User's Manual

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Innovator CHV400BTD ATSC Transmitter System Set Up Procedure

Technical Manual, Rev. 0 70

Figure 20: (A3) IF Pre-Corrector Board (1308796)

Linearity Correction Adjustment (Non-Linear Distortions)

As shipped, the system was preset to include amplitude and phase pre-distortion. The

pre-distortion was adjusted to approximately compensate the corresponding

non-linear distortions of the Power Amplifier.

NOTE: Refer to Figure 20. On (A3) the IF Pre-Corrector Board (1308796), check that

the Quadrature Correction enable/disable jumper W7 on J14 and the In Phase

Correction enable/disable jumper W4 on J13 are in the Enable position, between pins 2

& 3.

Set up a spectrum analyzer with 30 kHz resolution bandwidth and 30 kHz video

bandwidth to monitor the intermodulation products of the RF output signal of the

Tray at J2. A typical 6 MHz digital spectrum is shown in Figure 16.

There are five Corrector stages, two in phase and three quadrature, with

adjustments located on the IF Pre-Corrector Board. Each stage consists of a

threshold and a magnitude stage. The adjustments are adjusted as needed to correct

for any amplitude or phase intermod problems. R109 and R110 are the in phase

threshold adjustments. R114 and R117 are the corresponding magnitudes. The

threshold adjustments control the point in the signal’s amplitude where the

correction increases the gain, and the magnitude controls how much the gain is

increased for each correction stage.

The quadrature adjustments provide predistortion for fixing Amplitude and Phase

Modulation distortion that occur in the amplifiers. R67, R126 and R69 are the

threshold adjustments, and R125, R129 and R128 are the corresponding

magnitudes. The above pots are adjusted for the greatest separation between the

digital signal and the intermod at the channel edges.

J13

R67 Quad

#1 Threshold

J14

R126 Quad

#2 Threshold

R24, R25 &R26

J4, J5 & J6

R69 Quad

#3 Threshold

R125 Quad

#1 Magnitude

R129 Quad

#2 Magnitude

R128 Quad

#3 Magnitude

R117 In Phase

#2 Magnitude

R110 In Phase

#2 Threshold

R109 In Phase

#1 Threshold

R114 In Phase

#1 Magnitude