Operating instructions

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 DC-
coupled oscilloscope and trim the T
ONE LVL control (if necessary) to produce
30% modulation.
D) Navigate to S
ETUP > MODIFY TX PRESET > TX1/DAY.
E) If necessary, press N
EXT 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 O
FF.
If no overshoot is observed, skip to step (H).
G) Adjust the L+R HF  and L+R HF 
controls to minimize ringing and over-
shoot.
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 am-
plitude of the ringing on the leading edge of the square wave while in-
troducing 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 ring-
ing 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