Optimod-AM 9400 V1.2 Operating Manual - Orban

OPTIMOD-AM DIGITAL INSTALLATION 2-35
B) Make sure that the oscilloscope is synchronized to the square wave.
C) Turn on the carrier. Observe the RF envelope at the common point with a DCcoupled
oscilloscope and trim the TONE LVL control (if necessary) to produce
30% modulation.
D) Navigate to SETUP > MODIFY TX PRESET > TX1/DAY.
E) If necessary, press NEXT until you see the screen containing the four L+R
transmitter equalizer controls.
To avoid overheating the transmitter, perform steps (C) through (G) quickly.
Adjustment of the high frequency transmitter equalizer controls cannot be done
into a dummy load because the transmitter will overshoot and ring differently
when loaded by the reactance of your antenna system.
F) Set the L+R HF and L+R HF FR controls to OFF.
If no overshoot is observed, skip to step (H).
G) Adjust the L+R HF and L+R HF controls to minimize ringing and overshoot.
The L+R HF DELAY and L+R HF FR controls interact. First, adjust the L+R
HF FR control until any ringing is reduced to the same level as the flat
part of the square wave (you will still have ringing, but no overshoot).
Then adjust the L+R HF DELAY control (which will further reduce the amplitude
of the ringing on the leading edge of the square wave while introducing
a new ring on the trailing edge) until the amplitude of the
ringing at the leading and trailing edges is equal. The peaks of the ringing
at both edges should approach the flattop modulation level as closely
as possible without exceeding it. Note that the L+R HF FR control does
most of the work.
Note also that the L+R HF DELAY control will produce little or no visible
effect until you set it beyond 40.
Adjusting the L+R HF DELAY control like this usually reduces the level of
the ringing to below the flattop modulation level. Reducing the setting
Figure 2-11: Unequalized RF envelope
(showing ringing)
Figure 2-12: RF envelope showing
successful HF equalization