SLR5700 VHF and lightning

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SLR5700 VHF and lightning

Post by arlojanis »

I have a VHF SLR5700 that is 4 months old and receiver went very, very deaf during the first storm. There are no burn marks anywhere. Is this normal? I have several SLR5700 UHF repeaters and no problems with surges or lightning crashes. The VHF unit has a mobile type duplexer, DB222, and a 30 foot tower on flat land. It replaced a R1225 that never had a receive problem.
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Re: SLR5700 VHF and lightning

Post by com501 »

Check any jumpers or flexes inside the unit for scorching/continuity. They sometimes appear normal but on testing -are not-.
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Re: SLR5700 VHF and lightning

Post by Jim202 »

You may want to look at your grounding system and surge protection. The Motorola R56 Grounding Standard has some very good information.

BUT, there is some information missing that I have found out the hard way at 2 different homes over the years. The low ground resistance of your ground rods is where your protection comes from. The resistance is dependent on the ground rod having a low resistance to the soil. Over time, this low resistance can change due to the corrosion between the ground and the soil.

My first home I had in Covington took lightning surge damage. Blew out electronics all around the house. What blew my mind is that I had electrical surge protectors on each device that was damaged. Thought about it for a while and then it came to me. The surge protectors all used the house Neutral wiring as the ground system.

As I worked for a cellular company at the time, I brought home the ground resistance tester I used all the time as we built new cell tower sites. I killed the main breaker on the house, lifted the electric meter ground wire and did a 3 point ground resistance test of the house ground rod. I about fell over when it tested at over 600 Ohms.

I headed to town and got 2, 8 foot ground rods to meet the updated electrical code and installed them. One under the meter in a new hole, not the one the old ground rod was in. Then the second rod was installed 16 feet down the foundation away from the first rod. Connected both of them with a section of wire the same size as what was coming out of the meter.

By the way, the soil at both homes was red clay that was mostly dry, but hard.

Measured the combination of the 2 ground rods without the house meter connection. With the 3 point ground tester, it was just below the 2 Ohm point.

Connected the house meter back to the new ground rods and put the house electrical breaker back on.

My second house was a repeat of the first house many years later. What did I learn in the long run? If your house ground rod is over about 10 years old, the soil in this area causes the ground rod resistance to go sky high.

Another case was a pair of 500 foot towers the cellular company owned that had both towers taking damage. We took a back hoe and carefully dug to uncover the grounding ring around the towers. Both were done per the R56 standards. All the connections to the tower and the ring of ground rods were exothermically welded.

Believing the ground rods had lost their resistance, we were faced with the choice of replacing the entire grounding system. Thought about it for a while and had a chat with the boss. My idea was to add a 100 foot leg of new ground rods to opposite directions of the tower. We found the end of the original grounding leg wires and added on to them. Placed new ground rods at the 16 foot spacing.

While we were at the tower site, we also replaced all the guy wire anchor ground rods. The soil at the tower site was dark clay type soil you normally find in low wet areas. If we dug more than about 3 feet, we would have water coming into the trench.

Bottom line for the tower site was no more surge problems and sneak fuses on the telephone lines feeding the paging equipment.

So here are a number of examples that show ground rods and grounding systems do go bad with time. They do need to be looked at over time to make sure your ground system hasn't taken the route of these 3 I have talked about. Remember, that just because you have ground rods in the soil, they might not be working like you want them too.
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