why uplink frequency is higher than downlink

see the reason is that. 1) On the Earth Station we have to penetrate the atmosphere to reach the satellite station. so we need a lot of power to be generated. This is only possible with the help of High power transmitter circuits. which cannot be installed on the satellite. so uplink is at higher freq with higher power. 2)Now as the frequency is increased the amount of interference caused by the atmosphore reduces. as higher frequency signal has more signal energy in it. so it can penetrate the atmosphere more easily. (the same reason why we use modulation with higher frequency)
3) Unwanted distortion like rain (main cause of attenuation), fog, other frequency in neighbourhood, etc cause distortion. so we have to count to these factors and increase the frequency band to 100-1000Ghz range.

Now the Satellite is a small piece of equipment and needs to be light weight. so it cannot have high power amplifiers on board so by default the freq is lower than uplink. i hope this is informative. if it is press thanks. Cheers. Uplink Frequency The uplink frequency is the frequency which is used for transmission of signals from earth station transmitter to the satellite. The downlink frequency is the frequency which is used for transmission of signals from the satellite to the earth station receiver. The satellite transmitter generates a signal that would jam its own receiver; if both uplink and downlink shared the same frequency.

Trying to receive and transmit an amplified version of the same uplink waveform at same satellite will cause unwanted feedback or ring around from the downlink antenna back into the receiver. Frequency band separation allows the same antenna to be used for both receiving and transmitting, simplifying the satellite hardware. To overcome the above-mention difficulties satellite repeaters must involve some form of frequency translation before power amplification. So, Uplink frequency is different from downlink frequency. Uplink frequency is kept higher than Downlink frequency for the following reasons: At higher frequency attenuation is more hence more power will be required for signal transmission to ensure that it reaches the destination with the required minimum power.

Higher power requirements involve the use of high power amplifiers with high ratings and heat sinks. This will increase the weight and power supply ratings will not make any difference. However for the satellite this will result in higher power consumption, which results in avoidable inefficiency. The earth station antenna must direct the beam towards the satellite with as little spill over as possible i. e. the antenna must have high directivity. Beam width (measure if directional property) of the antenna is directly proportional to wavelength. Higher frequency means lesser wavelength and hence lower beam width, which implies greater directivity.

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