Instruction manual

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13
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 RDS or SCA
subcarriers. Green and red LEDs indicate the MODE
selection.
COMPOSITE
ADJUSTMENTS
The PILOT INJ. and SUB 1/SUB 2 INJ. controls set the
injection levels of the 19kHz stereo pilot and
externally-applied SCA or RDS subcarrier(s). The
OUTPUT LEVEL control varies the overall composite
output level delivered to the exciter or STL. OUTPUT
LEVEL is a “master” adjustment and does not affect
the relationships (level ratios) between the stereo
program, pilot and RDS/SCA subcarrier.
MPX EQUAL. is a composite (multiplex) equalization
trimmer in the output stage of the 708. This has been
factory-set for best stereo separation into a resistive
load, but can be used to compensate for frequency
response deficiencies in a composite STL or in the
input section of the exciter.
COMPOSITE
PROCESSING
In the fully-counterclockwise OUT position, an output
“safety” clipper acts on only those very fast program
peaks and overshoots which sneak by the earlier
protection circuitry. As the COMPOSITE
PROCESSING control is rotated clockwise, the level
applied to the safety clipper is increased by the dB
value indicated on the front panel. Composite clipping
will increase apparent loudness, but at the expense of
generating some spurious harmonic products. The
tabulation at the top of the next page is approximate;
please refer to the discussion about additional
implications of composite clipping on Page 17.