Batboard

All,

A brief description of a mess I am trying to untangle and need some advice. 120 Steel monopole with two levels of various fiberglass antennas. Mostly UHF but two low band sticks operating at 100 watts. One on top and one 20' down from top.

There are two dragon wave microwave radios (two different links) radio back mounted on dish with two shielded cat5 cables running up the pole into the radios, connected to a managed cisco switch in the equipment rack. The dish/radios are mounted on the lower level.

I don't manage the microwave nor do I have access to its gui or switch gui.

When it rains out heavy the link will drop out for a few seconds once.

When the dispatcher would key any one of the low band radios (and only when it was raining heavy out) the link would drop out and the cisco switch would spaz out, reset and come back to life. You would watch the port lights go bezerko until the dispatch unkeyed.

The system operates normally during dry weather, problems only manifest when there is heavy rain. This includes the link drop out and the switch spazing out.

I moved all low band operation off the pole to spare antennas on the building far away from the pole, now when the low band TX's, the link doesn't drop out and switch no longer spazes.... But when it rains heavy the link will blink. However, the switch doesn't spaz out just the link craps the bed and comes back on line.

What am I missing here, what should I start to look at. I have nothing to do with the links, however the customer is at there wits end and wants the problems fixed. The other link vendor is kinda throwing his hands up.

Thy used outdoor shielded cat 5. I don't think any one side is grounded, or that they used shielded rj45 connectors. Do you have to ground the cat 5 on one end? which end?

Why is the low band RF getting into the switch, I would assume via the cat 5. How do I stop this, can I stop this?

Forgive me as we use indoor radios always, so I am not so familiar with the cat 5 up the pole act

Any help would be awesome, Thanks Rob

As a note, the link vendor has done radio swaps, re terminated his pole top cat 5 ends and swears nothing is wrong with his equipment.

The low band RF is probably getting into the pairs, but I can't explain why rain enhances the problem other than the rain is completing a circuit someplace on the tower. Use shielded CAT5 with shielded connectors, and attach the ground at both ends. Ground the injector. Ground the rack and router too. You may have to put a ferrite bead on the CAT5 at the indoor / power injector end of the cable. And they may have to change models of link radios to something not affected by the RF.

You didn't say where your located, so have no idea about the type of rain that causes the links to drop out with heavy rain. My guess is that they don't have enough fade margin to continue operating in heavy rain. There are 3 choices on resolving the fade problem. The first is larger dishes at both ends. The second is higher powered transmitters for the links. The third is to change the radios out to a different brand. It may take a combination of all three before the issue goes away. The fix is not simple or cheap.

While on the subject of link radios, you didn't mention what they are. Some time back, and I can't even remember what site the thread was on, there was a discussion about a link system going out due to rain. Problem there was there were connectors on the bottom of the radio chassis that were having problems with the gasket sealing the door to the boxes. It was allowing moisture to get into the boxes and corroding the connectors. This might not be the issue here, but it could be the source of the low band RF causing problems.

No matter who the vendor is that makes the link boxes, the link radios are part of the problem. Who ever is responsible for them will have to work with you on solving that part of the equation.

The next place I would look at is the site grounding. Is the mono pole correctly grounded with multiple ground wires exothermically welded to it? Is there a ground bar just above where the coax cables exit the pole and go to the equipment cabinets or equipment shelter where all the coax cables are grounded? Are all the coax cables properly weather sealed to keep moisture out at all the ground kit locations and the coax connectors? These grounding connections to the ground bar should have some sort of anti oxidant grease used to maintain a low resistance connection. You didn't say if you had access to the other antenna equipment, but the question is there about surge suppression being installed on each of the coax cables.

Low band can go forever, but it can also cause all sorts of problems with external equipment in close proximity. So now the question is about the Cisco switch installation. Is the switch grounded to the master ground bar that everything else is connected to? The rack it is mounted in needs to also be grounded to the master ground bar. Make sure the paint is removed at the point that all ground lugs are attached at. Yes, the CAT5 shields need to be grounded to the same point the Cisco switch is grounded to.

You can look into the CAT5 jacks on the Cisco switch and see if there is a metal side to them. If it has the ability to use grounded connectors, you will see the SHINE to the side of the jack. But I wouldn't count on that being a good RF ground.

RF interference is one of the hardest problems to track down. It is also the hardest problem to fix. It is going to take a major effort on several people's part to make it go away. You also might consider putting some ferrite cores around the CAT5 cables near where they connect to the Cisco switch. The ones you use will need to be effective in the frequency range of the low band transmitter. You probably will have to order the low band ferrite cores special, as they generally won't be stocked by any local parts store.

How is the power applied to the Cisco switch? If it is from a wall wart, is the cable coiled up in a long bundle or a small bundle? It may also need to have a ferrite core placed around the power cable just before it enters the switch. Then again, there might be a rare case of the low band transmitter getting into the wall wart and screwing up the DC voltage going to the switch.

I may be pushing you to look in the wrong direction to solve your problem. But it won't hurt to investigate the different areas that I have pointed out. Have been there a number of times and it's not easy to resolve your type of multiple problems.

One other point I didn't mention. Have you looked at the SWR on the antennas the low band transmitter is using? High SWR can cause problems that you will never solve in other equipment, no matter how hard you try.

It might be easier to tackle them one problem child at a time. Like on the Cisco switch. If there are multiple cables going into it, try disconnecting one cable at a time and keying the low band transmitter after each cable is pulled. See if one causes the switch to stay going after it was removed. Plug that cable back in and do another. If so, then you have narrowed down part of your search. It will cause a network glitch doing this, so pick a time of the day when it will not cause that much of a commotion.

Good luck solving the problems you have.

Jim

Good suggestions by Bill & Jim. The only other thing I can think to ask is what type of outdoor shielded CAT5 cable is being used? There are various types of varying quality & effectiveness. The one I've had no issues with is the copper clad steel armour type...almost like Heliax for networking cable:

https://www.winncom.com/vi/products/WB3176A

We've used that before. It's gel filled to prevent water ingress, and can be direct buried so you don't have to put it in conduit if your careful with your choice of backfill agg. ie: a sharp rock is still a sharp rock, and though it may not penetrate the cable, it will still smash the cr@p out of it. I could never find suitable crimps that would capture the corrugated copper shield. I had to cut that back, cover the cut with heat shrink, crimp to the inner cable, and apply a 1/4 superflex ground kit to the cable somewhere back towards the master ground bar. Not the easiest cable to work with, but never had a problem either.