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Name: Drake
Status: Student
Grade: 9-12
Location: MA
Country: United States
Date: August 2007


Question:
Why is the transmission frequency from Earth to a satellite different from the frequency that the satellite transmits back to Earth?



Replies:
Drake,

The reason the "uplink" frequency is different than the "downlink" frequency is that these transmissions are occurring at the same time, so the frequencies are intentionally different to avoid interference.

Regards,

Bob Wilson


Radio frequency waves -- are waves -- and when waves pass through the same regions of space at the same time they tend to produce interference patterns with one another. A similar thing happens when your drop two pebbles in a pond. This interference produces more complex waves which would have to be sorted out at the sending and receiving stations. One simple way of minimizing the interference effects is to send the two signals at frequencies (wavelengths) that are NOT simple multiples of one another. In this way the receiving antenna can be constructed to reject the sending frequency and only pay attention to the receiving signal, and vice versa.

Vince Calder



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