VLF Reception (Natural Radio)
Daktologist
Global Moderator
The VLF frequency band can be very interesting to try and receive at times
Natural Radio is a fancy name for radio noise with natural origins, mainly lightning. At first, you might think that listening to lightning crackles is pretty uninteresting but as it turns out, electromagnetic radiation from lightning can travel great distances and undergo strange modifications along the way. The frequencies of the original pulse can be spread out in time (a process called "dispersion) because the higher frequencies travel a little faster than the lower.
The result is that the short impulse from a lightning strike in South America can sound like a chirp in Texas. Slower sweeping tones are called "whistlers" and they are a bit of a mystery. The energy from a lightning bolt streams out into space into a region called the "magnetosphere", magnetized plasma created by the interaction of solar wind with the earth's magnetic field. The lightning pulse is reflected or "ducted" back down to earth after a very long trip during which time the frequencies are spread out by a dispersion-like process. Short whistlers might be due to dispersion, but some whistlers last five seconds so ordinary dispersion is probably inadequate an explanation. A radio wave can travel a million miles in five seconds so to accumulate that much difference in arrival times, the signal would have to travel hundreds of millions of miles. When conditions are just right, numerous lightning strikes combine with numerous reflections to give an eerie chorus that sounds a bit like a flock of geese.
The ever-present power line hum makes listening to these signals difficult near power lines but reception programs are fast enough to digitally clean up the signal, making natural radio listening a practical activity. Spectrum Lab( Google it) is an excellent program for receiving VLF radio and has many different modes making it very versatile in receiving natural radio and submarine comms. an antenna can be made from a large coil of insulated solid core wire connected to the line in jack on your sound card. Many websites offer info on VLF and can provide more info then i can fit into a single post but hopefully i have got you wondering about this easy project that only needs a pc and a coil of wire.
Daktologist
Natural Radio is a fancy name for radio noise with natural origins, mainly lightning. At first, you might think that listening to lightning crackles is pretty uninteresting but as it turns out, electromagnetic radiation from lightning can travel great distances and undergo strange modifications along the way. The frequencies of the original pulse can be spread out in time (a process called "dispersion) because the higher frequencies travel a little faster than the lower.
The result is that the short impulse from a lightning strike in South America can sound like a chirp in Texas. Slower sweeping tones are called "whistlers" and they are a bit of a mystery. The energy from a lightning bolt streams out into space into a region called the "magnetosphere", magnetized plasma created by the interaction of solar wind with the earth's magnetic field. The lightning pulse is reflected or "ducted" back down to earth after a very long trip during which time the frequencies are spread out by a dispersion-like process. Short whistlers might be due to dispersion, but some whistlers last five seconds so ordinary dispersion is probably inadequate an explanation. A radio wave can travel a million miles in five seconds so to accumulate that much difference in arrival times, the signal would have to travel hundreds of millions of miles. When conditions are just right, numerous lightning strikes combine with numerous reflections to give an eerie chorus that sounds a bit like a flock of geese.
The ever-present power line hum makes listening to these signals difficult near power lines but reception programs are fast enough to digitally clean up the signal, making natural radio listening a practical activity. Spectrum Lab( Google it) is an excellent program for receiving VLF radio and has many different modes making it very versatile in receiving natural radio and submarine comms. an antenna can be made from a large coil of insulated solid core wire connected to the line in jack on your sound card. Many websites offer info on VLF and can provide more info then i can fit into a single post but hopefully i have got you wondering about this easy project that only needs a pc and a coil of wire.
Daktologist