User's Manual

Innovator CU250ATD, 250 Watt Transmitter System Alignment
Instruction Manual, Rev. 0 22
6 MHz
-35 dB
-110 dB
3 MHz
6 MHz
Figure 3: Typical Digital Spectrum
Linearity Correction Adjustment (Non-Linear Distortions)
As shipped, the transmitter 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: On (A3) the IF pre-corrector board (1308796), check that the correction
enable/disable jumper W4 on J8 is 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 digital spectrum is shown in Figure 3.
There are three Corrector stages, two in phase and one quadrature, adjustments located
on the IF Pre-Corrector Board. The adjustments are threshold settings that are adjusted
as needed to correct for any amplitude or phase intermod problems. Adjust in phase
linearity correction adjustment R67 threshold 1 cut in for the in phase amplitude
distortion pre-correction that is needed. Next adjust the linearity correction adjustment
R69 threshold 2 cut in also for the in phase amplitude distortion pre-correction that is
needed. Finally, adjust the quadrature linearity correction adjustment R89, threshold
cut in, for the quadrature phase distortion pre-correction that is needed. The above pots
are adjusted for the greatest separation between the digital signal and the intermod at
the channel edges.
Frequency Response Delay Equalization Adjustment at 44 MHz
The procedure for performing a frequency response delay equalization adjustment for the
transmitter is described in the following steps. Check that the jumpers on J4, J5 & J6 are
set for 44 MHz between Pins 2 & 3.
The center frequency for the first stage is 46.5 MHz. Adjust R24, located on the IF Pre-
Corrector Board, for the best depth of frequency response correction at 46.5 MHz. C14
may need to be adjusted to attain best depth at 46.5 MHz.