Sudden Ionospheric Disturbances Supplement

There is sad news to report this month. We have lost Danie Overbeek, A-52, in South Africa. Danie died unexpectedly of heart failure on 19 July. Danie was one of our most successful SID observers. He is the only one who ever recorded a gamma ray burst, GRB, and he also recorded a soft gamma ray repeater, SGR, in 1998. Danie was an air force veteran and after World War II went to work for South African Airlines where he worked most of his life. I got to know Danie through his letters in Variable Views and when he transferred to the New York office of SAA, I visited him where he lived then, near Kennedy International Airport. Besides being a famous AAVSO variable star observer, Danie also liked to build scientific instruments, so I had no difficulty convincing him he should build an SES receiver to record SIDs. He soon had it working and I assigned him A-52. He recorded the signal strength of Navy VLF station, NSS, in Annapolis, MD, which was a very sensitive propagation path at his distance from the NSS transmitter. When Danie retired from SAA he returned to his home in Edenvale near Johannesburg, South Africa. Danie had upgraded his SES receiver by adding a remote loop antenna preamplifier so he had no difficulty recording NWC in Northwest Cape, West Australia, at a distance of ~5000 miles East of Johannesburg to cover the early UT hours AAVSO observers, most of whom were in the USA, were not able to cover. Danie also built a McWilliams torsion balance magnetometer and many of his magnetograms have appeared in the Solar Bulletin. Another scientific instrument Danie was very proud of was his homemade seismograph, which easily detected earthquakes of magnitude 6 or greater anywhere in the world. It included a homemade seismograph drum that recorded the earthquakes on paper with a ball point pen. As an amateur seismologist, Danie was an active member of the Public Seismic Network, an amateur seismologist group that several other SID observers belong to. We will miss Danie but his A-52 station will continue to report and search for GRBs. It will be kept in operation by Danie's good friend Domenic Toldo, who built the three superhetrodyne SES receivers used to produce the multiplexed charts of three signals that recorded the GRB and the SGR. These receiver's are down-converting superhets of Domenic's own design tuned to NWC in West Australia, GBR in England and NAA in Cutler, Maine, USA. The three signals multiplexed on a single Rustrak chart made it possible to reliably identify the GRB and SGR because all three signals were enhanced at the exact time the events occurred.

Below is a computer recorded chart that Roberto Battaiola, A-96, made in Italy by recording the signal strength of VLF station HWU in LeBlanc, France, transmitting on 21.75 kHz. It shows an SES starting at 1000 UT and lasting over an hour. This chart was sent electronically for publication in the Solar Bulletin. Roberto also sent a list of VLF stations transmitting on frequencies below 150 kHz. The last two pages of this supplement show stations below 100 kHz which are the ones useful for detecting solar flares by the SID method. This list was compiled by Klaus Betke << Klaus.betke@epost.de >> No call letters are given for the station on 25.2 kHz which AAVSO sometimes calls TBD. Al McWilliams called this station in La Moure, ND on the phone and was told that no call letters have been issued for this Navy VLF station which uses the antenna of what was formally an Omega navigation system transmitter operating on about 10 kHz.

Jerry Winkler, A-50, has been experimenting with an ADR2000 A/D converter. Below are recordings he made of NAA and NPM. The recording of NAA in Cutler, Maine transmitting on 24 kHz show an SES starting at ~0845 UT. The NPM chart does not show this SES because its sunrise pattern has not finished at that time and the Houston, Texas to Hawaii propagation path is not sensitive to SIDs yet.

Kriss Larson wrote a very interesting article in the August issue of "the Lowdown", a publication of the Longwave Club of America about his visit to Navy VLF station NLK in Jim Creek, Washington, USA that transmits on 24.8 Khz. Kriss was not allowed on the military reservation but he did manage to talk to the duty radio technician in charge and learned some interesting facts about NLK. The antenna is three long wires strung between three pairs of towers on two 3000 foot high ridges 1.5 miles apart. The cables that span the valley between the ridges are 8000 feet long with downleads to the transmitter attached to the centers of the three heavy cables. Only the center 4000 feet of each cable is used as an antenna. Terminal insulators are located about half way between the centerpoint and the towers so the whole horizontal line is not energized. These cables spanning the valley are a serious flying hazard and are clearly marked as such on aeronautical sectional charts.

The NLK transmitter is rated at 1.5 megawatts but actual effective radiated power or antenna efficiency was secret information. Other information in The Lowdown tells how back in the ‘50s the Jim Creek antenna was tried out as an Omega navigation system transmitter antenna but its efficiency was disappointing so the Omega station was moved to Hawaii where the antenna spanned a mile-wide volcano crater. The ~ 10 kHz Omega transmitter there was an Alexanderson alternator, a high frequency alternator with its AC output fed directly to the antenna. Several SID observers belong to the Longwave Club of America and receive "The Lowdown". There is much of interest, both historical and technical, to be found in this monthly publication you can subscribe to for $18/year. The publisher is Bill Oliver, 45 Wildflower Road, Levittown, PA 19057 in case you are interested.

Another interesting fact Kriss found out is all Navy VLF stations have monitoring stations where they can monitor their signal and all other Navy stations. The Jim Creek monitoring station uses a large buried loop antenna at its monitoring station in nearby Bangor, Washington. The 24.8 kHz signal penetrates rock for some distance and is used by miners to detect ore bearing structures. NLK's buried loop antenna at their monitoring station in Bangor, WA explains why AAVSO observers have had good luck with loop antennas in basements and sitting right on the ground outside. It would be an interesting experiment to build a large loop antenna and lay it out on the ground.

Free software and other information you can use to record SIDs or other data are available from a company called Radio-SkyPipe. Some of what they have to offer may be of interest if you like to experiment. Their web site describes a wide variety of hardware and software that can be used mostly for radio astronomy projects. They show a simple MAX187 A/D converter that might be easier to build than Joseph Lawrence's MAX186 converter. If you feel like experimenting You can find out more from this web site:

http://www.radiosky.com/skypipeishere.html

Below are SID recording of flares that occurred during July . The first chart was made by Jim Ellerbe, A-63, in Spain, recording Italian VLF station ICV in Sardinia transmitting on 20.3 kHz. The others are Rustrak recordings made by Jerry Winkler, A-50.

Click image to enlarge

Click here to see radio signals below 150 kHz heard in Europe - (This is a .pdf file which requires the Adobe Acrobat Reader to be viewed. If you do not already have the reader, you may download it for free from the adobe website.)

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