Inteference with cabling going up the tower

Does anyone have any suggestions for this:

We have three cables going up this tower, one fiber cable going to the top where our CMM is and two ethernet cables going about 200-250 feet up for two backhauls. We have to have all three cables at 10baseT-half duplex so that they will work without losing lots and lots of packets. There is an FM antenna on the tower above the backhauls. Is it possible that the tower is improperly grounded and putting out voltage? If so how do we go about diagnosing this and is there anything we can do?
Our ethernet cable has a voltage on it accoring do our cable line tester.
The ground cable also has voltage on it, what’s normal for a ground cable?

These cables have voltage with reference to what? What is there a potential from the ground cable to?


I have this problem on any site with close proximity to FM transmitters. Close is relative, at 100watts, the FM station is “close” within a few feet of the canopy gear, at 50,000 watts EIRP the FM station is “close” within 500 feet.

I’ve never seen voltage on the lines with a tester, but moving to 10Mbps solves the problem. It makes perfect sense that lowering the modulation rate on the ethernet line makes the signal work better. Isn’t that why Canopy works so well in crowded RF environments?

Anyways, you should be using 10Mbps FDX. You’ll have to force both sides to FDX, but that way you are more likely to be able to totally max out a 14Mbps Advantage AP.

The cable meter is reading the 8 individual cables and the potential is between them and the shield(ground)on the cable itself.

Only one of our sites has an FM transmitter collocated on it so this is the only experience I have. This is a 1 kW transmitter, unity gain antenna - our cabling runs past the antenna, within a few feet of it. I have no issues here.

The basic premise behind cable shielding is to induce the same voltage as is by the data pairs. When the shield conducter is grounded at both ends, current will flow in it in the same direction as in the data pairs. Due to the close proximity, there will be coupling between the shield and data pairs which results in a secondary induction from the shield back to the data pairs. This causes current to flow in the opposite direction to that induced from the FM transmitter.

From this, you should expect to see some voltage potential, but proper grounding of the shielding should drastically reduce the effects. Then, as you have done, change the modulation and data transfer rates to combat any residual data loss.