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Solutions to EEE206, Spring Semester 2003
1. (a)
Improvement in signal to noise ratio
Ease of radiation in radio systems, since efficient radiation from an antenna
requires its length to be
≥
λ
/4
Use different carrier frequencies to separate signals with similar baseband
frequencies
Facilitates multiplexing
(b)
For AM, m = E
m
/ E
c
m should be kept less than 1 to avoid 'splatter' in output spectrum
(c)
(i)Total power = P
c
(1+m
2
/2) = 5 x 10
3
when m = 1
Hence carrier power =
3.33 x 10
3
watts
(ii) m = 0.85
Power in one sideband = m
2
P
c
/4 = 0.85 x 0.85 x 0.25 x 3.33 x 10
3
=
601.5 watts
if P
RC
= power in reduced carrier, 10 log
10
(P
c
/ P
RC
) = 25,
hence P
RC
= 10.5 watts
Total output power = 10.5 + 602 =
612 watts
(d)
m
1
= 0.7, m
2
= 0.5 and m
3
= 0.2
Composite m =
√
(0.7
2
+ 0.5
2
+ 0.2
2
) = 0.883
Total power output = 3.33 x 10
3
(1 + .883
2
/ 2) =
4.633 x 10
3
watts
2 (a) Diagram should show a single superhet circuit with RF amp, mixer, LO, IF amp,
demodulator, AF amp and LS. The demodulation process should be explained with the aid of
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 Spring '08
 LANGLEY

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