110 Chapter 15 - Spectrum analyzer
10713 Vxx.11
15.9
Level diagram in the broadband cable range
Assuming the measuring receiver is operating in the TV range, the mode is set to channel input
and the frequency segment is FULLSPAN respectively FULL EXT, the instrument provides a very
useful feature.
As you can see in Figure 15-3, the diagram shows the relationship of the levels in a broadband
cable system independent of the modulation (ATV or DVB-C) of the individual channels.
Figure 15-3 Level diagram
During the process, the instrument measures the levels of every individual channel and displays
them in the diagram as a green or red bar.
The green bars are analog and the red bars are digital channels. The cursor is marked with an “A”
or “D”.
In this diagram, tilted levels or abnormal drops in levels can be immediately detected with digital
channels.
15.10
TILT measurement in the TV range
This function is activated via the
TILT
menu item. You can end the tilt measurement by selecting
the
BACK
menu item.
This mode is an expansion on the level diagram in the TV range with the following additions:
You can select as many individual channels from the full channel table as you wish to include in the
tilt measurement. The fewer “active” channels, the higher is the repetition rate of the diagram. The
specific combination of channels can be saved in a profile. The measuring instrument can manage
two independent profile settings per FULLSPAN and per FULL EXT mode.
A second cursor appears for the tilt measurement. This can be moved with the
↑/↓
keys. The first
cursor is moved with the
←/→
keys.
If the channels upon which the two cursors are located are occupied, the device draws a reference
line between the peaks of the level lines. To facilitate a tilt analysis in a system with both analog
and digital channels, an “offset” line corresponding to the level reduction is added to the peaks of
the level lines for digital channels.
If the difference in level between an analog and a digital channel corresponds to the specified level
reduction, the level lines are displayed with the same height in the diagram.
The instrument also determines the modulation for digital channels, and the “offset” line is
displayed in a different color according to the modulation.
