sm9_15
1 pág.

sm9_15


DisciplinaTeoria de Telecomunicações239 materiais356 seguidores
Pré-visualização1 página
Problem 9.15 The average noise power per unit bandwidth measured at the front end of 
an AM receiver is 10-6 watts per Hz. The modulating signal is sinusoidal, with a carrier 
power of 80 watts and a sideband power of 10 watts per sideband. The message 
bandwidth is 4 kHz. Assuming the use of an envelope detector in the receiver, determine 
the output signal-to-noise ratio of the system. By how many decibels is this system 
inferior to DSB-SC modulation system? 
 
Solution 
For this AM system, the carrier power is 80 watts, that is, 
 
watts80
2
2
=CA (1) 
 
and the total sideband power is 20 watts, that is, 
watts20
2
2
2
=PkA aC (2) 
 
Comparing Eq.s (1) and (2), we determine that 412 =Pka . Consequently, that post-
detection SNR of the AM system is 
 
dB
WN
PkASNR aCAMpost
37~
5000
400010
20
2
6
0
22
=
×=
=
\u2212
 
 
For the corresponding DSB system the post detection SNR is given by 
 
higher7~
SNR5
1
SNR
1
SNR
AM
post
4
1
4
1
AM
post2
2
DSB
post
dB
Pk
Pk
a
a
×=
+=
+=
 
 
 
 
Excerpts from this work may be reproduced by instructors for distribution on a not-for-profit basis for testing or instructional purposes only 
to students enrolled in courses for which the textbook has been adopted. Any other reproduction or translation of this work beyond that 
permitted by Sections 107 or 108 of the 1976 United States Copyright Act without the permission of the copyright owner is unlawful.