why uplink frequency is kept higher than the downlink frequency?

5 ANSWERS

1. amomipais82
   

   Hi There,
   Because the uplink frequency can be sent from a way bigger antenna. If Up and Down were running on the same frequency, they would end up both garbled from meshing with each other.....separate frequency paths guarantee clear transmission In some cases, such as satellite communications, the uplink frequency (Earth to satellite) is of a higher value than the downlink to mitigate the free space spreading losses, and the tropospheric losses (gases, clouds, rain), all of which are related to wavelength and therefore to frequency (wavelength=speed of light in vacuum/frequency).
   
   
   Higher the frequency, lesser the wavelength. So high frequency can be received using smaller antenna in satellite, which is more practical. Whereas in earth we can have bigger antennas..
   Thanks

   Report (1) (2)  |   12 years, 9 month(s) ago  

2. jane
   

   hello
   
   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 up-link is at higher freq with higher power.
   
   2)Now as the frequency is increased the amount of interference caused by the atmosphere 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 neighborhood, 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 up link.
   
   hope it helps

   Report (1) (0)  |   12 years, 9 month(s) ago  

3. Guest1710
   

   uplink frequency is kept larger than downlink frequncy bcoz as frequncy increases wavelength decreases so it is more practical to keep size of transponder in satellite much less.we can use more space on earth for bigger antennas to transmit signal to satellite. however in mobile communication uplink frequency is less than downlink frequency becoz size of mobile should be as less as possible.

   Report (3) (0)  |   12 years, 9 month(s) ago  

4. Guest7987
   

   1)High power is required to penetrate the atmosphere and to overcome free-space spreading loss and other disturbances caused by the atmosphere....and high power can be achieved if the frequency is increased
   2)Also earth station must have high directivity i.e narrow bandwidth....narrow bandwidth is directly proportional to wavelength....lesser the wavelength higher the frequency...
   3)also high power requirement involves the need for high power amplifiers which will increase the weight and power supply ratings of the equipment.since earth station is huge ,increase in weight does not has any effect.But since satellite is small increase in weight requires high power consumption which cannot be afforded and can results in avoidable inefficiency.................  
   and hence uplink frequency is greater than downlink frequency
   
   Answered by Suchitra C Majumdar

   Report (3) (0)  |   12 years, 9 month(s) ago  

5. Guest9168
   

    Ashutosh

   
   

   Logically, the effort or energy required to move upstairs is greater than that of going downstairs. It's just an analogy. Similarly energy and hence the frequency required to uplink a signal from the earth station is kept higher than that of downlink signal. Thanks...

   Report (4) (0)  |   12 years, 9 month(s) ago