[Asterisk-Users] tuning an x100p in Australia for echocancellation

[Rich Adamson]

> > milliwatt generator. (Obviously its not as good as using a CO
> milliwatt
> > as now you have to take into consideration the loss from the second
> > pstn line, but it is a way to get a handle on the transmission loss
> > values, etc.)
> 
> Would the txgain on the 2nd line also come into play? I guess if you set
> it to zero then you only have to deal with an estimation of the line
> losses.

Yes, but if you set everything to zero's and measure the end to end
loss and divide by two, you have a pretty good indication what the
loss is for one leg.

> On an au configuration example for the pap2 I have seen on the web, the
> impedence is set to '220+820||120nF', which suggests that our standard
> here isn't 600.

That would suggest any x100p-type card designed for the US standards
isn't likely to function properly, and particularily on longer pstn
loops. (Someone will likely say they have it working, but that person
is most likely on a short loop.)

> > that had two primary windings and two secondary windings. One could
> buy
> > them as 1:1.5 (600 ohm to 900 ohm), 1:1 (600 ohm to 600 ohm), and
> other
> > commonly used impedances. The transformer along with two 2.0 ufd
> > capacitors allowed DC to pass through, but changed the impedence from
> > one value to another.
> 
> I've thought of using a transformer by itself, but obviously that
> wouldn't let the DC signals required for looping through. Could you give
> me an ascii schematic?

tip -------------) (------------ tip
                 ) (
        a1 |-----) (-----|a2
          ---           ---
    2 ufd ---           --- 2ufd
           |             |
        b1 ------) (------b2
                 ) (
ring ------------) (------------ ring

Where "a1" is connected to "a2" and "b1" is connected to "b2" (for the
DC path). (In the US, telephony impedance is referred to as 600+2uf.)

If memory serves correctly, the old Western Electric part number was 
something like a 91C repeating coil. The windings and iron core on the 
transformer were also kind of special to ensure impedance uniformity
over the 200 to 3500 hz range.

Might google for "repeating coil" and "impendance compensator".