Orban 8182A Operating Manual page 30

preemphasis
network), far
more
accurate
results are obtained
if
the exciter's
input
transformer, preemphasis network,
and any bandwidth-limiting
filters are entirely
bypassed,
and
the
preemphasized
output
of
OPTIMOD-TV
is
introduced
as close to
the modulator
stage
as
practical.
Some
exciters
have
an auxiliary or "test" input
available for
this
purpose.
Instructions
on
how
to restrap the
OPTIMOD-TV
output
for
preemphasized
operation are provided
in
Part
3 (Installation) of this
Manual.
Additional Aural Subcarriers:
OPTIMOD-TV
operates
well
with
subcarriers because
OPTIMOD-TV
provides
excellent baseband spectrum
control, thus
protecting that
part of the baseband occupied by
the
subcarrier.
No
special
subcarrier precautions
need
be taken; the subcarrier should be
implemented
according to the instructions
of
the exciter
manufacturer.
Older
aural exciters may
not have
separate subcarrier
inputs.
In
most
cases,
one
can
be added simply by
passively
summing
into
the modulated
oscillator through
a
resistor and small capacitor.
Note, however,
that such
older exciters
often suffer
from
narrow
RF
bandwidths which
may
cause
subcarrier
"birdies"
due to
intermodulation.
Stereo:
All
OPTIMOD-TV
mainframes
are
fully
equipped
for stereo.
An
explanation
of the relationship
between OPTIMOD-TV,
the Orban 8182A/SG BTSC
Stereo
Generator, and
other vendors' stereo
generators
is
provided
in
Part
1
of
this
Manual.
It
is
important
to note that
OPTIMOD-TV
has
only
one
control
circuit
which
adjusts the gain
reduction of both stereo channels based on the higher
of the two.
It
is
therefore unsuited for dual-mono
operation (such
as bilingual programming).
[In
the
BTSC
system used
in
the
United
States, bilingual
programming,
if
any,
is
provided
on
the
Separate Audio Program
(SAP)
subcarrier.
Orban manufactures
a
SAP
subcarrier generator with integrated
audio processing (Model
8182A/SAP)
to
provide
this subcarrier.]