Natural Radio, a term coined by Michael Mideke, first Natural Radio editor of The Lowdown; is electromagnetic energy from natural phenomena, occuring at Very Low Frequencies (VLF) and Extremely Low Frequencies (ELF). The frequencies are so low, in fact, that if they were acoustic waves instead of electromagnetic waves, many of these signals would be in the range of human hearing. Therefore, receiving natural radio is basically a matter of connecting a suitable antenna to a high-gain audio amplifier!  Some of these phenomena are not too hard to hear, though it helps to be away from power lines. The most interesting natural radio signals are a lot lower level than power line hum in the typical residential area.

Sferics" is short for atmospherics, the radio waves caused by lightning.  They sound like the static you hear on an AM radio when thunderstorms are nearby.

Tweeks are sferics where the frequencies have been subject to dispersion by travelling a long distance through the earth-ionosphere waveguide. They have a metallic ringing sound and are usually heard between sunset and sunrise and are more prevalent in the winter.

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.

Chorus or "Dawn Chorus" is a VLF emission that can sound like a flock of birds or the sound of a pond full of frogs or some combination thereof.  The name "dawn" chorus may have originated because it sounds like birds, frogs and insects in the morning or because it is most often heard just after sunrise. Chorus is often heard in the early morning hours during periods 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.

Natural Radio receivers are a high gain audio amplifier connected to an antenna. There are several kits and prebuilt receivers available. It is also easy to build your own if you have basic electronics experience. See the Equipment & Software section of this website.

Sferics and tweeks can be heard almost anywhere, but whistlers and VLF emissions are more prevalent in northern and southern latitudes. These signals are rarely heard in the tropics. Since whistlers and VLF emissions propagate along the earth' field lines, they tend to exit the ionosphere at higher latitudes and thus are more often heard there. Whistlers tend to be most prevalent around a geomagnetic latitude of 50 degrees. In the USA there seems to be better Natural Radio reception in the Western States as opposed to the eastern states and Midwest. I don't know of any studies that have been done on this, but it may be due to the fact that there are more open spaces away from power lines and thus better listening locations in the west. It also may be due to some other phenomenon.

Power line interference in the form of hum and buzz is very disruptive of Natural Radio listening. Your best listening will be when you are as far away from power lines as possible. You should be at least a couple of miles from transmission lines (The lines with big insulators, usually on metal towers) and a half mile or more from distribution lines (the lines that bring power to homes and businesses.) This isn't difficult in a rural area, but is tough for the city or suburban dweller. Look for parks and other open spaces, or even neighborhoods with underground power lines. Finding a quiet listening area that is accessible during the pre-dawn hours is often the biggest challenge for the natural Radio Listener.

Electrical transmission and distribution lines are almost everywhere. Since most of these lines carry AC power that signal tends to radiate. If it were just the 50 or 60 Hertz power frequency that were the problem it would be easy enough to filter out. Unfortunately, non-linearities on the power lines like motors, bad insulators and all the other things we connect to them tend to generate harmonics all the way through the audible range. Of course these are fairly strong and in the same band of frequencies as the weaker Natural Radio signals that we want to hear.  Although some filtering may help, the best solutions is to get away from the power lines. 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.)

Often those who are new to the hobby as well as casual listeners get frustrated by not hearing much more than spherics and tweeks. When I started listening, it was well over a year before I heard anything of significance, mainly because I was listening in the wrong place at the wrong time. My results got a lot better with experience. 1. Listen When You're Likely to Hear Something. Natural Radio phenomenon can happen at any time but there are times of day and times of the year when you are more likely to have a productive listening session. In general, winter is better than summer because there is less interference from local thunderstorms, allowing you to hear fainter Natural Radio signals. Whistlers tend to occur mostly after midnight with activity peaking just before sunrise -- you are much less likely to hear whistlers in the middle of the afternoon. Whistler activity tends to peak around the spring and fall equinoxes. VLF Emissions like chorus tend to peak just after sunrise and may continue into the morning hours. Geomagnetic storms almost always produce VLF emissions, so it's good to check the Spaceweather Today site at http://www.sec.noaa.gov/today.html or monitor WWV at 18 minutes past each hour for space weather reports. If the planetary K index is 6 or greater, there is a very good likelihood that you will be able to hear VLF Emissions. 2. Get Away From Power Lines. The strongest signals in the Natural Radio band are the power line frequency and its harmonics. In a typical suburban neighborhood the power line signals can be strong enough to obliterate all but the loudest spherics. For good reception, you should be at least two miles from power transmission lines (The ones on the steel towers, or on large wood poles with insulators at least a foot long). You should also try to be at least ¼ mile or more from distribution lines. (These are the ones that deliver the power to homes and neighborhoods.) There are a lot more weak Natural Radio Signals than strong ones, and getting rid of background hum and buzz will increase your ability to hear them. It's also easier on the ears without the obnoxious hum and buzz in the background. 3. Get Away From Trees and Other Obstructions. If you are using an E-Field receiver, make sure you are out in the open. Trees and other objects tend to short out the electrical field in their vicinity. Try this experiment. Walk out in an open field listening to spherics - then as you are listening, walk toward a tree. As you get close to the tree, the decrease in signal strength will be dramatic. If you are using a hand held receiver, try holding the antenna above your head, this should help increase signal strength. 4. Make Sure Your Equipment Is Working Properly. Verify that the batteries are good. When batteries weaken to a certain point they can cause a major gain reduction in many receivers - this can happen suddenly, so always carry a spare set of fresh batteries.

All electromagnetic waves have two components, the electrical component, called the E-field and the magnetic component, called the H-field. Natural radio receivers are designed to respond to one or the other component. An E-field receiver responds to the electrical component of the wave and usually employs a short whip antenna. An H-field receiver responds to the magnetic component and usually has a loop antenna.

All electromagnetic waves have two components, the electrical component, called the E-field and the magnetic component, called the H-field. Natural radio receivers are designed to respond to one or the other component. An E-field receiver responds to the electrical component of the wave and usually employs a short whip antenna. An H-field receiver responds to the magnetic component and usually has a  loop antenna.

It has been realized and appreciated only in the last few decades that solar flares, CMEs, and magnetic storms affect people and their activities. The list of consequences grows in proportion to our dependence on technological systems. The subtleties of the interactions between Sun and Earth, and between solar particles and delicate instruments, have become factors that affect our well being. Thus there will be continued and intensified need for space environment services to address health, safety, and commercial needs.

A geomagnetic storm is a worldwide disturbance of the earth's magnetic field, distinct from regular day/night variations.

The K-index is a code that is related to the maximum fluctuations of the horizontal components of the magnetic field measured on a given magnetometer, and relative to a geomagnetically quiet day. Each geomagnetic observing station generates its own K index and the weighted average of all stations is Kp or the Planetary K-index. Because of its method of calculation, the Kp-index is not real time. At SEC (Space Environment Center, NOAA), the final real-time K-index which is referred to as the "Estimated K_p", (as opposed to the official K_p) appears on the website http://www.sec.noaa.gov/today.html, and is determined after the end of the prescribed three hour intervals (0000-0300,0300-0600, ..., 2100-2400). The maximum negative and positive deviations in the horizontal components during a given 3 hour period are added together to get the total maximum fluctuation. The Kp-index ranges from 1-9, with 1 being very quiet and 9 indicating major geomagnetic activity. When the Kp approaches 6, Natural Radio activity is usually high. If the Kp is 6 or greater I am almost always able to hear chorus and VLF emissions for an hour or two after sunrise.

Sunspots are areas seen as dark spots on the photosphere of the sun. Sunspots are concentrations of magnetic flux, typically occurring in bipolar clusters or groups. They appear dark because they are cooler than the surrounding photosphere. Sunspots vary on an eleven year cycle. Geomagnetic activity on Earth roughly coordinates with the sunspot cycle. The period of minimum sunspots usually means low geomagnetic activity on Earth.

The outer solar atmosphere, the corona, is structured by strong magnetic fields. Where these fields are closed, often above sunspot groups, the confined solar atmosphere can suddenly and violently release bubbles or tongues of gas and magnetic fields called coronal mass ejections. A large CME can contain 10.0E16 grams (a billion tons) of matter that can be accelerated to several million miles per hour in a spectacular explosion. Solar material streaks out through the interplanetary medium, impacting any planets or spacecraft in its path. CMEs are often associated with flares but can also occur independently. If a CME hits earth, it can cause a geomagnetic storm. The intensity of the storm will be affected by the orientation of the CME's magnetic field, its speed and density. A strong CME hit often causes Aurora displays at low latitudes.

The Solar Wind is the outward flux of solar particles and magnetic fields from the sun. Typically, solar wind velocities are near 350 km/s.

Plasma is a very hot ionized gas -- that is, electrons have been stripped of atoms leaving negatively charged electrons and positively charged ions. Because it is ionized, it is conductive. The ionosphere and magnetosphere contain mostly plasma.

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The earth's magnetic poles are not at the north and south geographic poles. Therefore, geomagnetic latitude & longitude and the geomagnetic equator differ from the corresponding geographic values. The earth's magnetic poles tend to wander slowly and thus the geomagnetic latitude, longitude and equator will vary slowly over time.

INSPIRE (http://theinspireproject.org) is a non-profit scientific, educational orporation whose objective is to bring the excitement of observing natural and manmade radio waves in the audio region to high school students. Underlying this objective is the conviction that science and technology are the underpinnings of our modern society, and that only with an understanding of science and technology can people make correct decisions in their lives, public, professional, and private. Stimulating students to learn and understand science and technology is key to them fulfilling their potential in the best interests of our society. INSPIRE also is an innovative, unique opportunity for students to actively gather data that might be used in a basic research project.