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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
PROMAX-10
reason, that the
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
this measurement at one of the free adjacent channels (see section 4.2.3.3.
Channel-Frequency mode configuration).
MEASURING METHOD
When
pressing
selector [9] again, we will access 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 instrument has detected the absence or not of carrier.
At the lower part of the display it is shown the 4 measures made for the
estimation of the CSO value.
If the rotary selector [9] is pressed again, the unit will return to the measurement
screen of the video carrier + V/A +C/N (paragraph 4.2.3.1.1).
4.2.3.1.4
Power and C/N ratio measurement (DVB-C / DVB-T / DAB)
(only for digital channels)
When the tuned channel has been defined
as digital by means of the Edit Channel Plan
function (see section 4.2.1 Global Configuration
Menu) a screen as shown in the attached figure will
appear. This screen shows the digital CHANNEL
POWER (40 dBµV in the example) together with its
related channel bandwidth (BW = 8.0 MHz) and the
Carrier/Noise ratio (C/N=17 dB). At the bottom of
the screen, as in the case of analogue channels, a
bar-graph represents the channel power, with a resolution of 1 dB.
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makes this measurement at the same frequency
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the
rotary
USER'S MANUAL.
PROMAX-10
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allows, like approach, to make
Figure 18.- CSO and CTB
measurement.
Figure 19.- Measuring a digital
channel.
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07/2011
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