1859 or earlier – A geomagnetic storm in 1859 induced currents on long telegraph lines so high the coils at the receiving side sometimes burst into flames, or the operators received electric shocks. In other instances, the current induced by the geomagnetic storm led to diminishing of the signal, when subtracted from the battery polarity, or to overly strong and spurious signals when added to it. Operators in such cases learned to disconnect the battery and rely on the induced current as their power source. Other than Aurora, this was probably the first sensing of the effects of a geomagnetic storm. (Wouldn’t it be great to have a long antenna like that and absolutely no hum!)
1886 – Helliwell mentions that the first reports of whistlers came from a 22 km telegraph line at Sonnblick High Altitude Observatory in Austria with a telephone receiver connected. This is probably the first reception of a radio signal by humankind.
1894 – During an auroral display in March, British observers connected telephone receivers to telegraph lines and heard tweeks and possibly whistlers and chorus.
1899 – At his research facility in Colorado Springs, CO, Nikola Tesla reported hearing the voices of Martians while conducting experiments on locating lightning. In a 1989 column in The Lowdown, Michael Mideke speculated that what Tesla heard might have been Natural Radio sounds. That is still indeed a very interesting speculation.
1919 – During World War I, vacuum tube amplifiers connected to widely separated ground rods were used to eavesdrop on the telephone conversations of the other side by picking up ground currents induced by the field telephones. H. Barkhausen’s paper mentioned that at certain times strange whistling sounds could be heard on these devices. Those monitoring these units would report, “You can hear the grenades fly.” Barkhausen suggested that these strange sounds might correlate with meteorological disturbances. He even considered that the amplifiers themselves might be causing the sounds, but despite extensive testing, he never reproduced the phenomenon in the laboratory. He finally concluded that the sounds were of unknown origin.
1925 – 1929 – T. L. Eckersley published a series of papers and postulated the existence of a dispersive medium. His observations indicated that whistlers were associated with magnetic storms. An article titled “Musical Atmospherics was published in Nature in 1935.
1930 – In another paper, Barkhausen offered two possible explanations for whistlers. The first, which is caused by a series of multiple reflections between the earth and the ionosphere, is the same method that produces tweeks. In the second, Barkhausen proposed a dispersive medium. He indicated that a remote lightning stroke, a direct current impulse that contains all frequencies, was the initiating event. He was at a loss, however, to explain the long duration and low attenuation of whistlers. He concluded that more observation would be needed.
From 1931 to 1951, almost no Natural Radio research was being done. This was mostly due to WWII. Interestingly, until the 1950s, only about 15 papers had been published on Natural Radio phenomena.
Research surged in the ‘50s after the war and was aided by the invention of the tape recorder, which made capturing and studying these signals possible.
1950 – Professor Robert Helliwell and his associate Jack Mallinckrodt were studying tweeks at Stanford University and heard long (1-3 s) whistlers of descending frequency mixed in with the tweeks. This began his research into whistlers and other atmospheric phenomena.
1950s – L.R.O. Storey, in Cambridge, England, begins a serious study of the nature and origin of whistlers. Through his observations of whistlers, he formed the basis of the “magneto-ionic” theory of their origin, as well as a magnetic storm’s effect on whistlers. Story’s research made an important contribution to the growing body of knowledge about whistlers by showing that whistlers followed the Earth’s magnetic field lines.
1953 – L. R. Owen Storey publishes “Study of Whistling Atmospherics” in Phil. Trans. Roy. Soc., 1953
1953 – The Naval Research Laboratory begins studying whistlers in 1953. The lab’s VLF expert at the time was Harold E. Dinger, who made substantial contributions to radio propagation, radio interference reduction, frequency management, and geomagnetics. Dinger wrote a book in 1956 titled Whistling Atmospherics, published by the NRL. The abstract of Dinger’s book summarizes what the laboratory was doing in the early 50s:
Since 1953 NRL has been observing and recording audio-frequency atmospherics and their correlation with other geophysical phenomena. Beginning in April 1955, the diurnal variation in both whistler activity and the occurrence of “dawn chorus” has been determined. Whistler coincidence at several locations has been recorded in an attempt to prove L.R.O. Storey’s theory on the mode of propagation of these atmospherics. Many whistlers of unusual character have been spectro-analysed for the purpose of extending present theory to cover the general case. Plans have formulated for synoptic observations at a number of selected locations during the International Geophysical Year.
1955 – Emory Cook released several Natural Radio recordings on disk. One of them, Out of This World, featured sounds of whistlers, tweeks and the dawn chorus. These recordings were done in collaboration with Dr. M.G. Morgan, Thayer School of Engineering, Dartmouth College, Hanover, N.H.
Ionosphere was released in 1955 and contains simultaneous Natural Radio recordings made in Hanover, NH, near Dartmouth College, where Professor Morgan was on staff, and Washington, DC. Hanover and Washington are separated by about 415 miles or 665 km, which generates some very wide-spaced stereo. I assume that this recording was done in cooperation with the Naval Research Laboratory.
1956 – Don Gleason wrote a pair of articles in the December 1956 issue of Popular Electronics that introduced readers to Natural Radio sounds. Thus, the world of Natural Radio was opened to all interested hobbyists. Don Gleason’s article, “How to Hear Whistlers,” outlined plans for a simple whistler receiver. The radio used a loop antenna. A few months later, Popular Electronics ran a Carl & Jerry story about whistlers.
1957 – The International Geophysical Year (IGY) was a pivotal event for Natural Radio, with over 50 receiving stations set up worldwide. A receiving station and transmitter were set up at Siple Station in Antarctica, and thus began a very intense period of whistler and geomagnetic research,
1958 – James Van Allen discover the radiation belts that surround earth, later named the “Van Allen Belts.” This discovery confirmed L.R.O. Storey’s measurement from several years earlier.
1960 – The launching of several satellites carrying VLF receivers in the early 1960s (Allouette, IEEE-1, Injun) allowed the detailed study of whistlers in the ionosphere, which greatly built on the body of knowledge from the IGY.
1965 – Robert Helliwell, a professor and researcher from Stanford University, published the book, Whistlers and Related Ionospheric Phenomena. This book is still the “bible” for Natural Radio listeners. It presents a formal theory for whistler propagation and details much of the research done during the IGY.
1970 – By the 1970s, research into space weather and related Natural Radio signals had exploded, as understanding these phenomena was essential to keep the growing number of satellites in healthy condition.
It is impossible to list all the significant research papers and studies, but the body of knowledge grows daily, as does our ability to predict the effects of solar activity on Earth and the associated space weather conditions. At this time, Natural Radio listening also emerged as a hobby, so the events that marked the hobby’s rise and amateur observations are listed here. Please note that the amount of research and discovery in the past 30 years is immense.
1975 – The LWCA is founded, and The Lowdown is published in California by W. R. McIntosh. At the time, the publication was an 8 ½” x 11″ mimeographed bulletin.
1980 – Sometime in the 1980s, the GOES satellites, which sit in geostationary orbits and have a primary mission of producing weather photos of Earth, began carrying sensing instruments to measure space weather.
1981 – W. R. McIntosh became too ill to continue publishing, and Bill Oliver took over The Lowdown, and the publication assumed its present form.
1988 – The HSGS (High School Ground Station) was established by Bill Taylor of NASA; Bill Pine, a high school physics teacher; and two amateur scientists, Michael Mideke and Jim Ericson. ACTIVE/HSGS was a test-bed project that involved 100 high schools observing transmissions from the Soviet ACTIVE satellite.
1989 – Michael Mideke coins the term “Natural Radio” and becomes the first Natural Radio Editor of The Lowdown.
1990s – The Internet. The arrival and growth of the Internet facilitated the exchange of information between Natural Radio hobbyists and eventually made real-time solar and geomagnetic information available to everyone. It’s hard to imagine this hobby without instant access to GOES and ACE data, as well as the excellent articles and discussion groups on the net.
1991 – Steve McGreevey and Frank Cathell created the WR-3 handheld whistler receiver and began selling it on a casual basis.
1991 – Following the proof of concept demonstrated through HSGS, INSPIRE was formally organized and incorporated. INSPIRE is a non-profit scientific, educational corporation whose objective is to bring high school students the excitement of observing natural and man-made radio waves in the audio region.
1995 – SOHO, Solar & Heliospheric Observatory, was launched on December 2, 1995, for what was originally planned as a two-year mission. Ten years later, it’s still going strong. SOHO was designed to study the internal structure of the Sun, its extensive outer atmosphere, and the origin of the solar wind, the stream of highly ionized gas that blows continuously outward through the Solar System.
1997 – The Advanced Composition Explorer, ACE, was launched on August 25, 1997, from the Kennedy Space Center in Florida. ACE orbits the L1 libration point, which is a point of Earth-Sun gravitational equilibrium about 1.5 million km from Earth. ACE measures a wide range of energy and nuclear mass under all solar wind flow conditions and during both large and small particle events, including solar flares. ACE provides near-real-time solar wind information over short time periods. When reporting space weather, ACE can provide an advance warning (about one hour) of geomagnetic storms that can overload power grids, disrupt communications on Earth, and present a hazard to astronauts.
2001 – Shawn Korgan forms the VLF_Group on Yahoo. The Natural Radio VLF group is a discussion group dedicated to those who enjoy monitoring radio frequencies in the VLF radio spectrum and slightly below the VLF (very low frequency) spectrum (3-30 kHz). Mark Karney takes over ownership of the group in 2002.
2006 – Robert Helliwell’s book, Whistlers and Related Ionospheric Phenomena, is re-released as a paperback, 40 years after the original publication.
2008 – The Natural Radio Lab website is officially launched in January.
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