[asterisk-users] SPA3k wired to PAP2 for echo testing

[James Harper]

> On 05/11/06, James Harper <james.harper at bendigoit.com.au> wrote:
> > Even in this configuration, with my impedance settings set to the
> > Australian standard of 220+820||120nf, and the PSTN and PAP2 echo
> > cancellers enabled (or not, and all combinations of) I get local
echo as
> > soon as I pick up the handset (I hear my voice bounced back to me).
> > Surely this shouldn't be??? There is no hybrid involved at all!
> 
> 'course there is. The telephone interface on the one end and the line
> interface on the other are both 2 wire.

Ah. I was referring to the hybrid as the 2 wire to 4 wire interface at
the telco. I have enlightened myself now :)

> Did you have a phone line connected to the "other side". Running into
> an unconnected FXO port is likely to make echo because of the
> unbalanced impedance.

The FXO (PSTN) interface on the SPA3000 is connected to the PAP2, which
provides dialtone instead of the Telco providing it. I tried this to
take the Telco out of the equation, but it didn't solve anything. I'm
thinking there might be something wrong with my SPA3000, as with the
settings I have used the impedance should be matched perfectly and there
should be no echo.

One strange thing happened once though (before this testing). I picked
up the handset connected to the Line1 interface, which patched me
straight through to the PSTN interface (dialplan = '(<:@gw0>S0)'), which
was connected to the telco. I pressed '1' which stopped the Telco
dialtone while it waited for more numbers, and there was no echo at all.
It's never happened again, but the fact that it happened once gives me
hope that the echo problem might be solvable.

On the SPA3000 there is 'Echo Cancel', 'Adaptive Echo Cancel', and 'Echo
Suppression'. Enabling 'Echo Cancel' doesn't seem to do anything.
Enabling 'Adaptive Echo Cancel' causes a huge reduction in call quality
and actually makes the echo worse. 'Echo Suppression' isn't really a
solution.

One question though... if everything is balanced properly, should I even
need echo cancellation?

I'll keep testing...

Thanks

James