ATSC 25W TX Quick Start Guide
ACT-25-QSG-DOC-V1.2, 09/29/2014
Page 11 of 13
8.
Check the SNR and Shoulder (LIMD and UIMD) RF performance of your
system on the Exciter hi level status screen as shown below. Linear and Non-
Linear corrections were already performed and optimized at a TPO of 30W
(after the BPF) in the factory and so the stored correction coefficients should
produce good results.
If you are operating at a TPO less than 30W and wish to rerun corrections, please
proceed with the following steps, otherwise please skip ahead to step 12.
9.
(
Optional Step
- Rerunning Corrections) If you are operating at reduced power
and wish to rerun corrections to achieve better performance, you may now
perform Linear and Non-Linear corrections. (Please refer to the Exciter User
Manual for detailed instructions on running corrections). Before running
corrections, it is important to verify proper feedback signal levels. There are two
feedback signal samples used to compute corrections. “RF IN A” (After BPF)
is used to calculate Linear correction coefficients while “RF IN B” (Before BPF)
is used to compute the Non-Linear correction coefficients.
10.
(
Optional Step
) Navigate to the Exciter “DPD” submenu in the Advanced User
menu (simultaneously press Left and Right buttons, then simultaneously press
UP and Down buttons). Be sure the value of Feedback Sample Signal Input
(FSSI) for both A (after) and B (before) reads somewhere between 45% and 75%
- which roughly corresponds to a value of -15 to -5 dBm as measured on a power
meter (note: the FSSI indicator toggles between A and B and will “flash” when
the signal level is out of range, too high or too low). Add or remove the
appropriate attenuator padding to achieve feedback signal levels in the desired
range. Note the AFTER filter feedback sample is used to compute the SNR and
Shoulder Metrics displayed.
11.
(
Optional Step
) Navigate to the Exciter “SYSTEM” submenu and select
UPDATE under ADPC to run corrections. The exciter will then proceed through
4 stages of correction, computing Linear and Non-Linear corrections, and
automatically saving the coefficients into non-volatile memory upon
completion. The correction process typically takes from 8-10 minutes to
complete while real-time performance metrics of SNR and Shoulder
performance are displayed on the LCD.
