surface. Although this quantity is beyond the control of the user, 

 if does determine the antenna and receivei' noise temperature 

 requirements . 



The remaining four items — antenna/receiver, demodulator/decoder, 

 frame synchronizer, and data processing equipment — are under the 

 user's direct control and are discussed in Parts IV, V, VI, and 

 VII, respectively. A breakdown of the necessary equipment is 

 shown in Figure 1 . 



II. EQUIPMENT NEEDED FOR A TYPICAL DCS 

 DIRECT READOUT STATION 



The equipment that must be provided by the user in order to receive 

 DC replies directly is listed below: 



ANTENNA 



The antenna is usually paraboloidal and must be mounted on a 

 supporting structure or building; it should have an' unobstructed 

 view of the satellite. 



For normal operations, the ground station antenna is pointed 



at a single satellite — GOES East or GOES West. As these satellites 



are at fixed locations, the antenna can be adjusted to the proper 



look angles and locked in position. However, the mounting structure 



should be designed so that minor adjustments (say + 10 degrees) 



in both azimuth and elevation can be made conveniently to compensate 



for installation inaccuracies. Because the inclination of the 



satellite will be held to about ±0.1 degree, it should not 



ordinarily be necessary to reposition the antenna during normal 



operations . 



However, operation of the DCS may be changed from one satellite to 

 another during eclipse periods, so that direct-readout users must 

 reposition their antennas to another satellite to maintain continuity 

 of operations. While the satellite is in eclipse, operational 

 restraints are placed on the satellite, because of limited power 

 available. These eclipse periods occur for intervals up to 72 

 minutes a day each day for 6 weeks, twice a year. 



If the antenna will be used with more than one satellite or family 

 of satellites, it is recommended that repositioning of the antenna 

 be done by remote control. 



The S-band transmissions from the SMS/GOES satellites are linearly 

 polarized. If the full capability of the receiving antenna is 

 to be realized, the antenna must also be linearly polarized so that 

 it is parallel to the polarization of the received signal. Because 

 of different aspect angles to different satellites, the polariza- 

 tion of the signal cannot be predicted at the Earth's surface. 

 For this reason, the polarization of the antenna should be adjustable. 

 Where the antenna will be used with only one satellite, the 



48 



