Instruction manual

— —
15
(10X) circuit gain re-scales the measurements for these lower-level
signals. For these measurements, the 100% marking should be read as
10%, and 0dB as –20dB.
NORMAL SETUP PROCEDURE
This setup procedure presupposes a normal installation with the Model
708 PROGRAM LINE INPUT fed directly from the output of a properly
adjusted audio processor. As explained on Pages 3 and 4, the processing
system must maintain program peaks at a ceiling value corresponding to
100% modulation, and incorporate “pre-emphasis protection”
(independent high frequency) limiting in addition to broadband peak
control. This procedure further supposes 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, analog or digital, in either the input or the output path of the 708,
may call for considerations not addressed here.
At this point the 708 should be installed in the program chain with
power applied, and have all front-panel function switches ON.
Input Gain
Calibration
1. Double-check PC board jumpering options for proper line input
range selection and for proper pre-emphasis selection.
2. Feed the audio processor left channel input, only, with a 500Hz
sinewave test signal which yields 6dB to 10dB of indicated signal
limiting. This should drive the processor left channel line output to
its “ceiling” value and present the left channel input of the 708 with
a signal representing 100% modulation of that channel.
NOTE: Good engineering practice prescribes a standardized audio line
level at any equipment interface. This facilitates setup,
troubleshooting, and “patching” alternate gear in and out of the
program signal path. Take this opportunity to set the output level
of the processing system at a preferred “zero-dB” level: +6dBm,
+10dBm, or any other value common to station operation.
3. Set the bargraph meter to measure left channel (L) level. Adjust L
INPUT GAIN for a 0dB, or 100%, indication.
4. Repeat steps 1 -3 for the right program channel. Be sure that only
the right channel input of the processing system is driven.
Pilot and
Subcarrier
Adjustments
1. Set the bargraph meter to measure PILOT. Adjust the 19kHz stereo
pilot (PILOT INJ.) control for desired injection; typically 9%. Keep
in mind that the 100% point on the meter is actually 10% for this
measurement.
2. Cycle the meter to read any subcarriers applied to the 708. The
SUB 1 INJ. and SUB 2 INJ. controls may be adjusted for the desired
injection levels for subcarriers. Typically, RDS subcarriers are set
to about 5%, SCA subcarriers to 10%. Again, the 100% mark on the