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Underground Antennas

Discussion in 'General Technical Questions and Answers' started by N2NH, Oct 31, 2005.

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  1. N2NH

    N2NH Ham Member QRZ Page

    For years I've been coming across stories about underground antennas. Some claim they make good stealth antennas, some say they were used by spies in World War II. Does anybody know if they actually work? I'm not looking to get great performance, but to see if it can be used in a Ham hostile enviroment as a stealth antenna.

    Thanks
     
  2. AE4FA

    AE4FA Ham Member QRZ Page

    There's one that runs through large portions of Wisconsin and Illinois. It is (or was) used for ELF communications with submarines. Don't really know if it's still in use.
     
  3. AG3Y

    AG3Y Ham Member QRZ Page

    Smart-alacky answer " Only in caves! ! ! " [​IMG]

    I love it when I can fine a good web page to answer my questions ! Try this one:

    http://www.elfrad.com/

    73, Jim
     
  4. K6PME

    K6PME Ham Member QRZ Page

    That looks interesting.
     
  5. K7KBN

    K7KBN Ham Member QRZ Page

  6. WA4ILH

    WA4ILH Ham Member QRZ Page

    First, the Navy's facility at Clam Lake was decomissioned several years ago.
    Second, Don't know about "underground" but when I lived out in West Texas, where the ground conductivity was Really Really bad, I knew an extra class operator who lived in a house with restrictions who would run a long wire out his window along the ground for about 50 feet to the back of his property. Worked lots of DX on this. (with a tuner of course)
    Tom WA4ILH
     
  7. K8ERV

    K8ERV Ham Member QRZ Page

    Bet it heats up the worms.

    TOM K8ERV Montrose Colo
     
  8. K7FE

    K7FE QRZ Lifetime Member #1 Life Member Platinum Subscriber QRZ Page

    Stealth it is, great performance it is not.

    Subsurface (underground) antennas have been thought of for about as long as radio has been around.  They received a boost in interest during the "cold war" atomic tensions with the Soviet Union.  It was thought that underground antennas would survive nuclear attack, even if your house did not, so every bomb shelter needed an underground antenna for radio reception or transmission.

    Practical info:
    1 Velocity factor is dielectric dependent, so if you bury an antenna in soil (which is a dielectric) then the physical length will be shorter than the same antenna mounted above ground.  Expect very low velocity factors of 40% to 25%, depending on depth, conditions and soil type, so physical length will be half or less the length of an above ground antenna.

    2.  Soil attenuation will reduce signals substantially.  A dipole buried eight inches below the surface in “normal” soil will have a attenuation of about 16 dB over a 40 meter dipole mounted at 0.3 wavelength above ground.  Attenuation will increase with depth.

    More information may be found in RSGB publication “Practical Wire Antennas” by John Heys, G3BDQ or ARRL “Antenna Compendium Vol 1” article titled “Subsurface Antennas for the Amateur”.

    73,
    Terry, K7FE
     
  9. WA4ILH

    WA4ILH Ham Member QRZ Page

    Are you kidding, Do you think that anything can still be alive down there after Texoco and Amoco are through pumping their chemicals into oil depletion wells?
     
  10. WA9SVD

    WA9SVD Ham Member QRZ Page

    Ah, marinated worms! Micky D's would be jealous! <GRIN>
     
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