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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 - 10dBm.
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
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