Chapter 6 - TV Measuring Range
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The DVB-T standard is suitable for transmission in single frequency networks (SFN). In a single
frequency network, the involved stations operate synchronously on the same frequency. In order to
take into account differing transit times with simultaneous effect on the receiving location, the
DVB-T signal contains a so-called “guard interval”. The size of the guard interval tells you
something about the maximum station distance within a single frequency network.
The FEC value expresses the ratio between usable bits and transmitted bits. In this example, there
are two usable bits for every three transmitted bits.
Further DVB-T parameters
6.2.2.3.4
The menu item
PARAMETERS
opens a sub menu with further DVB-T parameters.
Figure 6-13 DVB-T parameter information
One of the parameters, the Cell ID, uniquely identifies the cell of the transmitter.
BER measurement (Bit Error Rate)
6.2.2.3.5
The measurement of the bit error rate aids in the determination of the quality of a DVB signal.
To determine the bit error rate, the error correction mechanisms in the digital receiver are used.
The data stream is compared before and after correction and the number of corrected bits is
determined from that. This number is placed in a ratio to the total throughput of bits and the BER is
calculated based on that.
For DVB-T, two independent error protection mechanisms work together. So-called internal error
protection (after the demodulator) is called Viterbi (named after the Viterbi algorithm) with DVB-T.
External error protection operates after that. With DVB-T, it is called Reed-Solomon.
For DVB-T, the bit error rates are measured before Viterbi (CBER) and after Viterbi (VBER).
Both values are shown on the display in exponential form.
The depth of measurement for the CBER is 1•10
6
bits, for the VBER is 1•10
8
bits.
