| Tikalon Blog is now in archive mode.
An easily printed and saved version of this article, and a link
to a directory of all articles, can be found below: |
|
This article |
| Directory of all articles |
Robert A. Helliwell
June 16, 2011
Transistors were still expensive when I was a
young experimenter, and it was only when I was in seventh grade that I built my first transistorized circuit. This was a one transistor "lie detector" that my science teacher and I tested on an obviously nervous young student. From what I can remember, the circuit measured
skin resistance with the idea that you
sweat when you're nervous, and this will lower skin resistance. Our data were inconclusive.
Shortly after that, I built several transistorized circuits that really interested me. These were
VLF (Very Low Frequency) receivers of the
audible frequency band of 20-20,000
Hz that monitored the natural
radio emissions of the
Earth environment. They would also indicate whenever anyone in the neighborhood was using a large
electric motor, or if there was a
lightning storm on the way.
Very low frequency signals, called
spherics, short for radio atmospherics, are produced by distant lightning strikes exciting the ionosphere. One interesting class of these are
whistlers, so called because they have a signal that descends in frequency. Every morning, I would tune into the
dawn chorus that consisted of random chirping sounds not unlike
birdsong. The dawn chorus appears to be related to the
Earth's magnetosphere.
Robert A. Helliwell, a pioneer in radio observations of this sort, died on May 3, 2011, at age ninety.[1-5]
Robert A. Helliwell.
(Stanford University Image).
Helliwell's greatest discovery was
accidental, as is often the case in science.
Lightning noise is common in radio, and that's what Helliwell and one of his students was investigating at
Stanford University in 1950.
Karl Jansky observed lightning noise in his experiments that resulted in the accidental (of course) discovery of the
first extraterrestrial radio source in 1933. The student, John Mallinckrodt, heard some whistling sounds and brought them to Helliwell's attention.[1]
As Helliwell recalled in an article in the October, 1982, issue of the Stanford Engineer, he thought it was an
artifact. Still, in the interest of science, he stood radio watch with Mallinckrodt until he heard these whistlers for himself. Helliwell described these sounds as "weird, strange and unbelievable as flying saucers" in a 1954 article in the Palo Alto Times.[1]
Whistlers do sound extraterrestrial. The early 1950s were the height of
UFO mania in the US. The movies,
The Day the Earth Stood Still (1951, Robert Wise, Director) and
Earth vs. the Flying Saucers (1956, Fred F. Sears, Director), are from that era. You can hear a whistler
here (300 kB MP3 file).[6]
In true scientific fashion, Helliwell tried to understand the mechanism involved in the production of whistlers. As VLF
hobbyists know, it's more likely that you will detect man-made electrical interference at these wavelengths than natural noise, so observations at the Stanford campus were difficult. Also,
transmission was out of the question. The solution, of course, was to go where no man has gone before; well, at least very few men, and that was
Antarctica. Thus was established Siple Station in West Antarctica, which was active from 1971-1988.[1]
The
wavelength of VLF radio signals is huge. A
frequency of 10 kHz corresponds to a wavelength of 30 kilometers, or 18.64 miles. That's why the Siple Station had an antenna that was thirteen miles long. The antenna was used to transmit VLF radio signals into Earth's magnetosphere, to be detected half a world away in
Canada. It was possible to inject these signals into the magnetosphere, since the
ionosphere is transparent to these low frequencies.[1] The transparency of the ionosphere to low frequencies is the same principle that
Grote Reber used in his
Tasmanian radio astronomical observations.
Helliwell was born in
Red Wing, Minnesota, and he and his mother moved to
Palo Alto after his father died.[1] He was associated with Stanford University for his entire career, receiving all his academic credentials there and becoming a member of the
electrical engineering faculty in 1946, even before receiving his PhD. Helliwell received his AB degree in 1942, a combined MA and electrical engineering degree in 1944, and his PhD in 1948.[4] Helliwell and his wife, whom he knew in
high school, were both
undergraduates at Stanford.[1]
Helliwell was the author of one book,
Whistlers and Related Ionospheric Phenomena, and more than 90 scientific papers.[1,7] Three of his papers deserve special mention. One of these reported on low frequency emissions associated with the
Loma Prieta earthquake of October 17, 1989.[8] Another describes how injection of a low frequency radio signal into the magnetosphere causes a radio quieting of the natural noise that's associated with these frequencies.[9] Another paper showed that the
alternating current power grids in North America (60 Hz) and Europe (50 Hz) affect chorus emissions.[10] It seems that man has been changing his environment in ways he never suspected.
Helliwell was a
fellow of the
IEEE and the
American Geophysical Union, and a member of the
American Association for the Advancement of Science and the
National Academy of Sciences.[7] The
National Science Foundation named a range of hills in Antarctica, along the coast of
Victoria Land on the
Ross Sea, the Helliwell Hills in his honor.[1,5]
My family will likely relate to one aspect of Helliwell's personality. Said his son, David, "He took a scientific approach to everything... If you voiced an opinion, you'd better be able to back it up."[1]
There are quite a few circuit designs for VLF receivers and antennas available on the Internet. There are also some published in engineering magazines.[11] All of these are quite simple, since low frequency circuits are quite easy to build. The common antenna design is a
loop of wire, so don't worry about a location and a source of wire for your thirteen mile antenna!
References:
- Melissae Fellet, "Robert Helliwell, Radioscience and Magnetosphere Expert, Dead at 90," Stanford Report, May 20, 2011.
- Melissae Fellet, "Robert Helliwell, Radioscience and Magnetosphere Expert, Dead at 90," Scientific Computing, May 20, 2011.
- Thomas H. Maugh II, "Robert Helliwell, Electrical Engineer who Expanded Understanding of Earth'S Atmosphere, Dies at 90," Los Angeles Times, June 13, 2011.
- Electrical Engineering Prof. Helliwell Dies at 90, Stanford Daily News, May 24, 2011.
- Listening in on lightning, Stanford Engineering Web Site.
- NASA VLF Sounds Page
- Robert A. Helliwell, Professor Emeritus of Electrical Engineering, Stanford Personal Web Site.
- A. C. Fraser-Smith, A. Bernardil, P. R. Mccwiil, M. E. Ladd, R. A. Helliwell, and 0. G. Villard, Jr., "Low Frequency Magnetic Field Measurements Near the Epicenter of the M 7.1 Loma Prieta Earthquake," Geophysical Research Letters, vol. 17, no. 9 (August, 1990), pp. 1465-1468.
- R. Raghuram, T. F. Bell, R. A. Helliwell, and J. P. Katsufrakis , "A Quiet Band Produced by VLF Transmitter Signals in the Magnetosphere," Geophys. Res. Lett., vol. 4, no. 5 (May, 1977), pp. 199-202.
- J. Luette, C. Park, and R. Helliwell, The Control of the Magnetosphere by Power Line Radiation, J. Geophys. Res., vol. 84, no. A6 (June, 1979), pp. 2657-2660.
- J. Witzel, "Sferic Detection-The First Line of Defense," IEEE Instrumentation & Measurement Magazine, vol. 4, no. 1 (March, 2001), pp. 52-53.
- The Stanford University VLF Group.
Permanent Link to this article
Linked Keywords: Transistor; Tom Swift; skin; electrical resistance; perspiration; sweat; VLF; Very Low Frequency; audio frequency; audible frequency band; hertz; Hz; radio; Earth; electric motor; thunderstorm; lightning storm; radio atmospheric; spherics; whistlers; dawn chorus; birdsong; Earth's magnetosphere; Robert A. Helliwell; accidental; lightning; noise; Stanford University; Karl Jansky; Sagittarius A; extraterrestrial radio source; artifact; unidentified flying object; UFO; The Day the Earth Stood Still; Earth vs. the Flying Saucers; hobbyist; transmission; Antarctica; wavelength; frequency; Canada; ionosphere; Grote Reber; Tasmania; radio astronomy; Red Wing, Minnesota; Palo Alto; electrical engineering; high school; undergraduate; Whistlers and Related Ionospheric Phenomena; Loma Prieta earthquake of October 17, 1989; alternating current; power grid; fellow; Institute of Electrical and Electronics Engineers; IEEE; American Geophysical Union; American Association for the Advancement of Science; National Academy of Sciences; National Science Foundation; Victoria Land; Ross Sea; loop antenna.