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The wireless system is operating at 2GHz. A base station and a mobile unit are separated by 16km. The maximum gain of the transmitting antenna at the base station is 20dB. The input power to the transmitter is 100W, and the power received by the antenna is 5nW. The antennas are aligned, and there are no re ections or loses. What will be the received power if the distance between the mobile unit and the base station increases to 20km?

Sagot :

If everything else remains constant, then the received signal power is simply an inverse-square function of its distance from the transmitter.

That is, down 6dB when distance is doubled etc.

If distance increases from 16 to 20, then received power decreases by the factor of (16/20)^2.

That's (0.8)^2 = 0.64

New receive power is 5x0.64 = 3.2 nW

=. ===== ==========

Here's how I do it at my job:

Initial RSL = 5nW ~ - 53 dBm

loss = 20log(20/16)= 20log(1.25)~1.94dB

New RSL = - 54.94 dBm or ~ 3.2 nW .