Two Cable Underground Antennas may make a Zenith Underground
Antenna. The antenna made similar to symmetrical spreading antenna
shown on Figure 133 A.
Zenith Antenna is common known as NVIS (Near Vertical Incidence Skywave)
Underground Cable Antenna has length of the radiation
part (L2 at Figure 146) approximately 10 meters. The length
was found by practice. There is no sense to use radiation part
with length more the 10 meters because far parts of the Underground
Cable Antenna do not radiate efficiently.
To increase efficiency of the Underground Cable Antenna
146) the radiation parts L2 placed into the trench
above dry sticks or straw. Then the same dry sticks or straw put
on above the parts L2. So, antenna wire is placed inside dielectric
sleeve. Ground is placed above the dielectric sleeve. Such design
allows easy remove the Underground Cable Antenna from the trench.