Chapter 6 - TV Measuring Range
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6.2.1.6
Noise Margin (NM)
In contrast to digital signals there is no fixed point here at which the image display is disturbed, but
a continuous deterioration of the image.
Therefore here the value S/N = 45 dB for the minimum quality at the BK socket according to
EN500083-7 is taken as reference value. The difference of S/N to this limit value corresponds to
the system reserve NM (noise margin). Just as S/N it is displayed in dB with the resolution 0.1 dB.
For an easier assessment of the signal quality NM is displayed in the colors red for bad, yellow for
limited and green for good signal quality.
6.2.2
DIGITAL (DVB-C, DOCSIS) operating mode
Here you can receive the digitally modulated DVB-C or DOCSIS signals and measure their signal
quality.
6.2.2.1
DVB-C
The DVB-C receiver of the measuring instrument is activated via the menu item
MODULATION
->
DVB-C
.
Figure 6-4 DVB-C mode
You enter the modulation scheme for DVB-C in another menu.
The selections
16QAM
,
32QAM
,
64QAM
,
128QAM
and
256QAM
are also available.
QAM means Quadrature Amplitude Modulation. That is the modulation method with DVB-C.
Automatic detection of the modulation schemes:
The measuring receiver uses the modulation scheme that was just selected as the starting point for
automatic detection of the modulation scheme. As soon as you enter a channel, the receiver
attempts to demodulate the signal that is present. If that is not successful with the set modulation
scheme, the receiver attempts additionally with 64QAM, 128QAM and 256QAM. The modulation
scheme of the DVB-C signal received is shown on the display.
