데이터통신 4장 연습문제

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Data and computer Communications 4장 연습문제입니다

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4.2
-Gdb = 10log10(Pout/Pin)
I was using this equation.
A telephone circuit`s loss is 20DB.
–20dB =10log10(Po/Pi)
I know Pi = 0.5 W.
Po/Pi = 0.01
So, Pi = 0.5W, Po = 0.005W

SNR is a signal-noise ratio.
This problem must calculate to Decibels of output`s SNR.
I do calculate output power / noise power.
SNR = 0.005/(4.5 × 10-6) = 1.11× 103
SNRdB = 10 log10 (signal power / noise power).
Therefore, SNRdB = 10log10 (1.11 × 103) = 30dB

4.5
Pt/Pr = (4πd/λ)2
This equation is transmitted power-received power ratio.
D is distance, λ is wavelength.
If I double the frequency, λ halves.
If I double the distance, d is double.
If I double the distance, Pt/2Pr is (8πd/λ)2.
L=10log(4πd/λ)2 db
This equation figures out the loss.
L= 10log(Pr/2Pr) = 10 log (22) = 6 dB

4.7
a.
λ = c/f
I was using this equation.
This equation figures out the carrier wave.
c= speed of light (3 × 108 m/sec)
f = frequency
λ = (3 × 108 m/sec)/(300 Hz) = 1,000 km.
Because of half-wave length, λ/2 = 500 km.
Antenna length decides to use the half-wave.

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