To demodulate a QAM or DVB QAM signal
This task shows you how to demodulate the 32 DVB QAM signal generated
in ‘’To prepare a QAM or DVB QAM measurement’’. Prior to demodulating
a video signal you must select the correct center frequency, frequency
span, and range as shown in that task. You use the same procedure to
demodulate both QAM and DVB QAM signals.
1. Prepare the analyzer for a DVB QAM measurement as shown in the previous
task.
2. Demodulate the signal:
Press [
Instrument Mode
], [
demod type
], [
Video Demodulation
], [
Return].
3. Select the correct demodulation parameters for the 32 DVB QAM signal (if you
are not using the signal provided on the Signals Disk, enter the parameters for
your signal) :
Press [
Instrument Mode
], [
demod type
], [
Video Demodulation
], [
Return] .
Press
[demodulation setup
].
Press [
demod format], [DVB QAM 32], [
Return
].
Press [
symbol rate
], 1, [
MHz
]
Press [
result length
], 400, [
sym
]
Press [
ref filter
], [
raised cosine
]
Press [
Return
], [
meas filter
], [
root raised cosine
].
Press [
alpha/BT
], .15
Press [
Time], [
points/symbol
], 5.
P ress [
pulse search off
], [
sync search off
].
4. View the created signal versus the reference:
Press [
Display
], [
2 grids
],
Press [
A
], [
Measurement Data
], [
IQ measured time
]
Press [
B
], [
Measurement Data
], [
IQ reference time
]
Press [
Shift], [A] to activate both traces.
Press [
Data Format], [polar (IQ) vector].
Press [
more format setup], [symbol dots] (if [symbol dots] is already selected, you still
must press this key to force both traces to display symbols as dots).
5. Scale both traces:
Press [
Auto Scale
]
If you are familiar using digital demodulation, you may have noticed that
setting up a video demodulation measurement and a digital demodulation
measurement is identical for QAM and DVB QAM measurements (you can
demodulate 16 QAM and 32 QAM signals with digital demodulation or
video demodulation).
Using Video Demodulation
(Opt. AYH)
9 - 10
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