frguency meaning (please help me)

[bayan1]

what is the difference between high and low freguencies?
and why we use high freguency for up link and low freguency for down link in satcom??

Added after 18 minutes:

i need someone help me

 

[ferdinand_leo]

frequency is simply the number of cycles a signal has completed per unit time.
unit of measurement is CYCLES per SECOND or Hz...

for downlink, the frequency is lower because lower frequencies could reach a greater distance given the same output power from the antenna. lower frequency would result to a lower Free Space Loss, absorption loss, etc...
And way above there, in the satellite, we actually need to conserve as much power as we can to keep the system running for a long period.

On earth stations, we can afford to transmit more power using the higher frequency.

 

[hiral.kotak]

HI,

the reasons are:
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...

For more answer search in this blog only..

Thanks..

HAK..