Besides 50 or 60 Hertz (and harmonics) alternating-current powerline "hum" from electric-utility power grids, the most noticeable sounds are going to be the snap, crackle and pop of lightning-stroke electromagnetic impulses (called "atmospherics" or "sferics" for short) from lightning storms within a couple thousand miles of the receiver--the more powerful the lightning stroke (or the closer it is your listening location), the louder the pops and crashes of sferics will sound in the WR-3 headphones. I should note here that some books and on-line texts use the term "sferics" to mean ALL natural radio phenomena, but more experienced listeners prefer to keep that term specifically for lightning-bolt (static) impulses (atmospherics).

Several million lightning strokes occur daily from an estimated 2000 storms worldwide, and the Earth is struck 100 times a second by lightning. The WR-3 makes quite an effective "lightning monitor"-at times the receiver's output is a cacophony of crackling and popping sferics in an ever-changing texture from lightning strokes originating in storms near and far.

These huge sparks of lightning strokes, whether from cloud to ground or within a lightning cloud cell, are tremendously powerful sources of electromagnetic (radio) emissions throughout the radio-frequency spectrum-from the very lowest of radio frequencies up to the microwave frequency ranges and the visible light spectrum. However, most of the emitted electromagnetic energy from lightning is in the very lowest part of the radio spectrum, from 0.1 to 10 kHz, which are the frequencies the WR-3 VLF receiver has been designed to monitor. The powerful electromagnetic radio pulses produced by lightning strokes travel enormous distances at these very-low radio frequencies, following the surface of the Earth as "groundwaves" or by other unusual propagation means.

It is quite interesting to note how generally quiet and lightning sferic free the hours are from just after sunrise to midmorning, when thunderstorms tend to be at their minimum. Later, the crackling and popping of lightning sferic activity picks up as afternoon thunderstorms build in numbers and intensity because of thermal heating and convection, especially in the summer and autumn months, when, by sunset, the sferics (snap, crackles and pops) are roaring in a varied and ever-changing texture as lightning storms rage on into the evening. Weather monitoring agencies employ special receivers that receive and direction find lightning sferics in order to determine where lightning strikes are occurring and the potential for wildfire ignition, hazards to aviation, and damage to electric power utilities from those lightning strikes.

In addition to the musical pinging, dripping, popping, and crashing sounds of lightning sferics and tweeks, you may be rewarded by hearing downward falling musical notes ranging from nearly pure to "swishy" or "breathy" sounding tones from 1/2 second to over 4 seconds in duration. These are the aforementioned "whistlers," and they may sometimes happen a couple of seconds after some of the static crashes and pops of sferics from lightning strokes, although quite often no preceeding lightning static sound is heard. One of the best known natural radio phenomena, Whistlers generally sweep downward in frequency from about 6 kHz to around 0.5 kHz, but the lower cutoff frequency does vary markedly as conditions change, and the upper frequency of whistlers can sometimes start higher than 10 kHz. Whistlers sound quite fascinating - sort of like some "science-fiction" sound effects - and besides lightning sferic "static" are one of the more common Natural Radio sounds you can hear with your WR-3. They occur in many varieties and characteristics.

The Earth's outer magnetic field (the "magnetosphere") envelopes the Earth in an elongated doughnut shape with its "hole" at the north and south magnetic poles. The magnetosphere is compressed on the side facing the Sun and trails into a comet-like "tail" on the side away from the Sun because of the "Solar Wind," which consists of energy and particles (plasma) emitted from the Sun and "blown" toward Earth and the other planets via the Solar Wind. Earth's magnetosphere catches harmful electrically charged particles and cosmic rays from the Sun and protects life on Earth's surface from this lethal radiation. Amongst the charged particles caught in the magnetosphere are ions (electrically charged particles), which collect and align along the magnetic field "lines" stretching between the north and south magnetic poles.

These magnetic-field aligned ions bombarding Earth's magnetosphere form "ducts" which can channel lightning-stroke electromagnetic impulse energy. Whistlers result when an electromagnetic impulse (sferic) from a lightning-stroke enters into one of these ion-ducts formed along the magnetic lines of force, and is arced out into space and then to the far-end of the magnetoionic duct channel in the opposite hemisphere (called the opposite "magnetic conjugate"), where it is heard as a quick falling/descending emission of pure note tone or maybe as a brief "swish" sound. Whistlers sound the way they do because the higher frequencies of the lightning-stroke radio energy travel faster in the duct/waveguide channel and thus arrive before the lower frequencies in a process researchers call "dispersion." A person listening with a VLF receiver like the WR-3 in the opposite hemisphere to the lightning stroke (at the far end of the Magnetospheric duct path) will hear this "1-hop" falling note whistler. One-hop whistlers are generally about 1/3 to 1 second in duration.

If the energy of the initial "1-hop" whistler gets reflected back into the magneto-ionic duct to return near the point of the originating lightning impulse, a listener there with a VLF receiver will hear a "pop" from the lighting stroke impulse, then roughly 1 to 2 seconds later, the falling note sound of a whistler, now called a "2-hop" whistler. Two-hop whistlers are generally about 1 to 4 seconds in duration depending on the distance the whistler energy has traveled within the magnetosphere. One-hop whistlers are usually higher pitched sounding than 2-hop whistlers - another sound illusion we hear with our ears but when displayed in a spectrogram we can see that they are fast versions of 2-hop whistlers.

The energy of the originating lightning stroke may make several "hops" back and forth between the northern and southern hemispheres during its travel along the Earth's magnetic field lines-of-force in the magnetosphere. Researchers of whistlers have also observed that the magnetosphere seems to amplify and sustain the initial lightning impulse energy, enabling such "multi-hop" whistlers to occur, creating long "echo trains" in the receiver output which sound spectacular! Each echo is proportionally longer and slower in its downward sweeping pitch and is also progressively weaker. Conditions in the magnetosphere must be favorable for multi-hop whistler echoes to be heard. Using special receiving equipment and spectrograms, whistler researchers have documented over 100 echoes from particularly strong whistlers - imagine how much distance the energy from the 100th echo has traveled - certainly millions of miles/Km! Generally, only 1 to 2 echoes are heard if they are occurring, but under exceptional conditions, several echoes will blend into a collage of slowly descending notes and can even merge into coherent tones on a single frequency -- hard to describe here, but quite unlike any familiar sounds usually heard outside of a science-fiction movie!

It should be reiterated that strong 2-hop (and echoes) can occur from lightning that is not necessarily close to the listener or even within a couple of hundred miles from the your listening location, but perhaps from lightning that is over 1000 miles distant. Magnetic field conjugate points are not fixed but always in flux as is Earth's magnetosphere. You may notice that "louder" sferics (i.e. closer lightning strokes) often do not trigger the loudest whistlers, if they do so at all, but then a loud whistler may come howling through from a relatively weak sferic from quite distant lightning. This is because the lightning impulse sferic energy may propagate within the earth-ionosphere region for considerable distance before entering a magnetospheric "duct." A vast majority of fine whistlers are heard during periods of locally fair weather - lightning need not be within visible distance. In fact, many extremely loud "big whistlers" are heard WITHOUT ANY preceding lightning sferic audible whatsoever, indicating the initiating lightning-strokes of those strong whistlers are very far away - possibly over 3000 miles!

Whistlers are best heard in latitudes between 30 and 60 degrees north latitude in North America, with the prime latitude being 30-45 degrees north. (More on this under the "WHERE TO LISTEN" section further on).

At higher latitudes such as in Canada, Alaska or Scandinavia , a type of whistler called "nose whistlers" can be easily heard when they are occurring. These are named for the way they appear in spectrograms, and often occur in clusters. They are quite spectacular sounding. Nose whistlers have both rising and falling frequency components. Compare the nose whistler spectrogram below to the one of the whistlers recorded in Nevada above.

Every whistler is triggered by a lightning stroke, and lightning that is DISTANT enough away not to pose a danger to a listener with the WR-3 but which is also visible (especially at night) can sometimes trigger whistlers (very weak to very loud) shortly following the simultaneous visible flash and loud radio static "pop"/"crack" of the local lightning sferic in the WR-3 receiver's headphones. If the whistlers you hear coming from the visible lightning strikes are very loud, this indicates a magnetospheric duct happens to terminate relatively close to your location. Because the sferics from lightning strokes within 50 miles to your listening location will sound EXTREMELY LOUD in the headphones, keep the audio gain setting low to protect your hearing.

Don't confuse the sounds of tweeks with the longer duration whistlers, which many newcomers to Natural Radio monitoring tend to do at first. Tweeks, as explained above, have a similar sound to water dripping into a bucket of water or gravel hitting metal sheeting, are of roughly the same duration as a "drip," and generally are accompanied with the "click" or "pop" sound of the lightning stroke impulse. Whistlers on the other hand are much longer in duration than a tweek - anywhere from 1/2 second to as long as 4 seconds in duration as I have previously mentioned above.

Occasionally, shortly after sunrise and occasionally extending into the midmorning, a phenomenon called "Dawn Chorus" may occur. Dawn chorus can resemble the sound of a flock of birds singing and squawking, dogs barking, or sound like whistlers raining down seemingly by the hundreds-per-minute (called a "whistler storm"). Dawn Chorus generally results from hundreds of overlapping, rapidly upward rising tones that can be continuous or appear in bursts, called "chorus trains." These chorus trains sound very fascinating -- the bursts of chirps and squawks (risers) seem to suddenly commence, and over the course of 2 to 5 seconds, weaken and fade away, then repeat over again, often in different pitches. During a chorus train, the sounds sometimes seem to be echoing or reverberating back and forth until fewer and fewer risers happen, then there may be a brief pause before the next chorus train commences. Chorus trains also seem to be harmonically related-a chorus train's center audio frequency may alternate randomly, first centered on about 1 kHz, then another chorus train will suddenly start up one octave higher at around 2 kHz, or maybe 4 kHz. Bursts of chorus trains happening at different octaves can overlap in a truly beautiful sounding cacophony.

(Much of the information following should be used concurrently with the above sources of geo-magnetic information for best listening results.)

Statistically, the time between local midnight and an hour after sunrise is when the greatest amounts of whistlers are heard, although dusk to midnight may reveal substantial whistler activity, and even (though not very often) loud whistlers may be heard a couple of hours before sunset. Over the long term, the period from two hours before sunrise until an hour after sunrise is the optimum time to listen for natural VLF phenomena of all sorts, as the amount of sferics (lightning stroke pops and crackling) are less -- natural VLF radio phenomena are not as "buried" under the sferics as in the evening when lightning storms are more numerous. Also, magnetospheric conditions are optimum around morning twilight time and an hour before for best whistler listening.

Interestingly, between April 1996 and March 1997, I had been hearing good whistler events during the DAYTIME and particularly late afternoon before sunset! Many times, these whistler events die out after sunset and are not heard at sunrise. But, after that through December 1997, whistlers were once again more frequently heard between 2 - 6 a.m. local time.

In early March 1997, whistlers started up around 4 p.m. local time and were going in earnest (several-per-minute) between 8 p.m. and 11 p.m. PST. This may be a solar-minimum phenomenon, but it points out the need to listen as much as one can for whistlersand at ANY time, as they occur when least expected. This recent late-afternoon trend has not always been the usual case a few years ago and many listeners got used to listening only after midnight to dawn, as did I. In early 1998 from near Death Valley, California, I caught the first " whistler storm" heard since 1992, fortelling of the wonderful natural radio events to come as we head into solar-maximum by the year 2000.

In early to mid-1999, especially in March and April 1999 (equinoctal periods), whistlers were frequently heard in great variety near Death Valley by myself during the midnight to 7 a.m. local-time period. Waek Dawn Chorus has been occurring

about 2 times a month in eastern California in early 1999 - and much more frequently farther northward toward the auroral-zone regions.

Therefore, whenever I am out hiking in areas even just a bit away from powerlines, I bring along my WR-3E and am sometimes plesantly surprised with nice whistlers to enjoy! (S .P. McGreevy)

So, in summary, while the pre-sunrise hours are generally the best time to listen for whistlers and other phenomena, intense whistler events of short duration can occur at any time between just before local sunset through 1 to 2 hours after sunrise. A good whistler event that is happening at 10 p.m. or even at SUNSET may not be occurring later on that night at the usually 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 a minute may be heard on average, but as is often the case, whistlers will not be heard at all. Occasionally during a geomagnetic storm caused by a solar flare, over 100 whistlers a minute or more may be heard - called a "whistler storm!" Whistlers may or may not have echoes and they may be few and far between and very loud, or may occur often but be quite weak. The sound characteristics, intensity, and number of whistlers can change rapidly hour to hour. Everything depends upon the sensitivity and conditions of Earth's magnetosphere and the location of lightning storms and magnetospheric ducts in relation to the WR-3 VLF Receiver user.

Whistlers are seldom heard midday at mid-latitudes, except during unusual conditions occurring with a severe geo-magnetic storm or unusually strong electron and proton output from the Sun impinging upon Earth's magnetosphere. Unfortunately, on a good number of days during the year there will not be any whistlers audible even though there is plenty of lightning activity and sferics within a few hundred to few thousand miles miles of your listening location. Often elusive, whistlers may not be heard for days or weeks at a time. Again, it is hard to predict when whistlers are going to occur based on the geo-magnetic indices, but they are generally more common in the spring and the fall surrounding the equinoxes, and at sunrise, or less frequently, at sunset.

In North America, higher latitudes where the Northern Lights (Aurora Borealis) are visible are excellent locations to hear whistlers, and particularly, very loud Auroral and Dawn chorus, and a myriad of other bizzare-sounding Natural Radio emissions when they are occurring. (This is the reason I make recording expeditions into northern Canada to capture all the lovely VLF activity up north). For instance, in the center of the Canadian Provinces of Alberta through Ontario, chorus of infinite variety is an almost daily occurrence, even when geo-magnetic indices would seem to indicate listening would otherwise be "dead" farther south! Spend a week or two in August, say, in central Alberta and/or Manitoba, Canada (as I did in 1996) or in central Alaska, and you too would be delighted and in awe of the Natural Radio sounds heard each day and the gorgeous auroral viewing at night if the sky is clear...

For those in Europe and the British Isles, similar fabulous chorus listening locations would be northern Norway and Finland; Iceland, and the extreme northernmost parts of the British Isles.

For middle-latitude listeners, Dawn Chorus (as previously mentioned) tends to peak in intensity between sunrise and one hour afterward, but at high latitudes, can peak as late as noon or even in the mid-afternoon, particularly if there is any geo-magnetic activity (Kp index > 2) and can take on incredibly beautiful sounds.

Whistlers of intense strength can be heard across the middle and southern-most United States and southern Europe and North Africa. The latitudinal zone where the loudest whistlers are heard falls roughly between 30-55 degrees north for North American listeners. In the United States, statistically, the "northern tier states" region is blessed with the highest number of whistlers and chorus occurrences (Washington State, northern Idaho, Montana, North Dakota, Minnesota, Wisconsin, Michigan, Pennsylvania, New York, and New England. In Canada, the southern parts of British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, Quebec and the Atlantic Maritime Provinces hear large amounts of whistlers and chorus. Throughout central Canada and Alaska, wonderfully strong chorus events lasting from morning to evening can occur, particularly in Feb. April and August - early October.

Strong events of chorus occurring at higher latitudes can be heard into more southern latitudes too, albeit somewhat weaker and less often. Southern Canada, all of Europe, especially northern Europe and the British Isles, are good locations to listen for both whistlers and chorus. Everywhere, the lightning impulse "static" sounds of sferics and tweeks from Earth's great number of electrical storms abound.

In the Southern Hemisphere, New Zealand, the Australian states of Tasmania, Victoria, South Australia and parts of Antarctica are also prime whistler monitoring regions, as would be locations along a radius of about 3,000 mi./4800 km. radius around the southern magnetic pole. Note that both the north and south magnetic poles don't fall on the true geographic poles of the Earth but are several hundred miles offset. The geographic coordinates of the north magnetic pole is approx. 75 degrees north latitude by 100 degrees west longitude. The south magnetic pole is approx. 67 degrees south latitude by 155 degrees east longitude. Whistlers have been reported in Saudi Arabia despite its southern geographic latitude. In rare cases and very strong whistler events, whistlers can be heard even at the Equator.

Whistlers have also been observed by unmanned spacecraft passing by the planets Jupiter and Saturn which also have considerable electrical storm activity and very powerful magnetospheres.

In summary, the zone where the loudest chorus events occur is higher in latitude than whistlers (please refer to the maps), and for North American listeners it is between 45-60 degrees north latitude. In some locations, such as northern British Columbia or in Alaska, the whistler rate is slightly lower than in places such as Washington state, Minnesota or Maine, but Chorus will occur far more often in Alaska and in central Canada than farther south.

Also, since we're now well into solar cycle (# 23 - due to peak around the year 2000), already increased sunspot/solar-activity means the regions of good dawn and daytime chorus and whistler events have shifted southward again. Places experiencing few Chorus events are already hearing hear more of it - and louder too. In a few years, locations in North America below 35 degrees geographic latitude; central and southern Europe; southern Australia and Africa will hear chorus and other events far more often, which were, at the bottom of the solar-cycle in 1996, heard only closer to the magnetic poles and the auroral zone, such as in Canada and northern Europe. AND, rare and spectacular sounding "whistler storms" (hundreds of whistlers per second) will make their presence heard again - by far my favorite natural radio event!!!

Nothing but static: You shouldn't be discouraged if after several listening sessions, whistlers, chorus, or other VLF phenomena sounds (besides lightning sferics "static") are not immediately heard. Perhaps 25 - 33% of days in a month result in nothing of interest being heard, especially below 35 north latutude, however, sooner or later, you will be rewarded with a variety of fascinating sounds from whatever VLF phenomena is occurring at the time you listen - as though the times of not hearing anything are suddenly "made up for" by a listening session filled with all types of beautiful natural VLF radio sounds! As a reminder, weather and outside temperature permitting, the period from about 0430 local time to around local sunrise will be the most rewarding time to listen - requiring you to be an early riser! Natural VLF Radio signals can sound truly eerie and awe-inspiring, especially when one realizes it is all naturally occurring - not man made, and that these radio emissions have been occurring for millennia.

The format is as follows:

Stations:

1) KO - Komosomolskamur (north of Khaborovsk), 50N/137E

2) NO - Novosibirsk (master station, Central Russia), 54N/83E

3) KR - Krasnodar (Black Sea), 45N/38E

Time Schedule: Cycle period 3.6 seconds, 6 time slots at 0.4 sec. duration, 0.2 sec. spacing

Estimated radiated power in wattage 50 kW to 100 kW. The table reads left-to-right and repeats every 3.6 seconds per Time Schedule above.

Beukers Laboratories, Inc.: VLF and LF for Navigation, Summer 1974, Vol. 21, No. 2

Kerckhoff, Manfred; Bremen, Germany - narrow-band and wide-band receiving observations (Manfred also supplied the article above)

The nearest Alpha transmitter to North American listeners is near Khaborovsk, Far eastern Russia, and is likely the loudest Alpha signal that will be heard with the WR-3 VLF Receiver for most listeners throughout North America, except for the eastern part of North America, where Alpha station near Krasnodar (Black Sea) will be the strongest Alpha signal. The same goes for listeners in the British Isles and Europe, with Novosibirsk the next strongest station.

The WR-3 VLF receiver should be operated well away-at the very least 1/8 to 1/4 mile (300-600 metres)-from any 50/60 Hz A.C. powerlines or structures that contain them, such as houses and buildings, or else a "hum" sound from the A.C. powerline frequency (and harmonics to well above 1 kHz) will dominate the WR-3 receiver's output. This is because the alternating current frequency of 60 Hz (50 Hz outside of North America, Hawaii, and most of South America) carried by power lines also puts out harmonic emissions every multiple of 50 or 60 Hz, and these power-line harmonics can be easily received by the WR-3. Locating a listening spot 1/2 to 1 mile (800-1600 meters) away from power lines if possible will probably eliminate most if not all "hum" interference. The farther away you can locate away from electric power lines, the less "hum" will cover the desired VLF Natural Radio phenomena, especially the weaker and more subtle ones.

Lower voltage underground power lines such as those within newer residential neighborhoods may not be an annoyance at 1/4 mile/1000 metres away from them, however, high-tension/high-voltage power lines in "utility corridors" can cause some hum even 2 to 3 mi./3 to 5 km distant in worst case situations. Powerline buzz and hum presents the greatest obstacle to Natural Radio listening for most listeners, and more-or-less eliminates "backyard" listening, thus requiring some sort of "expedition" to an electrically quiet location, which can often be quite challenging but fun! The WR-3 is a great receiver to take with you on wilderness trips or long walks on the beach, whether via car, boat or on foot.

It's also important to be in a clear, open place away from trees by at least 50 yards/meters - a meadow, field, or open hilltop is best. Trees act as electrical-field "short circuits" at these low frequencies - the WR-3 VLF Receiver will lose sensitivity as you get closer to trees and other obstacles. All VLF signals will be attenuated almost completely if the WR-3 is operated under trees, no matter how few of them are around due to e-field dampening and absorbtion.

Standing under a lone tree surrounded by miles of open space will be little better than being deep in the woods - relocate away from trees and be in the open. In short, AC power lines cause annoying "hum" that masks all other signals and trees reduce all the signals there are to hear, so it is best to locate a listening site away from both of them. You need not seek the highest location around to listen with the WR-3, but if you listen in deep valleys and canyons, signals will also be reduced a bit.

When using the WR-3 VLF Receiver, hold the whip antenna as vertically as possible while grasping the aluminum enclosure, whereby your body will act as a "ground." Additional grounding can be accomplished by clip lead attached to one of the screws on the aluminum enclosure of the WR-3 and to a 6-8 inch nail, or rod stuck into the soil where you use the WR-3, but this will not be necessary unless you tape record the output of the WR-3 or wish to eliminate capacitive "foot" noise caused when shoes are rubbed on the ground or when dry grass or shrubs touch your clothing or shoes.

CAUTION: DO NOT OPERATE THE WR-3 WHEN NEARBY LIGHTNING STORMS THREATEN AND TAKE APPROPRIATE LIGHTNING PRECAUTIONS!

A very interesting electrical effect easily observed with the WR-3 are insect wing sounds caused when insects such as bees, flies, and mosquitoes fly within a couple of feet of the WR-3 whip antenna. The resulting sound is a buzzing sound very similar to what can be heard by ear, however, this effect is caused by electrostatic discharges each time the insect's wings flap. It is thought that electrostatic charges (static electricity) are collected on the insect's wings and then and dumped during each wing beat, creating a "modulated" electrical field around the insect at the same frequency as the wings beat. Large insects, such as wasps, Yellowjackets, Bumblebees and honeybees, make particularly strong buzzing sounds in the WR-3 headphones-easily heard when those insect fly within 3-4 feet (1 meter) of the WR-3 antenna. High-pitched Mosquito wing beat sounds can be heard the small insects fly within a few inches of the WR-3 Receiver's whip antenna.

Certain kinds of flies and other insects have much more electrostatic "buzz" from them than other kinds - Bees and Horse Flies, in our observations, have the loudest "buzz" in the headphones! This may also have something to do with the composition of the insect's wing, with certain type of insect wings more prone to static electricity accumulation and subsequent discharge. There may also be insect bodily electrical discharges generated within the insect's wing muscles that contribute to this effect, and a some believe that the insect's carapace ( outer body shell) has a piezo-electric effect similar to quartz crystals, but not much is understood about this phenomenon yet and further studies are encouraged.

ABOUT HEADPHONES: The WR-3's output jack requires a pair of STEREO headphones (for dual-ear monaural sound). The most convenient and portable kind are the lightweight "personal-stereo" type of stereo headphones that have a 3-conductor 1/8 inch (3.5 mm) plug. These kinds of headphones have an impedance of 8 or 16 ohms, are widely available, lightweight, match very well with the WR-3 and are highly recommended. While the output of the receiver is not true "stereo" but "dual-ear monaural" sound, we designed the WR-3 to match with these very commonly available headphones.

Not all stereo headphones work the same with the WR-3, and ones with 32 ohms impedance or those that are rather "cheap" may have too low of a volume to be very satisfactory. It is highly recommended that you try out several pairs of good quality for greatest volume level output and sound quality.

Beware of the kind of headphones which are small, "plug"-like types designed for bass-boost listening -- these can emit excessive/harmful audio output from sferics and other sounds and they may also cause deafening audio feedback. Some of these kind, however, work fantastically with the WR-3 when used properly. But...these are the words of one regular WR-3E listener of natural VLF radio and is very good advice: Do not use "earplug" phones with soft, flexible seals that fit tightly within the ear to improve "bass" audio effects, which might inflict serious hearing damage on very powerful, sharp "cracks" due to strong, local discharges. The cheap kind of phones with the openly vented foam pads are acoustically perfect and pretty safe.

Other kinds of headphones such as full-size 8-16 Ohm stereo headphones designed for use with stereo component systems will work very well, though you may need an adapter to convert their 1/4 inch plug (7 mm) to the 1/8 inch (3.5 mm) plug. The audio volume from the WR-3 may be considerably louder with full-size headphones compared to some mini-stereo style headphones - plenty for most listeners-especially if their impedance is 8 or 16 ohms. Full-size headphones also give you the advantage of enclosing your ears better than mini-headphones, thus shutting out exterior noises and enabling you to hear natural VLF phenomena better.

High-impedance (600 to 1000 ohm) audiophile headphones will not work with the WR-3 because the volume is too low and inadequate due to mismatch with the WR-3's headphone amplifier. However, you could employ an audio transformer to convert the 8-ohm output of the WR-3 to 1000 ohms for far better results with high-impedance headphones if you're willing.

Whatever headphones you choose to use, they MUST have a 3-conductor (stereo) plug. Two-conductor (monaural) plugs will not work conveniently without an adapter to convert the 2 conductor (mono) plug to the 3-conductor (stereo) plug, although in a pinch you can use headphones with a mono plug (or patch-cord) by plugging them in about half way into the WR-3 headphone jack, perhaps with the assistance of a non-metallic washer and tape to hold the mono plug out at the proper distance for it to make good contact with the WR-3's headphone jack. If in doubt about the type of plug on the headphones, it should have three metal bands separated by two thin black plastic insulators. If it only has two metal bands separated by one plastic insulator (mono plug), it won't work without an adapter unless you plug it in only half way-enough to make contact.

BATTERY POWER: A 9-volt (rectangular snap-type) PP9 ALKALINE battery is best recommended for use with the WR-3 and will last from 30 to 40 hours of use depending on the audio gain level. Other types of 9 volt batteries such as "General Purpose" types will not have as long a life as Alkaline types but will last quite a long time anyway (about 10-15 hours of listening).

Rechargeable Ni-Cad 9-volt batteries can be used, but are not recommended because of their limited discharge life-which is shorter than an alkaline battery, and also due to their lower voltage (8.4 volts). Battery replacement is achieved by removing the four screws that secure the receiver's top cover and snapping on a new battery to the battery clip and carefully re-fitting the cover. Be sure the WR-3 is switched off to avoid circuit damage if you accidentally connect the battery backwards, ESPECIALLY is you are using a Ni-Cad or other newer rechargeable types which have high current.

WR-3: A tape recorder with an aux./line-level input can be used to record from the WR-3 headphone jack, but for MICROPHONE inputs, an attenuating patch cord will be required-as the audio level present in the headphone jack is not matched for mic. inputs on most tape recorders. Use an attenuating patch cord and adapters which will convert a stereo (3-conductor) 1/8 inch jack to the input jack style your tape recorder requires. Failure to use an attenuating patch-cord will result in recorder input overload and terrible audio quality.

WR-3E: The WR-3E has a microphone-level RCA-type output jack. This output has been designed to work well with 600-1K ohm MICROPHONE inputs (anything from small micro-cassette and standard analogue cassette recorders to DAT recorders).

BOTH units: The output level of the WR-3 and WR-3E from its headphone jack is compatible with LINE-LEVEL inputs however, and can be patched directly into the "auxiliary" or line-level input of recorders having this input option, using appropriate adapters. Use SHIELDED coaxial-style audio patch cords only, whether standard or attenuating type for the finest results.

Additional receiver grounding may be needed if a tape recorder is used to prevent audio feedback from the tape recorder into the WR-3 whip antenna. Better results are obtained if the WR-3 or WR-3E audio gain is kept at lower levels and not at full gain.

ANTENNA:

Normally, the telescoping whip antenna should be used fully extended for maximum receiver sensitivity and held vertically at arm's-length away from you, with the receiver at chest or shoulder level. In very quiet locations far removed from powerline hum, up to (but NO more than) 6 ft/2 M of additional antenna wire may be clipped onto the whip antenna screw post and suspended vertically (via wooden pole or on the outside of a white PVC pipe), if the wire is away from obstacles or foliage. Alternatively, a longer whip antenna can be substituted in place of the 33 inch antenna if it has the same type of threaded base. The WR-3 will not match well with longer wires or with ones laid out on the ground, on bushes or in trees, as its antenna input circuit has been optimized for a 3-10 foot (1-3 meter) vertical "whip" antennae.

The telescoping whip antenna needs only to be screwed on LIGHTLY to its screw-post mount. Over tightening the antenna may cause the antenna base and or/ screw-post mount to become loose.

WR-3 VLF RECEIVER SPECIFICATIONS:

Receive frequency range: 0.1-13 kHz (100 - 13,000 Hz),

WR-3: peak frequency approx. 1.5 kHz with roll-off below 400 Hz and above 2 kHz. RFI protected to reduce LF-VHF broadcast and utility station overload and IMD. Audio Output: Maximum 100 mW into 16-Ohm stereo headphones

Headphone jack: 1/8 inch (3.5 mm) stereo (3-conductor) audio jack

Size: 4.5 x 2.5 x 1.2 in. (11.5 x 6.5 x 3.7 cm) not including antenna length

Weight: Approx. 8 oz. (230 g) with battery Antenna: 33-inch (84 cm) telescoping whip (detachable)

Antenna input impedance: Approx. 20 Megohms @ 1 kHz

Power: Use a 9 volt battery for 15-40 hours of listening time depending on type (@7-20 mA current consumption). Alkaline preferred

Acceptable Headphone Impedance: 8-32 Ohms (16 Ohm mini-stereo type recommended)

Additional References and recommended reading for those interested in additional information about natural VLF phenomena:

The Lowdown, published by the Longwave Club of America (LWCA), is a monthly publication for people interested in this part of the radio spectrum. In addition to articles on Natural Radio sounds including writings by Mike Mideke, the publication covers lowpower Low and Medium Frequency experimental transmitting of voice and data, receiving techniques, radio wave propagation, and articles about controversial topics such as military radio transmissions, etc. Membership is $18.00 per year ($26.00 U.S. Overseas) from: LWCA, 45 Wildflower Road, Levittown, PA 19057.

Ionospheric Radio Propagation, by Kenneth Davies, National Bureau of Standards, Monograph 80 (1965/1990). Excellent text on radio propagation including verylowfrequencies. The old 1965 edition is nearly impossible to find but a new 1990 edition (priced at about $65.00) is available. Write to: Space Environment Services Center, NOAA R/E/SE2, 325 Broadway, Boulder, CO 80303-3328. Phone (303) 4975127.

Robert A. Helliwell ("Father" of VLF research), Whistlers and Related Ionospheric Phenomena, Stanford University Press, 1965. A very comprehensive introduction to whistler research before space flight plus the beginnings of "spaceage" research documenting early satellite data. It is accurate and concise with numerous diagrams and illustrations. The book has more information than a beginner would likely immediately use or pursue, but is fascinating nonetheless. ***RARE BOOK*** It is difficult to find copies of this book. Check large libraries. They may be able to obtain the book using the interlibrary loan system.

Syun-Ichi-Akasofu, The Dynamic Aurora, Scientific American, May 1989, pp. 90-94. Describes the functioning and structure of the magnetosphere and causative factors in the generation of Aurora. Examines the magnetosphere as an electrical "generator," field-aligned currents, electrojets and substorms, why Aurora are "curtain" shaped. While not directly examining VLF natural emissions, the article helps in understanding the magnetosphere and lends insight into its role in naturally occurring VLF emissions.

Jeremy Bloxham and David Gubbins, The Evolution of the Earth's Magnetic Field, Scientific American, December 1989, pp. 68-75. Examines geologic processes which generate Earth's magnetic field, describes the shape and functioning of the geo-magnetic field, magnetic field drift, magnetic lines-of-force, magnetic field polarity shifts, and so on.

George John Drobnock, Radio Waves from a Meteor?, Sky & Telescope, March 1992, pp. 329-330. Reports on the author's experiences with a homemade H-field "loop" VLF receiver and a noted "hiccup in the background noise" as well as a "swoosh" sound correlating with the sighting of a meteor on two separate occasions. Examines the possibility that large meteors may disrupt the magnetic field because of their ionized "wakes" created by swift passages into the upper atmosphere, causing VLF radio emissions. An under-researched and still-controversial premise demanding further attention.

Russ Sampson, Fire in the Sky, Astromony, March 1992, pp. 38-43. Beautifully illustrated article about the phenomenon of Aurora and the geo-physical processes responsible. Written more for the layman than the Syun-Ichi-Akasofu article above, but essentially covers the same topics including the influence of solar activity on the magnetosphere. The article is replete with excellent amateur photographs of various colors of aurora. Since Natural Radio emissions arise from the same processes, this is also recommended reading to gain understanding about the magnetosphere.

Donald Herzog (U.S. Geological Survey, Golden, Colarado), Hazards of Geomagnetic Storms, Earthquakes & Volcanoes, Fall 1991

David Schneider (Assistant Professor of Physics, Northern Kentucky University), Mother Nature's Radio, QST, January 1994, pp. 49-51. Discusses basic theory about VLF whistlers and the VLF frequencies of 0.1-10 kHz, Earth's magnetosphere, whistler VLF experiments, whistler sonograms, whistler recording and analysis setup, basic definition of Natural Radio terms, and how to get involved in whistler monitoring and research.

Tom Kneitel (editor of Popular Communications Magazine), Radio's Incredible Rock Bottom!, Popular Communications, September, 1992, pp.9-13. Introductory article on the amazing variety of "Earth Sounds" to be heard in radio's "Basement Band."

Don't Blame Solar Flares, Sky & Telescope, June 1994, page 12 (News Notes). Explains how sceintists have been mistakenly explaining solar flares as the causes of geo-magnetic storms rather than coronal mass ejections (CME's), which now appear to be the cause of many, if not most geo-magnetic storms. A CME injests plasma into the solar wind as speeds of 2,000 km/sec., often faster than the solar wind, causing a shock front which impacts Earth's magnetic field, triggering magnetic disturbances (and aurora along with natural radio emissions). With 4 photographs showing an expanding CME of 18 Aug. 1980, 1004-1310 UT. Syun-Ichi Akasofu, The Shape of the Solar Corona, Sky & Telescope, November 1994, pp. 24-27. Modern astronomical research has found the Sun's corona (outer atmosphere) to have the same structure throughout a Solar Cycle (from solar minimum to solar maximum), and that the apparent visual shape variances during a solar cycle are caused by polarity reversals of Sun's magnetic field during a solar cycle. Conventional solar photography has created the "myth" that the Sun's corona is uniform at solar maximum and non-uniform at solar minimum, due to over exposure of photographic film. (The sun's magnetic field can interact with Earth's in ways which enhance or suppress geo-magnetic storms and their accompanying auroral displays and natural ELF/VLF radio "chorus" emissions).

Neil Davis, The Aurora Watchers Handbook, University of Alaska Press, 1992 Fantastic book and a must for those interested in observing auroral displays visible in the far northern tier of the U.S. "Lower 48" states, Canada, or Alaska. Chapeters include: Cause of the Aurora, basic facts and definitions, such as the auroral zone, auroral forms, etc., kinds of auroras, variations in the aurora, control of the aurora by Earth's magbnetic field, aurorally-related phenomena (such as auroral sound/VLF radio, folklore and legends about aurora and auroral mysteries. I used this book and it was a VERY useful guide during my 2-week Manotoba VLF recording and auroral-viewing expedition to central Manitoba, Canada in August 1996.

This is a summary of what you can do to maximize your enjoyment of your WR-3 VLF Receiver and your success at hearing Earth's VLF radio emissions:

Listen for Natural VLF Radio sounds in locations as far as possible from above-ground electric utility power lines (A.C. power-lines). A minimum distance of ¼ - ½ mile (400-800 meters) away from power-lines is recommended. This is because the alternating-current frequency is 50/60 Hz (cycles-per-second or "Hertz") and this frequency is within the WR-3's receive frequency range. Plus, there are "harmonics" in the power-line frequencies well past 2-3 kilo-Hertz (kHz), often resulting in an annoying mix of "humming and buzzing" which masks Natural Radio sounds if you are too close to power lines. Good locations for you to listen might be large school playing fields away from nearby electric power lines, farmlands, large parks, empty lots not surrounded by buildings and power-lines, golf courses, etc.

If you have access to open-space areas such as meadows, hilltops, beaches, etc., that's all the better! If you can listen at remote locations such as rangelands, deserts, hills or mountains many miles from electric lines, you may not hear ANY background "hum," and thus, you'll hear even the most subtle Natural Radio phenomena. And, just being in a beautiful and remote location will enhance your enjoyment and awe at Natural Radio phenomena-it IS a part of Nature. NOTE: Motor Vehicles with their engines OFF usually do not create interference to Natural Radio.

Second to listening to Natural Radio away from electric power-lines is to locate yourself away from nearby obstructions such as trees and large bushes as these tend to dampen the "E-field" that the WR-3 is sensitive to. The WR-3 will be essentially useless even if you try to listen while next to or under even ONE tree even though that tree may be located in an otherwise open area. Locate meadows and fields if possible, in locations which have many trees. Listening at "high ground" locations is better than listening in deep valleys, gorges, and canyons, as the VLF "E-field" is also reduced by being near steep terrain if it is above you.

Listen from 1 hour before sunrise (beginning of morning twilight) if possible, as the vast majority of times you will hear Natural Radio sounds, especially whistlers and "The Dawn Chorus" will be at dawn and shortly after. 2 hours before sunrise up to 9 a.m. local time is the best. If you like the ringing/pinging sounds of "Tweeks" and the popping and crashing sounds of lightning "Sferics," you may want to listen just after local sunset up to midnight, when Tweeks are at their best. Whistlers may also happen beginning late afternoon and peak in activity between 8 p.m. and midnight your local time, particularly in late winter and early spring.

The ferocious sounds of lightning-storm "Sferics" are also best in the evening hours of the Summer and Fall when lightning storms are at their greatest number and intensity, though the amount of whistlers and chorus will generally be far less than on towards sunrise.

If you have limited time to listen and want the greatest chances to hear interesting Natural VLF Radio Sounds, 5-7 a.m. local time would be the best period to do your listening sessions. The period of day when you are generally LEAST likely to hear any Natural Radio sounds other than the popping and crackling of lightning storms is between 11 a.m. to 2 p.m. local time. However, midday activity DOES occur, especially at higher latitudes, and these events should be considered extraordinary. We urge you to avoid listening when lightning is nearby (within 5 miles/8 Km) as you run the risk of being struck by lightning if out in the open with your WR-3 (The receiver doesn't attract lightning, but your body CAN, just like trees and other objects).

Resist the temptation to listen when lightning is nearby as the impulses in the headphones will be VERY loud. Watching lightning flash while listening to the static impulses with the WR-3 can be exciting, but S. P. McGREEVY PRODUCTIONS can not be held responsible for injury or death due to misuse of equipment or by being struck by lightning.

If you have a World Band (Shortwave Radio), listen to WWV Colorado, USA on 2.5, 5, 10, 15 & 20 MHz at 18 minutes past the hour (or WWVH Kauai, Hawaii on 2.5, 5, 10 & 15 MHz at 45 min. past the hour) for "Geo-Alert" indices-if they say the "K-index" is at 3 or higher, conditions are enhanced for Natural VLF phenomena to occur. If the K-index is 4 or higher, and they say there is a "minor geo-magnetic storm" or "major geo-magnetic storm" in progress or forecasted for the next 24 hours, by all means listen the following morning at dawn for eerie and beautiful "Dawn Chorus," which is likely to occur.

If you live far enough north to see the Northern Lights (Aurora), try to listen when they are happening or on toward sunrise after nights of good displays-you will very definitely hear some intriguing VLF radio sounds off of the Aurora such as Auroral Chorus! Geo-magnetic storms cause Aurora, and reported WWV/WWVH K-indices of 4 or higher greatly increase your chances of seeing Auroral Lights and hearing Auroral Chorus or Dawn Chorus with the WR-3. Northern listeners will probably hear chorus last past local noon during magnetic-storm periods. Surprisingly, active auroral displays at night may not produce much VLF radio sounds other than "hiss," but loud chorus surely will start up before local dawn and sunrise, and go on many hours into daylight with exciting variety. Strange sounding whistlers with sustained echoing may also occur.

HEADPHONES

Not all headphones are created equal--if the volume from the WR-3 seems too low with your headphones, you may wish to try another pair of different make or model. 8 ohm and 16 ohm mini-stereo headphones will be louder sounding than 32 ohm models-check your headphones' specifications for their "impedance" in "ohms." Full-size stereo 'phones are fine, though you may need an adapter plug.

It is my hope that these tips will enhance your enjoyment of Natural VLF Radio listening and helps you increase the amount of fascinating naturally occurring VLF phenomena heard with your WR-3!

Natural Radio Recordings on CD Demonstration CD included with the WR-3

"Auroral Chorus (I)
Music of the Magnetosphere"

23 tracks of field-recordings by Stephen P. McGreevy recorded in Alberta, Manitoba, Oregon, Nevada, and California. Mastered by Frank A. Moreno May 1999, re-mastered by Stephen P. McGreevy August 2001. Tracks are mono.

Brief track descriptions for reference:

1) Alberta Wavering tone emissions - In a deeply remote Whitemud River region near Dixonville, AB, in a clearing surrounded by boreal forest. Taped during the June 1996 solar-minimum VLF expedition - June 02, 1996 - 7.30 p.m. Mountain time, 0130 UT. An amazing day - this natural radio sound was beautiful. - Duration: 10:49

2) Growler Whistlers and subtle background Dawn Chorus, Nightengale, northern Nevada, 19 April 1996 - about 7.00 a.m. Pacific time, 1400 UT - Duration: 2:28

3) Pure-tone whistlers after strong lightning static bursts - Waterton Peace park, Alberta (Belly River campground - loop receivers) 20 June 1998 - 8 p.m. Mountain time, 0200 UT - recorded while I was making stereo recordings on another recorder. duration: 2:02

4) Nice recording of Dawn Chrous and risers, Waterton peace Park, Alberta, Canada, 20 June 1998 - about 1400 UT. - Duration: 3:07

5) Alvord Desert Dawn Chorus - strong hiss and undulating chorus - Alvord Desert, Oregon, 18 August 1993 - 1430 UT. Previously unreleased recorded segment of this lovely chorus event. - Duration: 3:41

6) Periodic emissions (hooks) and nose whistlers, Whitemud River region, Alberta, 02 June 1996 - about 1400 UT - Duration: 4:07

7) Panamint Valley Whistler Shower - Panamint Valley, Death Valley Nat. Park, Calif. - 11 March 1998 - 1400 UT. The could be called 'Gentle Whistlers' by their soft tones, there are also some chorus 'risers.' . - duration: 1:57 (some tape azimuth problems in this segment from the original field recording, but worth including on this CD)

8) Strong hissband, chorus, weak whistlers, Grass River Provincial Park, Manitoba (GRPP), 23 August 1996 - about 1410 UT. This and the next 6 tracks were taped during my August 1996 solar-minimum VLF expedition to Manotoba, Canada where the Northern Lights were seen every night. - duration: 3:48

9) Auroral-zone Chorus mixture - Manitoba (GRPP) 23 Aug. 1996 - 1545 UT - duration: 2:33

10) Vigorous chorus mixture - GRPP, Manitoba, 23 Aug. 1996 - 1630 UT - duration: 4:29

11) Hiss, chorus, diffuse whistler train after lightning static burst, GRPP, manitoba - 23 August 1996 - 2245 UT duration: 2:01

12) "Ghostly tones" (whooping, low-pitched chorus) GRPP, Manitoba, 24 Aug. 1996 - 1430 UT, duration: 1:19

13) Strong auroral chorus, GRPP, Manitoba, 24 Aug. 1996, 1630 UT - kinda like a flock of shorbirds! duration: 1:36

14) Low-pitched chorus, squawking, dog-bark-like, 27 Aug 1996, 1545 UT, GRPP, Manitoba - durtion: 1:12

15) Fine example of parallel/paired risers, GRPP, Manitoba, 23 Aug. 1996 - 1500 UT. duration: 0:39

16) Beautiful overlay of nose-whistlers and wavering tones/hooks, Whitemud River region, Alberta, 02 June 1996, 0130 UT. Astoundingly strong reception. - duration: 2:58

17) Pure-tone whistlers recorded on two loop receivers, Waterton Peace Park, Belly River campground, Alberta, 20 June 1998 - about 0130 UT. duration: 1:14

18) Mixture of risers (chorus), Waterton Park, AB, 20 June 1998, 1500 UT duration: 3:30

19) Short track of a couple of "growler" whistlers, Nightengale, northern Nevada (60 miles northeast of Reno), 17 Sept 1993, about 0300 UT. duration: 0:33

20) Nice ringy tweeks, taped near beautiful Wheeler Peak, eastern Nevada, 13 Sept. 1996 about 0800 UT. duration: 0:38

21) Lovely mixture of dawn chorus and whistlers, Black Rock Desert, n.w. Nevada, 22 Sept. 1996, 1330 UT duration: 3:00

22) Semi-diffuse (growley) whistlers recorded on a WR-3 near the lowest part of Death Valley, Calif. (Badwater) at about 0230 PST, 27 March 2000. duration: 0:19

23) Compilation of near-pure-tone whistlers recorded in central Nevada near Area 51/Rachel, NV, 17 Sept. 1999, approx. 0500 - 0505 PDT. duration: 3:18

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These brief descriptions fail to fully convey the sheer beauty and wonder of Earth's Natural VLF Radio phenomena. I take pride in presenting to you these beautiful recordings of Earth's natural radio phenomena, and hope you hear good Natural Radio with your own WR-3.Stephen P. McGreevy, August 2001