towers, but occasionally poles. They carry electricity from the power generating stations to the sub-stations.) You’ll want to be a half mile or more from distribution lines (These lines carry the power from the sub-stations to homes and businesses.)
Large parks and Nature preserves are the obvious places to start. Finding places with access in the pre-dawn hours is often difficult, but once you have searched out your “quiet sites” you’ll be set. Aeronautical maps sometimes show the larger transmission lines or you can locate them out by driving around and plotting them on a map. This will help you locate parks or other open areas in potentially quiet locations. Spending a few weekends driving around with a portable receiver should enable you to locate some good listening locations.
Natural Radio signals can be heard at any time of day but are most likely in the predawn hours. Chorus and VLF emissions can be heard up to several hours after sunrise, especially when there is strong geomagnetic activity. Sferics are heard almost all of the time, and tweeks are usually heard during the night time hours.