Natural Radio signals occur within the range of human hearing, so no frequency conversion or demodulation is necessary. All that is necessary is to amplify the signal and convert it from a radio wave to audio so that it can be heard. At its simplest, a Natural Radio receiver is a high-gain audio amplifier with an antenna on the input and headphones or a speaker on the output.

(There are naturally occurring signals that extend above and especially below the range of human hearing, but the most common signals fall within our hearing range.)

I remember stories of the early Natural Radio pioneers in the 80s, going out into the desert with a cassette recorder and hooking up a long wire to the hot side of the microphone input, and that was all that was needed to hear spherics and whistlers.

The only real complexity you need to add to a receiver is low-pass filtering on the front end to prevent overloading from strong out-of-band signals, plus some form of filtering to remove some of the annoying hum and buzz from power mains that plagues the Natural Radio listener.

Receivers are of two basic types: E-Field and H-Field. An electromagnetic wave has both an electric-field component and a magnetic-field component.

Natural radio receivers using a whip are called E-Field receivers, and those using a loop are called H-Field receivers. The advantage of the whip is that it makes for a small, light, easily transportable receiver.

Loop receivers (H-Field) typically use a loop two or more feet in diameter. Fixed H-field receivers often use a triangular single loop, often 10 feet or more per side. A portable loop can reduce noise because it is highly directional. Loops also work better in the woods, as trees tend to attenuate E-field signals, whereas trees do not eliminate H-field signals. The downside of a loop is that it is bulky to carry. Currently, the only commercial loop receiver available is extremely expensive.

A pair of crossed loops combined with an E-field probe and the appropriate electronics can provide a directional display, usually for spherics, so you can see the direction of a thunderstorm.

 Page created by Mark Karney