ANTENTOP- 01- 2019, # 023

Spreading and Underground Antennas

Figure 6

Underground Short Wave Radio Site

Counterpoises are buried close to the ground surface. Antennas and counterpoises may be made from bimetallic tubes (iron tube plated by copper) in diameter of 20 millimeters. With the matching devices connected to the phase shift circuits the antennas can be combined in groups for creation of a desirable Radiation Diagram. Figure 7 shows top view on the antennas of the short wave underground radio site.

Antennas are installed in half-sphere trenches in depth of 2-3 meters underground. Then the trenches are filled up with dielectric stuff. Underground communication site is masked by ground covering with grass and sometimes with trees. Underground communication site may be fed by underground power cable from local electricity station or may have own underground nuclear or diesel electrical generator.

Vertical Underground Antennas

Through hours of searching in the internet the files about underground antennas I found data for vertical underground antennas. These antennas may be named as Mountain Antennas, because these antennas are

installed inside of mountain where rocks have low absorption of HF frequencies. Figure 8 shows design of a vertical mountain underground antenna.

Antenna is installed or in the natural funnels or in the artificial adit. Equipment room is placed at the bottom of the adit or in the cave from which the natural funnels come through the mountain. The vertical part of the antenna depends on length of the opening and how close the opening is to an aquifer stratum, which usually (if it is present) is used as the grounding for the mountain vertical antenna. The grounding for underground vertical antenna consists of several non-resonant short ground rods and wire counterpoises, which are placed under the antenna base. The vertical radiator of the underground antenna is tuned to resonance with the help of Antenna Tuning Unit.

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