using a pointing guide called the Equatorial Satellite
Antenna Pointing Guide. This guide is normally
available through the Navy Supply System.
The antenna pointing guide is a clear plastic
overlay, which slides across a stationary map. It
indicates AZ and EL angles in degrees to the satellite.
The values obtained are useful to the operator in setting
up the antenna control unit of a satellite system.
To use the guide, follow these procedures:
1. Center the overlay directly over the desired
satellite position on the stationary map.
2. Mark the latitude and longitude of the ship on
the plastic antenna pointing guide with a grease
pencil.
3. Determine the approximate azimuth angle from
the ship to the satellite.
4. Locate the closest dotted line radiating outward
from the center of the graph on the overlay in
relation to the grease dot representing the ship’s
location. This dotted line represents degrees of
azimuth as printed on the end of the line. Some
approximation will be required for ship
positions not falling on the dotted line.
5. Determine the degrees of elevation by locating
the solid concentric line closest to the ship’s
marked position. Again, approximation will be
required for positions not falling directly on the
solid elevation line. Degrees of elevation are
marked on each concentric line.
Example: Assume that your ship is located at
30° north and 70° west. You want to access
FLTSAT 8 at 23° west. When we apply the
procedures above, we can determine an azimuth
value of 115° and an elevation angle of 30°.
RHOMBIC ANTENNA
The rhombic antenna, usually used at receiver sites,
is a unidirectional antenna. This antenna consists of
four long wires, positioned in a diamond shape.
Horizontal rhombic antennas are the most commonly
used antennas for point-to-point HF naval
communications. The main disadvantage of this
antenna is that it requires a relatively large area.
MULTIWIRE RHOMBIC
A rhombic antenna improves in performance if each
leg is made up of more than one wire. An improved
antenna, known as a curtain rhombic, uses three wires
spaced 5 to 7 feet apart for each leg and connected to a
common point (figure 2-30).
SLEEVE ANTENNA
The sleeve antenna is used primarily as a receiving
antenna. It is a broadband, vertically polarized,
omnidirectional antenna. Its primary uses are in
broadcast, ship-to-shore, and ground-to-air
communications. Although originally developed for
shore stations, there is a modified version for shipboard
use. Figure 2-31 shows a sleeve antenna for shore
stations.
Sleeve antennas are especially helpful in reducing
the total number of conventional narrowband antennas
that otherwise would be required to meet the
requirements of shore stations. With the use of
multicouplers, one sleeve antenna can serve several
receivers operating over a wide range of frequencies.
This feature also makes the sleeve antenna ideal for
small antenna sites.
CONICAL MONOPOLE ANTENNA
The conical monopole antenna (figure 2-32) is used
in HF communications. It is a broadband, vertically
polarized, compact omnidirectional antenna. This
antenna is adaptable to ship-to-shore, broadcast, and
ground-to-air communications. It is used both ashore
and aboard ship.
When operating at frequencies near the lower limit
of the HF band, the conical radiates in much the same
manner as a regular vertical antenna. At the higher
frequencies, the lower cone section radiates, and the top
section pushes the signal out at a low angle as a sky
wave. This low angle of radiation causes the sky wave
to return to the Earth at great distances from the antenna.
Figure 2-30.—Three-wire rhombic antenna.
2-24
