2022-07-27 | Technical improvements, changes in design, printing- and other errors reserved.
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Parameters
Norm:
In this selection field, you can set the norm for the output channel spacing.
Note: Changing the norm works now according to following rules:
CCIR-->Australia : all modulators forced to 7MHz
Australia-->CCIR : all modulators forced to 8MHz, however with following
exception: low channels S2-S20 are 7MHz only, so those remain in 7MHz
Output channel:
The first modulator can be set to any output channel between S2 and CH 69.
The other three modulators are automatically set by incrementing the output
channels in accordance with the chosen channel spacing.
For example: modulator 1 = Channel 21
modulators 2, 3 and 4 = Channels 22, 23 and 24
Common Output level
The
Common Output Level
option include a general attenuation of all
modulator outputs. The highest output level is reached with a setting of 20 dB,
the lowest level with a setting of 0 dB.
DVB-T modulation:
The modulation 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 allows reaching higher data rates, so that more
programs can be transmitted on a channel. The QAM 64-modulation gives the
highest data rate.
•
QPSK (2 bit/symbol) – small data rate – very robust signal.
•
QAM 16 (4 bit/symbol) – middle data rate.
•
QAM 64 (6 bit/symbol) – high data rate.
DVB-T FEC (forward error
correction):
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 a 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.
DVB-T bandwidth:
The DVB-T standard plans a broadcast on 6, 7 or 8 MHz channels. A bigger
bandwidth means that more data can be transmitted on a single channel.
In the CCIR channel spacing, the lower channels: C5…S20 have a provided
bandwidth of 7 MHz. The other channels have a bandwidth of 8 MHz.
If the bandwidth is changed, the channel does not correspond any longer to
the set channel spacing. Therefore, the output frequency for all 4 modulators
also changes.
