Installation manual

When multiple channels are fed to Remote Stations, the amount of crosstalk between channels is pro-
portional to the DC resistance of the ground return path back to the channel terminations. To minimize
this crosstalk between channels when running more than one channel in a multi-pair cable, keep the
DC resistance of the ground return as low as possible. Ideally, this should be less than 2 Ohms. This
can be achieved as follows:
Keep cable runs under 500 feet. If a longer cable run is unavoidable and approaches 1000 feet or
more, make sure the appropriate lone line option switches or jumpers are set in the stations. Refer
to the individual station manuals for further information.
Use a cable whose common shield has a low DC resistance.
Connect unused cable wires of a multi-pair cable to the Pin 1 shield.
NOTE: All multi-pair cables must have individually shielded pairs.
Clear-Com recommends the Belden 1800 Series of multi-pair cables. They offer a common shield with
a low DC resistance in addition to individual shields on each pair.
The performance of a Clear-Com system depends upon the use of Clear-Com or Clear-Com approved
compatible headsets. Use of headsets other than these can induce crosstalk into a multi-channel sys-
tem through the headset cable. Clear-Com also recommends against the use of headset extension ca-
bles or headset "Y" cables, as they will increase crosstalk into a multi-channel system.
Intercom Cable Considerations
The Clear-Com intercom line is intended to run on one shielded cable pair per intercom channel. One
conductor carries audio, and the other conductor carries the DC power for Remote Stations. The shield
serves as the ground return for the audio and power conductors. When choosing interconnect cable,
keep the following considerations in mind:
Keep cable runs under 500 feet. The DC resistance of the ground or common conductor affects
crosstalk. For permanent installation runs longer than 500 feet, do not use wire smaller than 20
gauge. The capacitance of the interconnect cable affects system frequency response and sidetone
stability. Total capacitance should not be greater than 0.25 uF.
Ground Isolation:
The Pin 1 ground connection of each XLR connector must be isolated from the
chassis. Pin 1 should not be connected to the shell of the XLR connector.
Multi-pair Cable: Individually shielded multi-pair cable is acceptable for use in multi-channel sys-
tems. For crosstalk considerations the shields must be tied together on both ends of the cable to
produce the lowest possible DC resistance path for the ground return.
Suggested Cable Types:
The following chart lists the specifications of various BELDEN cables:
BELDEN SHIELDED CABLES
Trade
#
# of
Pairs
AWG &
Stranding
Nom. O.D.
(inch)
Nom. Cap.
(pF/ft)
Shield
Nom. D.C.R.
(Ohms)
Max.* Cable
Run (ft)
Recommended
Application
8412 1 20 (26x34) 0.268 30 5000 Portable
8762 1 20 (7x28) 0.196 27 5000 Permanent (short)
8760 1 18 (16x30) 0.222 24 5000 Permanent (long)
1814A 2 22 (7x30) 0.319 31
3.9
Ω
/M'
1500 Permanent
1815A 4 22 (7x30) 0.384 31
3.9
Ω
/M'
1500 Permanent
1817A 8 22 (7x30) 0.503 31
3.6
Ω
/M'
1500 Permanent
1818A 12 22 (7x30) 0.889 31
3.4
Ω
/M'
1500 Permanent
* for better than 50 dB channel crosstalk
Clear-Com System Installation Manual
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