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DVB-T
DVB-T
Constellation diagram DVB-T (optional)
For the terrestrial digital transmission of television signals (DVB-T), the modulation
type OFDM (Orthogonal Frequency Division Multiplex) is used.
In 2k mode, 1705 carries and in 8k mode 6817 carriers either QPSK-, QAM16- or
QAM64 are modulated.
DVB-T signals are transmitted in the so-called hierarchy modulation. Two MPEG
transport streams of difference priority are simultaneously transmitted.
The demodulated QPSK signals are decoded in the MPEG decoder and their con-
stellations are represented on the screen of the MSK 33.
THE MSK33 can automatically represent the constellations of all possible modula-
tion types and display the respective values.
param.
on►
By pressing this softkey,
you receive all data of
the DVB-T signal (see
left).
Measurement of bit error rate
(BER)
Since it deals with the transmission of binary
data for DVB-T, the bit error rate can be
observed as measurement for the occurring
transmission error in the data stream. The
BER measurement is carried out before the
viterbi decoder and displayed on the screen.
The bit error rate is the ration of the number
of the received defective bits divided by the
entire number of receive bits. The low bit
error rate, which the MSK 33 can measure, is 1.0 e-8. If the measured value is be-
low this value, the display of BER skipped to zero „0“ (no bit error available). The
highest displayed BER is 1 e-2. Generally, it can be assumed, that the picture dis-
turbance can occur for a BER of ca. ca. 2.2 e-2.
Measurement of signal noise ration (SNR)
The conception of the MSK 33 allows the S/N ratio of the I- and Q- data stream to
be displayed in addition to the C/N measurement on the digital carriers in the
Const-menu. The measurement is carried out after the QPSK demodulation and
can be called in as an indicator for the noise on the I/Q signals. Differences in the
result to the C/N measurement in the spectrum menu can be caused by the com-
plex interfering influences of the digital signal or by differences in the input level.
The SNR value is displayed on the upper edge of the TFT screen.
The best value, which the MSK 33 can measure, is 32 dB.
Carrier offset
The carrier offset display represents the difference between set receiving fre-
quency on the MSK 33 and the transmission frequency of the digital signal in MHZ.
With the cursor buttons, ◄►, you can switch to the next channel.
Carrier mode
Displays how many carries of the DVB-T signal are modulated. It is modulated be-
tween the 2k mode (1705 carriers) and the 8k mode (6817 carriers).
Modulation
Displays the modulation type, with which the DVB-T carriers are modulated. The
modulation types QPSK, QAM16 and QAM64 are possible.
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