ANTENTOP- 01- 2019, # 023

Spreading and Underground Antennas

Spreading and Underground Antennas

Igor Grigorov, VA3ZNW

It was in the end of 1980s, during at my trip by bus from Gorkiy (now Nizniy Novgorod, Russia) to a small town at this region, while on route to my destination, I observed a huge field fenced with barbed wire. I asked my local fellow traveler what it might be and he replied that it was a military communications site. However, I noticed there weren't any antennas visible. My companion remarked that they were installed under ground! So, for the first time I had seen an underground communications site.

The manner of constructing the underground antennas used on these sites especially interested me, but at the times I cannot found any information about underground antennas. Information of these antennas was considered highly confidential just before 90s. Recently with development of satellite and meteor radio communications systems such unusual antennas became almost obsolete. Classifications have been removed from underground and spreading antennas and information on the antennas may be found in the internet.

However, underground and spreading antennas are old type of antennas used by military of different countries. These antennas usually were exploited on classified signal radio communications sites.

Underground and spreading antennas are normally not used by the radio amateurs. Usually there are enough places where it is possible to install an antenna of choice. However, with cities getting larger and architectural demands to keep the exterior of houses and communities attractive, underground and spreading antennas may be one of the only solutions to be on the Air. 

History of Underground and Spreading Antennas

During the First World War, an antenna mast of a field radio set had a significant altitude of 15-30 meters (50-100 feet) thereof it represented an easy target for enemy's artillery. But even when shells were downed the mast the spreading above the ground antenna allowed makes radio communication. It was found that the spreading antenna enabled fair communication in the same direction of the antenna wire leading from the transmitter. Knowing thus fact sometimes mast was not be installed for field radio set and military use the spreading antenna that represented just wire in thick insulation lying on the top of the ground which follows and blends with the irregularities of the earth surface and vegetation coverage.

Before the Second World War early researches into the operation of underground and spreading antennas were made for the purpose of espionage installation of invisible antennas. These antennas needed be easily installed and set up for operation on short-wave bands of 2-5 or 8-12 MHz, which was commonly used at the times by the spies for clandestine operation.

In practical way it was found that an effective spreading antenna may be formed from a wire of about 1 mm diameter enclosed by a dielectric with approximately 10-mm diameter to protect the wire from touching the ground surface. However as usual for clandestine spreading antenna it was used general electric wire in rubber isolation in length of about 30-45 meters. The wire may be placed on the ground, on the bushes or attached to a fence. It was easy installed and easy removed for radio operation and the wire may be easily found in a local electrical store.

Old direction-finding equipment had some irregular errors in finding location of transmitters using spreading and underground antennas.

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