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ISDN30 in the UK

I have the following

A NM-1CEU installed in a 3640 router and a BT ISDN 30 circuit, which is a balanced circuit (120ohm). At some sites this seems to work ok, but at other sites the controller will not come up. I'm I missing something here ie. do we need an NM-1CEB, if so I don't understand why it work's at some sites with the NM-1CEU card.

Thanks

1 REPLY
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Re: ISDN30 in the UK

Your right that an ISDN 30 is 120 Ohm Balanced in the UK so you should be using a NM-1CE1B, the NM-1CE1U is 75 Ohm Unbalanced.

This will usually work (as you have seen) but may fail for any number of reason such as distance, electrical interferance, type of NTU used by BT.

To guarantee it to work you should change the module to a Balanced one (some modules are also selectable via a strap, however I beleive the 3600/2600 NM-1CE1U/2U's are not).

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