EARTH STATION PARAMATERS

JENIL.J

What is Earth Station? Any transmitting or receiving system which sends or

receives signal to and from satellite Earth station is 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 in the most cost-effective and reliable manner while retaining the desired signal quality.

The design of earth station configuration depends upon many factors and its location

Earth Station Subsystems

Transmitter Receiver Antenna Tracking Equipment

ES Parameters:

•    Transmitter power•    Choice of frequency•    Gain of antenna•    Antenna efficiency•    Antenna pointing accuracy•    Noise temperature •    Local conditions such as wind, weather etc,•    Polarization•    Propagation losses

G/T Ratio:

G/T is Gain / Noise Temperature G/T = Antenna Gain (dB) - System Noise Temperature (dB) [10

Log(Tsys/1°K )] Signal at the receiving antenna is increased by the antenna

gain Subtract out the System Noise Temperature Result is signal level with respect to Thermal noise

Calculating G/T:

TSYS = TA + TLNA TA is the antenna noise temperature TLNA is the LNA noise temperature (Receiver Noise) Antenna: TA = 43° K, Gain = 38 dB LNA: TLNA = 51° K TSYS = 43 ° + 51 ° = 94 ° K G/T = Antenna Gain (dB) - 10 Log(Tsys/1°K ) G/T = 38dB –19.7dB = 18.3 dB -

Noise:

There are two main sources of noise in a satellite system: Noise arising in the satellite and earth-station equipment Noise collected by the satellite and earth-station antennas Noise power radiated by the Earth is collected by the side lobes of the

earth-station antenna and the main beam of the satellite antenna. Noise power N is related to an equivalent noise temperature by the

expression: N = k . T . B watts

Where, K is Boltzmann's constant (1.38 x 10-23 J/K) B is the bandwidth in which the noise is measured (in Hz)

Radiated Power:

EIRP = Transmitter Output Power + Antenna Gain EIRP includes the effects of:

1. Antenna Gain2. Antenna Efficiencies3. Transmitter Output Power4. Coupling and Wave guide Losses, Etc.

Once the EIRP is known, no additional information about the transmitter is required.

EIRP information assumes the transmitter is pointed directly at the receiver -

Transmitted Power

Typical Required EIRP = 42 dBW / 4kHz (Clear Sky) Determined by the satellite operator Assume Signal Bandwidth = 8MHz + 33 dB (with respect to

4kHz) i.e 10Log(8MHz/4kHz) For 8MHz the required EIRP = + 75 dBW Antenna size

1.10 Meter antenna @ 6 GHz 53.3 dB of Gain Misc Loss = 4 dB Pout= +75 dBW -53.3 dB + 4 dB = +25.7dBW Required transmitter Pout = 372 Watts

Path loss:

Signal Radiates out from a point Source Flux Density is less at receiving antenna as the distance increases Path Loss is actually a dispersion of the transmitted signal

Calculation of Path loss:

Path Loss in dB = 10 Log(PL) Path Loss is related to Number of Wave Lengths Path Loss proportional to (D / λ) 2 Example Frequency: 14GHz Lambda (λ) = 0.021429 Meters Distance: 22,300 Miles (35,888 kM) Path Loss: 206.46 dB

PROPAGATION EFFECTS OF EARTH

Some Effects.,

Operating frequency Antenna Elevation Angle Polarization ES Altitude ES Noise Temperature Local Meteorology Climate

Operating Frequency. With the exception of signal attenuation by gaseous absorption lines, the severity of tropospheric impairments increases with frequency. Earth Station Altitude. Because less of the troposphere is included in paths from higher altitude sites, impairments are less. Earth Station Noise Temperature. This determines the relative contribution of sky noise temperature to system noise temperature~ and thus the effect of sky noise on the downlink signal-to-noise ratio.

Antenna Elevation Angle and Polarization.

The length of the part of the propagation path passing through the troposphere varies inversely with elevation angle.

Accordingly, propagation losses, noise, and depolarization also increase with decreasing elevation angle.

Rain attenuation is slightly polarization-sensitive. Depolarization is also polarization-sensitive, with circular polarization

being the most susceptible.

Local Meteorology.

The amount and nature of the rainfall in the vicinity of the Earth station are the primary factors in determining the frequency and extent of most propagation impairments.

Rain caused impairments depend on the rate of rain fall, so how the rain tends to fall (thunderstorms versus steady showers) is as important as the cumulative amount of rainfall.

The type and extent of cloud cover, and local humidity characteristics are other meteorological factors that determine the magnitude of propagation impairments.