[Asterisk-Users] Echo - UK Impedance problem with X100P?

[Rich Adamson]

> I have an X100p interface (clone).  The system works fine but I get
> echo to a level where the system is all but unusable for IP  PSTN.  I
> seem to remember reading somewhere that the UK line impedance is 
> different from the default compile and needs changing.   I have
> Wikied etc, but found nothing yet.

The x100p (and presumably the clones) have an integrated circuit on the
board that was manufactured for use in the US with 600 ohm pstn lines.
The chip cannot be changed to any other impedance. However, there can
be many different sources for the echo and impedance matching is only
one of them. Others include:
 - incorrect * zapata.conf parameters
 - poorly engineered motherboards (eg, poor PCI bus, interrupt latency)

For zapata.conf, try something like:
echocancel=yes
echotraining=800

For poorly designed motherboards, there is no consolidated list of
which ones are good/bad so you're left with trying another one on your
own to see if it impacts the echo.

The TDM04B digium card (as an example) does not use that same pstn
chip, but rather another one from the same chip manufacturer. That
chip does have support for something like 18 different "country"
telco standards.