[Asterisk-Users] Huge Echo

[Rich Adamson]

> On Friday 09 of September 2005 19:04, Mojo with Horan & Company, LLC wrote:
> > Did you try to get a milliWatt test phone number from your telco?  It
> > was really easy for me.  I called the business office and told them that
> Well, unfortunately not everyone has similiarly helpful telco providers ;)
> To just give you a hint, ten years ago here when you applied for a phone line 
> you would have to wait about 3-7 YEARS to actually have it installed. Its 
> improving now, but even now if the line is dead it takes them up to a few 
> days to repair it ;) try not to laugh :)
> I'm pretty sure if i'd call them to ask for a balancing line they would 
> probably assumed it an abuse ...
> Seriously however, even if i could get some reference signal, how can i tune 
> the card apart from changing the rx/tx gain? even with these two down to -6.0 
> dB i'm still getting awful lot of echo ... The card is a simple X100P clone.

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.

> The only piece i have not yet tampered with is the load the card places 
> towards the PSTN line. The card's input circuits are all SMD - no 
> old-fashioned (but good) separation with a transformer :(
> 
> 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.