axing MIE 8-00 Betriebsanleitung Seite 107

DVB-T Constellation
DVB-T FEC Coderate
(forward error correction)
DVB-T Bandwidth
DVB-T Guard Interval
DVB-T Transmission Mode
Fine Level
Fine Tune
2022-05-31 | Technical improvements, changes in design, printing- and other errors reserved. | BA_MIE.pdf |
The constellation can be set on QPSK, on QAM 16 or on QAM 64.
The QPSK-setting provides the smallest data rate to the output channel. The QPSK-modulation
process is used in bad distribution networks because of its robustness against disturbances and of
its safe transmission.
The QAM-modulation process allow reaching higher data rates, so that more programmes can be
transmitted on a channel. The QAM 64-modulation gives the highest data rate.
•
QPSK (2 bit) – small data rate – very robust signal.
•
QAM 16 (4 bit) - middle data rate.
•
QAM 64 (6 bit) - high data rate.
Thanks to the error correction, errors resulting from high-disturbed transmission routes can be
balanced by restoring data.
The data required to restore the signal are included in the transmitted FEC bits.
Changing the FEC factor modifies the part of the FEC data in relation to the application data.
A higher part of FEC data means an higher transmission redundancy. But this reduces the
bandwidth for the useful data too.
A FEC of 7/8 means the highest rate for the useful data and the smallest transmission
redundancy.
•
FEC 1/2 - small data rate - strong protection against errors.
•
FEC 7/8 - high data rate - weak protection against errors.
If CCIR is selected as the Norm, the bandwidth of the channels can be changed. With a larger
bandwidth, more data can be transmitted in one channel.
By adjusting the bandwidth, the channels no longer correspond to the channel grid specified by
the Norm.
A guard interval is transmitted between the transmitted symbols of the useful signal. The guard
interval protects against inter-symbol interferences.
A very long guard interval (e.g. 1/4) leads to a very low data rate. A small guard interval is usually
sufficient for transmission in a coaxial distribution network.
2k is fix
The level fine adjustment attenuates the output level of each individual modulator output
separately from 0 to -3 dB.
In addition, each modulator output can be disabled (Off option).
The fine Tuning of the output channel is performed in 1 MHz steps.
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