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New Member

FXS interference

I have a 3725 router with an NM-HDA card in it. The installation was done about a month ago and worked fine. I have on pair of wires for an FXS port coming off the router to a boegn paging system. All of a sudden last week it stopped working. I am picking up a local AM station on all 4 pairs of the FXS wires. The only thing that I can figure is that the building is acting like a giant antenna. I have the router grounded but Im not sure how solid the ground is. THere is a transmitting station for the radio about 5-7 miles form the site. Has anyone ever had this happen or have any ideas on how to stop it? Even if I shut the ports down I still get the noise. This happens with a butt set connected directly to the wires of the amphenol cable.


Re: FXS interference

You hear the interference on the IP phone calls to the paging system or is coming across the paging system all the time ?

Unplug the paging system and anything else on the NM-HDA card and put a telephone handset on to the FXS ports and test with just this device plugged in. Any difference ?

If this is OK the problem could be an earth has somehow been connected to the PA system and this is injecting the noise. Take appropriate steps to fix this.

If you still get the noise with just a singlrhandset plugged into the FXS port then recheck the cable - pinouts should be :



1 & 26 - port 1

2 & 27 - port 2

3 & 28 - port 3

4 & 29 - port 4

let us know what happens

New Member

Re: FXS interference

After more testing I found out the noise was coming from the Verizon pots lines. After talking to one of our wiring contractors I found out that it is a common occurance in that area. He said Verizon can put filters on the lines to get rid of the interference.

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