Alcad 918 Serie Manuel D'utilisation page 182

Reminder :
Remember: In terrestrial TV broadcasting, the received signal on the antenna comes from several possible
ways: the echoes.
In digital TV DVB-T/H and DVB-T2, these echoes may help or degrade the image according to the time
delay between the various signals that reach the antenna.
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
directive antenna.
The Echo function of the appliance enables you to display possible echoes that disturb the received signal.
Main signal
Pre-echo
Measurements
form arrow
position
73
Guard interval
limit
Echoes out off
the guard
interval
Echoes
search keys