Planar IT-088, Руководство по эксплуатации

Страница: 21 / 82

21
Figure 4.9
The three upper lines display the setting parameters. The top line shows channel
number, channel name within the channel plan (if a channel plan was selected), and the
symbol of DVB-T/H signal synchronization. If synchronization has been achieved,
«LOCK» message is displayed.
The second line indicates the set frequency and the measured value of input signal
frequency shift in MHz (resolution for measurement of frequency shift is 0.167 MHz). If
there is no synchronization of DVB-T/H demodulator, zero will be displayed in the
frequency shift position.
The third line indicates the modulation type and the number of orthogonal subcarriers,
if the DVB-T/H demodulator synchronization has been achieved, otherwise empty line will
be shown.
When operating in channel plan, if one of the channel synchronization parameters does
not comply with the corresponding parameter specified in the channel plan, modulation
type is displayed in inverse color (for example:
COFDM-QPSK ).
The next four lines display the values of the measured parameters. The first parameter
is the modulation error ratio MER and immunity margin in dB related to BER threshold
value ( Margin ). Both parameters are displayed in one row and are separated from each
other by «/» symbol. The second parameter is the bit error rate in the digital stream before
Viterbi decoder ( perBER ). The following line represents bit error rate in the digital stream
after Viterbi decoder ( postBER ). The postBER value will be indicated depending on
achievement of the threshold value 2x10
-4
. If the postBER value is under the threshold
you will see pass (allowed value) message, otherwise you will see fail message. The
bottom line shows parameter Real Err , which indicates the number of error blocks after
Reed-Solomon decoder and the interval of time of their counting.
Modulation error ratio MER parameter associates with the input signal C/N ratio, and in
keeping with the immunity margin Margin , allows to estimate the capability of the receiver
to decode the signal without errors. The postBER parameter as well as MER
characterizes the quality of the input signal and shows the amount of errors after Viterbi
decoder. The threshold value of this parameter is 2x10
-4
. If postBER is under the
threshold, this ensures the probability of errors at Reed-Solomon decoder output less than
10
-10
…10
-11
. In this case the data stream can be considered quasi error free, and ensuring
reliable television reception. The preBER parameter shows the amount of errors before
Viterbi decoder and is auxiliary due to its interconnection with postBER parameter. Joint
analysis of preBER and postBER parameters can be used for assessment of the Viterbi
decoder operation quality. The Margin parameter characterizes the margin (in dB) of
MER parameter until BER threshold value. If the current MER value shows that there is
immunity margin but postBER value is over 2*10
-4
, then Margin value will be indicated in
inverse colors, for example: MER/Marg=18.6/ +2.4 dB .
Frequency adjustment