Exam Prep

Question 1

Answer 1

(c)

Question 2

Answer 2

(b)

Question 3

Answer 3

(c)

Question 4

Answer 4

(c)

Question 5

Answer 5

b

Question 6

..and why?

Answer 6

b (see Bessel table)

1x carrier, and 3x sidebands x2 (one on either side of carrier)

Question 7

Answer 7

a

Question 8

Answer 8

a (Phase Modulation)

Question 9

What is 4b5b encoding? Why is it used over, say, Manchester?

Answer 9

• encodes 4 input bits and adds an extra 5th
• uses much less bandwidth than Manchester, particularly when paired with MLT-3 (multi-level) signalling
• always has at least 2 transitions - this can be used for clock recovery

Question 10

Why and how (mathematically) does AM have sidebands?

Answer 10

Assuming a sinusoidal m(t) input, we’re left with two sines being multiplied in the ‘sideband’ portion of the equation.

Using trig identities, we get an cos(f_c+f_m) and cos(f_c+f_m); this translates to two sidebands on either side of the carrier.

Question 11

Show how phase and frequency are related mathematically.

Answer 11

Question 12

State the equation for Phase Modulation.

Answer 12

Question 13

Wavelength = ?

Answer 13

velocity / frequency

Question 14

State the abbreviation + freq. band:

1600kHz

10MHz

88MHz

Answer 14

1600kHz = MF

10MHz = HF

88MHz = VHF

Question 15

State the freq. band:

2MHz

2.45GHz

6GHz

Answer 15

2MHz = MF

2.45GHz = UHF

6GHz = SHF

Question 16

What does ‘10BaseT’ ethernet stand for? What type of encoding scheme does it use, and why?

Answer 16

10 = 10Mbps

B = Baseband (vs. Broadband)

T = unshielded twisted pair

Manchestor; higher speed ethernet might use 4B5B/MLT