Electric Enigma: The VLF Recordings of Stephen P. McGreevy - Irdial

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Few people know of and even less peoplehave been fortunate enough or had thegumption to tune into the beautiful radio

“music” produced naturally by several processesof nature including lightning storms and aurora,aided by events occurring on the Sun. I havebeen fascinated with listening to naturally-occur-ring radio signals since about the middle of1989, hearing my first whistlers almost immedi-ately after first trying out a rudimentary receiv-ing apparatus I had put together for the occa-sion.Whistlers, one of the more frequent naturalradio emissions to be heard, are just one of manynatural radio “sounds” the Earth produces at alltimes in one form or another, and these signalshave caught the interest and fascination of asmall but growing number of hobby listenersand professional researchers for the past fourdecades.

“Natural Radio”, a term coined in the late1980’s by California amateur listener andresearcher Michael Mideke, describes naturally-occurring electromagnetic (radio) signals ema-nating from lightning storms, aurora (TheNorthern and Southern Lights), and Earth’s mag-netic-field (the magnetosphere). The majority ofEarth’s natural radio emissions occur in theextremely-low-frequency and very-low-frequen-cy (ELF/VLF) radio spectrum specifically, atAUDIO frequencies between approximately 100

to 10,000 cycles-per second (0.110 kHz). Unlikesound waves which are vibrations of air mole-cules that our ears are sensitive to, natural radiowaves are vibrations of electric and magneticenergy (radio waves) which though occurring atthe same frequencies as sound cannot be lis-tened to without a fairly simple radio receiver toconvert the natural radio signals directly intosound.

Whistlers are magnificent sounding bursts ofELF/VLF radio energy initiated by lightningstrikes which “fall” in pitch. A whistler, as heard inthe audio output from a VLF “whistler receiver”,generally falls lower in pitch, from as high as themiddle-to-upper frequency range of our hearingdownward to a low pitch of a couple hundredcycles-per-second (Hz). Measured in frequencyterms, a whistler can begin at over 10,000 Hzand fall to less than 200 Hz, though the majorityare heard from 6,000 down to 500 Hz.Whistlerscan tell scientists a great deal of the space envi-ronment between the Sun and the Earth andalso about Earth’s magnetosphere.

The causes of whistlers are generally wellknown today though not yet completely under-stood.What is clear is that whistlers owe theirexistence to lightning storms. Lightning strokeenergy happens at all electromagnetic frequen-cies simultaneously that is, from “DC to Light”.Indeed, the Earth is literally bathed in light-

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ning-stroke radio energy from an estimated1,500 to 2,000 lightning storms in progress atany given time, triggering over a million light-ning strikes daily. The total energy output oflightning storms far exceeds the combinedpower output of all man-made radio signalsand electric power generated from powerplants. Whistlers also owe their existence toEarth’s magnetic field (magnetosphere), whichsurrounds the planet like an enormous glove,and also to the Sun. Streaming from the Sun isthe Solar Wind, which consists of energy andcharged particles, called ions. And so, the com-bination of the Sun’s Solar Wind, the Earth’smagnetic field surrounding the entire Planet(magnetosphere), and lightning storms allinteract to create the intriguing sounds ofwhistlers.

How whistlers happen from this combina-tion of natural solar-terrestrial forces is(briefly) as follows: Some of the radio

energy bursts from lightning strokes travel intospace beyond Earth’s ionosphere layers and intothe magnetosphere, where they follow approxi-mately the lines-of-force of the Earth’s magneticfield to the opposite polar hemisphere along“ducts” formed by ions streaming toward Earthfrom the Sun’s Solar Wind. Solar Wind ions gettrapped in and aligned with Earth’s magnetic

field. As the lightning energy travels along afield-aligned duct, its radio frequencies becomespread out (dispersed) in a similar fashion tolight shining into a glass prism. The higher radiofrequencies arrive before the lower frequencies,resulting in a downward falling tone of varyingpurity.

In this manner, a whistler will be heard manythousands of miles from its initiating lightningstroke and in the opposite polar hemisphere!Lightning storms in British Columbia and Alaskamay produce whistlers that are heard in NewZealand. Likewise, lightning storms in easternNorth America may produce whistlers that areheard in southern Argentina or even Antarctica.Even more remarkably, whistler energy can alsobe “bounced back” through the magnetospherenear or not-so-near the lightning storm fromwhich it was born! There will be additional dis-cussion of this “theory of whistlers” in the nextfew pages.

Considered my many listeners to be the“Music of Earth”, whistlers are amongst theaccidental discoveries of science. In the late

19th century, European long-distance telegraphand telephone operators were the first people tohear whistlers. The long telegraph wires oftenpicked up the snapping and crackling of light-ning storms, which was mixed with the Morse


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code “buzzes” or voice audio from the sendingstation. Sometimes, the telephone operators alsoheard strange whistling tones in the back-ground. They were attributed to problems in thewires and connections of the telegraph systemand disregarded. The first written report of thisphenomenon dates back to 1886 in Austria,when whistlers were heard on a 22-km (14mile) telephone wire without amplification. Apaper by W.H. Preece (1894) appearing in NatureMagazine describes operators at the BritishGovernment Post Office who listened to tele-phone receivers connected to telegraph wiresduring a display of aurora borealis on March 30& 31, 1894. Their descriptions suggest theyheard whistlers and the “bubbling/murmuring”sounds of “Chorus” from aurora.

During World War I, the Germans and Alliedforces both employed sensitive audio-amplifiersto eavesdrop on the enemy’s telephone commu-nications. Metal stakes were driven into theground next to enemy telephone wires and wereconnected to tube-type high-gain amplifiers,whereby the audio signal in the telephone wirescould be eavesdropped.This early form of elec-tronic espionage worked fairly well most of thetime, despite the bubbling and crackling back-ground noise made by lightning but not always.On some days, the telephone conversations theywere eavesdropping on were partially or wholly

drowned out by strange whistling sounds.Soldiers at the front would say,“you can hear thegrenades fly”. These whistling sounds, describedas sounding almost like “piou”, were at first attrib-uted to the audio amplifiers’ circuitry reactingadversely to strong lightning discharge noises.When laboratory tests on the high-gain audioamplifiers failed to recreate the whistling sounds,the phenomena was then considered “unexplain-able” at that time. (H. Barkhausen, 1919).

In 1925, T. S. Eckersly of the Marconi WirelessTelegraph Company in England, described dis-turbances of a musical nature that had been

known to “radio” engineers for many years. Theywere heard when a telephone or any other“audio-recorder” system was connected to alarge aerial.What they were hearing are nowknown as “tweeks”, a common ringing and ping-ing sound that lightning discharge radio energy(sferics) atmospherics sound like at night with aVLF receiver or audio amplifier. Several peoplebegan to observe how lightning and auroral dis-plays coincided with many of the strange soundsthey were hearing with their audio apparatus(Barkhausen, Burton, Boardman, Eckersly, et al.).In the 1930’s, the relationship of whistlers andlightning discharges was hypothesized, and in1935, Eckersly arrived at the commonly acceptedexplanation that lightning initiated radio waves


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traveling into Earth’s “ionosphere” caused thesetweek sounds.They were getting “close”.

Interest in whistlers waned during World War IIbut was renewed with the development of soundspectrographs and spectrum analyzers, whichcould trace the time-versus-frequency compo-nent of audio sounds.This technology was devel-oped mainly for the study of the sound charac-teristics of speech and other sounds, but thesealso were fine tools for the exploration ofwhistlers, as well (R. K. Potter, 1951).

It was during this time that L.R.O. Story inCambridge, England, had begun an in-depthinvestigation into the nature and origin ofwhistlers. Armed with information presented byBarkhausen, Boardman, et al., a homemade spec-trum analyzer and other audio-frequency radioequipment, Storey studied whistlers in earnest,discovering several types of whistlers that wereor were not audibly associated with lightning dis-charge “clicks” in the receiver. He was able tomake graphs of many kinds of whistlers, formingthe basis of the modern “magneto-ionic” theoryof their origin, and also the effects of Earth’smagnetic storms on whistlers.

Storey’s conclusion that whistlers were formedby lightning discharge energy echoing back andforth along the lines-of-force of earth’s magneticfield suggested that there was a much higherthan expected ion density in the outer ionos-

phere and beyond, and that the source of this“extra” ionization was linked to the sun. He also(correctly) presumed these ions from the sun alsowere responsible for magnetic storms and auroraldisplays.

Storey, while mainly concentrating onwhistlers, was able to hear and categorize a num-ber of other audio-frequency emissions that heheard, including Dawn Chorus, steady hiss, andcertain “rising whistlers”, also known as “risers”.Story’s studies throughout the early-to-mid1950’s made an important contribution towhistler theory by showing that whistlers travelvery nearly in the direction of Earth’s magneticfield. In 1952, the results of Storey’s work werepresented by J. A. Radcliffe to the Tenth GeneralAssembly of the URSI held in Sydney Australia,exciting considerable interest among the dele-gates in attendance. Radcliffe’s report greatlystimulated whistler research at StanfordUniversity, headed by the “Father of WhistlerResearch”, R. A. Helliwell.

In 1954 at the next URSI General Assembly heldin the Hague (Netherlands), whistler theorywas discussed in depth, and plans were

devised to study whistlers at opposite “conjugate”points of Earth’s magnetic field. Lightning stormatmospherics observed in one hemisphere wereheard as “short whistlers” (1-hop whistlers) in the


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opposite hemisphere.This notable observationwas conducted by Helliwell at Stanford inCalifornia and aboard the U.S.S. Atka located inthe South Pacific near the opposite magneticconjugate point. Lightning storms generatingatmospheric static “pops” as heard in the ship’sonboard VLF receivers were heard nearly simul-taneously in Stanford as short whistlers. Evenmore verification of Storey’s whistler was con-firmed by the observation of whistler “echotrains” simultaneously heard in Alaska and inWellington, New Zealand, which lies at the oppo-site magnetic conjugate from Alaska.

With this generalized history of whistler dis-covery and research in mind, I should pause thishistory lesson and now explain whistler theory insomewhat greater detail. The generally acceptedtheory of whistlers (Storey, Morgan, Helliwell) isas follows (the following few paragraphs aretaken directly from the text of my WR-3“Whistler Receiver” Listening Guide and repeatsome information presented earlier in this articleas well as hopefully making clearer some termsI’ve been tossing about):

The Earth’s outer magnetic field (the“magnetosphere”) envelopes the Earth inan elongated doughnut shape with its“hole” at the north and south magneticpoles. The magnetosphere is compressed

on the side facing the Sun and trails intoa comet-like “tail” on the side away fromthe Sun because of the “Solar Wind”which consists of energy and particlesemitted from the Sun and “blown”toward Earth and the other planets viathe Solar Wind. Earth’s magnetospherecatches harmful electrically charged parti-cles and cosmic rays from the Sun andprotects life on Earth’s surface from thislethal radiation. Among the charged par-ticles caught in the magnetosphere areions (electrically charged particles),which collect and align along the mag-netic field “lines” stretching between thenorth and south magnetic poles. Thesemagnetic-field aligned ions bombardingEarth’s magnetosphere form “ducts”which can channel lightning-stroke elec-tromagnetic impulse energy. Whistlersresult when an electromagnetic impulse(sferic) from a lightning-stroke entersinto one of these ion-ducts formed alongthe magnetic lines of force, and is arcedout into space and then to the far-end ofthe magneto-ionic duct channel in theopposite hemisphere (called the opposite“magnetic conjugate”), where it is heardas a quick falling/descending emission ofpure note tone or maybe as a brief “swish”


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sound. Whistlers sound the way they dobecause the higher frequencies of thelightning-stroke radio energy travel fasterin the duct and thus arrive before thelower frequencies in a process researcherscall “dispersion”. A person listening witha VLF receiver like the WR-3 in theopposite hemisphere to the lightningstroke (at the far end of theMagnetospheric duct path) will hear this“short” or “1-hop” falling note whistler.One-hop whistlers are generally about1/3 of a second to 1 second in duration.If the energy of the initial short/1-hopwhistler gets reflected back into the mag-neto-ionic duct to return near the pointof the originating lightning impulse, a lis-tener there with a VLF receiver will hear a“pop” from the lighting stroke impulse,then roughly 1 to 2 seconds later, thefalling note sound of a whistler, nowcalled a “long” or “2-hop” whistler. Two-hop whistlers are generally about 1-4 sec-onds in duration depending on the dis-tance the whistler energy has traveledwithin the magnetosphere. One-hopwhistlers are usually higher pitched thantwo-hop whistlers. The energy of theoriginating lightning stroke may makeseveral “hops” back and forth between the

northern and southern hemispheres dur-ing its travel along the Earth’s magneticfield lines-of-force in the magnetosphere.Researchers of whistlers have alsoobserved that the magnetosphere seems toamplify and sustain the initial lightningimpulse energy, enabling such “multi-hop” whistlers to occur, creating long“echo trains” in the receiver output whichsound spectacular! Each echo is propor-tionally longer and slower in its down-ward sweeping pitch and is also progres-sively weaker. Conditions in the magne-tosphere must be favorable for multi-hopwhistler echoes to be heard. Using specialreceiving equipment and spectrographs,whistler researchers have documentedover 100 echoes from particularly strongwhistlers—imagine how much distancethe energy from the 100th echo has trav-eled—certainly millions of miles!Generally, only one to two echoes areheard if they are occurring, but underexceptional conditions, long “trains” ofechoes will blend into a collage of slowlydescending notes and can even mergeinto coherent tones on a single frequency,hard to describe here, but quite unlikeany familiar sounds usually heard outsideof a science-fiction movie!


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Back to the history of whistler research. Plansfor studying whistlers, chorus, and otheraudio-frequency natural radio phenomena

were formulated by Dr. J. G. Morgan of theUniversity of New Hampshire in Hanover as wellas Dr. Helliwell at Stanford, for the InternationalGeophysical Year which would begin in 1957.Over 50 receiving stations were set up at manylocations all over the globe, including remotelocations in northern Canada, Alaska, Europeincluding Scandinavia, and even Antarctica. Thisperiod was the beginning of the most intensiveprofessional study of whistlers ever. In the early1960’s, a couple of satellites (IEEE-1, Injun,Allouette) destined for low Earth Orbit were out-fitted with VLF receivers. These satellite-basedVLF radio receivers successfully recordedwhistlers, and greatly enhanced scientific knowl-edge of natural VLF radio emissions. During the1970’s, space probes, such as Pioneer andVoyager, would discover whistlers happening onother planets of our Solar System, such as Jupiterand Saturn, which both have enormous andpowerful magnetospheres.These Gas Giants alsohave huge magnetospheres and their own polaraurora as well.

The 1980’s saw increasing hobbyist and ama-teur observations of whistlers, thanks to theincreasingly easy availability of solid-state elec-tronic parts and VLF receiver construction articles

and notes. By 1985, whistler articles and receiverdesigns would appear in several electronic andradio hobbyist magazines, and also radio clubbulletins most notably the Longwave Club ofAmerica’s monthly bulletin, THE LOWDOWN.Several LWCA members including MichaelMideke, Mitchell Lee, Ev Pascal, Ken Cornell, andothers, would publish and or design and usetheir own successful whistler receiver versions.These hobbyist whistler receivers tended to usesmall loop or wire antennas, unlike the “profes-sional”VLF receivers used during the late 50’sand early 1960’s, which used very large loopand/or tall vertical “pole” antennas.

One radio “mentor” who sparked my fascina-tion with whistlers and Natural Radio is agentleman named Michael Mideke, who

has been an avid enthusiast involved in variousesoteric radio (and non-radio) pursuits since theearly 1970’s. Mike taught me quite a considerableamount of knowledge about longwave radioreceiving and transmitting experimentation atradio frequencies much higher than NaturalRadio, and he himself began regularly monitor-ing Natural Radio about the middle of 1988,more than a year before I would hear my firstwhistler in the Oregon desert. For the past 25years, Mike, his wife Elea, and two sons lived ascaretakers on a large ranch in a remote central


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California canyon, far from electric powerlines.Here, Mike was able to string out antenna wiresover thousands of feet in length and running inseveral different compass directions, and connectthem to his plethora of radio receivers. Hisremote, electrically-quiet location was also idealfor listening to whistlers. Over the years, Mike hasalso made many hundreds of hours of recordingsof amazing radio sounds of the Earth. He wasparticularly fortunate to be able to monitor 24hours a day during the height of the sunspotcycle from 1989-1991 when solar activity, geo-magnetic disturbances, and whistlers were mostnumerous. Mike also passed along the results ofhis own receiver experimentation, thus positivelyinfluencing my own receiver experimentation.

In late summer of 1990, I began experimentingwith whistler receivers employing short “whip”antennas no longer than 5 to 6 feet in length.These “whip receivers” successfully monitoredwhistler activity, though my earliest versionslacked sensitivity. I must credit the original ideaof using a short whip antenna to a longtimeclose friend and fellow whistler enthusiast, GailWest, who lives in Santa Rosa, California and hasaccompanied me on many of my road trips andwhistler listening expeditions. Gail repeatedlywitnessed my frustration with stringing outunwieldy wire antennas, and on one particularmorning (summer 1989) in the northern Nevada

desert, commented “it sure would be nice to usejust a small whip antenna rather than long wiresfor a whistler receiver antenna”. Also, while on asolo listening session in the hills of Marin County,California in February 1990, I heard a strongwhistler howl from the tape recorder’s speakerwith nearly all but about 10 feet of antenna wirerolled back onto the spool. This experiencereminded me of Gail’s idea and made the whipantenna idea seem more plausible.While the ideaof a hand-held whistler receiver seemed some-what wishful thinking early on in my experi-mentation with whistler receivers, it wouldbecome reality in just over two years of whistlerlistening and receiver tinkering.

Increasingly better and more sensitive yetsimpler whip antenna whistler receivers werecontinuously devised on my workbench. On a

beautiful spring morning in May 1991 while hik-ing on a trail in the mountains east of San Diegowith friend Frank Cathell of ConversionResearch, I demonstrated my BBB-2 whip anten-na whistler receiver. Frank was so fascinatedwith this receiver that he jumped on the band-wagon, and by August 1991 after a furious 3months’ of receiver tinkering, Frank and I createda sensitive battery-powered whistler receiverthat required only a small 33-inch antenna, wascigarette pack sized and very portable, called


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the “WR-3”, and we shortly began selling thisnew pocket receiver on a casual basis. The WR-3opened up whistler monitoring to practicallyeveryone-even non-technical people willing toat least undertake the effort of finding a rea-sonably powerline “hum” free location wherewhistlers and other natural VLF radio phenome-na could then be listened to and enjoyed aseasily as listening to regular broadcast radio. Atthis point thanks to the WR-3, whistlers andlightning sferics were very easy to hear now itwas just up to Mother Nature to put on a show.

My difficulties with whistler receivers andantennas was now behind me, but I still retainvery fond memories of the beginnings of myown interest in whistler listening and study. InJune 1989, Gail and I heard our first whistlers“live” while camped deep in the eastern Oregondesert near Steens Mountain. In anticipation ofthe trip and not yet aware of more advancedreceiver circuits available for this pursuit, I built acrude “whistler-filter” which I knew would atleast block out a lot of the potential man-madesignals which might overload my tape-recorder’saudio-amplifier. During the days leading up todesert trip, Summer thunderstorms had beenplaguing the Great Basin areas of central andnorthern Nevada the result of the typical sum-mertime “monsoonal” moisture which sometimesgets driven up northward from the southwestern

states of Arizona and New Mexico toward theinter-mountain region of the western U.S.(including Utah and Nevada). July and August arethe months of the most spectacular lightningstorm displays that pound almost daily through-out the deserts and mountains of western NorthAmerica.

As Gail and I arrived at our intended camp-site in the Black Rock Desert of northernNevada, one of the more fiercer-looking

cumulonimbus clouds drifted in our direction,and a light rain began to patter the parcheddesert dirt. Shortly thereafter, the wind picked upaccompanied by the rumble of thunder. It lookedlike we were going to be in for quite a bit of thisjudging by the looks of the clouds. As we tried toset up our “Tahjmatent” a huge dome tent whichwas tall enough to stand up in and roomyenough for 10 people to sleep in the winds start-ed to blow so hard all Gail and I could do wasjust stand there holding the now horizontallyflailing tent.The situation seemed rather dismal,however the skies to the north looked almostcloud-free, so we decided to cram our big wad ofa tent and other supplies back into my smallToyota coupe and head farther north to an alter-nate location in Oregon about 100 miles away.We would return to the Black Rock Desert thefollowing month under clear skies.


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Arriving in the Alvord Desert of south-easternOregon with about 1½ hours of sunlight left, weset up the tent under clear blue skies while occa-sionally stealing glances at the still ominous-looking skies to the distant south, hoping itwould not come up our way. Fortunately, we werespared any further harassment from the weatherand I became confident I could unroll my nearly500 meter-long wire across the sagebrush. I con-nected my whistler filter to this wire and“grounded” the other connection to the car.Connecting my tape-recorder to the filter, I wasrewarded by loud snapping and crackling from allthe lighting happening south of us.

The following morning at sunrise under cloud-less skies, I turned on the tape-recorder and lis-tened to the now greatly reduced amount oflightning static. But, a few of the louder lightning“pops” had whistlers (or what I thought soundedlike “whizzers”) happening a second or two after-ward! I shouted for joy and thrust the head-phones at Gail for her to listen, too.We werehearing our first whistlers, though they soundeddifferent from the few I had heard recorded oncassette tape by Michael Mideke back in centralCalifornia.The whistlers went on for an hour or sothen died away.The following morning, thewhistlers were back, but even louder! An alreadyvery enjoyable desert trip had turned into a mile-stone for me!

Now that I had heard whistlers on my own, Ibecame “hooked” with this very esotericaspect of radio listening. I had been enjoy-

ing shortwave listening to stations around theworld and amateur “ham” radio for the pastdozen years, but this was something very newand fascinating something that played well intomy other casual and hobby interests in geo-physics, meteorology, and radio wave propaga-tion studies.

Over the next few years, I would learn agreat deal about natural radio phenomenaand how to build excellent receiving equip-

ment to listen for whistlers and the like. One ofthe main goals was to build a whistler receiverthat would not require a whole roll of antennawire but only a small whip antenna desire whichcame to fruition in the spring of 1990, when I“accidentally” heard a loud whistler while rollingup the final few meters of antenna wire. I knew itwas possible to hear whistlers with small anten-nas, and as I’ve already mentioned, a prototype tomy portable hand-held “WR-3” receiver wasdevised a in the spring of 1991 with the help ofanother radio friend, Frank Cathell of ConversionResearch.

In addition to all of my whistler receiver tinker-ing, trials and successes mentioned above, seriousand regular natural radio listening (and quality


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recordings) began in February 1991, when nearlyevery Sunday morning well before sunrise (the“prime time” to listen for whistlers), I would packmy favorite whistler receiver, a small reel-to-reeltape recorder, and lunch into a knap sack andbicycle to the nearby hills. Upon reaching thebase of the hills, I would then dismount and walkthe bike up via a fire access-road to my favoritelistening spot a flat ridgeline overlooking muchof Marin County, San Francisco, and San PabloBay at an elevation of about 600 feet above sea-level which I began calling “Whistler Hill”. Here, Iwould listen for whistlers, and if there were anyhappening, run the tape recorder. I was rewardedby many beautiful sunrises and many nicewhistlers on my weekly visits to Whistler Hill, andI was quite happy with my current receiver, aunit which used a 66-inch whip antenna, calledthe “MC-1”. One memorable morning near Easter1991, a “huge” whistler the loudest of the morn-ing occurred just as the sun began peekingabove the north-northeastern horizon. It was inthis year that I would really discover the aesthet-ic beauty of whistler listening while out innature!

While I was always glad to hear whistlers in thehills, it was not always easy to awake at 4 a.m. inthe cold and bicycle the few miles up to WhistlerHill. Many of those Sunday mornings would havebeen better spent sleeping a few hours longer, but

Oh!, was I so glad when those whistlers would bepouring forth in my receiver’s headphones asanother gorgeous sunrise was forthcoming then Iwas always glad I made the effort to get up early!But then again, I would sometimes get up toWhistler Hill only to hear NOTHING except theeverpresent crackling of Earth’s ongoing electricalstorm commotion. And if the weather wasgloomy, I was usually tempted to ride back homeinstead of continuing on my usual 8-10 mile bikeand hike.

Why DIDN’T I stay home and listen to whistlersfrom the comfort of my bed, as is generally possi-ble with more conventional broadcast radio? Theproblem lies with the electric-mains grid whichhas spread nearly every place man has settled.Alternating-current electric power lines emit“hum” at 60 cycles-per-second in the Americas,and 50 c.p.s. (Hz) in Europe and Asia. In additionto these “fundamental” AC power frequencies,“harmonic” energy is also radiated (120, 180, 240,300, 360 Hz, etc.), or as in Europe and Asia: 100,150, 200, 250, 300 Hz, etc.) often to well above 1or 2 kHz. Since whistler receivers are sensitive tothese electric power frequencies, any natural radioevents which might be occurring get masked bythis terribly annoying humming sound, should onetry to listen anywhere near AC powerlines.

The only solution to AC power-line “hum” is tolocate a listening spot away from AC power poles


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and wires often as far as several miles before thehum levels are reduced to low or nil levels.Thisnecessitates walking, hiking, bicycling, or driving toremote locations where there are few or no ACpower lines easy to do in many parts of Californiaand the West but often very difficult in flat land orurban locales. Sometimes and with good filters inthe whistler receiver one can listen as close as acouple-hundred feet (or maybe even closer) to res-idential AC electric wires. On a few fortunate andastounding occasions, whistlers can get so loud asto even be heard through the loud power-linehum levels encountered in a suburban backyard,demanding the whistler listener to immediatelyrelocate to their favorite “quiet” listening spot inorder to hear and tape record such magnificentlygiant whistlers, and at the same time praying thatthe monster whistlers still are going on when thewhistler receiver is again turned on! Murphy’s Lawand my experiences generally suggest they will begone and not to return until another inopportunetime...

My tape libraries of whistlers and other naturalradio phenomena vastly increased in late 1992and throughout 1993 and early 1994.The stimu-lus to get out and make natural radio recordingscame when, after purchasing a “camper-van” inJuly 1992, Gail and I headed up California’s NorthCoast, stopping for the night at Westport UnionLanding Beach north of Fort Bragg.We heard nice

whistlers that evening and morning during dark-ness using our WR-3’s clamped in the van’s reardoors while laying in our comfy beds.Occasionally, however, one or both WR-3’s wouldslip out of the door and nearly hit our heads. Gailcame up with an idea to have a whistler receiverwith an antenna that could remain outside whilea control box could be put next to the beds.Well,I got right to work on this great idea of hers uponreturning home, and quickly designed an excel-lent “WR-4” whistler receiver in which the receiv-ing antenna (2.5 meters in length) is mounted onthe van’s read door ladder and the control-boxcontaining filter switches, headphone and tape-recorder jacks, etc. could be placed next to thebed! Now, I could make recordings while com-fortably in bed, even while dozing off letting therecorder run for 45 minutes or until I awoke tomonitor the situation. Since recording becamevery “convenient” while camping no more sorearms holding the receiver out the window orstanding out in the cold and win, and not asmuch sleep deprivation as before I (alone or withGail) am now able to locate to superbly quietcamping/listening locations deep in the desert ornear mountainous areas and wait for conditionsto present interesting natural radio sounds.Thepast couple of years has seen the combining ofmy enjoyment of camping and road trips withnatural radio listening.


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The ease of whistler listening with the WR-4and our love or camping trips has resultedin about a hundred hours of recording in

1993 and 1994 from over 10,000 miles of travel anatural radio tape library which has become oneof the better ones from an amateur, but I haveno doubt that Mike Mideke’s has to clearly be theFINEST amateur/hobby tape library in the world,since he LIVED in a quiet location free fromstrong powerline "hum" and has not had to trav-el to enjoy natural radio.

When Donald Cyr initially inquired if I wouldlike to contribute some thoughts on whistlerlistening and experiences during the past coupleof years since I last contributed material to hisbook: America's First Crop Circle; Crop CircleSecrets Part 2, I said "sure, I'd love to write some-thing for your new book”. Don was interested inany information I might be able to offer, such aswhere the best places to hear whistlers are, or if Ifound any particular places that whistlers wereconsistently stronger than in other locations. Iassume he was hopeful that my findings mighttie in to his theory, which I'll call "The MarionIsland-Wiltshire Plain Crop Circle Theory”, (a nameI have created for this article) that suggestswhistlers at least the ones which might havecaused many English Crop Circles in the late1980's and early 1990's-are highly localized phe-nomena that are launched at a given point, such

as Marion Island in the south Atlantic Ocean, andare ducted via the magnetosphere along a line-of-force to the northern hemisphere, specifically,to southern England, where they, if they do notcause odd impressions in wheat fields of theWiltshire Plain, will nonetheless be very LOUDindeed to one listening for them with a whistlerreceiver.

Don's theory, backed by his friend and col-league James Brett, was first presented tohis readers in CROP CIRCLE SECRETS, PART

1, published in 1991 and highly recommendedreading for this discussion as is PART 2, publishedin 1992.This particular book of Don's generateda good deal of interesting dialogue, and discus-sion. Of course, Don and James's Crop CircleTheory was really aimed at stimulating queryand discussion about the what the mysteriousforces which might be creating such incredibleand beautiful impressions in the English land-scape and that is the true driving force of inquiryand research. Other theories were pondered, sug-gested, debated, and dismissed by various con-tributors to Don's books, and they ranged fromelaborate UFO theories, vortices and balls oflight, military exercises (there are several militaryinstallations in that English region), undergroundforces of electromagnetic nature, to suppositionsthat they were plain and simply, artistic hoaxes


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concocted in the night by creative people armedwith poles and chains.

Don and James were fascinated by the whistlertheory as presented by researchers StoreyHelliwell, The Institute of Radio Engineers (I.R.E.),et al., and they thought this theory was as good(if not better than most) at explaining a possibleorigin of Crop Circles.What seemed fascinating toDon and James was that Marion Island, alsohome to a secretive military installation, was atthe far end of a magnetospheric duct, i.e., at aconjugate point to south-western England.Perhaps lightning storms, enhanced by the oddgeography of Marion Island, or perhaps, a secretmilitary experiment there, were generating greatbursts of electromagnetic energy that wouldenter a magnetospheric field-aligned duct andarrive in England as a powerful whistler, whichwould cause Crop Circle by perhaps affecting thestems of the wheat stalks in odd manners.

From a scientific point of view, however andfrom what both amateur and professionalwhistler listeners and researchers have found it ishard to believe whistlers were so concentrated intheir energy area and also "intelligent" to createsuch lovely patterns in the English fields. Radioengineers and other "technical" people involvedwith radio waves generally know that it is impos-sible to confine a radio wave to an area or vol-ume less than 1/2 its wave length. In the case of

whistler energy emerging from the confines of itsduct and resuming the velocity of light (300,000km/186,000 miles per second), its (full-wave) sizeis from 19 miles at 10 kHz to almost 190 miles at1 kHz pretty large! Mike Mideke eloquentlyexpressed this reality in the final few paragraphson page 27 and the first few paragraphs of page28 of CROP CIRCLE SECRETS. Part 2. Also, thepower of a radio wave (also known as the "field-strength") from even the strongest and loudestwhistlers ever heard and/or recorded by anyonehave never been as strong as the VLF radio wavesgenerated from nearby lightning storms, thoughthe lesser energy from whistlers is of course sus-tained much longer than the split-second burstof energy from a lightning stroke, and, or course,whistler radio energy does differ substantiallyfrom a lightning bolt's.

While whistlers would hardly seem to beso super-concentrated in their strengthand focal area to cause such intricate

and sharply defined impressions in plant materiallike crop circles, data gathered in the past 35years by manned and un-manned monitoringstations located worldwide has found thatwhistlers do occupy a "footprint" that is-they areheard loudest at a given location at ground level,and then gradually weaken as one moves con-centrically away from "ground zero". Most


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whistlers are heard in a 500 to 1000 mile radiusfrom the exit point region of its duct, though it'ssound characteristics may be different from oneplace to another within this whistler receptionarea.Whistlers also tend to cluster in the middleand upper-middle latitudes of the globebetween 25 and 60 degrees north/south, and arerarely heard at the "geomagnetic equator" awandering latitudinal line on the globe at thehalf way point of any great-circle line drawnfrom Earth's magnetic north pole to Earth's mag-netic south pole.

Most of the continental United States andsouthern Canada are between these latitudes tohear not only splendid whistlers but also beauti-ful VLF radio "chorus" from Auroral displays.Thesame goes for most of Europe, especially theBritish Isles and Scandinavia. In the Southernhemisphere; southern Argentina and Chile; thesouthern parts of Australia, particularly Tasmania;New Zealand; and perhaps, the Cape Horn regionof South Africa, are similarly at the right latitudesto hear whistlers and chorus.The South Island ofNew Zealand and the Tierra del Fuego region ofSouth America, plus the Antarctic Peninsula, arewhere the good displays of Aurora and auroralchorus can be seen and heard.

Listening to whistlers from near one's hometown or on road trips can be very enjoyableand inspiring, but it is even more fun to

travel abroad and check out whistler reception inother parts of the world. In late May of 1992, myfather and I went on holiday to Ireland, enjoyinga 12-day coach tour of the entire country. Ibrought my pocket-sized WR-3 whistler receiver,hoping to catch and record some "Irish whistlers”.The first night happened to be at the Clare Innnot far from Dromoland Castle and Newmarket-on-Fergus. Surrounding this hotel was a beautifulgolf course, small lake, meadows, and woodlands.There were only a few powerlines near the hoteland main road to Ennis, leaving much of the golfcourse and meadowland fairly free from exces-sive Ac power hum, and therefore, good spots tolisten for whistlers, as I tested out a few hoursafter we arrived bleary-eyed from an all nightflight across the northern Atlantic.

In anticipation of hearing whistlers in thisquiet and exotic location, I spent much of thepre-midnight period walking around with mySony LW/MW/SW/FM radio, enjoying the IrishRadio Telefis Eireian (RTE) 1 & 2 radio networks,and the nighttime reception of British andEuropean mediumwave (AM) stations, taperecording much of this reception with my trustymicro-cassette machine. At around midnight,after the BBC on longwave 198 from Droitwich


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signed-off after the maritime weather report anda cheery "good night”, I flicked on my WR-3. Loand behold, there were nice whistlers, albeit onlyoccasionally, since it still was a bit "early" for thereally good whistler shows, which like to start upafter 4 am. Catching some sleep in the woods(the hotel was rather far-off at this point) I awokearound 3 am, turned on the WR-3 to hear morewhistlers and there were LOTS of them, followedby weak "Auroral chorus" that rose up from thestatic at around 0400, and remained past my firstIrish sunrise, when I drifted back to the hotelroom to catch an hour or so of terribly-neededsleep!

That night would prove to be the only placeour tour group would spend the night wherethere was open space the rest of the hotels westayed in would be located in towns or deepwithin Dublin, and surrounded by hundreds ofelectrical lines with no access to large openspaces. I had to be happy with broadcast listen-ing with the Sony, which was always very inter-esting, anyway. It sure was great to now havenatural radio recordings from outside the WestCoast.

While scientists and hobby whistler listen-ers have pretty much determined whatregions of Earth are in "whistler country”,

it is never possible to predict where, at any given

time or on any given day, whistlers will be heardloudly, weakly, or even at all. It's conceivable thereare days where a whistler hardly occurs any-where on the globe undeniably there are daysand even weeks when not a single whistler isheard by listeners located in otherwise idealwhistler reception regions of Earth, such asIreland and Europe, the northern tier of the U.S.,southern Canada, New Zealand, and so forth.

Conversely, there are days when there seem tobe whistlers happening nearly everywhere, asthough a giant switch was turned on somewherein Earth's magnetosphere to issue forth a barrageof weak and strong whistlers too frequent tocount! Like weather fronts and hurricanes, itwould appear that given a day when things areripe for strong whistler production, the locationsthat strong whistlers are heard constantlychanges, depending on the locations of lightningstorms; the magnetospheric whistler duct begin-nings and end points; and the day/night regionof the globe particularly the midnight to 6 a.m.period which, as we all know, moves westward15 degrees an hour.

Thanks to simultaneous whistler monitoringand tape recording efforts, first by 1950's and60's whistler researchers such as Storey, Morgan,Helliwell, etc.; and later by coordinated amateurand student study groups, hundreds of individualwhistlers have been documented.Their findings


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have determined that the average whistler isheard in an area of about 500 miles radius,though the "big whoppers" may be heard as faras 2000 to 3000 miles from its loudest "arrivalpoint”.

One of my favorite examples of intense scruti-ny of individual whistlers (by at least 25-30 lis-tening groups or single monitors), was of "TheGiant Whistlers" of the morning of March 28,1992, specifically, of two whistlers occurringabout an hour apart. In and of itself, these twohuge whistlers are not really different from otherstrong whistlers which occur in the hundredsand maybe thousands throughout any season,but it WAS remarkable in that they wereserendipitously caught on tape by so many lis-teners, who were participating in a high schoolstudent monitoring effort coordinated by a teamof scientists and high school professors, called"PROJECT INSPIRE”.

The INSPIRE effort was sanctioned by NASAto study the ground reception pattern ofradio wave emissions from a special "modu-

lated electron-beam" generator (called "ATLAS")aboard the Space Shuttle (STS-45), which flew inlate March, 1992. A schedule of ATLAS "transmis-sions" was established in hopes that the ground-based VLF radio receivers set up by the studentgroups would hear its emissions. Unfortunately,

the shuttle-based ATLAS unit failed after onlytwo (unheard) transmissions. Fortunately, it wasdecided the students groups and other individu-als should adhere to their INSPIRE listeningschedule, and also to "backup" listening sched-ules arranged for the mornings of March 26-30,1992. It was during many of these scheduledregular and backup listening periods that manyinteresting natural radio events were captured,including several strong and powerful whistlers.A very detailed report entitled PROJECT INSPIREDATA REPORT was produced in August 1992 byMichael Mideke, who was the project's data ana-lyst. It is from this report where the followinginteresting scenarios of whistler reception hasbeen interpreted.

Back to the two "Giant Whistlers" of March28, 1992. Bill Hooper, shivering at 4 a.m.Pacific time in his camper near California's

Death Valley, started his tape recorders runningonce again. Bill was one of many experiencedwhistler enthusiasts who was monitoring indi-vidually but part of the larger INSPIRE studenteffort. He had set up one of the most sensitivewhistler receiving stations by far of the entiregroup participating in the INSPIRE listening ses-sions, thanks in part to his remote desert loca-tion, great distance from any electric power linescombined with plenty of room for a large anten-


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na and very sensitive whistler receivers of hisown original design.

At precisely 4:02:38 a.m. PST, or 12:02:38Universal (Greenwich Mean) Time, an extremelystrong (long, 2-hop) whistler was recorded by Billat his Death Valley listening site. So very strongwas this whistler that it briefly overloaded Bill'sreceiving system. It also produced a "4-hop echo"which was also clearly recorded on his tape.Thiswhistler was also heard and recorded as far awayas the U.S. midwestern region and easternseaboard, but much weaker and "truncated” thatis only a fairly narrow spectrum of this hugewhistler, in the 3-6 kHz range, propagated east-ward.This whistler was also heard weakly tomoderately in south-central Texas but again wassomewhat truncated there like farther east.Interestingly, a large part of Texas was experienc-ing heavy rains and lightning storms-whistlerreceivers in southeastern Texas were picking upvery strong, local-like lightning stroke "sferics”. Ifthe source lightning of this whistler was in Texas,one wonders how it arrived so loud in theCalifornia desert! Perhaps it was generated bylightning strikes somewhere else, perhaps to thenorth or northeast of California, and far enoughas to not really make much of an obvious sferic"pop" in the whistler receiver.

An hour later, a nearly identical strong whistlerto the one at 12:02 UT occurred at 13:03:03 UT,

this time heard by myself as well as Mike Midekeand others listening in Arizona New Mexico, andeven Minnesota. Unlike the earlier big whistler,this particular whistler as heard in Minnesotawas stronger. It also was not as "truncated" aswas the earlier strong whistler. Interestingly, thesferic generated from the causative lightningstroke was rather weak in California, unlike itswhistler. Clearly, on this morning the big whistlerswere concentrated in the western United Stateseven though the lightning storms weren't. Itshould be noted there were days when thewhistlers were stronger in the eastern UnitedStates and were weaker "out West”, and point outhow the locations of strong whistler activitychange day-by-day and can't easily be tied towhere lightning is happening. More on this in abit.

While we are on the subject of loudwhistlers and speculation on their origi-nating lightning strokes, I have an anec-

dotal whistler story of my own to bring in at thispoint.While on our September 1993 "Big Trip" inmy van and eventually to tour the Canadianprovinces of Manitoba westward to BritishColumbia, Gail and I stopped in the easternNevada desert about 20 miles west of Wendover,Utah to catch several hours of sleep. Gail and Ihad driven most of the night across the Silver


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State after a brief stop the evening before atanother favorite natural radio listening spot anhour’s drive east of Reno, where we had heardand taped a marvelous variety whistlers, somevery strong like the ones recorded by the INSPIRElistening groups in March 1992.

Very sleepy and exhausted after 250 mileseast-bound on Interstate 80, we took a remoteexit off the freeway and headed south down awide, unpaved road running alongside some rail-road tracks. In the dark, we noticed there werepowerlines running along the train tracks, butdetermined to stop in a spot where we could getsome sleep and record whistlers (which I wassure must still be roaring), we kept on goinguntil we saw another smooth dirt road branchingaway at right angles away from the tracks andpesky wires. Making occasional checks for power-line hum with my WR-3, we drove far enoughfrom the wires at least 5 miles-to where I could-n't hear any hum with my WR-3 whatsoever. Bythis time, we was just too tired (and now cold) toeven set up the better WR-4B whistler receiver'santenna. I just had enough energy to get in theback of the van and tuck myself under the cov-ers, falling quickly asleep.

Awaking a few hours later, I noticed it wassomewhat light with a slate-gray sky.Timeto set up the WR-4's 10-foot copper-pipe

antenna and check out the whistler band. As pre-dicted, there were wonderfully loud "growler"type whistlers roaring out of fairly light back-ground sferic static. I hopped back into bed andswitched on my cassette recorder, capturingthese great whistlers onto a 90 minute tape. MyWR-4B whistler receiver was once again provingto be a truly superb receiver with its van-attached pipe antenna and convenient bedsidecontrol box, while the trusty WR-3 made a nicespot checking receiver.With the WR-4B, I couldsnuggle under the covers and run tape even if Ifell asleep while recording. It certainly was a vastimprovement over holding our WR-3's out thevehicle window or clamped in the van's door aswe did that August 1992 night up the CaliforniaCoast, and Mike Mideke even commented in aletter: "I was wondering when you'd get out ofhand-held mode”! This September 17, 1993morning, Gail and I were having a nice timeparked once again in the beautiful high desertsurrounded by beautiful mountains, pungentsagebrush, whistlers roaring in the headphones,and few cares in the world.

The entire 4,500 mile trip through 10 statesand 4 provinces was completed in about 2 weeksand over 10 hours of natural radio recordings,including wonderful "auroral chorus" whilewatching the northern lights dance overhead inAlberta. While many of my whistler and chorus


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tapes were recorded while tired, semi or fullyasleep, I was not able to critically scrutinize whatthings I was recording until I got home. Hereinlies the beauty of taping what you hear eventscan be listened to again and again in my caseusually for the sheer beauty of Earth's naturalradio sounds, but also for scientific analysis ifnecessary. Also, subtle elements are sometimesmissed while monitoring live due to fatigue, thedistraction of beautiful surroundings, and soforth.

What I can explain about those great big east-ern Nevada whistlers of September 17, 1993 is asfollows: They were coming from rather weak butdistinct and clean "tweeking pops”, the kindwhich are produced by fairly distant groundstrikes. Now, I've listened to a lot of lightningsferics while watching the lightning strikes mak-ing them, and the sounds of lightning static canbe as varied as the visual strikes. I've noticed thatthe big, bright, single cloud to ground lightningstrikes can deliver a very loud but clean "pop" inthe whistler receiver's output. Cloud-to-cloudlightning, sometimes tripping other nearby in-cloud lightning, sounds more "crackly" or like thecrushing of a Walnut in a nutcracker.

Anyway, interspersed amongst the numer-ous weak sferics and occasional, hugewhistler generating popping tweek were

occasional strong and semi-local lightning sfericsdry sounding and not tweeking that were gener-ating very weak and quite diffuse ("hissy")whistlers. These strong sferics were coming fromlightning within about 50-100 miles of my lis-tening location. Seems they just weren't generat-ing big whistlers or if they were, the whistlerswere arriving SOMEWHERE ELSE strong but dis-tant enough to explain their rather weakstrengths near their source lightning. So, thisidea of lightning stroke energy entering a ductor ducts to travel to the magnetic conjugate andthen back again to the general area of their gen-erating lightning strokes is a fairly simplisticexplanation and not entirely satisfactory. And, assimplistic explanations tend to do, it fails to con-sider more complex events taking place...

It is my supposition that, somewhere, as theymerrily arch along the magnetic-field lines,whistler ducts can cross, combine, and/or exciteeach other. In my mind this helps explain why 2-hop whistlers don't always "land" near wheretheir originating lightning stroke occurred, butcan wind up a thousand or more miles away! Ifyou will, whistlers can "jump rail" and enter adja-cent ducts, winding up curiously far from wherethey should arrive whistler wanderlust. As such, itis hard to believe southern England and MarionIsland would have a dedicated whistler duct con-necting them "together" and transferring Marion


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Island Lightning into Wiltshire whistler crop cir-cles! More than likely, lightning energy fromMarion Island winds up occasionally as a shortwhistler in southern England, but maybe an hour,day or week later, is sending whistlers intoFrance, Spain, Iceland, or maybe Moscow andthese wandering whistlers are "bouncing back"as 2-hop whistlers now even more removed fromtheir parent lightning storms!

I think conjugate points (and their associated"impact zones"), caused by variations in theexact position of Earth's magnetic field, can varydaily and even hourly call it "conjugate end-point drift”. If the solar wind is pushing againstthe magnetosphere, either gently or as can bethe case after solar flares and "coronal mass ejec-tions" from the Sun rather violently, then themotion of Earth's magnetic field lines and anywhistler ducts present within them must also gettugged and pulled to various degrees from their"normal" positions.This and my suggestedwhistler duct crossings, jumps, and re-combina-tions must be partial explanations of why light-ning in Texas sometimes causes strong 2-hopwhistlers in California, or why Nebraska lightninggenerates huge whistlers in Manitoba that areweaker in Nebraska.Where was the Nevadalightning of the morning of September 17, 1993sending strong whistlers (if any) to? Where werethe rather weak lightning sferics that generated

such giant eastern Nevada whistlers? I can alsoask, just where was the lightning that spawnedsouthern England's artistic whistlers?

One can't neatly package the fascinatingwhistler phenomenon with magnetic conjugatepoints, lightning stroke counts, fixed impactzones, et cetera, et cetera, and expect to easilyexplain what in reality is a mind-bogglingdynamic process that changes like a kaleidoscopeand never repeats.While it is intriguing and funto try and scientifically unravel the phenomenonof whistlers, part of their allure is that they arejust there to be listened to they are as nice tohear as sunsets are to see, and the reasons fortheir existence must sometimes take a back seatto the beauty of their tones.

Neither myself or anyone else have yet todetermine if there are "special places"where, perhaps due to local terrain or

geology, whistlers are louder and more frequentthan average. But, they may exist somewhere.Intriguingly, Edson Hendricks, a researcher intothe mysterious "Marfa Lights”, heard extremelyloud whistlers issuing forth from a very crudeand seemingly insensitive whistler receiver dur-ing a display of these strange and spooky coloredballs of lights occasionally seen in the desertnear Marfa Texas for nearly 50 years. Ed was lis-tening right near powerlines, and their "hum"


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would have surely been overpowering to moresensitive whistler receivers like my WR-3/4's orBBB-4, and also Mike Mideke's fine RS-3/4's, butEd tells of these very pure whistler-like notes farstronger than the weakish background hum, asheard in the output of his simple receiver.Something is going on there in west Texas thatneeds further checking out, and it again points tothe great need for more people to join in thewhistler listening movement.We would knowvastly more about whistlers if there were as manypeople listening to whistlers as were watchingthe prime-time fare on television a silly andhopeless wish but even 100 or more people join-ing the whistler listening movement and coordi-nating listening schedules would give a cleareridea of when and where whistlers are comingand going.

If whistlers aren't enough of a fascinating pur-suit, there are a host of other natural radio"sounds" which can be heard at the 0.1-10 kHzaudio-frequency portion of the radio spectrum tokeep enthusiasts hooked on these Earth radiosounds. One of the more common (but less fre-quent than whistlers) are "chorus”, which consistsof a series of sharply-rising notes, called "risers”.This fairly common phenomenon (but not ascommon as whistlers) can mimic the sounds of aflock of birds chirping, frogs croaking, or sealsbarking. Chorus occurs during magnetic storms,

when Earth's magnetosphere receives a barrageof high-speed energetic particles cascading intoit from solar flares on the Sun or from energyejections from the Sun's "coronal holes" whichallow to escape the Sun in streams traveling atsub-light speeds.This phenomenon of magneticstorms is also responsible for the Aurora Borealisand Australis the Northern and Southern Lightsseen in the sky at higher latitudes close to Earth'sArctic and Antarctic regions. Chorus can happenduring visible aurora and is called "AuroralChorus” this sometimes can also be heard over awidespread area at around local sunrise, when itis called "the Dawn Chorus”. Often accompanyingEarth's magnetic storm associated auroral dis-plays and natural radio chorus is "hiss”, "waver-ing-tones”, and other endless varieties of naturalradio sounds.

Just when lightning seemed a rather commonand well studied phenomenon, awesome as itis, Mother Nature throws another "wow!” at

mankind. It seems we can now add the terms"red sprites" and "blue blobs" to our lightningstorm vernacular. I am fascinated by recent video-taped evidence presented to the world scientificcommunity and also general public pertaining tomassive red and blue bursts of lights occurring ashigh as 20 to 30 miles above lightning storms.For years, pilots of high-altitude aircraft were


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reporting sightings of strange blue and red lightsseen above lightning storm clouds which wereoccurring at the same time as lightning flashesin the clouds below.

In the summer of 1994, scientists from theUniversity of Alaska Geophysical Institute inFairbanks, Alaska were at last able to very clearlyvideotape these incredible lights using high-speed video cameras located on the ground andaboard two aircraft flying over storms in the U.S.Midwest. As though squirted out of a spray bot-tle, bursts of red light can be seen burstingupward in a stream right over lightning strokesand flourishing in a great cloud of light, lastingfor about 1/10th of a second.

Fascinating as these baffling red and bluelights are, what's even more intriguing to naturalradio listeners like myself is a quote from one ofthe researchers, David Sentman of the U. ofAlaska Geophysical Institute, who says that theradio signals, when played through an audiospeaker "sound like eggs hitting a griddle”.Sounds like the hundreds of thousands of "crack-ling" sferics I have heard and tape recordedthrough the years, many of them (but certainlynot all or most) have set off nice whistlers. I havealways pondered at the sheer LENGTH of manyof these lighting sferic crackles quite a few ofthem are about a second in duration, and thereare occasionally crackles which carry on for

almost 2 seconds! These times seem far longerthan any actual flashes of lightning I've ever wit-nessed, although it would seem lightning strokescan trigger other lightning strokes (via theseimmense radio energy impulses), seemingly sup-porting the reasons for such lengthy sferic"crackles”. Now, it would seem I've been hearingthe radio sounds of sprites and blobs I wonder ifre-naming my WR-3 "Whistler Receiver" to a"Sprite & Blob Receiver" might be appropriate.Seriously, there is thought amongst whistler lis-teners that these weird lightning strike emissionsare what may be causing whistlers, since theyoffer visible evidence of a linkage of energy fromabove the lightning storm clouds toward theionosphere.They do not occur during every light-ning stroke, just like whistlers do not happenafter every lightning stroke.

Since the Aurora Borealis and Australis morecommonly referred to as the Northern andSouthern Lights also generate fantastic VLF

radio sounds, it remains a dream of mine tovideo-tape the Northern Lights while simultane-ously recording their radio emissions onto theaudio sound track. I have watched aurora inCanada dance in the skies and listened to theirbeautiful whistling and squawking in thewhistler receiver bursts in intense aurora wouldalso create bursts of auroral radio sounds. I


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understand the U. of Alaska Geophysical Institutein Fairbanks (the same folks studying the "RedSprites" and "Blue Blobs" over lightning storms)has created an extremely sensitive (equivalent to2 million ISO) video camera.They videotapedbeautiful auroral displays in the Alaskan night-time skies with astounding high clarity anddetail, something never before achieved. Mostauroral photography requires time-exposureswith still cameras to turn out brightly. But then,the fine detail of the auroral curtains becomessmeared due to the motion of the auroral dis-plays.

The most basic receiver required to pick-upand record whistlers and all of the other NaturalRadio signals of Earth is a tape-recorder audioamplifier connected to a wire antenna (aerial) ofsufficient length to transfer enough radio energyinto the tape-recorder's audio amplifier to suc-cessfully record them. In actual practice, however,this crude tape-recorder/audio-amplifier "receiv-er" will most likely also intercept your localbroadcast station transmitting in the long ormedium-wave band as well as other signals, andit may not have enough "sensitivity" since tape-recorder inputs rarely are well "matched" inimpedance for wire aerials but prefer micro-phones and such.

Fortunately, whistler receivers are rather easyto construct and are for the most part less com-

plicated than $5 AM "pocket" radio. A handful ofparts and a couple of fairly commonplace transis-tors can form the basis of a very good whistlerreceiver that will perform very satisfactorily andalmost as well as the professional study unitsthat cost upwards of several hundred dollars.This whistler receiver circuit has proven to be avery fine "basic" whistler receiver that I havebeen using (along with several other VLF receiverdesigns) during the past 5 years of my NaturalRadio recording efforts. This receiver is called theMcGreevy BBB-4 (Bare Bones Basic, version 4). Itis also similar to Mike Mideke's RS-3 and RS-4designs except it does not include the secondaudio filter that is present in Mike's designs, andthe "front-end" of the BBB-4 is of the design Iprimarily employ in my whip-antenna receivers.

In closing, I invite readers to join in and listento the wonderful radio sounds of MotherEarth.You needn't be interested in science or

be a radio buff, but need only to have the desireto lend an ear to the extraordinary yet ordinary.Like star gazing, Natural Radio listening redirectsthe mind and heart toward the wonder andbeauty of the natural world.


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1Chorus, Sferics, Tweeks & Whistlers

2Classification of VLF Sounds

3Recording Notes

vlf booklet B with pictures.qxd 8/9/01 9:16 PM Page 2

1Chorus, Sferics, Tweeks & Whistlers


Welcome to the realm of very low fre-quency (VLF) “Natural Radio”! A rapidlygrowing group of people are interested

in monitoring the Earth's huge variety of natural-ly-occurring VLF phenomena, whether for casualcuriosity and aesthetic appeal or for seriousresearch purposes. Naturally occurring VLF radioemissions of Earth will occur in the 0.2 to 11 kHz(audio frequency) VLF electromagnetic spectrum.

Planet Earth (along with several other planetsin the Solar System including Venus, Jupiter,Saturn, Uranus, and Neptune) produces a varietyof naturally occurring radio emissions at the low-est end of the radio spectrum.These emissionsare primarily in the form of electromagnetic(radio) impulses generated by the planets' ongo-ing lightning storms, and from the Sun's solarwind interacting with the magnetic envelope sur-rounding the Earth, called the “Magnetosphere.”These VLF naturally occurring radio emissions arethe subjects of ongoing scientific research byboth amateur and professional groups, and arebeing monitored both on the ground by special-ized VLF receivers such as the WR-3 and byunmanned space probes and satellites.

It is at these lowest frequencies of the radiospectrum (0.2 to 10 kHz) in which no man-madesignals are assigned, that planet Earth's ownmysterious radio emissions have been happeningfor eons.These fascinating “sounds” are “primal

radio”, indifferent to the affairs of humankind andinsight into the causes of these ancient phenom-ena has only begun to be unraveled in the pastfour decades.

Besides 50 or 60 kHz (and harmonics) alter-nating-current power line “hum” from elec-tric-utility power grids, the most noticeable

sounds are going to be the snap, crackle, and popof lightning-stroke electromagnetic impulses(called “atmospherics” and “sferics” for short) fromlightning storms within a couple thousand milesof the receiver; the more powerful the lightningstroke or the closer it is to the VLF receiver's loca-tion, the louder the pops and crashes of sfericswill sound in the headphones. Several millionlightning strokes occur daily from an estimated2000 storms worldwide, and the Earth is struck100 times a second by lightning. At times thereceiver's output is a cacophony of crackling andpopping sferics from lightning strokes originatingin storms near and far.

These huge sparks of lightning strokes arepowerful sources of electromagnetic (radio)emission throughout the radio frequency spec-trum--from the very lowest of radio frequenciesup to the microwave frequency ranges and thevisible light spectrum. However, most of the emit-ted electromagnetic energy from lightning is inthe very lowest part of the radio spectrum, from


0.1 to 10 kHz.The radio pulses produced bylightning strokes travel enormous distances atthese very-low radio frequencies, following thesurface of the Earth as “ground waves.” It is inter-esting how generally quiet and lightning sferic-free the hours are from just after sunrise to mid-morning, when thunderstorms tend to be at theirminimum. Later, the crackling and popping oflightning sferic activity picks up as afternoonthunderstorms build in numbers and intensity.This is due to thermal heating and convection,especially in the summer and autumn months,when, by sunset, the sferics (snap, crackles, andpops) are roaring in a varied and ever-changingtexture as lightning storms rage on into theevening.Weather monitoring agencies em- ployspecial receivers and direction-finding lightningsferics in order to determine where lightningstrikes are occurring and the potential for wild-fire ignition, hazards, to aviation, and damage toelectric power utilities from those lightningstrikes.

While to some, the popping and cracklingof lightning sferics may sound like “stat-ic”, keep in mind that each click or pop is

a lightning stroke flashing somewhere, and notejust how much lightning is going on eventhough your local weather may be cloudless.Additionally, distinct seasonal variations in the

density of moderate to strong lightning sfericsare very noticeable. During the winter months inthe mid-latitudes, when the electrical storm den-sity is generally at its lowest, the amount ofstrong sferics are also at a minimum. Mid-winter,especially in the higher latitudes north of 40°,can be quiet with little lightning sferic activity.However, a weak but continuous backgroundlevel of lightning sferics may be audible betweenthe few strong sferics--these are from the higheramounts of lightning storms occurring in thetropics and from the opposite hemispheres' sum-mer lightning storms. Contrast that to local sum-mer evenings, when there is a continuous “roar”of lightning sferics heard.The Earth is “awash”with lightning storm activity!

At night, many of the popping and cracklingsounds of sferics take on a pinging/drippingsound, called “tweaks”, and can be quite musical.Tweaks are a result of the impulse path from thelightning stroke to the receiver being influencedby the Earth surface-to-ionosphere (D and E lay-ers) region, which is about 45 to 75 miles inheight, measured vertically during the nighttimehours.This region between the lower ionosphereand surface of the Earth acts as a “duct” or “waveguide” at these VLF radio frequencies, which havewave- lengths ranging from 10 miles/29 km. at10 kHz to over 186 miles/289 km. at 1 kHz,allowing lightning stroke impulse energy to trav-


el considerably farther than during the daytime.As the energy travels and is reflected within thisEarth-ionosphere wave guide, the energy under-goes a “dispersion” effect whereby the higher fre-quencies of the lightning impulse arrive beforethe lower ones within a fraction of a second.Thewave guide dispersion effect abruptly cuts offbelow about 1.5 to 2 kHz (1,500 to 2,000 Hz) infrequency, resulting in the ringing/pinging“tweak” sound which is also centered around 1.5to 2 kHz.This “tweak” sound is the lowest reso-nance frequency of the ionosphere-Earth surfacewave guide.This is similar to what sound wavesexperience in a pipeline.

If you have your hands inside a pipelinebetween one to three feet in diameter, you willnotice a sound similar to the radio sound oftweaks. Because the Earth surface to ionospherewave guide cannot support radio energy belowabout 1.5 kHz, the dispersion effect is cut offbelow the frequency, creating the resonance-likepinging and ringing sound.

The sounds of tweaks can change on an hourlybasis from night to night, with the ringing andpinging effect intense and musical at times, espe-cially at night in summer and autumn whenthere is a higher density of relatively strong sfer-ics. Only a few pops and crackles of sferics maybe “tweaking”, or all of them can be, and thetweaks may sound “crusty” or be very clean pings

and rings.Tweaks can be indicators of the condi-tion and height of the lower layers of the ionos-phere to researchers.

In addition to the sounds of lightning sfericsand tweaks, you may be hearing downwardfalling musical notes ranging from nearly pure to“swishy” or “breathy” sounding tones from ½ toover four seconds in duration.These are“whistlers”, which sometimes happen a couple ofseconds after the static crashes and pops of sfer-ics from lightning strokes.Whistlers generallysweep downward in frequency from about 6 kHzto around 0.5 kHz but the lower cut off frequencydoes vary remarkably as conditions change, andthe upper frequency of whistlers can start higherthan 10 kHz.Whistlers sounds quite fascinating.Like “science fiction” sound effects, they are oneof the more common Natural Radio sounds youcan hear.

The Earth's magnetic field (the magnetos-phere) envelops the planet in an elongateddoughnut shape with its “hole” at the north

and south magnetic poles.The magnetosphere iscompressed on the side facing the Sun and trailsinto a comet-like “tail” on the side away from theSun because of the “Solar Wind”, which consists ofenergy and particles (plasma) emitted from theSun and “blown” toward Earth and other planetsvia the Solar Wind. Among the charged solar par-


ticles caught in the magnetosphere are ions(electrically charged particles), which collect andalign along the magnetic field “lines” stretchingbetween the north and south magnetic poles.

These magnetic-field aligned ions bombardingEarth's magnetosphere form “ducts” which canchannel lightning-stroke electromagneticimpulse energy.Whistlers sound the way they dobecause the higher frequencies of the lightning-stroke trade energy travel faster in the duct andarrive before the lower frequencies in a processresearchers call “dispersion.” A person listeningwith a VLF receiver in the opposite hemisphereto the lightning-stroke (at the far end of themagnetospheric duct path) will hear this “one-hop” falling note whistler. One-hop whistlers areabout 1/3 of a second in duration.

If the energy of the initial one-hop whistlergets reflected back into the magneto-ionic ductto return near the point of the originating light-ning impulse, a listener there with a VLF receiverwill hear a “pop” from the lightning-strokeimpulse, then roughly on to two seconds later,the falling note sound of a whistler, now called atwo-hop whistler. Two-hop whistlers are aboutone to four seconds in duration depending onthe distance the whistler energy has traveledwithin the magnetosphere. One-hop whistlersare usually higher pitched than two-hopwhistlers.

The energy of the originating lightning strokemay make several “hops” back and forth betweenthe northern and southern hemispheres duringits travel along the Earth's magnetic field lines-of-force. Re- searchers have observed that themagnetosphere seems to amplify and sustain theinitial lightning impulse energy, enabling “multi-hop” whistlers to occur, creating long “echo-trains” in the receiver output which sound spec-tacular! Each echo is proportionally longer andslower in its downward seeping pitch and isalso progressively weaker. Conditions in the mag-netosphere must be favorable for multi-hopwhistler noises to be heard. Using special receiv-ing equipment and spectrographs, researchershave documented over 100 echoes from particu-larly strong whistlers-- imagine how much dis-tance the energy from the 100th echo has trav-eled--certainly millions of miles/Km! Generally,only one to two echoes are heard if they areoccurring, but under exceptional conditions, sev-eral echoes will blend into a collage of slowlydescending notes and can merge into coherenttones on a single frequency quite unlike anysounds heard outside of a science-fiction movie!

It should be reiterated that strong two- hops(and echoes) can occur from lightning that iswithin a couple of hundred miles from the listen-er location, but perhaps from lightning over 100miles distant.You may notice that “louder” sferics


(i.e. closer lightning strokes) often do not triggerthe loudest whistlers, if they do so at all, but thena loud whistler may come howling through froma relatively weak sferic from quite distant light-ning.This is because the lightning impulse sfericenergy may propagate within the earth-ionos-phere region for considerable distance beforeentering a magnetospheric “duct.” A majority ofwhistlers are heard ULC during periods of locallyfair weather. In fact, Many extremely loud “bigwhistlers” are heard without any preceding light-ning sferic audible whatsoever, indicating the ini-tiating lightning strokes of those strong whistlersare far away, possibly over 3000 miles!

Whistlers are best heard in 30° and 55° northlatitude in North America, the prime latitudebeing 40° and 50° north.

Occasionally, shortly after sunrise and evenextending into the mid-morning, a phe-nomenon called “Dawn Chorus” may occur.

Dawn chorus can resemble the sound of a flockof birds singing and squawking, dogs barking, orsound like whistlers raining down by the hun-dreds- per-minute (called a “whistler storm”).Dawn Chorus results from hundreds of overlap-ping, rapidly upward rising tones that can becontinuous or appear in bursts, called chorestrains. Chorus trains sound fascinating--the burstsof chirps and squawks (risers) seem to suddenly

commence, and over the course of two to fiveseconds, weaken and fade away, then re- peatover again, often in different pitches. During achorus train, the sounds sometimes seem to beechoing or reverberating back and forth untilfewer risers happen, then there may be a briefpause before the next chorus train commences.Chorus trains seem to be harmonically related--achorus train's center audio frequency may alter-nate randomly, first centered on about 1 kHz,then another chorus train will suddenly start upone octave higher at around 2 kHz, or maybe 4kHz. Bursts of chorus trains happening at differ-ent octave can overlap in a beautiful cacophony.

Dawn chorus occurred several times a monthduring years of high sunspot activity (1989-1993)after solar flares and/or coronal mass ejections onthe Sun send a barrage of charged particles intothe Earth's magnetic field, causing a geomagneticstorm and also producing Aurora (the Northernand Southern Lights). In years of low-sunspotcounts and few solar flares (1994-1997), coronalmass ejections from the Sun can still cause mag-netic storms once or twice a month.

Chorus doesn't always only occur at dawn,especially for listeners located at higher latitudes,particularly in southern and central Canada (50 to55° north latitude), Alaska, and in northernEurope.This auroral zone is source to a vastamount of natural VLF phenomena.When a solar


disturbance on the Sun (such as the solar flare orcoronal hole mass ejection) sends highly chargedand high-speed particles and ions towards Earthvia the Solar-Wind, Auroral displays often occur,and are visible to people near the auroral zoneoval. Earth's magnetic field also undergoes a“storming” process as well, called a “magneticstorm.” During auroral displays, chorus is oftenheard, as well as “hiss” of various pitches,“sliding-tone emission” which eerily and weirdly rise inpitch slowly over one to several seconds dura-tion.The chorus which occurs during displays ofAurora is called “Auroral Chorus”.

Both Auroral chorus and dawn chorus arerelated in that they occur during magneticstorms.The more severe the magnetic storm, thefarther south away from the auroral zone andthe louder the chorus will be heard.The AuroralZone “oval” surrounding the magnetic polesexpands during magnetic storms and reachesfarther southward (and the southern AuroralZone “oval” in the southern hemisphere expandsfarther northward). Aurora is a daytime phenom-enon, but it is not visible to the naked eye due todaylight illumination of the sky. Particularlyintense events of nighttime and dawn choruscan get loud even for listeners below 40° northlatitude (in the U.S.), and point to the evidencethat aurora can reach southward into the middlelatitudes despite it not being visible.

The maximum intensity region of chorus emis-sions, like aurora, can spread southward duringmagnetically disturbed periods. Daytime auroracan be more intense than nighttime aurora, andevents of auroral and dawn chorus reveals quitea bit about the nature of aurora.

Even if geomagnetic conditions seem “quiet”and chorus events seem likely, conditions maystill be very good for whistlers to occur. However,determining when whistlers are going to happenis still a rather unpredictable affair.

The time between local midnight and an hourafter sunrise is when the greatest amounts ofwhistlers are heard, although dusk to midnightmay reveal substantial whistler activity, and even(though not very often) loud whistlers may beheard a couple of hours before sunset. Over thelong term, the period from two hours beforesunrise until an hour after sunrise is the opti-mum time to listen for natural VLF phenomenaof all sorts, as the mount of sferics (lightningstroke pops and crackling) are less---natural VLFphenomena are not as “buried” under the sfericsas in the evening when lightning storms aremore numerous. Also, magnetospheric conditionsare optimum around morning twilight time.

Intense whistler events of short duration canoccur at any time between just before local sun-set through one to two hours after sunrise. Agood whistler event that is happening at 10


p.m., or even at sunset may not be occurring lateron that night at the usual optimal sunrise period,so don't rule out the evening hours to listen,especially during geo-magnetic storms.

On several mornings a month, one whistler aminute may be heard on average, but as is oftenthe case, whistlers will not be heard at all.Occasionally during a geomagnetic storm. causedby a solar flare, over 100 whistlers a minute ormore may be heard--called a “whistler storm”!Whistlers may or may not have echoes may befew and far between but occur loud, or mayoccur often but quite weak.The sound character-istics intensity, and number of whistlers canchange rapidly hour to hour. Everything dependsupon the sensitivity and conditions of Earth'smagnetosphere and location of lightning stormsand magnetospheric ducts in relation to the lis-tener.

Whistlers are seldom heard mid-day, exceptduring unusual conditions occurring with a geo-magnetic storm and when lightning is within afew hundred miles of the listener. Unfortunately,on a good number of days during the year, therewill not be any whistlers audible even thoughthere is plenty of lightning activity and sfericswith- in a few hundred miles of the receiver.Often elusive, whistlers may not be heard fordays or weeks at a time. Again, it is hard to pre-dict when whistlers are going to occur based on

the geomagnetic indices, but they are generallymore common in the spring and fall, surroundingthe equinoxes.

Auroral chorus, like whistlers, is best heardbetween midnight and sunrise. Dawn chorustends to peak in intensity between sunrise andone hour later.

Listeners to natural VLF radio phenomenashouldn't be discouraged after several listeningsessions, whistlers, chorus, or other VLF phenome-na sounds are not heard. Soon. you will berewarded with a myriad of fascinating soundsfrom whatever VLF phenomena is occurring atthe time you listen. Remember, weather and out-side temperature permitting, the period aroundlocal sunrise will be the most rewarding time tolisten. Natural Radio sounds can sound eerie andawe-inspiring, especially when one realizes it isall naturally occurring--not man-made and thatthese radio emissions have been occurring formillennia.

Stephen P. Mcgreevy1995


2Classification of VLF Sounds


Omega: All of the recordings presented onthese 2 CDs have, to a greater or lesserextent, a high-pitched beeping sound towardthe high-frequency end of audibility. Theseare the sounds of the worldwide OmegaRadionavigation System. Omega--rapidlybecoming obsolete thanks to the advancedGPS (Global Positioning System) satellitenavigation system--consists of eight 10,000watt transmitters in the following locations:Australia (Victoria), Japan; Hawaii (Oahu);North Dakota (USA); Liberia (Africa); LaReunion Island; Argentina; and Norway.Each transmitter transmits eight pulses of 0.8to 1.2 seconds duration, repeating the processevery 10 seconds. During each cycle, eachtransmitter occupies a unique frequency, andover the course of each 10 second cycle, all ofthe eight transmitters hit on several commonfrequencies spanning 10.2 to 13.8 kHz. Also,each transmitter transmits on its own uniquefrequency on 1 of its 8 transmitted pulses.

Omega receivers sample the relative phaseand timing of each Omega signal. Best resultsare obtained when at least 4 Omega transmit-ters can be received and analyzed, and thenearest resolution, called a lane, is about 5-6miles (8-10 km) wide , though in criticalregions, supplemental transmitters of verylow power may be used in order to increase

navigation accuracy. Omega is subject to thesame VLF propagation disturbances whichaffect Natural Radio, particularly duringmagnetic storms. When Dawn and AuroralChorus roar, Omega is probably experiencingaccuracy problems! There are also daily (diur-nal) variations in the accuracy and phase ofthe Omega signals as day becomes night,which for the most part can be taken intoaccount within an Omega receivers internalmicroprocessor. GPS does not suffer any ofthese propagation errors as does Omega, andit is figured that by the year 2005, the Omegasystem will be shut down.

Power line hum from alternating currentelectric wires: Switch on a VLF receiverwithin your home or office, and you will nothear anything BUT this sound! Today, allelectricity generated at power plants is alter-nating-current (AC), as opposed to direct-current (DC) produced from batteries in yourwatch and portable radios. With AC, thepolarity changes a many times a second. InEurope, Asia, most of Africa, andAustralia/New Zealand, the electric mainspower changes polarity 50 cycles-per-second,or 50 Hz. In North America and in mostCentral and South American countries, it isat 60 Hz. While convenient for long- dis-


tance transmission and easy voltage transfor-mation, AC generates hum in poorly filteredaudio equipment and especially in whistlerreceivers! If this wasn’t bad enough, most elec-trical grids seem to cause the 50 or 60 Hzcurrent to generate harmonics--multiples of50 of 60 Hz, causing hum/buzzTHROUGHOUT the VLF radio spectrum.Those immense, high-voltage, high-tensionelectric wires sagging between the tall metalpylons and marching off toward the horizoncan generate impossible amounts of hum andbuzz if you try to listen with a VLF receivertoo close to the--and I’m talking about milesor kilometers near to them!

To have hum-less recordings of VLF phe-nomena (such as the Eves River or AlaskaAuroral Chorus segments), you have to findlistening sites far removed from above-groundpower lines. Its fairly easy to find absolutelyquiet hum-free listening spots in desert andmountainous or tundra regions of NorthAmerica, Australia, or the remoter parts ofEurope and the British Isles (ScottishHighlands particularly) if you’re willing tomake a few days of it, but finding quiet spotsto listen close to home and/or in populatedregions such as the English Midlands or U.S.east and Midwest (including farmed areasaway from towns) usually mean pesky power

lines will be around somewhere, usuallyalongside the road you’re traveling along.

Willingness to walk/hike into listening sitesgreatly increases your chances that a quietspot will be found. In most cases, you have tolive with SOME background hum, as must I.Thus, some of the recordings on these CDshave some weak background hum.Surprisingly, reasonably quiet natural VLFradio listening spots can be found in placessuch as large ball fields, large urban/suburbanparks away from light poles, farm fields wherewires are hidden behind trees, along manybeaches (especially if electric wires are below-ground), and so forth. It has been found thatwithin southwest London’s Richmond Park,quite a few low-hum listening spots exist.This is also true for San Francisco’s GoldenGate Parks soccer playing fields.

Naturally-occurring VLF Radio sounds:Lightning-stroke static: If you’ve already lis-tened to ANY of these recordings, you willhave certainly noticed (or may even be fed-upwith) the nearly constant crackling and pop-ping noises on each and every one of theseCDs tracks. An unavoidable part of NaturalVLF Radio, lightning static is ALWAYS audi-ble, though, depending on the location andtime of year, the amount of lightning static


can widely vary. Generally, recordings madein local summer are plagued with lightning-storm static and those made in mid-wintertend to be wonderfully quiet.

While a nuisance to some listeners, VLFlightning static is trying to tell us something.Imagine a bolt of lightning--say--a bolt oflightning that strikes the ground from a cloudabove. The length of this awesome spark canbe many miles long and as wide as an auto-mobile. Between 10,000 to over 100,000volts are generated in this instantaneous jolt.Furthermore, a single lightning bolt rarelyfires just once, but as much as 100 times asecond, giving it that odd flickering effect.

As such; each and every one of those inno-cent pops evident in these recordings is oneof those huge sparks just described. But asyou may have already observed, there areseemingly HUNDREDS of them per secondoccurring in many of the recordings, some ofthem really loud, but most quite moderate tofaint. They seem to permeate the back-ground--sort of like playing an old, wornvinyl record. Obviously, there is A LOT oflightning going on out there! And there IS--acouple million lightning strokes (flashes)occur each day, worldwide, from approxi-mately 1500-2000 lightning storms inprogress at any given time. A VLF receiver is

quite good at picking up lightning from as faras 3000 miles distant (perhaps more), andgives you a nice idea of the SHEER amountof lightning strokes firing off in any givensecond! You may experience days or weeks ofsunny, delightful weather where you live, butthe VLF receiver NEVER lets you forget thatlightning is lurking all round you!

Whistlers: Most people get introduced toNatural Radio by hearing a recording of awhistler. Indeed, whistlers are the most com-mon Natural VLF Radio sound besides light-ning static, especially for those listening inmiddle latitudes. The term Whistler broadlydefines downwardfalling sounds whichrange from nearly pure whistling tones towindy/breathy sounds more similar to a sighthan a whistle. Between these extremes are avast variety of whistler types. In the case ofthe whistlers recorded in the eastern Nevadahigh desert, I called those whistlers growlers,since they sounded more like growls thanwhistles. Of course, there are many samplesof whistlers in these CDs.

Whistlers are the direct result of a lightningstroke firing off, and usually occur 1-2 sec-onds after an initiating lightning flash. Veryfew of any lightning strokes ever producewhistlers, but enough do to make things very


interesting on the good days, and sometimeswhistlers are so numerous as to be calledWhistler Showers or even Whistler Storms.Earth’s magnetic-field, which keeps compassesnicely pointing in one direction only (hope-fully!), plays a major role in the formation ofwhistlers. Not fully understood to this day,the traditional theory assumes that SOME ofthe radio energy from SOME of the lightningstrokes in just the RIGHT location get duct-ed into channels formed along the lines of

Earth’s magnetic field, traveling out intonear space and to the opposite hemisphere,where they are heard as a short, fast whistler(explained in more detail in the accompany-ing booklet with this CD set). If conditionsare favorable, some of the energy from theseshort, fast whistlers rebounds back the way itcame to arrive near (within several thousandmiles of ) the point of its initiating lightningstroke, and becomes magically louder andlonger. Essentially, during its globe- hoppinground trip, the all-frequencies-at-once radiosignal of a lightning pop gets the privilege ofbeing pulled and stretched apart, with itshigher audio frequencies arriving sooner thanits lower frequencies, hence the downward-falling tone.

Some (if not MOST days) are DEAD--entirely devoid of the sounds of whistlers, but

there can be those days where whistlers raindown too many to count, like a huge switchwas thrown by somebody up there. Listen tothe recordings, and you get the idea...

Chorus: Another general term used to definea number of Natural VLF Radio sounds, cho-rus defines several types of sounds when theyoccur in a rapid, intermixed form. The indi-vidual squawks, whoops, barks, and chirps oftriggered emissions tend to get lumped intothe general term of chorus when they occur inlarge amounts together. Depending on thetime of day, location of event (or at leastwhere it was heard), Chorus becomes AuroralChorus (it was occurring near auroral sourcesor during visual displays of aurora), or aroundthe pre to post-sunrise period, when it iscalled Dawn Chorus. Both sound generallysimilar, though chorus can manifest itself inendless variety.

Chorus is a product of magnetic storms,when events on the Sun, such as a solar flare,or holes in the Suns outer atmosphere (theCorona) allow a barrage of high-speedcharged particles to impact Earth’s outer mag-netic field (magnetosphere), causing it todeform and pulsate, much like air currentsdeform the thin film of a soap bubble.Phenomena such as Aurora (Northern and


Southern Lights) also increase dramaticallyduring magnetic storm periods, as do suchnatural VLF Radio sounds such as chorus.Notice the similarities of the various Chorusevents presented on these two CDs, yet alsonotice the variations. Short- lived repeatingbursts of the individual sound components ofchorus are sometimes referred to as ChorusTrains.

Auroral Chorus tends to be heard moreoften and at generally higher latitudes thanwhistlers, except for the widespread DawnChorus, which, when heard at lower-middlelatitudes, is strictly a magnetic-storm timephenomena.

Periodic Emissions: Other sounds differentthan whistlers or chorus get lumped into thiscategory, but is the term implies, they tend tooccur only occasionally (periodically) and inrepetitious fashion with a predictable repeti-tion time (period). A fine example of thissound is in the Kenai Crazy Whistlers track,which actually are NOT true whistlers at allbut are rarer Natural Radio emissions arisingfrom magnetic storm/auroral phenomena andheard this strongly only at higher latitudessuch as Alaska, central or northern Canada,Iceland, northern Scandinavia, or Antarctica.Notice that the Periodic Emissions in this

Kenai track seem to trigger subsequent ones(rather like a good tennis volley) until itwinds down.

Tonal Bands: Strange-sounding hissy or amultitude of whistling sounds which abruptlybegin and end, usually for only 5-10 secondsin duration. Many of these can be heard inthe Alberta Auroral Chorus tracks, particular-ly the longer recording.

Tweeks: You might have already noticed a lotof the lightning static (sferics) seems to haveodd pinging and ringing characteristics. Thistweeking effect, sometimes quite beautifulsounding (such as in the Fish Rock RoadWhistlers track), is generally a nighttimeeffect, with a few tweeks audible in the lateafternoon/early evening and reaching theirbest and most numerous around midnight,then gradually tapering off of the effect oncesunrise occurs. At about 50-55 miles in alti-tude (80-88 km), the E-layer of Earth’s ionos-phere (a layer of charged particles, calledions) acts similar to a mirror to VLF radiowaves. The same goes for Earth’s surface(more-or-less), and the two sides form a sortof pipeline which channel VLF radio signals,especially lightning stroke static impulses.Static impulses from very distant lightning


storms (thousands of miles) can travel betterat night in this huge radio wave pipeline ofEarth, but, below a certain frequency, there isan abrupt cut-off, whereby the pipeline effectceases. This is at about 1700 Hz audio fre-quency, which is also the frequency whichmost of the ringing and pinging sounds oftweeks are taking place. Tweeks slowed downabout 10 times almost begin to mimic low-pitched whistlers! Like Whistlers, one can getlost in the explanation of what causes aTweek, and so its sometimes more fun just toenjoy their odd sounds. Like Whistlers,Tweeks can sound very different from night-to-night--sometimes very pure and ringy,other nights they have a crusty sound.During those (frequent) times no otherNatural Radio sound can be heard besidesincessant static, listening to Tweeks them-selves can be mesmerizing!!

Hiss: Also called Hissband, is a VLF radioemission arising directly from Aurora, possi-bly emitted right from the same location aswhere the visible light (usually greenish incast) is produced. Hiss can vary in its fre-quency band, sometimes it has a high-pitchedsound like a slightly open water valve or toi-let-tank filling up, and on other occasions cansound much like the low-pitched roar of a

waterfall. While generally stable in character-istic, it can sometimes abruptly change in vol-ume and/or pitch.


3Recording Notes


CD 11. 7:06 Alvord desert dawn chorus Sometime around the 17th of August, 1993, the Sun spewed forth a barrage of energetic atomicparticles, some of which walloped Earth’s magnetic field, causing it to deform and pulsate. ThePolar Auroras became more brilliant as well, and were seen farther toward the Equator than usual.The skies dawned a brilliant blue in Oregon’s Alvord Desert, and the remnant patches of wintersnow upon the uppermost reaches of Steens Mountain shone a bright white. This tranquil scenebelied the fact that Earth’s magnetic field was undergoing utter chaos. Tremendous VLF radio ener-gy was released by the storming magnetic field. Had they not been outshone by the daylight skies,Auroral Borealis would have danced in the skies overhead. These are the sounds of the DawnChorus, a relative of Auroral Chorus but heard into middle latitudes around sunrise. If you listenclosely, you will hear the chorus and hiss gently rise and fall subtly every 10 seconds or so. This isthe actual sound of Earth’s magnetic field pulsating in and out. Because it was local summer, theradio energy static of lightning storms across North America was denser and more vigorous thanif it were in winter.Techie notes: (Strong Dawn Chorus recorded in the Alvord Desert of southeast Oregon. Some ofthe strongest dawn chorus heard south of latitude 45 degrees north. Undulating hiss, chorus, evi-dence of magnetic field micropulsations. 18 Aug. 1993, 1415 GMT )

2. 5:26Eves River auroral chorusOnset of big British Columbia auroral chorus recorded in northern Vancouver Island, BC, Canada,on 21 February 1994 at 1010 UT. Beginning of awesome chorus from visible aurora during major-severe magnetic storm. Extremely discreet, loud barks and squawks (risers). There are also a fewpure whistlers with sustained echoing. No powerline hum. very low level of lightning static.

3. 8:10Fish Rock Road whistler showerSpring-time in northern California is delightful. The hills are ridiculously green and full of wildflow-ers, and the air pervades with a potporri of scents. Thoughts turn to the outdoors... Suffering froman intense case of cabin-fever, I tossed a few necessities and a couple of my VLF receivers intothe van and headed northward from the San Francisco area into Californias Redwood Empire. With


no specific route plan, I just drove on with the single goal of getting as far from the city as possible.Driving into the night, I spied a sign pointing out a turn-off to Fish Rock Road. I thought to try it out,having never been that way before. It also looked promising as a power-line free road, winding asit did into the coastal mountains peppered with groves of Oak and Redwoods. Locating a nice turn-out suitable for overnight parking, I did another of my VLF-checks, instantly rewarded with gor-geous, almost pure whistlers ringing in my ears! These ones sounded BEAUTIFUL, with a hollow,cavernous quality to them, and the lightningstroke tweeks were also quite nice sounding. Thisearly April night felt almost warm, and the sky was full of starsthis recording segment is part of sev-eral hours of tape run during the night.Techie notes: (Purer whistlers occurring up to 20 per minute in clusters. Beautiful, hollow, cav-ernous sound quality to these whistlers. Intense tweeks (with harmonics). Recorded 02 April 1994,Fish Rock Road, Mendocino County, northern Calif at 1100 UT.)

4. 5:24Dawn chorus with whistlers in the Carrizo Plain Bisecting California nearly in two, the San Andreas Fault scores a rugged line from the Salton Seanorthward to Cape Mendocino, threatening residents with destruction and fury at any time, but alsorewarding them with fascinating geological sights. One of the best spots to view the amazing workof this vast fault line is in central Californias Carrizo Plain, where tree-barren, oat-grass coveredhills reveal its slow, determined work in the form of offset streams and wierd folds in the hills (clear-ly visible in satellite photos taken overhead). It is also a fairly nice place to travel to in the winter,shielded from cold, damp fogs shrouding the great central Valley as well as from coastal rain show-ers. Driving along a smooth dirt road alongside the fault-line hills this New Years Day, we chose aspot to camp with wonderful views of the surrounding terrain and also as far as we could get froma couple sets of large power-line pylons marching away in the distance. A magnetic storm was inprogress, though it was winding down from the day before. Camped next to electric lines, we wereunable to listen the previous night and now welcomed the electrically quiet location we had found,as well as the amiable weather. At 5a.m. the next morning, this recording segment was made. Weakchirping sounds of Dawn Chorus can be heard (had I been farther north in latitude, the Choruswould have been much louder) and also a good deal of pure whistlers are forthcoming. The weakhum sounds of high-voltage power lines about 4 miles distant can be heard.Techie notes: (Numerous pure whistlers and background Dawn Chorus chirping sounds. Weakbackground power-line (60 Hz & harmonics) hum. Taped in the Carrizo Plain, central Calif. 02 Jan.1994 1300 UT)


5. 4:24Eastern Nevada growler whistlersWhile on our September 1993 "Big Trip" in my van and eventually to tour the Canadian provincesof Manitoba westward to British Columbia, Gail and I stopped in the eastern Nevada desert about20 miles west of Wendover, Utah to catch several hours of sleep. Gail and I had driven most of thenight across the Silver State after a brief stop the evening before at another favourite natural radiolistening spot an hours's drive east of Reno, where we had heard and taped a marvelous varietywhistlers, some very strong like the ones recorded by the INSPIRE listening groups in March 1992.Very sleepy and exhausted after 250 miles east-bound on Interstate 80, we took a remote exit offthe freeway and headed south down a wide, unpaved road running alongside some railroad tracks.In the dark, we noticed there were powerlines running along the train tracks, but determined to stopin a spot where we could get some sleep and record whistlers (which I was sure must still be roar-ing), we kept on going until we saw another smooth dirt road branching away at right angles awayfrom the tracks and pesky wires. Making occasional checks for powerline hum with my WR-3, wedrove far enough from the wires--at least 5 miles-to where I couldn't hear any hum with my WR-3whatsoever. By this time, we was just too tired (and now cold) to even set up the better WR-4Bwhistler receiver's antenna. I just had enough energy to get in the back of the van and tuck myselfunder the covers, falling quickly asleep. Awaking a few hours later, I noticed it was somewhat lightwith a slate- gray sky. Time to set up the WR-4's 10-foot copper-pipe antenna and check out thewhistler band. As predicted, there were wonderfully loud "growler" type whistlers roaring out of fair-ly light background sferic static. I hopped back into bed and switched on my cassette recorder, cap-turing these great whistlers onto a 90 minute tape.Techie notes: (Eastern Nevada Big Growler Whistlers, a few with enormous strength with accom-panying triggered emission chirp and faint echo. 17 Sept. 1993, 1330-1500 UTC Recorded 30 kmsouthwest of Wendover, NV. Some loud, semi-local lightning sferics initiating very breathy, windysounding whistlers, though not as loud as the big growlers. Several loud lightning static bursts dig-itally removed from track and edited/compiled into several whistlers per minute rate.

6. 4:12Slow-falling Alberta whistlers (preceding the Auroral Chorus several hours later) About half an hour before sunset, we reached Alberta, and stopped briefly to snap a photograph ofus standing next to the "Entering Alberta, Wild Rose Country" sign. Whew!, we had crossed into yetanother huge and awesome province. Remembering that the next morning was "VLF Sunday"adate arranged in advance by Michael Mideke to record natural VLF radio at pre-arranged times, westarted looking for a back road off of what was now Alberta Provincial Highway 12. We were in a


sparsely populated and rather hilly area near Kirriemuir and Monitor, AB, and hoped we could finda location to spend the night which was away from electric power-lines by at least a mile. As wedrove down the highway, we tossed our heads left and right, spying a few interesting looking dirtand gravel roads on both sides of the main highway.Braking to a halt on the empty highway, we did yet another of our multiple point turns in the vanand headed back the other way. The first gravel road we chose ended up looking a bit too well-trav-eled and also not far enough from AC power-lines. The second choice couldn't have been better--a lightly rutted dirt (and mud) track into some low hills and trees next to an arroyo. The road termi-nated at what appeared to be ranch homestead with only a trailer and fallen-down windmill atopone of the small hills. A quick check with my WR-3 confirmed this level hill-top location was greatfor natural radio listening, being quite some distance from electric wires. With some trepidationsince we didn't like the idea of trespassing, we walked up to the trailer prepared to ask permissionto park nearby. But, nobody was home and the place looked like it had been unoccupied for at leasta week, so we elected to stay and set up the WR-4B VLF receiver's antenna mast then ate dinnerwhile watching the perfectly clear sky turn colors as night approached. It felt like it was going to bea cold night, though the very dry air would make the cold bite less, and I hoped the aurora wouldreturn.At about 3 a.m. MDT, I awoke and was startled then joyous to see the northern sky filled with agreen glow. Looking closer, I also spied faint bursts of green "splotches" moving ("squirting") in aleft-to-right (west-to-east) direction! Wow, it was much better than the night before! Apparently, aminor magnetic storm was happening, though I really wasn't alerted to it since the geo-magnetic"indices" put out on shortwave time and frequency standard station WWV from Colorado wasreporting only "unsettled" magnetic conditions. I quickly awoke Gail, who had missed out on see-ing the fainter aurora the night before. The next thing I did was turn on the WR-4B whistler receiv-er and start up the tape recorder. I was instantly rewarded by a faint squawking sound of "chorus"as well as weird tones slowly rising then falling. When these weird "sliding tones" would appear, theaurora would slightly brighten and the "squirting green splotches" also seemed to speed up! By this time, it was at or below freezing, and frost was rapidly building up on the outside of the van'swindows though the air inside the van had been considerably warmer--at least until I threw openthe back doors and began watching the auroral show while still tucked tightly in my sleeping bag.Gail borrowed the whistler receiver's headphones and listened to the weird VLF radio sounds com-ing forth, but sleepiness overcame her again and she dozed off. As the initial excitement wore off,I also felt very sleepy again and decided to doze for a while with the tape recorded still running--Iat least wouldn't miss out on the great VLF radio sounds.As the 1100 UTC period approached, I flipped the cassette over and prepared to tape the auroralradio chorus, which by this time was become quite vigorous. Alas, I waited until about 1104 UTC


to begin the taping, thinking the appointed monitoring time was to begin at 1105 UTC, when actu-ally it began at 1100. I rolled the tape and taped an entire side of a C-90 (45 minutes) of the fan-tastic Alberta auroral chorus. This recording was made several hours before the actual aurora wasvisible, at around 10:45 p.m. local Mountain Daylight Time.Techie Notes: (Slow descending, breathy/windy sounding whistler trains recorded in easternAlberta (near Monitor and Kirremuir off of Hwy. 12) at approx. 0445 UT on 26 Sept. 1993.Two hourslater, there was visible aurora and the VLF auroral chorus began at approx. 1015 UT Weak back-ground power-line hum (uninterrupted recording of 2:25) to end of side A, repeated at start of sideB) NOTE: Also Refer to CD #1, track 8 & 9, and CD #2, track 1

7. 10:57Kenai crazy whistlersKenai Crazy Whistlers--otherwise known as periodic emissions. Rising then falling wavery puretone emissions of fairly loud stength. Some tweeking sferics. Great recording! Recorded nearSkilak Lake on Alaskas Kenai Peninsula on 09 Sept. 1995 at 0945 UT on an overlook looking outover the lake and of beautiful, glacier-topped mountains to the south. The moon was shining andthere was also some aurora visible off to the north.

8. 5:07Alberta auroral chorusRefer to written story introduction to Selection 6, CD 1. This recording came after the slowdescending, breathy/windy sounding whistler trains recorded in eastern Alberta (near Monitor andKirremuir off of Hwy. 12) at approx. 0445 UT on 26 Sept. 1993. Six hours after the slow whistlers,there was visible aurora and the VLF auroral chorus began at approx. 1015 UT.. Weak backgroundpower-line hum (uninterrupted recording of 2:25) to end of side A, repeated at start of side B. Thistrack has the beginning of the Auroral Chorus.

9. 8:40Alberta auroral chorusRecorded during visible pulsating aurora (non- discrete) while we were in eastern Alberta (nearMonitor and Kirremuir off of Hwy. 12) at approx. 1110 UT on 26 Sept. 1993. Squawking and bark-ing chorus, plus intriguing tonal bands abruptly starting and ceasing. Six hours earlier, there hadbeen very diffuse, slow-falling whistler trains as in Tape 1, recording tracks 6 and 7. Weak power-line hum in background. Overall very beautiful recording! Original recording has some FAINTacoustic sounds picked up inadvertantly via the headphones (talking and Gail snoring!)


CD 21. 16:30Long version of the very beautiful segment of Alberta Auroral ChorusRecorded during visible pulsating aurora (non-discrete) while we were in eastern Alberta (nearMonitor and Kirremuir off of Hwy. 12) at approx. 1110 UT on 26 Sept. 1993. Squawking and bark-ing chorus, plus intriguing tonal bands abruptly starting and ceasing. Weak power-line hum in back-ground. Overall very beautiful recording! (uninterrupted 18:20 recording). Original recording longer,but has some FAINT acoustic sounds picked up inadvertently via the headphones (Steve and Gailtalking and also Gail snoring!)

2. 23:37Eves River Auroral ChorusLonger recording of the big B.C. chorus, this time starting at 1010 GMT of 21 Feb. 1994. Greatsquawking, chirping chorus along with the occasional weak pure whistler and numerous echoesafter each whistler (called whistler echo trains). At this time, the chorus was really starting up,revealing many variations.

3. 8:17Second recording of Eves River Auroral ChorusRecorded about 6 hours after the recording on track 2, in the morning at 1600 GMT on 21 Feb.1994 AFTER SUNRISE (Hence it is now called Dawn Chorus).The squawking/chirping of the Dawnchorus was fairly homogeneous by this time, with vigorous chirping but with little overall variationand sounding quite different from its start-up period in track 2 above. No whistlers occurring at thistime.

4. 10:59 and 5. 6:13Chatanika River Auroral Chorus Normally heard either during the night at middle-upper latitudes or at sunrise in middle (as in theAlvord Desert Dawn Chorus recording), this was recorded IN THE MIDDDLE OF THE DAY 40 milesnortheast of Fairbanks, Alaska, right within the Auroral Zone. It went on continuously for 3 days!Had it not been daylight, the Auroral Borealis would have been dancing in the skies right overhead!Weird squawks, chirps, hiss, and occasional very low groans can be heard. Recorded in centralAlaska on 06 September 1995 between 1945-2200 UT. A week long major magnetic storm with


accompanying beautiful auroral displays at night and strong auroral VLF chorus audible around theclock! Amazing variety of hissband, tonal emission bands, chorus barks, croaks, whoops, a fewwhistlers, etc. The weather during the recording session by the Chatanika River was very windy attimes, but also sometimes just a slight breeze. Many strong gusts of wind induced some mechan-ical noise in the WR-3E VLF receiver. A such, the approximately 2 1/2 hours of tape recordingswere marred at times by this receiver/mechanical wind noise. However, there are up to 10-minutesegments free of this undesired noise.


About the AuthorName: Stephen Paul McGreevy.Born in San Francisco, California on 5 October 1963. Began MW Dxing in 1974-5 and SW listening in 1976. Began Longwave and trans-Pacific MX Dxing in 1982. Attained General Class Amateur Radio License in 1986 (N6NKS). August-October 1986, DXed LW, MW and SW from Hawaii.April 1987 worked several Japanese Amateur stations using 3-5 watts,CW mode on 40 meters from California. Initial interest in Natural VLF Radio started in December 1988. Heard first whistler live in eastern Oregon high-desert on crude audiofilter and 500 meter wire in June 1989. July 1989 - July 1990, experimented with various homebrew VLFreceivers. September 1990, developed first successful whip antenna receiver forWhistler Listening.

February 1991, weekly listening and recording of natural VLF Radio began in earnest. Heard first Dawn Chorus April 1991. Developed better whip antenna receivers May-July 1991, including WR-3 prototypes. With friend FrankCathell, developed final WR-3 prototype. October 1991 began selling WR-3. September 1992, developed WR-4 Van-based VLF receiver and purchased Marantz portable tape recorder. Thisbegan period of excellent VLF recording successes. July 1993, developed enhanced WR-3, called the WR-3E. September 1993, saw first aurora in Saskatchewan, Canada and recorded Auroral Chorus. Recorded and sawbetter aurora the following night in Alberta while on 4500 mile road trip. February 1994, during trip on Vancouver Island British Columbia, recorded stunning auroral chorus duringsevere magnetic storm. September 1995, witnesses spectacular auroral displays in central Alaska, and recorded many hours of excep-tional daytime auroral chorus with WR-3E. November 1995, contacted by Irdial-Discs with offer of this CD project.


Electric Enigma: The VLF Recordings of Stephen P. McGreevy - Irdial

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Transcript of Electric Enigma: The VLF Recordings of Stephen P. McGreevy - Irdial