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

[Rich Adamson]

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.
> 
> On Oct 12, 2004, at 12:58 PM, Rich Adamson wrote:
> 
> > Impedance does not equal resistance. Apples and oranges.
> >
> > ------------------------
> >
> >> If you're certain it is an impedance problem and the impedance of your
> >> line is lower than that of the CO, you can increase the impedance of
> >> your line by putting a potentiometer in-line and adjusting it until 
> >> the
> >> sidetone disappears.  This is a bare-bones solution and decreases the
> >> efficiency of the line because you're putting in pure resistance.
> >>
> >> If your impedance is higher than the CO, or if you want to be more
> >> efficient, you'll need a more complicated impedance matching network.
> >>
> >> On Oct 12, 2004, at 10:26 AM, Kris Boutilier wrote:
> >>
> >>>  I have Asterisk connected to a channel bank via a t100p card. There
> >>> excessive sidetone generated on the analog side due to an impedance
> >>> mismatch
> >>> - I am very close to my serving CO which brings the line down to 
> >>> about
> >>> 150ohms and the channel bank is expecting 600ohms. However, the very
> >>> loud
> >>> sidetone is being fairly effectively supressed by the zap echo
> >>> canceller and
> >>> I have quite usable lines as a result.
> >>>
> >>>  From time to time calls are placed to other PSTN numbers (even
> >>> terminating
> >>> off of the same CO) that are introducing their own far end echo
> >>> component on
> >>> the line and it isn't being supressed at all - thus my outbound 
> >>> callers
> >>> begin to hear thei          rownvoiceandgetveryfrustrated.Ihaveto
> >>> assume the
> >>> second reflection couldn't be supressed by design - the zap echo can
> >>> has
> >>> already locked on to the sidetone echo after all.
> >>>
> >>>  So, I have a fix for the sidetone/impedance problem (PRI on order)
> >>> however
> >>> is it possible to insert another can into the system somehow? For
> >>> example,
> >>> if I were to run TDMoE to a second box and access to the 
> >>> t100p/channel
> >>> bank
> >>> through there?
> >>>
> >>> Any suggestions welcome (apart from curing the sidetone)  :-)
> >>>
> >>> Kris Boutilier
> >>> Information Systems Coordinator
> >>> Sunshine Coast Regional District
> >>>
> >>> _______________________________________________
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> >>
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> >
> >
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