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15
the
AUDIO PROCESSING
switch in the
IN
position
unless outboard provision is made for pre-emphasis
and limiting. Without external pre-limiting, program
material will be driven hard into the clipping circuits
and result in egregious distortion..
PILOT
The
PILOT
switch lets the user manually turn off the
19kHz stereo pilot for certain tests. Since the 19kHz
pilot is necessary for proper system operation, the
switch should always be left
ON
. The green LED
indicates normal operation, the red LED lights
whenever the pilot has been turned off.
MODE
Under some circumstances it may be advisable to
broadcast monaurally. For example, should the
station suddenly suffer an emergency power loss,
temporarily reverting to mono transmission would
help regain some of the lost coverage until full power is
restored.
When switched to
MONO
, the
MODE
switch removes
both the stereo subcarrier and the 19kHz pilot. The
transmitted signal will consist of L+R, the algebraic
sum of the left and right program channels. The
MODE
switch does
not
remove an RDS or an SCA
subcarrier.
POWER
‘Nuf said.
NORMAL SETUP PROCEDURE
This setup procedure presupposes a normal installation with the
DAVID-II
PROGRAM LINE INPUT
fed
directly
from the output of the
audio console and a
direct
connection of the
COMPOSITE OUTPUT
to the
wideband input of an exciter/transmitter. Variations from these
conditions, such as an intermediate STL (or other link) in either the
input or the output path of the
DAVID-II
, may call for considerations
not addressed here.
At this point the
DAVID-II
should be installed in the program chain
with power applied, and have all front-panel function switches
ON
.
AVERAGE COMPRESSION
should be set at
6dB
and
COMPOSITE
PROCESSING
turned
OUT
.
Input Gain
Calibration
Left (
L
) and right (
R
)
INPUT GAIN
controls are set individually to
center the AGC operating range at the nominal “Zero-VU” program
line input level. If the following procedure shows control range to be
outside adjustment limits, recheck circuit board jumpering for Line
Input Range Selection as described on Page 8.
