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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
reason, that the PROMAX-8+ 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-8+ 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 PRESS TO MEASURE.
REMOVE CARRIER. 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.
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 of digital channels (DVB-
C / DVB-T / DAB).
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.
Page 24
INSTRUCTION MANUEL. PROMAX-8+
Figure 18.- CSO and CTB
measurement.
Figure 1.- Measuring a digital
channel.
May 2001
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