Operating instructions

OPTIMOD-AM DIGITAL INSTALLATION
2-21
Turn the knob to set the Digital OUTPUT SAMPLE RATE to 32, 44.1, 48, 88.2,
or 96 kHz.
This control sets the sample rate of Digital Output #1, which is the output
most likely to be used to drive your transmitter.
The internal sample rate converter sets the rate at the 9400’s digital out-
puts. This adjustment allows you to set the output sample rate to ensure
compatibility with equipment requiring a fixed sample rate. In all cases,
the 9400’s sample rate is 32 kHz and multiples thereof up to 256 kHz.
12. Prepare to set output levels.
A) Press the N
EXT button.
The positive peak threshold for all outputs is now set to 100%.
You can set asymmetry as desired after you have completed Quick Setup.
The P
OSPEAKTHR control in the active transmission preset determines
asymmetry. (For Quick Setup, the active transmission preset is TX1/D
AY.)
You can use either program material or tone to set the output level (and
thus, the on-air modulation).
 To use tone, press the Y
ES button.
 To use program material, press the N
O button.
We recommend using program material because it automatically takes
into account any bounce, overshoot, and ringing in the transmission
plant. A tone setup can cause overmodulation with program material
unless the modulation control in your facility is “textbook perfect.”
13. Set the digital output level.
A) Press the N
EXT button.
B) [Skip this step if you are not using the digital output.]
This Quick Setup procedure causes you to adjust Digital Output #1 and
automatically sets its source to AM
PROC. If you are also using Digital
Output #2 (to drive a second transmitter, for example), you can adjust it
after you complete Quick Setup.
Turn the knob to set the desired digital output level corresponding to
100% modulation, in units of dB below full-scale.
If you plan to modulate asymmetrically, you must leave headroom for
the positive peaks. For example, you must set the DO
100% control lower
than –2.0 dBfs to support 125% modulation.
The most accurate way to set this control is by observing a modulation
monitor or oscilloscope connected to your transmitter’s common point.
An oscilloscope is the most reliable method because it will unambigu-
ously show negative carrier pinch-off, whereas some monitors have over-
shoot that can cause them to under-indicate peak modulation.