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Amplitude Modulation vestigial side band
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AM VSBA.J.Wilkinson, UCT EEE3086F Signals and Systems II510 Page 1 April 14, 2014
EEE3086FSignals and Systems II
2014
Andrew Wilkinsonandrew.wilkinson@uct.ac.za
http://www.ee.uct.ac.zaDepartment of Electrical Engineering
University of Cape Town
AM VSBA.J.Wilkinson, UCT EEE3086F Signals and Systems II510 Page 2 April 14, 2014
5.5 Vestigial-Sideband Modulation (VSB)
A.J.Wilkinson, UCT AM VSB EEE3086F Signals and Systems II510 Page 3 April 14, 2014
Vestigial-Sideband Modulation (VSB)
DSB modulation is wasteful of bandwidth. SSB is difficult to generate when modulating signal bandwidth
is wide or has low frequency components. VSB is a compromise :
Partial suppression of one sideband reduces bandwidthFiltering requirements are not as severe as SSBCan demodulate via synchronous detection or envelope detection if large carrier transmitted
c
DSB
SSB
)(VHFilter
VSB
A.J.Wilkinson, UCT AM VSB EEE3086F Signals and Systems II510 Page 4 April 14, 2014
Vestigial-Sideband Modulation (VSB)
Transmitted signal
We must design the roll off of such that simple synchronous detection results in perfect signal recovery.
To design , need to consider demodulation. e0 t =[VSB t cosc t ]LPF
HV
VSB =[12
F c 12
F c ]H V
HV
e0 =[12
VSB c 12
VSB c ]LPF
=14
F HV c 14
F HV c
=14
F [HV c H V c ]
A.J.Wilkinson, UCT AM VSB EEE3086F Signals and Systems II510 Page 5 April 14, 2014
Vestigial-Sideband Demodulation
c2 c2Note: Anti symmetry in roll over region
H V c H V c
c c
H V
Sum has aflat response
Consider the demodulation process
A.J.Wilkinson, UCT AM VSB EEE3086F Signals and Systems II510 Page 6 April 14, 2014
Vestigial-Sideband Modulation (VSB)
Thus we need to arrange
Examples of antisymmetry roll off.
c2
[HV c H V c ]=constant
c2Note: Anti symmetry in roll over region
H V c H V c
constant
The illustration showsthe spectrum afterthe mixer.
A.J.Wilkinson, UCT AM VSB EEE3086F Signals and Systems II510 Page 7 April 14, 2014
VSB is used for analogue television transmissions to conserve bandwidth.
South Africa uses the PAL-I standard for analogue TV broadcasts, same as UK. It is similar to the NTSC standard used in the USA.
There are many different variants of the PAL standard.
A.J.Wilkinson, UCT AM VSB EEE3086F Signals and Systems II510 Page 8 April 14, 2014
AM VSBA.J.Wilkinson, UCT EEE3086F Signals and Systems II510 Page 9 April 14, 2014
EEE3086FSignals and Systems II
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