USER’S MANUAL. PROMAX-10
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Figure 17.- CSO and CTB
measurement.
Figure 16.- Interpretation of the CSO and CTB measures.
The PROMAX-10
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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).
The CTB measurement is performed equivalently to the CSO. If all the channels
that are transmitted have the video carrier at the same position within the channel, then
the CTB beat will show up at the same frequency as the video carrier. It is for that
reason, that the PROMAX-10
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makes this measurement at the same
frequency as the video carrier and, as consequence, to make this measurement it is
necessary to turn off the video carrier of the channel we want to analyse. If it is not
possible to turn off the carrier at the head-end, the PROMAX-10
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allows, like
approach, to make this measurement at one of the free adjacent channels (see section
4.2.3.3. Channel-Frequency mode configuration).
MEASURING METHOD
When pressing the rotary selector
[9] again, we will accede to the CSO-CTB
distortion products measuring screen.
First of all it will appear the message REMOVE
CARRIER. PRESS TO MEASURE. That is to say,
once the video carrier level on which it is desired to
make the measurement appears on the screen,
you must press the rotary selector [9] in order that
the unit retains the carrier level and comes to
calculate the CSO and CTB ratios; next you must turn off the video carrier of the
channel you want to make the measurement (at the right of the CTB measurement will
appear the message Carrier OFF).
The display will show the level of the video carrier (80 dBµV in the previous
figure) and the CSO ratio (accompanied by the frequency offset for which the minimum
ratio has been obtained) and the CTB ratio (with the message Carrier OFF or Carrier
ON according to the equipment has detected the absence or not of carrier).
The lower part of the screen shows the 4 measures made for the estimation of
the CSO value.
