[Asterisk-Users] Huge Echo

[Adam Robins]

Does anyone know how to use ztmonitor to set gain on a PRI circuit via a
TE410P card, or is it just for FXO?

 

-----Original Message-----
From: asterisk-users-bounces at lists.digium.com
[mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of Marek
Zachara
Sent: Friday, September 09, 2005 2:55 PM
To: Asterisk Users Mailing List - Non-Commercial Discussion
Subject: Re: [Asterisk-Users] Huge Echo

>
> 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
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