Operating instructions

OPTIMOD-AM DIGITAL INSTALLATION
2-33
There are four analog outputs and you will be using two at most while
adjusting any given Transmission Preset. You may have to move the sync
connection between outputs if you need to set up Transmission Presets
for two transmitters.
C) Turn on the 9400's built-in square wave generator:
a) Navigate to S
ETUP > TEST.
b) Set the T
ONE MOD to 0%.
c) Set the M
ODE to SQUARE.
d) Set S
QR FREQ to 125 HZ.
D) Turn on the carrier.
E) Observe the RF envelope at the common point with a DC-coupled oscilloscope
and advance the T
ONE LVL control to produce 30% modulation.
F) Navigate to S
ETUP > MODIFY TX PRESET > TX1/DAY.
G) If necessary, press N
EXT until you see the screen containing the four L+R
transmitter equalizer controls.
H) Review the RF envelope display.
Many transmitters (particularly older designs) will produce an RF enve-
lope resembling Figure 2-9. If the oscilloscope display looks like this,
con-
tinue to step (I).
If the oscilloscope display
looks like Figure 2-10, no low frequency equali-
zation is necessary. Skip to step 13 on page 2-34.
I) Set the L+R
LF GN to 10.0 dB.
Setting the L+R LF GN control to maximum low-frequency boost ensures
response that is closest to true DC-coupling, optimizing square wave re-
sponse.
Depending on the transmitter, this large amount of boost at sub-audible
Figure 2-9: Unequalized RF envelope
(showing tilt)
Figure 2-10: RF envelope requiring
no tilt equalization