[Asterisk-Users] Huge Echo

[Marek Zachara]

>
> Pull the clone card out of the system and look for the chipset numbers
> on the card. Go to the chip manufacturers web site and find the specs
> for that chip set. The specs will likely tell you the chipset was designed
> for the US 600 ohm impedance telephone network, and if your country's
> telco specs are different (which I'm very sure they are), through away
> the clone card. Without proper impedance matching there isn't anything
> your going to be do to fix the problem.

I can check the chip on monday, but local telco impedance requirements are 600 
ohms - just like US.

> >
> > I'm thinking about playing around with increasing/decreasing resistance
> > by placing additional resistors in the circut. Messy, but if it could
> > help... What do you think?
>
> Adding resistance has nothing at all to with impedance matching. Resistance
> will impact the DC loop, but not the AC impendance. The AC impedance is a
> function of how the chipset was designed.
>
AFAIR, the impedance is not a simple factor, but a combination of passive 
resistance plus reactance - which usually varies within measured frequency 
range. Therefore channging the device resistance WILL change its impedance. I 
know the result will not be perfect, but at least i hope for better load 
match than it is now. I assume the specified impedance is required within 
PSTN frequencies which will be roughly 100-4khz, right?

Marek