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CHAPTER 7
Transmission Media
Solutions to Odd-Numbered Review Questions and Exercises
Review Questions
1. The transmission media is located beneath the physical layer and controlled by
the physical layer.
3. Guided media have physical boundaries, while unguided media are unbounded.
5. Twisting ensures that both wires are equally, but inversely, affected by external
influences such as noise.
7. The inner core of an optical fiber is surrounded by cladding. The core is denser
than the cladding, so a light beam traveling through the core is reflected at the
boundary between the core and the cladding if the incident angle is more than the
critical angle.
9. In sky propagation radio waves radiate upward into the ionosphere and are then
reflected back to earth. In line-of-sight propagation signals are transmitted in a
straight line from antenna to antenna.
Exercises
11. See Table 7.1 (the values are approximate).
13. We can use Table 7.1 to find the power for different frequencies:
Tab le 7.1 Solution to Exercise 11
Distance dB at 1 KHz dB at 10 KHz dB at 100 KHz
1 Km โ3โ5โ7
10 Km โ30 โ50 โ70
15 Km โ45 โ75 โ105
20 Km โ60 โ100 โ140
1 KHz dB = โ3P
2 = P1 ร10โ3/10 = 100.23 mw
10 KHz dB = โ5P
2 = P1 ร10โ5/10 = 63.25 mw
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