– 7859 –
p.
76
The broadcasting norms DVB-T and DVB-T2 define a modulation parameter called "
guard interval
" where
echoes won't disturb the reception.
The transmission of digital data (
Symbol
) is interrupted during the
guard interval
.
A delayed (or advanced) symbol of any
shorter
duration than the guard interval will not disturb the reception.
A delayed (or advanced) symbol of any
longer
duration than the guard interval will disturb the reception.
You have to reduce the level of reception of the echoes by orienting the antenna or by selecting a more di-
rective antenna.
The
Echo
function of the appliance enables you to display possible
echoes
that disturb the received signal.
Relative amplitude in dB and delay in µs (distance in km) from the main signal (0 pulse) can be measured.
The yellow line represents the end of the guard interval.
Echoes and pre-echoes (pulses) above the yellow line disturb the signal and must be reduced as much as
possible.
The echoes (pulses) beyond this line disturb the reception and must be as weak as possible.
Attention: a high amplitude echo pulse within the guard interval will also disturb the signal
quality.
Yellow line,
Guard interval
limit
Main signal
Pre-echo
Echos out of interval
Measurements
form arrow position
