Echo canselling on magneto exchange trunk line

[dsk]

The SB-22/PT  field telephone exchange with trunk line on Linksys PAP2T is callenge.  The trunk is extremely simple, a capacitor on one line to stop DC to the magneto lines, and a holding coil for "playing" off hook.

The line impedance is far from constant and some echo seems to be impossible to get rid of, but it has been much better with these 2  changes:



The rest of the setup to callcentric was just to follow the callcentric pages. 
And yes I may use the FO, F, I, and P buttons on the Autovon pad,  but only as short numbers in the dial plan. E.g.: FO= call wife :-)

Why the polarity setup?  My trunk has a LED depending on polarity, lights up on off hook, dark when party answers, lights up when party hangs up, so that is kinda ringoff signal.   Works on incomming calls too.

[dsk]

Now it works OK, still some echo, but I can use it :-)
https://www.classicrotaryphones.com/forum/index.php?topic=21824.msg269799#msg269799