USER’S MANUAL. PROMAX-10
Premium
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Figure 15.- Audio demodulation
and measurement.
4.2.3.1.2
Audio carrier measurement and demodulation
For the PROMAX-10
Premium
to
demodulate an audio signal and show its
characteristics (level and frequency
offset), press the rotary selector [9] again.
In the attached figure, the audio carrier level (AUDIO
Carrier) is 64 dBµV and the frequency offset is 5.50
MHz ( F). It also shows if the audio (whether Level,
FM or AM) is activated (a speaker appears) or not (no
icon appears). To change the audio carrier offset ( F)
and the audio modulation (Level, FM or AM) accede to the Channel-Frequency
configuration menu (section 4.2.3.3).
4.2.3.1.3
CSO-CTB distortion products measurement
The active devices present in the distribution systems, when working in its
nonlinear zone, generate interferent 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, see Channel-
Frequency mode configuration menu (section 4.2.3.3).
