Precorrection; Functions Of Nonlinear Precorrector; General; Linear Basic Precorrection - R&S N 8000 Series System Manual

4

Precorrection

This section describes the non-linear precorrection sequence in manual mode.
4.1

Functions of Nonlinear Precorrector

4.1.1

General

In the basic version, the graphical user interface of the non-linear precorrector for DTV and
video signals consists of the Nonlinear control panel and the FreqCorrection control pan-
el. In the case of ATV split, two further control panels are provided: Dynamic Control for
the video precorrector and Nonlinear Audio for the audio signal. In combined mode an au-
dio phase precorrector is also provided for audio.
4.1.2

Linear Basic Precorrection

The basic functions of the non-linear precorrector can be accessed via the Nonlinear and
Nonlinear Audio control panels. Additional functions can be performed in the other control
panels.
Every non-linear precorrector consists of an amplitude precorrector and a phase precorrec-
tor, each independently affecting the phase distortion and amplitude distortion of the same
signal. The setting of the characteristic is displayed in a graphic in which the X axis repre-
sents the instantaneous signal amplitude. The figures 0% and 100% stand for no signal am-
plitude and maximum amplitude respectively. The Y axis represent the effect and is scaled
to ±50 % for amplitude precorrection and ±45° for phase precorrection. 50% means that at
100% amplitude the level is increased by 3 dB.
Every precorrector has a series of frequency reference points which are used to model the
characteristic. Frequency reference points can be user-defined, shifted in the X and Y di-
rections, be given a fixed or free slope and be deleted. In the X direction a frequency refer-
ence point can only be shifted between the two adjacent reference points. The connections
between frequency reference points are computed by means of spline functions.
Every characteristic consists of at least two points, one of which must be at 0% and the oth-
er at 100%.
In the case of amplitude precorrection the first point is at [0%, 0%] and cannot be shifted.
The second point is at 100% and can be shifted without restriction in the Y direction. A rising
or falling straight line between the two points represents only an amplification or attenuation
of the signal and does not create non-linear products.
In the case of phase precorrection the first point is at 0% and the second point is at 100%.
Both points can be shifted without restriction in the Y direction. A straight line parallel to the
amplitude axis creates only a signal phase shift and does not create non-linear products.
2098.0188.72
Chapter 4
- 4.31 -
Commissioning
E-1