FXO Analog call audio getting mixed between lines

Bit of a weird issue haven’t been able to find others that have had the same issue.

We have a Sangoma A200 FXO FXS Analogue Card PCI Express installed in a Sangoma FreePBX Phone System 60.

Currently there are two FXO lines plugged into the card.

We have an issue where if both lines are being used the call audio is heard on both calls, in a sense the card seems to be mixing the call audio across two completely separate lines. I am not sure if this is a hardware or software fault however all signs seem to point towards it being the card rather than software config.

If i initiate a call on one extension using one of the FXO lines and answer it on my mobile, and then initiate another call on a completely different extension to a completely different mobile both parties on the first call can heard the dial tone and ringing of second call that i am making. The same thing will happen if two people dial into the PBX, they will both hear each others auto attendant and IVR.

I’d appreciate any suggestions on this as it seems to be quite an uncommon issue.


This is ALWAYS a wiring issue. Both ends are digital and generally isolated. The only place crosstalk can happen is in the wires

My only question here then would be why is this only happening on our new PBX machine? These lines used to lead into an old Grandstream box which managed them perfectly and there was never any cross talk. We are using the exact same phone lines, ports and cables so i cannot understand how the wires would suddenly become the issue. I even tried plugging them back into the old Grandstream box and they were fine.

Impedance differences. When I was a cabler we had mandatory maintenance when doing a move/change. Everything got inspected physically and with a cable tester. Depending on age you could see a 40% failure rate. This leads to angry customers and a potential loss of new customers that you get via word of mouth.

The point is your wires are bad somewhere. If you do a home run from the dmarc to your card you will likely see the issue clear up. It is possible to have an issue prior to the dmarc but it is unlikely and a whole different can of worms

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So just to confirm, you are saying its defiantly cabling? There is no chance it is software config or the analog phone card itself? Obviously i get what you are saying, I should just test the run from the telecom provider the card and go from there.


Are they handled by the same module?

If I understood you correctly it sounds like they are…

If you can swap the module for a known good one I would try it…

I had an FXS module (on a Sangoma A200) introduce noise on the phone line and the problem completely disappeared when it was swapped out…

It was not crosstalk in my case though, simply added noise…

Good luck and have a nice day!


Thanks for the Suggestion on that Nick. Yes they are being handled by the same module and we dont have a spare one to swap it out with although if checking the wiring as jfinstrom suggested leads me nowhere it looks like it would be best for us to order another just to confirm its not the module.