AP01-HD_rev.09_UK
45
9.
MPEG4/MPEG2 DECODER
9.1.
Introduction
The MPEG module makes it possible to view non encrypted (free to air) digital
transmissions. This, however, is not the most useful function it performs in the instrument
where it has been fitted, since the quality of a digital signal should not be judged according
to the TV-picture, but only by means of specific measurements such as BER or the C/N ratio
(although much less reliable and accurate).
The real value of this module lies in the identification of channel contents. Digital channels
appear as noise bands of variable width: a few MHz for SCPC transmissions, around 7 MHz
for terrestrial-cable or aerial transmissions, approximately from 18 to 30 MHz for MCPC
transmissions. Specialized magazines supply all the information concerning satellite
transmissions, but when dealing with frequency conversion installations an exchange
between channels is always possible. The same problems may be caused by QPSK to QAM
transmodulation
2
.
The MPEG module receives the TS (Transport Stream) coming from the QPSK, QAM or
OFDM decoder and provides the name of the transponder, the Network data, the television
or audio programs which are separately available, the list of audio channels associated with
each video program; if the program is not scrambled, it is decoded and may be viewed.
9.2.
Use of module
The MPEG signal to be decoded and displayed must be supplied by QPSK/8PSK, QAM or
OFDM modules. See the related chapters to use them correctly.
The module is activated pressing the
TV
key from the digital-measure screen.
9.2.1.
Description of the Network Information Table
If present in the TS, on top you will see the name of the Network on one line and, in case
of satellite signal, the information about the satellite and transponder on the following line:
1.
Orbital position in degrees followed by
E
or
W
(East or West).
2.
Polarization with indication LH (Linear Horizontal), LV (Linear Vertical), CR (Circular
right) or CL
(Circular Left).
Please note that data may not be reliable due to transmodulation, transponder relay from
the satellite or other causes.
Then there is the list of available video or radio programs, taken from the NIT
3
, and the
HELP of the operations that may be carried out. Each line is composed by:
3.
Sequential number.
4.
Name of channel.
5.
PID video.
6.
Number of available audio.
Lines are green for programs declared as non-encrypted by the Broadcaster and they are
red for programs declared as encrypted.
2
Transmodulation demodulates and decodes the digital channels of a satellite
transponder, which normally occupies 30 MHz and generates a digital carrier in a terrestrial
band which, in 7 MHz of the band, contains all the same channels.
3
Network Information Table
