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The difference levels between the measured values and the tilt line are displayed on
the screen. The digital channel levels are additionally compensated using the A-D value.
4.3.6. TV channels parameters measurement in Echo Diagram mode
The echo diagram deal with displaying DVB-T or DVB-T2 channel impulse response
diagram, as well as basic reception quality parameters. The screen view and the data
displayed are presented in Fig. 4.14:
Echo diagram features the bar graph of signal amplitudes which arrive with delay
after the main signal (of peak amplitude). Signal amplitude is measured in reference to the
main signal amplitude in dB, while the main signal amplitude is assumed to be equal to 0
dB. The delay value can then be negative, i.e. the echo signal arrives to the signal
reception point before the main signal. This is true if there reflected signal amplitude is
higher than that of the main signal (for example, when the signal arrives from the
transmission antenna and retransmitter).
The echo diagram is intended for high precision positioning of the reception antenna.
The main quality criteria for the selection of signal arrival direction is minimum echo signal
level, especially outside the guard interval limits. The positioning procedure requires
controlling basic reception quality parameters, such as level, MER and BER.
To change the cursor position, use the ◄ and ► keys. Press one of these keys along
with the Shift key to move the cursor by several positions. By pressing the F3 / ◄Max and
F4 / Max► key, the cursor will shift through echo signals with maximum amplitude values.
The echo signal delay and amplitude in the marker position are indicated under the
diagram.
The echo diagram updating is indicated by the
the diagram. To make the echo signal analysis easier, the table of maximum amplitude
Figure 4.13
Figure 4.14
•
marker in the upper right corner of
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