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#572974 06/12/14 01:37 PM
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jsaad Offline OP
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I have a 200EL in a hotel. I have two trunks on different cards in different bays with a loud chatter noise on the trunks. This only occurs if you make a call from the mitel side. The trunks are good from the telco side.

I've replaced LS/GS cards and changed the pair and the 25 pair cables and added more ferrite cores. I've even put the cards in a different bay. Same problem

I believe there is some sort of interference from a fire alarm cable but I can't find it.

Do you have any recommendations?

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Remove the CO line from one of the trunk ports and take a know, good line from another trunk port and connect it on the trunk port in question. Make a call on that trunk. If the call has no "chatter" then the problem is not the Mitel trunk port.

What make you think there may be interference with a fire alarm cable?

Rcaman


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jsaad Offline OP
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The problem follows the line, not the mitel port. So somewhere there is some sort of interference that the Mitel picks up. This is an old multi building hotel, trunks come from two buildings away on a combination of old aerial cables. I've changed pairs where I can and there is still loud chattering noise only on the mitel side, though. Directly on the trunk with a butt set, no noise.

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I hear you saying that the trunks are all good at the demarc. You say that the problem follows the line, not the port, so I assume that you've isolated specific analog trunks that are making the chatter.

Since it does not follow the port, it is not in the Mitel. Since it's good at the demarc, it's not at the Telco. This is a building inside-wire issue.

A couple of things you can do to cut to the chase:

1. Run a new cable(s), preferably CAT 6, from the MPOE to the switch. Use this cable(s) for all affected trunks.
2. Busy out the affected trunks. The affected trunks will be in the outbound trunk group, in case you haven't completely isolated them yet (because you say that it happens with calls originating in the Mitel only).
3. Look for sources of radio interference.

Interference can be a tough issue. I had a call once on a office with crackling and hiss over their speakers, overhead and on the phones. I found a power cord going through the MDF loom. I separated the power cord, and suddenly music was coming through all the speakers -- they had background music turned on, and the power cord had been overriding it with hissing.

Best of luck.

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Here is where a good, old fashioned, line quality test tool comes to play. I have a Triplett Model 7, Dynatel 965TD and a Sidekick 7B. Each has a unique way of testing line quality and revealing hidden troubles. Even though it "sounds OK" in a butt set, any of these instruments will reveal if there is a real problem.

That said, you may have a grounding issue that is playing tag with the Mitel. I'm sure you have the Mitel grounded BUT is the cable ground feeding the Mitel with the CO pairs, grounded AND bonded? The Telco brought the pairs to a demarcation on a cable, most likely a PIC cable with a metal foil shield bonded to a ground. Is that bonded ground carried all the way to the Mitel? My guess is that it is not.

The solution may be as simple as replacing a section of cable that is missing that bond or as complicated as installing transformers and chokes to bleed off the offending imbalance. In the good old copper days, the telco fought the noise battle with load coils and other ingenious methods of filtering out imbalances. Today, especially with high cap circuits, load coils and other filtering transformers are taboo. But, for your situation, this may be the solution.

Rcaman


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Here's a tech bulletin by Sandman that might be helpful.

https://www.sandman.com/rfbull.html

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jsaad Offline OP
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Thanks. I have a plan to replace about 150Ft of cable. The lines come out of a channel bank 2 buildings away. I tried some old filters from Sandman from many years ago, no solution yet.


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