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ENGLISH
TV & SAT Level Meter MTD 120
User Manual
5.- BER MEASUREMENT OF QPSK & QAM MODULATED SIGNALS
5.1.- Description
By means of the options BER measurement for DVB-Satellite (QPSK modulation), DVB-Cable signals (QAM modulation) and DVB-
Terrestrial (COFDM modulation), it is possible to make Bit Error Rate measurements on digital signals. Besides, these options incorporate the
DCI function (DVB Channels Identifier) which provides information on the tuned channel, in this way it is possible to identify it with total
certainty with no need to decode the digital signal.
5.2.- BER measurement mode selection
To select the BER measurement mode:
1) Select the TV operating mode. If present operating mode is the spectrum analyser mode press key SPECT [21].
2) Select the terrestrial band for the measurement of QAM or COFDM modulated signals or the satellite band for the measurement of
QPSK modulated signals.
QAM signals
47 MHz to 862 MHz
QPSK signals
950 MHz to 2150 MHz
COFDM signals
470 to 862 MHz
3) Select the DIGITAL operating mode by means of the key A/D [20].
4) Select the BER measurement mode: to do this press key LEVEL [22], press keys
[6] to select the BER measuring mode, next,
to activate it press key ENTER [5] or key LEVEL [22].
5.3.- QAM modulation
Before to measure the BER it is necessary to define some parameters concerning the digital signal, which are described next. To see its
present value or to modify it, being in the BER measuring screen, press key ENTER [5], a multiple-choice menu showing the functions relative
to the BER measurement will appear on the screen:
1) Modulations
It defines the modulation type. When selecting this function and pressing key ENTER [5], a multiple-choice menu will appear on the
screen, this menu permits to choose one of the following modulations: 16, 32, 64, 128 and 256.
2) Symbol Rate
When selecting this function and pressing key ENTER [5], a multiple-choice menu will appear on the screen, this menu permits to choose
one of the following values: 6875, 6111, 5000, 4443, 1528, 1500, 1408, 1333, 1266, 1000 kbauds, or well to define any other value by
means of the Other option.
When selecting the Other option, a screen titled QAM SYMBOL RATE will appear, this screen shows present Symbol Rate value, to
modify it press key SHIFT [31], enter the new value (four figures) and finally press key ENTER [5] to activate it.
3) Spectral Inv.
If necessary, activate the Spectral inversion. If the spectral inversion is not correctly selected, reception will not be correct.
4) Attenuator
It permits to select attenuation between 0 and 30 dB. It is advisable to activate the 30 dB attenuator under that measurement conditions
where the signal level is near to the maximum input level (approximately starting from 20 dB under the maximum level) and it is possible
that the tuner becomes saturated. Under no-saturation conditions, when increasing the attenuation value the BER measure must to
maintain or to increase (insufficient signal level) but never to decrease.
Once you have defined the QAM signal parameters, it will be possible to measure the BER.
When the BER measuring mode is selected, the monitor will show a picture like the following:
Figure 26.- BER measuring screen for QAM modulated signals.
QAM
1.0E-5
BER before FEC
-8 -7 -6 -5 QEF -3 -2
Freq: 800.00 MHz + 1.2kHz
W.P. 0 in 00:22:59
MPEG-2
