P S - 7 0 4 F O U R - C H A N N E L P O W E R S U P P L Y
2 - 6
CROSSTALK CONSIDERATIONS
When multiple channels are fed to remote stations, the amount of crosstalk
between channels is proportional 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
Ω
. This can be achieved as follows:
•
Keep cable runs under 500 ft. (152.5 m).
•
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.
If shielded multi-pair cables are used to connect multiple channels between the
PS-704 and remote stations, the cables should be wired to maximize the number
of ground connectors to minimize crosstalk. In the following cable wiring
diagram, note that it is not necessary to run redundant power connectors on each
channel to the remote station. The spare wires which would normally conduct
power are instead used to augment the drain wire ground connection.
Figure 2-5: PS-704 to 4-Channel Remote Station
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.
Typical system performance for a Clear-Com system is contingent on the use of
Clear-Com or Clear-Com approved compatible headsets. Use of headsets other
than these can induce crosstalk into a multi-channel system through the headset
cable. Clear-Com does not recommend the use of headset extension cables or
headset “Y” cables, as they will increase crosstalk into a multi-channel system.
2
3
1
PS-704
Power
Supply
A
B
C
D
2
3
1
2
3
1
2
3
1
2
3
1
4-Channel
Remote
Station
A
B
C
D
2
3
1
2
3
1
2
3
1
P ower
C h. A Audio
C h. D Audio
C h. B Audio
C h. C Audio
G nd*
G nd*
G nd*
* = S pare W ire used for G nd
Drain wire G nd
C h. D Audio
G nd*
C h. C Audio
C h. B Audio
G nd*
G nd*
C h. A Audio
P ower
Drain wire G nd
** = If the s hields from individual
pairs are brought out s eparately,
they mus t als o be connected to
P in 1.
S hield**
S hield**
S hield**
S hield**
S hield**
S hield**
