[Asterisk-Users] Chaining more than one zap echo canceller?

[Kris Boutilier]

To be clear then, my subscriber loop may have a DC resistance of 150ohms due
to the physical loop length but should have an AC impedance of 600ohm (+/- a
few)? I have to assume that as the telco cable guy was performing the test
he's telling me the AC impedance.

If so, then would I need to insert some sort of complex impedance network to
build out a match rather than just a single resistor?

> -----Original Message-----
> From: Rich Adamson [mailto:radamson at routers.com]
> Sent: October 12, 2004 2:58 PM
> To: Asterisk Users Mailing List - Non-Commercial Discussion
> Subject: Re: [Asterisk-Users] Chaining more than one zap echo 
> canceller?
> 
> 
> Adding resistance to one side of the line only begs for problems
> as it creates a tip-ring imbalance that will "cause" echo, etc,
> when other imperfections exist.
> 
> If that approach works at all for anyone, its addressing a symptom
> and not the root cause.
> 
> Try this one: Each customer loop is made up of copper and the longer 
> the copper, the more resistance. Yet the impedance (in the US) is
> consistently 600 ohms. A short loop might be a 100 ohms while a long
> loop might be well over 1500 ohms; still both are 600 ohm impedance.
> 
> ------------------------
> 
> > Impedance is the measure of total opposition (resistance, 
> capacitance, 
> > and inductance) to alternating current flow.  Adding 
> resistance will 
> > raise the impedance of the line.
> > 
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