[asterisk-users] using E1 PRI lines

[Gareth Blades]

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