Promax PROLINK-4/4C Premium Manual De Instrucciones página 194

3) Select the DIGITAL operating mode by means of the key
4) Select the DVB-T (COFDM) measurement mode: to do this press key
and turn the rotary selector [4] to select the BER (COFDM) measuring mode, next,
to activate it press the rotary selector [4] or key
Before visualizing the representation of the impulsive response is necessary to
define some parameters concerning the digital signal (see section '4.9.1.5.2 Measuring
BER of COFDM Digital Channels (COFDM)' ).
5) Press the rotary selector [4] to access the functions menu in digital mode, and
select the Echoes Detection option to access the impulsive response screen.
The Echoes Detection function represents graphically the different instances
from the same signal that arrive at the receiver, based on the time and the distance.
The graph always locates the signal of maximum amplitude in t=0, and shows to
the different echoes analysing an approximated time interval of 200 µs (see the
attached table).
PRE-ECHO
BW
20 µs
6 MHz
23 µs
7 MHz
26,25 µs
8 MHz
NOTE: When an echo or a pre-echo from a delay surpasses the margins defined in the
previous table, the equipment will not be able to discern which type of reflexion
has ocurred and it could appear represented, due to a cyclical scroll, in the
opposite side of the graph.
First, appears on the screen the computing time percentage for the acquisition in
progress.
Turn the rotary selector [4] to analyse the signal echoes that have been registered
in the acquisition. For example in the following figure at 70 µs of the reference signal
appears an echo of a level of — 25,2 dB with respect to the main signal. Between
parenthesis an estimation of the difference of routes (20.9 km) between the signals that
originate the echo and as well as the dynamic margin of the analysis (10 dB/div) is
indicated.
Page 58
ECHO Time
Time
148 µs
173 µs
197,75 µs
USER'S MANUAL. PROLINK-4/4C
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Premium
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06/2005