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

[Chad Scott]

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 their own voice and get very frustrated. I have to 
> 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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