Orban 8182A Operating Manual page 36

Mounting And
Grounding:
As
a
matter
of
good
engineering practice,
it is
desirable
that the
OPTIMOD-TV
chassis be properly connected
to a
good earth ground. Wire
is
totally ineffective
at
VHF
and
above; the best
way
to
ground
the
OPTIMOD-TV
chassis
is
to
mount
it
solidly
in a
well-grounded rack
(or
the transmitter
cabinet).
The
rack
or
cabinet must be connected
to
earth through
a
wide,
thin copper ground
strap.
To
assure
good
electrical contact
between
the
OPTIMOD-TV
chassis and
the rack,
it
may
be necessary
to scrape the paint
from
the rack and/or the
OPTIMOD-TV
mounting
flanges.
Measure
the resistance
between
the
OPTIMOD-TV
chassis
and
rack,
and
verify that
it is
less
than
0.5
ohm.
Input Signal Connections: These
instructions apply to the audio inputs
of single-
chassis
OPTIMOD-TV
's,
and
to the audio inputs
of
both Accessory and Main
Chassis'
in
dual-chassis
OPTIMOD-TV
's.
If
you
are operating
in
mono,
output
signal
connections
may
be
made
to the
left
or right
channels
since
OPTIMOD-TV
is
symmetrical. However,
use
of
the
left
channel
is
customary, and
later setup instructions are written assuming
that the
left
channel
is
used.
IMPORTANT
Regardless
of
whether
the left or right output
is
used, both
inputs
should
be
driven
in
parallel during
mono
operation, and both
INPUT
ATTEN
controls should be
set
approximately
equal.
If this
is
not done,
the range
of the
GATE THRESH
control
will
be approximately 6dB
higher than normal, compressor dynamic performance
will suffer
slightly,
and the Loudness
Controller threshold
will be
6dB
too
high,
making
the
Loudness
Controller
essentially useless.
It
may
be desirable to wire the unused output
to a
patch bay
or
even
to
a
remote-controlled
switching
facility
to
make
the
unused channel
available
in
case
of a failure of the
ordinarily-used channel,
and
to facilitate troubleshooting by the
"card
swap" method
described
in
Appendix
F.
In a
high
RF
field,
the audio input to
OPTIMOD-TV
must
be fully-balanced, and
should be run
in
100%
foil-shielded cable
like
Belden 8451. The
shield should be
connected
to earth (chassis) ground
at
both ends.
In
addition, you should
make
sure
that the telephone
line
termination box
or
STL
receiver
is
properly grounded
to
earth.
In
low-RF
environments,
the
shield
should be
grounded
at
one end
only
.
Audio
may
be run balanced
for long distances, or
unbalanced over
distances
of less than 20
feet (6m).
OPTIMOD-TV
should
be
operated with
its
integral
20dB
input
pad
for levels
between
-10 and
+10dBm,
and without the
pad
for levels
between -30 and -lOdBm.
Instructions
for
restrapping the
pads are found
above
in
Initialization
Options.
The
OPTIMOD-TV
input
is
balanced
bridging,
and
its
impedance
is
200K
with
the
20dB pad
defeated and
11.
2K
with the
20dB
pad operative
.
If
the source
requires
a
600
ohm
termination
(such as a
telephone
line),
connect
a
620
ohm +5%
1/4
watt
carbon film
resistor across
each
audio input.
Two
such
resistors
are provided
for
your convenience.
3-6