What are Earth segments?
The earth segment of a satellite communications system consists of the transmit and receive earth stations. the only of those are the homeTV receive-only (TVRO) systems, and therefore the most complex are the terminal stations used for international communications networks.
Also included within the earth segment are those stations which are on ships stumped, and commercial and military landand aeronautical mobile stations.
As mentioned in earth stations that are used for logistic sup- port of satellites, suchas providing the telemetry, tracking, and command (TT&C) functions, are considered as a part of the space segment.
Design consideration and General configuration
Earth station may be a vital element in any satellite communication network. The function of an earth station is to receive information from or transmit information to, the satellite network within the most cost-effective and reliable manner while retaining the specified signal quality. the planning of earth station configuration depends upon many factors and its location. But it's fundamentally governed by its
Location
- In land
- On a ship stumped
- Onboard aircraft
The factors are
- sort of services
- Frequency bands used
- Function of the transmitter
- Function of the receiver
- Antenna characteristics
Earth station consists of 4 major subsystems
- Transmitter
- Receiver
- Antenna
- Tracking equipment
- Two other important subsystems are
- Terrestrial interface equipment
- Power supply
The earth station depends on the subsequent parameters
- Transmitter power
- Choice of frequency
- Gain of antenna
- Antenna efficiency
- Antenna pointing accuracy
- Noise temperature
Receive-Only Home TV Systems
This service is known as the direct broadcast satellite(DBS) service. There is some variation in the frequency bands assigned to different geographic regions.
The comparatively large satellite receiving dishes, which may be seen in some “backyards” are used to receive downlink TV signal sat C band (4 GHz).
Equipment is now marketed for home reception of C-band signals, and some manufacturers provide dual C-band/Ku-band equipment. To take full advantage of C-band reception the home antenna has to be steerable to receive from different satellites, usually by means of a polar mount. Another of the advantages, claimed for home C-band systems, is the larger number of satellites available for reception compared to what is available for direct broadcast satellite systems.
The major differences between the Ku-band and the C-band receive only systems lies in the frequency of operation of the outdoor unit and the fact that satellites intended for DBS have much higher equivalent isotropic radiated power (EIRP).
The figure shows the main units in a home terminal DBS TV receiving system.
The outdoor unit
This consists of a receiving antenna feeding directly into a low-noise amplifier/converter combination. A parabolic reflector is generally used, with the receiving horn mounted at the focus. A common design is to have the focus directly in front of the reflector, but for better interference rejection, an offset feed may be used as shown.
 |
| DBS TV receiving system |
0 comments:
If you have any doubts,please let me know