On 30/07/13 05:35, Duncan Turnbull wrote:
E1 PSTN line interfaces are either unbalanced 75 ohm( and used to use
BNC connectors ) or a 120 ohm balanced twisted pair.
The other standard is T1 and digium cards can let you choose between
T1 & E1 and definitely do 120 ohm
Telco's will usually provide 120ohm twisted pair interfaces as it
travels further and has less interference from noise.
120ohm is the standard for E1 RJ45 while T1 normally has a 100ohm
impedance. The E1/T1 jumper on the Digium cards is actually changing the
impedance.
BNC is 75ohm and if your telco provides these you need a balun panel to
convert the impedance and the wiring to RJ45. e.g
http://www.tekmos.co.uk/baluns/panel/rj45/rj45-balun-panel-16e1-coax-front-mount.shtml
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