Chapter 6 - Measuring range
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Start the scan by tuning the measuring receiver to a frequency at which the scan should begin (see
“Frequency input”). Pressing
ENTER
begins the process, as indicated by the “SCAN” message in the
frequency window. When the instrument finds a transponder, the search is halted and the measuring
receiver measures the frequency found. You can stop the scan by pressing a number key, an arrow
key (
Up
/
Down
) or the
ESC
key.
During the scan, the instrument also detects DVB-S and DVB-S2 signals and adjusts the measuring
receiver to the relevant operating mode.
Note:
In the UNICABLE and JESS operating mode the scan function is deactivated.
6.3.3 DVB-S2
parameters
The parameters are shown in the parameter window. If the measuring receiver is tuned to a
frequency (see “Frequency input”), the DVB-S2 channel decoder attempts to synchronise with the
signal that is present; this activity can be traced using the “SCAN” message in the parameter
window.
The receiver first attempts to synchronise to the DVB-S2 signal that is present using the set symbol
rate. If this is not successful, all of the preset symbol rates are set one after another. In addition, the
instrument automatically detects the DVB-S/DVB-S2 operating modes.
If a QPSK/8PSK signal with the set symbol rate is present, the channel decoder locks and
LOCKED
is displayed in the parameter window. Otherwise, the
UNLOCKED
message is shown. This may be
caused by the following: none of the set symbol rates fit; the receive level is too low; the signal is too
noisy; or there is no DVB-S2 signal at this frequency.
When the DVB-S2 channel decoder receives a signal, the instrument shows its code rate and
modulation scheme in the parameter window. At the same time, bit error rate and MER measurement
is activated. The measured values are shown in the BER window and the MER window. The MPEG
window is also displayed; here you can follow the search for PSI (program service information) in the
transport stream. Further information can be found in the “MPEG Decoder” section.
6.3.4 BER
measurement
(bit error rate measurement)
As mentioned in the previous section, the BER measurement result is displayed in the BER window.
The measuring receiver can measure the bit error rate before LDPC (CBER) and afterwards (LBER)
at the same time. The LBER is displayed in a smaller font on the top line of the BER window. CBER
is below in a large font.
Note:
The internal error protection is called LDPC (Low Density Parity Check) in the DVB-S2 standard, and
the external error protection is called BCH (Bose Chaudhuri Hocquenghem). In particular, the
performance of the LDPC error protection is significantly better than that of the inner error protection
of DVB-S (Viterbi).
6.3.5 MER
measurement
The MER value of the signal in the baseband (after the demodulator) is displayed in dB in the MER
window. The measuring range extends to 20.0 dB; the resolution is 0.1 dB.
6.3.6 Packet error measurement
Short interruptions in the DVB-S/S2 signal usually cannot be detected using MER or BER
measurements. They can make entire packets in the transport stream unusable for the MPEG
decoder, however. This can cause the picture to freeze temporarily or the sound to crackle. The
extent of this depends largely on the receiver hardware.
In the MODE menu, a function can be activated which sums up all corrupt transport stream packets
starting from the time of activation or when a new frequency is entered. The number of packet errors
(PE = Packet Error) and the amount of time that has passed since the last tuning process is
displayed in the BER window instead of the VBER or LBER. This function can be deactivated again
in the above menu or by performing a restart.
