AP01-HD_rev.09_UK
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6.
DIGITAL MEASURES
According to the instrument configuration, on the AP01-HD the following options may be
installed:
QPSK/8PSK demodulator
for digital satellite signals DVB-S /DVBS2
OFDM demodulator
for terrestrial TV digital signals DVB-T
QAM demodulator
for cable TV digital signals DVB-C
MPEG4/MPEG2 decoder
to display and listen to free-to-air digital signals
Noise generator (optional)
to calibrate switchboards
7.
DEMODULATION MODULES FOR DVB-S/DVB-S2, DVB-T, DVB-C
7.1.
INTRODUCTION
The modulation systems used to transmit digital signals are optimized for the different types
of transmission:
•
QPSK/8PSK: satellite transmissions, due to its considerable resistance to noise;
•
QAM: cable transmissions, due to its particular efficiency in using the available band;
•
OFDM: over-the-air signals, to ensure reception even when there are signal multiple
paths and echoes and when signal is received from a moving vehicle.
A digital transmission looks like noise that takes up all the channel, generally about 30 MHz
in QPSK/8PSK, 7/8 MHz in QAM and OFDM.
⇒
In order to decode the signal is necessary to know some transmission parameters. A lot
of them are standardized, however some may vary from one channel to another and
need to be set on the instrument.
7.2.
QPSK/8PSK MEASUREMENTS
When the QPSK/8PSK module is active, the screen displays the variable parameters of
transmission and measures described as follows:
SYMBOL RATE:
it indicates the set value.
Please note:
this value must be set by the
user.
MODE:
it indicates the type of modulation (DVB-S or DVB-S2), which must be set by the
user.
CODE:
it indicates the Code Rate of modulation; it is followed by writing
AUTO
since
identification and setting are automatic.
SPECT:
it indicates the polarity of modulation; it is followed by writing
AUTO
since
identification and setting are automatic.
LOCKED:
it is green when the signal is locked; or
UNLOCKED:
it is red when SYMBOL RATE and/or MODE values do not correspond to the
correct values and the signal is not locked; or
NO SIGNAL:
it is red when there is no input signal.
