Underground Antennas
My
underground antenna basically looks like the diagram attached in Figure
1. I put the break in the shield in the middle, 25 feet on each side
and did not use a ferrite choke. The inner diameter is about 6 inches
and the outer 12 inches, with about 13 turns. It is buried a foot below
the ground in a generally damp area. I waterproofed the shield break area
and the far end of the coax. I will discuss my experiences with it at
the meeting. If you are interested in the subject of underground antennas,
there are a few links for you to explore below. A few hams have constructed
and tested various buried coils and dipoles. The older references circa
1850 -1930 are rather interesting, compared to what we know today.
I also built a Five Element 2 Meter Yagi for about $25 following the design in the July 1999 QST article. The antenna offers a gain of about 10 dBi, is lightweight, mechanically strong and rivals the performance of similar commercial antennas. The SWR response I measured is in the attached Figure 2. If you are an ARRL member, you can get the article at: http://www.arrl.org/members-only/tis/info/pdf/9907034.pdf
REFERENCES: Underground Antennas
KM5KG's web site with documentation and measurements made on some buried dipole antennas. http://www.qsl.net/km5kg/dummy.htm
A site with descriptions, test data and documentation on an underground solenoid type antenna. http://www.borderlands.com/newstuff/research/FelixRadio/FelixRadio.htm
Very informative article on the characteristics of Earth Dipole antennas. Primarily focused on VLF/ULF frequencies. http://www.vlf.it/ed/earthprobes.html
A simple AM radio circuit using the ground as an antenna. http://www.tricountyi.net/~randerse/gndradio.htm
Some interesting ideas regarding ground radio including schematics for a couple of simple receiver circuits. http://www.geocities.com/lemagicien_2000/elecpage/ugr/undr.html
Ground Antennas - A historical perspective / By Gerry Vassilatos and/or Michael Theroux http://www.borderlands.com/newstuff/research/ground-ant.htm http://www.icehouse.net/john34/groundradio.html
Dennis = = = = = = = = = = = = = = = Dennis Mennerich K4THE 2403 Commonwealth Drive Charlottesville, VA 22901-1621 434-973-5407 k4the@arrl.org = = = = = = = = = = = = = = =
Fig. 2
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