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