Specifications

SYSTEM INTERCONNECTION,
CONTINUED
Portable Interconnection
Methods
Portable
Remote
Stations each
have a
pair of input
and output
connec-
tors which are wired
in parallel, allowing
you to set
up a "daisy-
chain"
when instal lating
the system. A diagram
in this section
illu-
strates
the daisy-chain method.
As an alternative,
Clear-Com's
Model
QP-100 "Quadropuss
Line-Splitter" is
a small interconnect
device that
accepts one
cable input and provides
three outputs.
Both the daisy-
chain
and line-splitting
methods lessen the
cable needed and simplify
the installation
process.
PERMANENT INSTALLATION
CABLE
To install wall-mount
and custom-mount
remote stations,
we recommend
you
use vinyl-insulated
and
jacketed cable;
it costs
less and
is
easier to pull
through conduit than
the rubber-insulated
cable. Use
low
capacitance cable.
We suggest you
try:
BELDEN
8762 (20 gauge, stranded)
for applications
up to 500 feet,
and
BELDEN 8760 (18
gauge, stranded) for up
to 5000 feet.*
If
conduit is avai lable
when installing permanent
Remote Stations,
run
interconnect
cable through
the conduits to
each wall-mounted
unit.
NOTE: "Signal
ground" (Pin
I on intercom connectors)
and "chassis
ground"
are NOT the same
point. Do NOT connect
Pin I and the
chassis
together. The
chassis is insulated
from the signal
ground with a
capacitor (.01 microfarad,
1.4kv). This
eliminates the hum
and poten-
tial
shock hazards that
can arise if stations
are at a different
ground
potential.
In
installations where
conduit is NOT used,
and equipment doesn't
share
a common
ground, it is
good engineering
practice to run an
additional
ground wire to
tie all chasses together
(this decreases
susceptibility
to
electrical noise fields).
*If you choose
not to use Belden
cable, use an equivalent
type with
similar
wire gauge
and capacitance.
Cable, especially
in
longer runs,
should have low DC
resistance (less than
15 ohms per 1000
feet; large
diameter
conductors)
and low interconductor
capacitance (less
than or
equal to
50 pF per foot of cable:
capacitance between
conductor and shield).
Multi-Channel
Cable Considerations
When installing
a system that
includes two-channel
(or more) stations,
each channel
may be routed individually
to the
remote station with
separate
mic
cables, OR
two channels
may be routed
together
with two-
pair,
individually-shielded
cable
(Belden 8723).
Crosstalk
When multiple
channels are fed
to remote stations,
the amount of cross-
talk
is proportional
to the amount of
DC resistance in the
ground
return. Two ohms
of resistance or less
is ideal; 2 ohms
will give you
40
dB of isolation. Anything
greater than
2 ohms will increase
cross-
talk. Each channel
must be fed
in its own separate
shield. Tie any
unused wires
in the interconnect
cable to ground
(Pin 1), thereby
further
improving the
crosstalk.
6