ARRL

K2EIR

Joined: Sat, Apr 4th 1998, 00:00 Roles: N/A Moderates: N/A

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Topic Author Posted On
Common-Mode Interference from Cable System W1MG on 25/8/13
I saw substantially the same info from N0IVN when I searched the internet today looking for info about a difficult RFI situation I and a friend are experiencing. We essentially have white noise from at least 80 meters through 10 meters at the S8 to S9 or more level.

This seems to be most associated with the cable system. Taking a receiver with a short antenna attached, the noise is intense next to the outside of the cable. In my case it is also strong around the A/C and furnace ducting which the cable is likely to run over,or, by, in the attic.

I have not been able to null the noise with a noise canceller. Going away from the building by 25 feet or so and the noise drops off to a negligible amount.

So how do we determine if this is common-mode or not? And, if it is, and the cable system is not responsible for it, how then can we find and fix it?

I have had this same symptom at a rental apartment where I used to live and solved it there by passing coax out of the building, burying it a half inch in the ground while running the coax to a tree about 30 feet away and running a vertical wire up the tree. But I am now in a condo and am not allowed to have a wire or cable egress from inside.

Another ham friend had the same symptom and when I moved a ham stick on coax out from his deck to a tree about 30 feet away, he also reported that the S meter rapidly decreased. My friend, and my rental apartment and my condo are all in the same town and separated by about 2,000 feet one from the other.

At the rental apartment the noise disappeared when power lines failed and there was no power except that I powered my rig with batteries. Also the rental apartment did not have Verizon FIOS (fiber optic) service which the other locations do.

Turning off all circuit breakers in my own condo apartment and defeating all UPS units has no effect on the noise.

73,
Howie, K2EIR

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