Promax 10 SE, Manual

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Premium USER’S MANUAL. PROMAX-10
11/2008 Page 23
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4.2.3.1.3 CSO-CTB distortion products measurement (only for
analogue channels)
The active devices present in the distribution systems, when working in its
non-linear zone, generate interfering signals, called distortion products, that can fall
within the video bandwidth. From a certain level this interference becomes visible on the
TV image.
The distortion products of greater level and which usually fall within the channel
bandwidth are those of second and third order beats.
The CSO distortion ( Composite Second Order ) is defined, as a ratio of the peak
level of the video carrier to the peak of the distortion products of second order beat,
produced by the rest of channels. The ratio is expressed in dB and can be resembled to
a C/N measurement as it is desired to be maximum.
Similarly, the CTB , Composite Triple Beat , is defined as a ratio of the peak level
of the video carrier to the peak of distortion products of third order beat, which show up
at the same frequency as the video carrier.
In order to obtain these measurements, the carriers of the channel plan that is
desired to transmit, must be present in the network and the measurements must be
carried out for each one of the channels of the system.
Second order beats show up within the channel, around the video carrier, but as
the relative position of the video carrier in all the channels can be different, it is difficult
to determine where they are going to appear, as a consequence we would have to be
made a sweep within all the channel. The
PROMAX-10 Premium performs this
measurement automatically at four frequencies around the video carrier (-1.5, -0.5, +0.5
and +1.5 MHz). These frequencies can be modified by the user (refer to the section
4.2.3.3.
Channel-Frequency mode configuration menu ).
Figure 17.- Interpretation of the CSO and CTB measures.
The PROMAX-10 Premium displays as CSO value the worst measurement
(that is to say, the CSO ratio that has minor value) accompanied of the frequency offset
for which it has been obtained (for example, in the figure previous at +0.5 MHz).