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Summertime Grounding Projects

One of the biggest hassles for an engineer is keeping his shop organized.

(click thumbnail)Fig. 1: Mount tool cases on your workbench to improve shop organizationOne of the biggest hassles for an engineer is keeping his shop organized. Finding tools quickly not only expedites repairs, but lessens the frustration level when things have to be repaired quickly.

Randy Kerbawy at WTNJ(FM) in Mount Hope, W.Va., mounted his nutdriver and hex-wrench set by screwing the plastic cases into the workbench shelf as seen in Figure 1.

Not only are the drivers readily available, you can spot a missing driver instantly. For me, having that reminder that a tool is missing from its proper place ensures that it will be found. It’s easy to leave small tools around a studio and a greenie can be deadly in the hands of a wannabe engineer.

Summertime construction always keeps the engineer busy. Another good reason to visit your transmitter sites periodically are the possibility of discovering construction projects that you might not know about.

A few years ago, a client station was knocked off the air. When we arrived at the site, we saw that the gas company had trenched across the tower field.

Where was Miss Utility to mark the appropriate area to dig? When Miss Utility shows up, marking underground lines with paint or flags as seen in Figure 2 is a good idea. Get out your camera to document the lines.

(click thumbnail)Fig. 2: Document flags or painted underground cables as provided by Miss Utility
Keep a record of where underground lines traverse. This will help if you must replace transmission lines or a ground system. Place the pictures in a small photo album or file at the transmitter site.

If you see construction adjacent to your property, be proactive. Find out what is going on.

Morris Blum, who ran WANN in Annapolis, Md., since the 1940s, demonstrated this point when a contractor petitioned to build houses next to his 10 kW site.

Morrie not only notified the contractor of potential interference if shielded telephone wire wasn’t used, he also notified the zoning board and building permit office. When the builder cut corners, and did not use shielded wire, the homeowners knocked on WANN’s door and complained about the station interfering with their phone lines.

They were presented with a copy of the letter. The builder, not Mr. Blum, had to correct the problem. Take a few moments at the outset of the project, and you may save a fortune later on.

The letter also demonstrated how the station had attempted to look out for its new neighbors.

Construction always brings problems.

The cut satellite cable in Figure 3 is just another example. In this case, the satellite cable was strung across the ground and a bush-hog chopped it in half.

(click thumbnail)Fig. 3: Splice satellite cables properly. An electrical tape connection will permit water to spoil the splice eventually.
Know where your cables run. If you’ve just taken over a group of stations, take a walk and see where satellite, RPU or receive antenna cables go.

Burying the cable will guard against lawn-mower damage, but placing the cable in plastic PVC conduit, or the new flexi-conduit, will further protect the cable run. This is the best choice.

A temporary quick fix to get the satellite feed back up is appropriate. Just don’t leave it as a permanent fix. Although an electrical tape splice will work for the moment, spend a few extra dollars for a true weatherproofing kit.

Andrew and Cablewave manufacture weatherproofing kits; check with your equipment distributor. You can even pick up weatherproofing compound at Radio Shack. A good weatherproofing kit should be on your shelf anyway. The kits will include material to weatherproof several cables.

(click thumbnail)Fig. 4: Identify ground radials so they can be repaired
If you’re digging in an AM field, remember there will be copper radial wires in the ground. Dig carefully; don’t break these. If a radial is broken, dig around the edges of the broken wire so each end can be identified. Tag the ends with colored electrical tape for ease of identification. See Figure 4.

Remember that in order to provide an effective bond, ground radials must be silver soldered. Use crocus cloth to clean the ends of the radial until the copper is shining, coat with a silver solder flux and solder with a torch. Hand-held MAP gas torches will make the job easier, because they generate a hotter flame.

If there is poor ground, what do you do? Installing ground rods is a start.

John Stortz e-mailed to tell us that while he was improving grounding around his site, he was able to get a friendly telco technician to measure the resistance between his ground rods using a Megger. The resistance ranged from 15 to 35 ohms.

John’s local power company drives rods, for their own use, to whatever depth is takes to obtain a resistance under 3 ohms. That’s the number they they consider to be adequate.

In John’s case, he was trying to improve grounding at his guy anchor points. After some thorough research, he used 3/4-inch copper-clad ground rods at a depth of 30 feet at each guy anchor point.

The same technique was used at the transmitter building, where a 3-inch interior ground strap was bonded to the ground rod outside. Another rod was used for the utility entrance ground.

So how do you drive 30-foot ground rods?

John and his staff used an electric jackhammer and a tall stepladder. Taking the time to do the job right paid off. Although he couldn’t get the Megger back, a Simpson 260 shows less than 2 ohms between the ground rods and the ground system.

John cautioned that care be used in order not to polarize the rod by passing DC current from the VOM’s battery. Don’t leave the meter on any longer than necessary to get a reading and try reversing the polarity.

While you’re measuring, also check for a low value of DC on the ground rod, caused by galvanic action in the soil. This will affect the VOM, if present, and is the reason why ground measurements are not normally taken with a VOM.

Use a cable obtained from the tower riggers when attaching grounds to tower guys. John’s cable was silver-gray and had a coating to prevent a chemical reaction with the galvanized guy cables.

It’s not a good idea to allow bare copper to come in contact with galvanized steel. If you add a little acid (as in acid rain) to a copper-zinc connection, you will have a small, short-circuited battery because the zinc will yield to the copper, destroying the galvanizing on the steel.

Submissions for this column are encouraged and qualify for SBE recertification credit. Fax your submission to (703) 323-8044, or send e-mail to [email protected]