DreamGEAR MSK 33 Dvb-T, Constellation diagram DVB-T optional, Measurement of bit error rate BER

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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