User's Manual

Innovator CU5-1800BTD/BRD ATSC Transmitter/ System Set Up Procedure
Regenerative Translator
Instruction Manual, Rev. 0 63
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 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.
There is also a frequency response correction network on the board consisting of
R24-R26 and C14-C16. This has been factory set. Any adjustment of these controls
will result in having to reload taps into the digital modulator (See the Linearity
Correction Adjustment (Linear Distortions) section below).
Linearity Correction Adjustment (Linear Distortions)
As shipped, the digital linear precorrector is preset in the factory for optimal system
performance of the system and output filter. This precorrection should not require
readjustment in the field.
However, in the event that field adjustment of the digital linear precorrection is
required, Axcera does offer an optional Precorrector Tap Converter (PTC) application.
This application allows the frequency response and group delay precorrection to be
adjusted using one of the following pieces of test equipment:
- Rohde & Schwarz EFA-53 Demodulator with the FIR Coefficient Readout option
- Tektronix VSA-5000 Vector Signal Analyzer
The PTC application allows tap settings to be downloaded from the test equipment to
a PC and then loaded into the Innovator CX through the serial interface. The
instructions included with the PTC application software provide the detailed setup
procedure.
If a problem occurred during the set up, help can be found by calling Axcera field
support at 1-724-873-8100.