atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Telecom Service & Providers Impedance Mismatch

Let me know if this is possible?

I have been having issues with half-duplex for a while now. While talking on analog trunks if we talk on top of a customer the customer cuts in and out. So if my phone system's analog ports impedance is 600Ohms and the carrier has 800 Ohms on their lines, could this create a duplex issue?

If so is it possible to get the carrier to match my system or should I forget about the whole thing and look for a device to gain me the impedance match?

What device should I try, hopefully from experience. Someone has to have had this issue before.

What is the carrier using to drop to your location? Are they coming off to you from a channel bank or IAD? From copper?

Is this service delivered though an IXC, CLEC or ordered directly from the LEC?


ETA:
800 Ohms from the carrier? Really? I kept buggin’ me that 800, the more I thought about it… The only thing we ever use or typically have options for are: (remember I’m coming from the Telco side)

* 600 non-loaded cable pair, station sets and “most PBX.” (pretty much default.)
* 900 ohms loaded cable pair and 2-wire devices.
* 1200 ohms for 4-wire interfaces.

And what kind of phone system and have you contacted that manufacturer?

Well I found a good tech to come on site and he said the trunks were associated with digital path some how. Not sure what he said but he did mention digital and that he removed them and put them on a physical copper pair.
The issue seems to have went away.

Thank you for the update on the solution… I’m going to guess there was a pair gain device of some sort from the C.O. to your location then.

Just a thought on your original question of “can a impedance mismatch cause a half-duplex talk path.” ... “Technically no” that would not be a direct symptom, BUT... BUT... BUT... The typical symptoms of an impedance mismatch of noise (squealing, howling line) or excessive talk-back (aka side tone or echo) when coupled with noise cancelling circuitry, could squelch the talk-path. That sure would sound like half-duplex.

That’s why I, (and I’m sure John) were asking more questions, rather that just saying yes or no. (Sorry John, not trying to speak for ya here.)

No problem, Bryan. I was just thinking about the fact that some systems have the capability to connect to 900 ohm as well as 600 ohm. Still a mismatch, but probably 'closer' enough to clear the problem.
Does anybody know why 900 ohm is an option in some systems? Is that more common in some countries? John C.

900 ohm impedance should be used to face loaded cable pairs