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In
stereo installations, it is important that both left and right
audio inputs be in
phase.
This
is
ordinarily
assured
simply
by
connecting
the
red
and
black
wires
within all shielded cables symmetrically and consistently when wiring the two stereo
channels. If a phasing error occurs,
it will be
indicated in on- air
testing by the
stereo monitor's indicating more L- R than L+R level.
Accessory
Chassis
Output
Connections:
In
the
dual- chassis
configuration
of
OPTIMOD-TV,
the
output
of
the
Accessory
Chassis
presents
a 600
ohm
pure- resistive source impedance, balanced to ground, with a nominal output level of
+10dBm when loaded by 600 ohms. It is thus suited for driving a land- line directly,
or for driving the balanced input of a microwave STL transmitter.
If
you
wish
to
drive
an
unbalanced
input,
connect
such
an
input
between
the
Accessory Chassis "+"
output
and
circuit
ground.
Do not
ground
the "-"
output;
while
no damage will occur, it will short the output
of the "-" line amplifier to
ground through a 300 ohm resistor, unnecessarily stressing the opamp.
Main
Chassis Output Connections:
The
outputs
of
OPTIMOD-TV
are
balanced
to
ground from
an active
source.
They are designed to be
loaded by
an essentially
resistive load of 600 ohms + 10% to assure correct frequency and transient response.
Some
high- quality
transformers
are
suitable.
However,
most
transformers
will
degrade
the
pulse response of the system, and use of active input stages at the
aural exciter or stereo generator is advised, as discussed in Part 2 under Exciters.
(The output RFI suppression network was designed to have no overshoot or ringing
when properly terminated).
The
output
should be run in 100% foil- shielded cable ( like Belden 8451). See the
comments on grounding in Input Signal Connections above.
If bypassing the exciter's input transformer, preemphasis network, and any filtering
(as
recommended above
for
best peak level
control) requires that
the exciter be
driven
unbalanced, this driving signal should be taken between the (+) output and
circuit ground on the rear- panel barrier strip. Total load impedance should be 300
ohms, + 10%.
Usually,
the
exciter
presents
a reasonably
high
impedance
when
operated in this configuration, and the load must be provided by an external 300
ohm resistor ( not supplied).
IMPORTANT
Do
not
ground
the (-)
output
in
an
attempt
to
get
an
unbalanced
output;
you will short the output of the (-) amplifier to ground through
the RFI suppression filter. Just leave the (-) output floating.
If
the
exciter
modification
results
in
very
high
input
sensitivity,
then
the
input
may
have
a tendency
to
pick
up
noise
due
to RFI.
If
this
occurs,
operate
the
OPTIMOD-TV output at a higher level, and build an " L" pad at the exciter. This
"L" pad can be designed to have an input impedance of 300 ohms, correctly loading
the OPTIMOD-TV output.
Interfacing
A
Noise
Reduction
Encoder:
Instructions
for
interfacing
a noise
reduction encoder to OPTIMOD-TV are found in Appendix G.
The
details
of
alignment
are
dependent
upon
the
design
on
the
noise
reduction
encoder, and its manufacturer should be consulted.
3-7
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