CHAPTER 2

SATELLITES AND ANTENNAS

LEARNING OBJECTIVES

Upon completing this chapter, you should be able to do the following:

Identify the theory relating to satellites.

Calculate azimuth and elevation, using plotting guides.

Identify the types, basic system and fleet broadcast subsystem equipment of communication satellites.

Identify the characteristics of antennas and antenna selections.

Identify the types of antennas.

Explain how the distribution systems interface with antenna assignment and selections.

Identify the procedures for setting up antenna couplers, multicouplers, transmitters, and transceivers.

Explain how the patch panel is used in conjunction with the equipment.

Identify the procedures for raising and lowering antennas.

Determine the optimum reception of a directional antenna by rotation, alignment, and tuning.

Identify safety precautions that should be observed when working on antennas.

Satellite communication (SATCOM) systems satisfy many military communications requirements with reliable, high-capacity, secure, and cost-effective telecommunications. Satellites provide a solution to the problem of communicating with highly mobile forces deployed worldwide. Satellites also provide an alternative to large, fixed ground installations. They provide almost instantaneous military communications throughout the world at all but the highest latitudes (above 700).

SATCOMM ANTENNAS

The antennas shown in figures 2-1 and 2-2 are used for satellite communications. The OE-82C/WSC-1(V) antenna (figure 2-1) is used with the AN/WSC-3 transceiver and designed primarily for shipboard installation. Depending upon requirements, one or two antennas may be installed to provide a view of the satellites at all times. The antenna is attached to a pedestal. This permits the antenna to rotate so that it is always in view of the satellite. The frequency band for receiving is 248 to 272 MHz; the band for transmitting is 292 to 312 MHz.

Figure 2-1.-OE-82C/WSC-1(V) antenna group.

The AN/SRR-1 receiver system consists of up to four AS-2815/SSR- 1 antennas (figure 2-2) with an amplifier-converter, AM-6534/SSR-1, for each antenna. The antennas are used to receive satellite fleet broadcasts at frequencies of 240 to 315 MHz. The antenna and converters are mounted above deck so that at least one antenna is always in view of the satellite.

The newer satellite systems use the SHF band. One of the major advantages of these systems is that they use a very small parabolic antenna measuring only 12 inches in diameter.

A satellite antenna must be pointed at the satellite to communicate. We must first determine the azimuth (AZ) and elevation (EL) angles from a fixed location. Figure 2-3 illustrates how these angles are derived,

Figure 2-2.-AS-2815/SSR-1 antenna physical configuration.

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:

Center the overlay directly over the desired satellite position on the stationary map.

Mark the latitude and longitude of the ship on the plastic antenna pointing guide with a grease pencil.

Determine the approximate azimuth angle from the ship to the satellite.

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.

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 discussed above, we can see the example indicates an azimuth value of 115 and an elevation angle of 30.