ANTENTOP- 01- 2019, # 023

Spreading and Underground Antennas

Length of Spreading and Underground Antenna

How does length affect the overall performance of spreading and underground antenna? It could be used very long wire to improve efficiency of the antenna?

Probably not, because in radiation from an antenna wire the basic role is played by the length of the antenna, during which the amplitude of a current in the antenna diminishes by a factor of 10 as contrasted to being at feed terminals of the antenna. In the Reference [2] is shown, that for the underground or spreading antenna installation (on basic types of soils), the length of the wire in 30 meters is enough for effective operation on HF bands. If the installation of the underground or spreading antenna is on dry, sandy soil, or on top of deep snow, the length may be greater than 60 meters. Then absorption RF energy from a long wire makes the long wire useless in antenna radiation.

Antenna Efficiency

As it shown in Reference [2], with sufficient approximation it is possible to take that the efficiency of spreading antenna on HF ranges would be no more than 10 percent in comparison to an antenna of the same length and installed at a height of 2 meters above the same soil and operating on the same frequency. However ever with the efficiency it is possible to make QSOs on amateur bands at normal propagation conditions with power 100 watts going into the antenna.

The directivity of low height spreading antenna is almost similar to the above mentioned raised at the altitude of 2 meters above the ground antenna. However the vertical angle of radiation of a spreading antenna is going to be 10-20 percent higher, than for the raised antenna. It allows assume that a spreading antenna could be a choice for local QSO (up to 500 km) in the 160 and 80 meter Bands. On the bands higher than 40 meters, both local and long-distance QSO's are possible.

Files about Underground and Spreading Antennas

Let's take a look to practical design of the spreading and underground antennas used by the USSR military.

All these files were found by me in the internet and were declassified by 2000 year.

Practical Design of Spreading Antennas in the USSR

I have got some descriptions of Russian spreading antennas, which has now been declassified. Figure 4 shows Russian spreading antenna named SA - 60/15 (CA- 60/15, in Russian letters it means Spreading Antenna 60 meter length, counterpoises 15 meter length).

Figure 4

Spreading Antenna SA- 60/15

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