Natural ELF Whistler Radio
Extremely Low Frequencies (ELF) can be thought of primarily as that portion of the electromagnetic spectrum which, upon being transduced (not converted nor demodulated) directly into acoustic audio energy, could be perceived as “sound”. In this article we are reporting on the special significance now being given to receiving a portion of the electromagnetic energy that exists within the frequency range of 0 to 10 kHz.
The ARRL Handbook does not use the term ELF, but it does identify the range of frequencies from 10 through 30 kHz as Very Low Frequencies (VLF). So, it follows that the term Extremely Low Frequencies (ELF) should logically be used to classify those frequencies existing below 10 kHz.
“ELF Reception” is also being called “Whistler Radio” by some, and “Natural Radio” by others, so let’s combine the terms and call it a “Natural ELF Whistler Radio”. Many references to whistler reception are to be found under “VLF radio”, but most of the desired whistler signals exist outside of and below VLF, at frequencies between 0.5 to 7-kHz.
There are many types of electromagnetic energy existing now that have probably existed since prehistoric times in this ELF portion of the r-f spectrum, in addition to that made by man (whether intentionally or non-intentionally), and by wildlife and even insects.
This article may provide answers to some of the questions that you, as well as to questions a lot of other people may have once they become aware of Natural ELF Whistler Radio. At the very least, I would like to think this article will create an experimenter’s interest within you of yet another impressive and fast growing facet of electronics. (I also realize it may create more questions than it answers, and I certainly do not have all the answers.) Many experimenters are now adding this very interesting, inexpensive, and expanding area of experimentation to their hobby of electronics. So please read this article on ELF Radio and let’s learn together!
QRM and QRN
By way of review, the commonly used Morse code “Q” abbreviation terms used by radio amateurs for interference are “QRM” and “QRN”. Interference is anything that keeps me from hearing the message I am trying to receive. (If I am trying to hear some other person, then even your transmission to another person can be QRM to me.) QRM refers to any manmade interference. One of the worse sources of QRM is the 50/60 Hertz “hum” with all of its harmonics being radiated by electric power lines. When an indifferent electric power company is careless about maintaining its equipment, such as failing to replace all of its bad insulators, they waste a lot of power and generate a lot of r-f pollution to all communication services by radiating the wasted energy throughout the entire electromagnetic spectrum. Neon signs and some fluorescent lights are frequently at fault, too, when they radiate 100/120 Hz with a huge family of “hum harmonics”. The laws against this interference should be strictly enforced.
QRN refers to electromagnetic radiation from Natural sources through natural mechanisms which can be assumed to have been in operation since the creation of the world. These sources include the universe, the galaxy, our sun with its sun spots and its solar flares, corpuscular radiation, solar wind, Rutherford scattering, planets (some of them have fierce lightning), lightning from geomagnetic storms, magneto plasma waves, auroras, radioactive decay, moving ionization layers, etc. Regular radio communication and reception goes to great lengths to avoid the natural interference (QRN) in order to receive the intended manmade messages. Regular radio limits its received instantaneous bandwidth to receive no more of the natural noises than absolutely necessary in order to include the desired information bandwidth to achieve satisfactory communications.
Natural ELF Whistler Radio
A natural ELF radio, sometimes called a “whistler receiver”, should NOT be like a normal receiver that tries to select a given frequency and reject all others; it should be just the opposite. It should NOT use a detector; it should be as linear as possible so as NOT to introduce any mixing process products! It should NOT use a demodulator; the signals to be received were not modulated onto a carrier frequency so there is no reason to demodulate. It should NOT use a converter; it should only serve as a transducer to allow one to listen to the r-f that exists at “natural” audio frequencies.
Natural ELF Whistler Radio does just the opposite, its like an “upside-down” radio, it tries to avoid receiving any man made energy (QRM). In other words, a Natural ELF Whistler Radio is an “upside-down” radio! Something as inexpensive as an antenna plus a simple battery-powered audio amplifier with earphones, or a loud speaker, can serve to meet these basic requirements! The earliest Natural ELF Whistler Radios were even simpler. They only consisted of an earphone with a telephone line serving as an antenna!
Antennas
Types of antennas used for natural ELF radio, in addition to telephone lines, vary from long wires, various vertical whips as short as one meter long to sense voltage charge changes, and to large as well as small loops to sense the magnetic fields which provide directional information when finding magnetic storms and whistler arrival angles, both in azimuth and elevation. W8MIA shared with me that he had used 2 ground rods, 8-feet long, as electrodes spaced about 15-feet apart in the ground (with shielded leads) as a receiving antenna for an audio amplifier to hear the “roaring” earth noises. (I remember using two small shovels as electrodes spaced a few feet apart in the ground to cause fishing worms [night crawlers] to come to the surface for easy collection for fishing trips. Now I wonder if the worms made noises, too?) Years ago dual pairs of electrodes were also used to couple telegraph and telephone signals across rivers.
History
Natural ELF radio sounds were listened to in the late 1800’s by some telegraph operators while waiting for messages and were reported as troubles by some rural telephone users, who, being remote enough from today’s 50/60 Hz electrical power lines to hear background noises other than “hum”, thought their phones had some minor problems or loose noisy connections. The older telephone transmitters frequently used powdered carbon as voice controlled variable resistor microphones, which did contribute some but not all of the sounds. (Their performance could sometimes be improved by lightly tapping the transmitter button with a hammer to loosen the carbon powder that has a tendency to become hard packed. But, even when the transmitter buttons were removed from the instruments then some of the weird natural sounds could still be heard.)
Very alarming observations were made on many Army field telephones during World War I. Sometimes, during phone communications, each operator would sometimes think the operator at a distant location on the other end of the phone line was under attack because violent battle sounds could be heard in the background, even though no guns were being fired, nor rockets flying, nor shells falling with the familiar closing Doppler type sounds at either location! When audio amplifiers were added to the system people became even more impressed.
Research revealed the “bullet pops” or “gun sounds” were due to lightning strikes, which could be occurring anywhere from near by up to distances a few hundred miles or so away. These caused static crashes called “sferics” (a shortened corruption of the word atmospherics) to be induced on the rural phone lines and antennas.
For instance, a few days ago, while talking with my daughter on the telephone, she heard for her first time some of the more active natural ELF radio sounds I had been collecting for this article’s streaming audio demonstration and told me very excitedly, “There’s a fierce battle going on over there!” Except for my voice, the streaming audio clip that can be heard at the beginning of this article consists entirely of ELF/VLF radio sounds, all of which are natural except for the two bursts of “machine gun” like sounds at the end, which resulted from receiving VLF LORAN signals. They were thrown in to make it sound even more like a battlefield!
The shorter duration “falling shell” type noises, or “falling tones”, were found to be caused by lightning strikes occurring thousands of miles away in the southern hemisphere from areas located approximately the same distance below the magnetic equator as the observer was above the magnetic equator. These became known as “one-hop whistlers”. (Some say that at times they sound like the falling ending part of the sound a boy makes when he whistles at a girl he finds attractive.)
Whistlers twice as long in time, with longer falling tones, were logically named “two-hop whistlers”. (These sometimes sound like the falling ending part of the boy’s extended whistle when he excitedly whistles at a girl found extremely attractive.) These were generated by lightning strikes in the northern hemisphere from a location at a latitude close to the observer. The resulting signals traveled to an area near the equal magnetic latitude in the southern hemisphere and reflected off the ionosphere back to the northern hemisphere to the original location, or to an area somewhat near the same magnetic latitude, and were received by the observer.
Whistlers longer than two-hops are called “whistler echoes”. Some can have multiple reflections, being reflected off of areas in the ionosphere at both locations and be heard stretched out for several seconds to result in very deep low frequencies that almost become coherent on a Natural ELF Whistler Radio. (The “swish” sound of some types of whistlers, thought to be multiple-hop, or echo whistlers, can be compared to the “sigh” a boy emits after his attractive girl ignores him and goes away.)
The immediate, but I think wrong, conclusion is that the velocity of propagation is faster for higher frequencies than for lower frequencies, thus accounting for the gradually falling frequencies being heard by an observer listening to a Natural ELF Whistler Radio. Instead, most researchers think the lower frequencies have propagated via higher and longer spiraling paths in the magnetosphere, than did the higher frequencies, in going from hemisphere to hemisphere, and thus arrive a lot later to be received as “falling tones”.
Uses
An excellent fast and free “search engine” for many subjects, including “whistlers”, is found at: http://www.google.com There are many good references to “Whistlers” (other than to puckering musicians) that provide sounds as well as spectrographs. These include many good sound clips links which have been provided courtesy of NASA.
I served as the interface coordinator between the NASA space science experiment called SEPAC and the Spacelab that flew on NASA’s Space Shuttle Mission STS-45. The Space Experiment with Particle ACcelerator was designed, in addition to other things, to control injection of whistler type ELF/VLF signals at several wavelengths from space back to earth using a giant electron gun. The purpose of this was to gain knowledge of the medium through which it was traveling; knowledge supplemental to that provided from whistler analysis obtained by using considerably more powerful energy sources originating on earth in the form of lightning strikes.
Lightning, by contrast, is the ultimate example of an extremely wide-band frequency generator. It produces a spread spectrum continuum of all wavelengths of electromagnetic energy from d-c through x-ray. Energy from a given lightning strike, in addition to that going up into a whistler path, is also propagated by ground waves and is sometimes ducted by the Kennelly-Heaviside E and F ionization layers to arrive at a whistler receiving location just prior to the reception of the first whistler of its family of delayed whistler echoes.
When received (and sometimes they aren’t), these static impulses reveal no noticeable time delays, or time warps, as a function of frequency. The received static impulse appears as a vertical static crash line on a spectrograph. The resulting variations of the static impulse’s signal intensity existing at various frequencies may indicate attenuation by selective absorption, and/or the absence of complete reflections by the ionosphere, but in no case do differential time delays, as a function of frequency, appear on the static impulses.
The average time spacing, or separation, at any given single frequency chosen for reference on a given series of two-hop whistler echoes, may be used to identify the static impulse that served as the energy source that originated that given string of echoes. For example, on one given series of two-hop whistler echoes, the average time-spacing between the six-kHz frequency position on each whistler was three seconds. The average time-spacing between the two-kHz frequency position on each whistler was 4.6 seconds. Each whistler grew longer each time it bounced and its resulting slope, as seen on the spectrograph, became less steep, thus revealing the appearance of a time-constant discharge curve that progressively increased with each hop. It has the general appearance of a standard exponentially dampened half-life decay curve of a radioactive source.
By going back in time in a three second interval from the six-kHz frequency position on the first whistler, and going back in time in a 4.6 second interval from the two-kHz frequency position on the first whistler, a convergence time common to each regression can be found. This identifies the time that the originating static impulse was received for this given series of two-hop whistler echoes. Sometimes the given source static impulse may or may not be received and displayed. If the series started with a one-hop whistler, the source impulse burst could be present and displayed at one-half of the average interval time later than the position it would have appeared at for the two-hop whistler. Both possible time positions for the initial impulse should be examined.
In the example chosen, six-kHz and two-kHz, were the highest and lowest useful frequencies received from this given whistler echo series. They represented the start and end of each individual whistler echo, yet the displayed impulse revealed a much greater range of frequencies, both higher and lower, and it was not time warped. One could possibly conclude from this that the magnetosphere was, at that time and from those two locations, limiting the propagation of the family of considerably longer spiral whistler paths to this small but continuous band of frequencies. The frequency limits and the relative signal strength intensity of the received whistlers may possibly have been useful in defining some of the magnetosphere’s characteristics.
Considering the speed of propagation of electromagnetic energy to be 186,000 miles per second, then each round trip distance made by the two-kHz energy in 4.6-seconds was approximately 855,600 miles (1,377,307 meters)! Now add to that an equal amount of distance for each of the several more round trips the signal makes in a multiple hop series of whistler echoes! That initial lightning stroke was really some energizer! However, the signal is said to make spiral paths that go no higher than 3.5 Earth radii above the center of the Earth when it goes over the magnetic equator. (Talk about D-X!!) Also, think about all that energy having been created by those little ice crystals falling through its cloud and creating a charge by stripping off electrons from those little floating water droplets.
Let’s keep in mind that the energy emitted by the original lightning strike responsible for initiating all of this action could be considered to have been an ultimate spread spectrum electromagnetic source of energy. We are hearing and seeing only what remains of that transmitted wide band energy after it has encountered an amazing number of processes.
Looking at it another way, it’s amazing that anything was left of it after going such incredible distances. On the other hand, I was able to send a one-watt laser beam from the Earth that was seen by the Surveyor Spacecraft while it was parked on the moon’s surface. Also, the Surveyor Spacecraft was able to send TV signals back to Earth from the moon while transmitting in low-power mode with a carrier power of one-watt! (The normal power mode was 15-watts.) QRP anyone?
When the early NASA Space Shuttles were being flown, we were amused at the many rumors being circulated, and even published in some magazines, that lightning on the tops of clouds, as observed from space, occurred in brilliantly saturated red, green, and blue colored flashes. Those making the reports had not taken into account that early Space Shuttle missions used rotating color filter-wheels on the old TV cameras that had red, blue, and green filters. This resulted at best in non-NTSC, sequential color, frame by frame sampling of a given view (that had to be scan converted to NTSC and PAL back on the Earth), and a lightning stroke never lasted long enough to be sampled by more than one color filter before it become extinguished.
An even greater mystery for the heedless was created whenever a TV camera viewed, within a few seconds of time, different lightning strikes on top of a given common cloud. The different lightning strikes were usually displayed in very brilliant but separate highly saturated colors! This went to prove that one should know all the facts!
Conclusion
The motto “True science should have all the facts!” should certainly be applied to whistlers as well as TV! So, we invite you to add this intriguing area of Natural ELF Whistler Radio experimentation to your electronic hobby. Then, as you learn, please share with us the new facts you learn about whistlers. Streaming audio (Real Audio) sound clip contributions of your unique results that you send to antenneX may result in a special sound display Forum or article with sound displays. The publisher of antenneX is always looking for new and clever things that are way ahead of the rest. If you need more understanding about the best way to record sound clips for publication, feel free to just ask. Send your questions to either myself at the e-mail address below or use the Interactive NotePad below for your convenience.
Remember, a major key to enjoying listening to and having success in making good of Natural ELF Whistler Radio recordings is to be removed as far as possible from the many man-made noise sources that would mask what could otherwise be excellent results. If you make recordings, and it is suggested you do, keep in mind they can be signal processed in many ways at playback, and be shared with many, too!
The second article of this two-part series is planned to be published next month. Until then, keep in touch and enjoy your experimenting!
Natural ELF Whistler Radio - Part 2
This is the second part of a two-part article discussing some of the amazing sounds that can sometimes be heard on a high gain audio amplifier and speaker when an antenna is connected to the input to the amplifier. This basic equipment combination can be called a “Natural ELF Whistler Radio”. In essence it is transducing the existing Extremely Low Frequencies of electromagnetic (radio) energy existing between 0 to 10 kHz into audio that can be heard.
If you missed the first part of this article, please go to Archive III of antenneX and review the article. Once there, you will also be able to hear for yourself, on your own computer, some of these fascinating natural sounds that are provided, courtesy of NASA, via streaming audio.
I wish to thank Bryan Eyre, VK7KBE, from Tasmania, Australia, whose reader comment question on the antenneX Discussion Forum about Whistlers led to my writing of this article. Bryan is now experimenting with his own homemade portable ELF receiver and may provide an article about his experiences in next month’s issue of antenneX.
Also, I wish to thank many of the readers who did provide very nice reader responses to the first part of this article. There is one point I need to expand on, though, in order to remove some more speculation about there being brilliantly colored red, blue, and green lightning strokes being observed on the tops of clouds, via TV cameras on various Shuttle Spacecraft. I should have added that common lightning strokes were at times observed simultaneously by more than one TV camera, with the resulting video pictures revealing highly saturated but different hues or colors! In other words, it is extremely unlikely that the lightning at the top of any cloud would provide a brilliant green stroke, to be immediately followed by a brilliant red or blue stroke. The facts should be taken into account.
Whistler Characteristics
Whistlers can be very useful in determining real-time size as well as other information about the magnetosphere medium they propagate through. By bouncing back and forth and echoing through it in both north to south and south to north magnetic directions between equal magnetic latitude areas on both hemispheres of the earth, the remaining whistler energy reveals those frequencies that were attenuated the least.
To learn more about whistlers, we should be knowledgeable of lightning characteristics since lightning is the source of whistler energy.
Lightning Characteristics
It has been estimated that lightning strikes the earth an average of 400 times per second. It is rare for a lightning strike to consist of only a single stroke or bolt, three or four strokes is common, and as many as twenty strokes per strike have been observed and documented on the “Lightning Cameras” I worked with at the Kennedy Space Center in Florida.
Each single stroke can initiate a whistler. Therefore, the more strokes occurring within a given lightning strike, the less pure sounding the resulting whistler will be and the wider it will appear on the time display of a spectrograph or waveform analyzer. (See the LINK reference at the end of this article to download a free FFT waveform analyzer program for your own computer. This will allow you to analyze the audio tape recording of any whistlers at a later time.)
Longer lightning strikes may also result in a slightly less pure whistler tone. Some horizontal strikes have been reported to have been 90-miles (140-km) long, while some vertical strikes were said to be nine miles (14-km) high. Lightning strikes with many multiple strokes may account for the “swish” sounds.
Normal parabolic radio navigation, such as used by LORAN and SHORAN, depend on comparing the timed reception by a vehicle receiver at an unknown location of the leading edge of r-f pulse trains transmitted from several precisely timed transmitters at known fixed locations to determine the location of the receiver. Using this “parabolic navigation system” the locations and speeds of aircraft, ships, and others can be determined. (During WW II, I devised the method of controlling autopilots with LORAN as an aircraft navigation option.)
In contrast, “upside-down” natural ELF radios can be used at combinations of multiple fixed receiving locations with an application of “reverse parabolic navigation” to provide the unknown location of the source of a static crash, namely where the lightning struck. By analyzing the time of the leading edge of lightning signal arrivals at some of the natural radio receivers, this technique not only permits determining the latitude and longitude of a single strike of lightning, but it will permit determining the elevation of the top of lightning strikes! This system was developed at the Kennedy Space Center in Florida (KSC).
Reverse parabolic navigation lightning detection systems can be used to provide valuable storm information to be relayed to pilots of small aircraft and ships that do not have weather radar installed. Several lightning strikes can then be used to also provide information as to the speed and direction of an electrical storm’s movement, thus allowing valuable advance warning to be used in determining alternate navigation routes. This information has also been a factor in making missile launch “go-no go” decisions, too.
The rate and number of strikes is usually proportional to the severity of the electrical storm. This information can be automatically computer processed and displayed on color CRTs with altitude being displayed by assigned false colors. Storage CRT display retention time can be selected by the computer operator to easily provide observable storm tracking information. Strike information displayed over area maps is sometimes displayed by TV weathermen as a public service to TV viewers.
Magnetosphere
The earth is surrounded by a giant magnetic field called a magnetosphere. The earth spins within this giant magnetic field. The magnetosphere’s theoretical doughnut shape surrounding the earth magnetic equator is greatly distorted by the pressure of corpuscular radiation and the solar wind pressing it down closer to the earth over the earth’s “daylight” side. The greatest pressure is exerted on it over the earth’s local “noon” position. At the other extreme, it is pushed the greatest distance from the earth over the earth’s local “midnight” position resulting in a comet-tail like elongation. The final shape is sometimes called a “tear-drop” shape.
The areas above the earth normally encountering the greatest rate of change in its overhead fields can be expected to occur within a few hours of the local dawn and sunset positions. This is when “dawn chorus” and many other weird sounds are more likely to be heard.
The amount of charges accumulated by the Van Allen radiation belt and the many ionization layers floating above the earth within this magnetic field can be greatest during daylight hours with the greatest amount of charges being accumulated near local “noon”.
To the surprise of many people including myself, the greatest aurora activity can be expected to occur then too, even though it’s not visible (unless there is a total eclipse of the sun). I have spent the greater portion of many nights looking upward at the dynamic horizon to horizon sky-filling displays of aurora when the northern lights were very active. Natural ELF radio is one of the ways of monitoring for this activity.
Equipment Considerations
When some power line “hum” remains, even after attempting to find a receiving location free of it, a comb filter, with its primary frequency selected to match the fundamental 50 or 60 Hz power line “hum” frequency can help some by notching-out the “hum” and its “hum harmonics”. However, if other signals have been modulated by this interference, the resulting sidebands will not be notched out. Therefore, receiver linearity is very important in a Natural ELF Whistler Radio to prevent generating modulation cross-products.
Seeing how many power line harmonic frequencies exist near faulty power lines, it would be ineffective to use a single frequency filter to notch out just the fundamental 60-Hz “hum” frequency. A band pass filter that would pass every thing from 0.5 to 7-kHz may be the most useful for monitoring most of the whistler frequencies. 2×60, 2x”hum”, or “double hum” may be dominant because a faulty insulator breaks down twice during each cycle of the fundamental power line frequency.3………………………………………
However, some of the ELF radio spectrograms examined revealed a separation of 360-Hz between dominant harmonic horizontal lines which indicates that odd harmonics of the third harmonic of 120-Hz contain the most energy, as compared to the anticipated odd harmonics of 120-Hz being dominant.
Recorders should not include, or use, automatic volume controls (ALC), or automatic level controls (ALC), which negate accurate signal strength measurements.
Some spectrographs are difficult to use when the time and frequency are hard to decipher. The addition of a small amount of a 0.5 or a 1-kHz signal injected after the band pass filter, or on the tape recordings, as a frequency marker, would be valuable in speeding-up and improving the accuracy of data reduction. Similarly, injection of a small amount of timing signal into the data chain from an accurate wide band timing “tick-mark” generator would simplify data reduction, also. A combination of the two can be achieved by gating on the frequency markers only at the occurrence of the “time-ticks”. Extremely accurate time can be obtained from hand held GPS receivers if you use one that has an external signal connector.
However, if real-time is not important to you, the timing ticks may be injected into the data when the tape recordings are played back, to provide accurate relative-time for simplified data reduction.
Remember, whistlers only come from lighting. Viewing the global weather reports on TV, or on your computer, may allow you to find when electrical storms are forecast for the area of the world existing at an equal latitude in the hemisphere opposite to yours and existing on the same magnetic longitude as yours. If lightning is not occurring there, such as in one of the great desserts of the world where it never storms, then do not expect any one-hop whistlers.
Of course there is still the possibility of receiving two-hop whistlers if an electrical storm is occurring in your region. Lightning will have to be occurring within approximately 500-miles (800 km) of you location for you to receive two-hop whistlers. (But, if it is within 5-miles (8 km)of you, turn off the receiver and head for cover!) I do not think there is any preferred time to listen for whistlers since they only occur when lightning originates them.
It is desirable to use two types of antennas; a vertical whip and a magnetic loop antenna. The best position for a fractional wavelength magnetic loop receiving antenna is vertical. Placing it horizontally is not good.
The plane of a receiving magnetic loop should be mounted vertically and should be aligned with the needle of a magnetic compass, i.e. the loop needs to be aligned with the earth’s magnetic north-south lines.
Remember, you are not trying to achieve “common mode rejection” of vertically polarized signals: you are trying to receive them, so avoid placing the feed point at the bottom center of the loop. Experiment with the magnetic loop antenna’s feed point being placed at various positions in the plane of the loop, such as on the corner toward the earth’s equator.
A vertical whip antenna should be available to allow frequent antenna trade-off, in order to compare which mode is best at a given time. I suggest nothing shorter than 3-feet (one meter) long whip.
Caution: Once I was using a 12″ clip lead as a vertical antenna, I connected it directly to a MOS-FET preamplifier. The preamplifier’s output was connected directly to the vertical input of an oscilloscope operating in d-c mode. When I moved my feet, even very slowly the scope displayed my motion from over ten feet away. Quick motions would abruptly saturate this simple sensitive natural ELF radio system. Because of this, d-c coupling of an electrostatic antenna to the system should be avoided, unless one is trying to make an electrostatic field mill to sense dangerously charged clouds in the area. (But, that’s another subject area about instruments used at the Kennedy Space Center in Florida.)
ELF Radios
Several versions of natural ELF radios are available on the web as are schematics and instructions for making your own battery powered receiver (audio amplifier). Some very high gain audio amplifier IC chips, such as the LM386, are available that could serve as the basis of a natural ELF whistler receiver.
Non Scientific Uses
If one’s interest in Natural ELF Whistler Radio is not scientific but only to hear the unusual music of the spheres and other weird non-manmade sounds in order for them to be combined into new exotic music, or sound effects to be combined with music, one may wish to mix (multiply) “echo chorus” signals with each other, or with other sounds. This may help introduce many interesting cross-product novel sounds, provided low-pass signal filtering is used to reject anything above 7-kHz prior to a mixing circuit. (Doing this would reject signals from the antiquated Russian ALPHA navigation system, signals radiating from poorly-designed TV horizontal sweep amplifiers, or any other manmade VLF signals. )
The OMEGA navigation system transmitters have now been turned off and the extremely useful LORAN navigation system is being phased out (prematurely, I think), in favor of the very accurate Global Positioning System (GPS) navigation system. (During WW II, I participated in the installation of the first LORAN system on the West Coast.) Of course, this and other signal processing can be done more conveniently at a later time using playbacks of tape recordings of the basic signal made out in the countryside far, far away from electric power lines.
If one does not wish to build a natural radio and make field trips to low “hum” regions, then it would be less expensive, less time consuming, and much simpler to purchase tape recordings or CDs from those who are prepared to provide impressive copies of their very best results which were obtained over years of collecting.
If obtaining ideas for music is the only purpose, vs. the awareness of dynamic real-time scientific activities, another great variety of natural sounds can also be heard from speeding-up recordings (about twenty times) of the huge number of and variety of earthquakes that can be detected daily. When I was a senior scientist on the staff of the Space Sciences Division of the Jet Propulsion Lab of the California Institute of Technology at Pasadena, California, Dr. Charles Richter, the creator of the method for classifying earthquake intensities called the Richter Scale, treated me with a play back of a tape recording of earth quakes that he had made. First he played it at normal speed. The normal speed play back was muffled, dull, and not interesting. Then he played it at 20X. It was fantastic! I will never forget it!
This experience motivated me to quickly build a seismometer using a 20-pound junk power transformer as the weight. The resulting instrument was much more sensitive than I ever expected. I was able to easily see deflections of several centimeters at times, and especially when a series of underground atomic bomb tests were being conducted hundreds of miles away in Nevada. By eaves-dropping on short wave radio to their count-down clock for detonation time reference, I found the predicted seismic propagation times even proved to be extremely accurate, too!
Originally posted on the AntennaX Online Magazine by Harold Allen, W4MMC
Last Updated : 14th May 2024