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Telecommunications Tech Blog May 2014

Odd Problems with Data Noise on IP Office Systems (and others)...
   Both Noise you Can Hear and Noise you Can't Hear!


By Mike Sandman  •  mike@sandman.com

I've been hearing about a lot of odd problems occurring on Avaya's IP Office systems connected to fake phone lines from cable companies and VoIP stuff, and even sometimes on real copper POTS lines.

The symptoms seem to be different at different premises. It probably depends on the brand / model of the box the cable or VoIP company put in? Or how the phone company delivers the copper POTS lines (the data noise may be induced from other pairs in the cable)?

The bottom line seems to be that the cable company and VoIP boxes that try to make POTS lines tend to put out a lot of data noise above voice frequencies. The engineers who designed these boxes didn't think the data noise would make any difference on a phone or phone system Trunk / CO line so they didn't think about it. But you get to fix the problem they created.

This noise causes really strange things to happen on some phone systems - both odd operation that effects the processors in the system, and noise that you can hear (probably a harmonic of the data noise?).

You probably can't hear this data noise on a butt-set since the noise is common mode (the same on the tip and ring), and your butt-set has no reference to ground like a phone system does through AC power.

KSU-less phone systems are almost universally effected by this noise because it's right at the same frequency the KSU-less manufacturers use to communicate between their phones, usually above the voice frequency on Line 1 only.

So far, our Data Noise Filters seem to be solving the problems if they're placed in-front of the phone system - either at the cable box (which is the right place for a KSU-less system) or at the KSU / PBX.

We make RJ-11 and RJ-14 (2 line modular) versions of the Data Noise Filter, and a 1 Pair Hard-Wire version.


If you have modular jacks on the cable or VoIP box, or on the phone system, it will be easy to just plug in the Data Noise Filter on the line(s) from the cable or VoIP box to see if it helps. If it doesn't fix your particular problem you can take it out and try it on the next job.

On a KSU-less system you probably only need the filter on the first line... BUT you must put it at the cable or VoIP box - not between the phones! If you put it in-front of a phone it will block the data sent between the phones, and you won't have lights, hold, intercom or other features.

We can make an RJ-45 version, but you can't use that by putting one in-front of each KSU-less phone, so there's probably no need for it.

It's a good idea to keep one in your truck. There's no way to know if it will fix a particular symptom without trying it! On an IP office, you might want to disconnect the lines without the Filter, since just putting it on one line wouldn't prevent the data noise on the other lines from screwing up the system. If it fixes the problems on the one line, you can get more to fix the whole system.

To read more on data noise problems, and to see where to place the Filters on KSU-less systems, see our Data Noise Elimination Tech Bulletin:


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