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AM VSBA.J.Wilkinson, UCT EEE3086F Signals and Systems II510 Page
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EEE3086FSignals and Systems II
2014
Andrew [email protected]
http://www.ee.uct.ac.zaDepartment of Electrical Engineering
University of Cape Town
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5.5 Vestigial-Sideband Modulation (VSB)
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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
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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 ]
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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
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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.
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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.
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EEE3086FSignals and Systems II
End of handout
