Tektronix 1705A instruction manual Applications

Introduction

APPLICATIONS

The principal application for the TEKTRONIX 1705A Spectrum Monitor is to provide a convenient method to locate and identify Ku-Band satellites, find the correct transponder and check on its availability, and optimize antenna position- ing and polarization. The remainder of this section provides basic satellite communications application data. Specific operating instructions are located in Section 2, Operating Instructions.

Locating Satellites The communications satellites that the television industry is interested in lie in a band directly over the earth’s equator, at a distance of approximately 35,900 km (or about 3.7 times the earth’s diameter). Traveling at approximately

11,000 km/h the satellite completes one full orbit in 23 hours, 56 minutes,

4.9seconds, which is referred to as a sidereal day. When a satellite completes one orbit in a sidereal day it is geographically stationary (geostationary) to a point on the earth’s surface. Without being geostationary, using a satellite would be extremely complicated and the calculations required to determine when they were in the usable window, and how long they would stay there would, in most cases, require a computer.

At 35,900 km distance the earth subtends an angle of 18˚, which provides coverage of approximately 40% of the earth’s surface. See Figure 1-2. Forty percent (40%) of the earth’s surface corresponds to an area stretching from 70˚ North latitude to 70˚ South latitude. For rough assumptions, a satellite, in geostationary orbit over the equator, could cover latitudes from the Arctic circle (66˚ 30’ N) to the Antarctic circle (66˚ 30’ S). However it should be noted that even though the satellite is capable of covering 40% of the earth’s surface the actual coverage will be less in most cases because of the antenna design and available transmitter power.

	70° N
	18°
	70° S
35,900 km	9,675 km

Figure 1-2: Relationship of a communications satellite to earth

Determining the exact angle from the horizon to a satellite (other than at the equator) requires a knowledge of trigonometry, because of the relatively close

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