#)Earth stations may be classified based on the size, mobility, the type of links and the type of services etc. as follows to cater to options

1.    Depending Upon The Types Of Services Are

1. Fixed
2. Mobile

• Maritime
• Aeronautical
• Terrestrial (trucks etc)

3.  Broadcasting

#)Low system noise is important for all the applications some possible options of INTELSAT earth stations are as follows First is encountered in two-way communication systems.

#)The second is the direct TV broadcast satellite systems.

#)The third is the data collection systems

Standard A earth station:

• G/T = 40.9 db/k at C-band
• Dish diameter  = 30 m
• Antenna gain = 6.4 db

Standard B earth station :

• G/T = 31.7 db/k at C-band
• Dish diameter  = 31 m
• Antenna gain = 51.5 db

Standard C earth station:

• G/T = 39 db/k at C-band (at 14/11 GHz)
• Dish diameter  = 19 m (at 14/11 GHz)
• Antenna gain = 65 db (at 14/11 GHz)

2.    Depending Upon The Application
•    Transmit and receive
•    Receive only (DBS)
•    Transmit only (DCS)

3.    Depending Upon The Type Of Size
•    Large earth station
•    Small earth stations
•    Micro earth station:
•    Very small aperture terminals (VSAT)
•    Large earth station

#)Typically for communication applications cassegrain geometry is used diameter around 30m

Small earth stations

#)Antenna size less than 60 wavelength in diameter.

#)Diameter of antenna = (say) 5m at 4GHz
= 1.6 at 11 GHz
Gain = below 44db

#)Type of parabola = Front feed parabola

#)Fixed pointing: no need of expensive auto-track system.

#)Application: TURO (TV receive only) systems, load mobile services, maritime services, Direct broadcast satellite (DBS).

Micro earth station:

#)Size: 2 to 6 feet antenna

#)Very inexpensive

#)DBS application

Very small aperture terminals (VSAT)

#)Low cost earth station. Low speed, packet data Networks applications.

#)Antenna size: 1.2 to 2.5m dia

#)G/T <15 db/k

#)LNA is uncooled GaAs FET of about 100k

#)HPA:

• 1 to 5w power also GaAsFET Low cost solution for route data communication between control host computer and a large no. of remote sites.
• Generally employs star topology. VSAT employs packet transmission with switching at the master station.
• Such networks are ideally suited for non-voice applications like computer and other forms of data communication.
• These employ spread spectrum multiple access (SSMA) techniques.
• The data transmission rates are generally limited to 19.2 bits at 4 GHz.

Applications of VSATs are

•    Data broadcasting services and
•    Two-way data services
•    News dissemination including text and graphic information
•    Transmission of charts and documents.

#)It is believed that in future, with spread spectrum technique with 20/30 GHz band, the size of the earth may come down o 12 cm, making earth stations truly portable.

#)VSAT find applications in aircrafts ships and rural areas and mobile communications.

Mobile and Transportable earth stations:

#)The small earth stations are portable and the antenna must be capable of relating in all directions.

#)Application is the communication for shipping through IMMARSAT (International Maritime Satellite Organization) satellites.

#)IMMARSAT: Earth station characteristics are

• Antenna diameter: 12 m
• Gain:23 db
• Beam width: 100
• Capacity : single duplex telephony or telegraphy.
• Frequency: 1640/1540 GHz

TURO systems

#)It has only the downlink section consists of dish (reflector), feed –horn , polarizer, LNA, down converter and TV/Video monitor.

#)The dish can be spherical or parabolic, generally the later.

#)The receiver part of TURO consists of down converter,  IF amplifier, demodulator and video/audio processor.

#)Once the video and audio are properly processed, they may be received on the monitor.

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