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.
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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).
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