Rain, Rain, Go Away

All types of weather can affect cables and connectors, but water is by far the biggest threat. It doesn't take a hurricane or even a major rainstorm to wreak havoc. Less than a teaspoon of water in the wrong place can damage your system.

Water migration into coaxial connections in the base station and antenna can increase signal loss, which reduces the coverage area and leads to revenue loss.

"Bottom line is it's going to cause poor system performance and ultimately customers will be calling you and complaining about the service," said Darin Miller, Sprint PCS senior engineer, national site development department.

Maintaining cables and connectors is an ongoing job.

"That's one of our technician's biggest jobs," said Steve Swing, Sprint PCS construction manager. "Water's the main culprit as far as damaging our performance."

WATCH OUT FOR WATERAccording to Graham Hale, Andrew Heliax cables and connectors product line manager, even heat and wind create water problems for cables and connectors. For example, if the hot sun beats on the cable all day, and then the temperature drops at night, the cable will expand and contract, producing gas and condensation.

The problem starts at the first nighttime cycle, Hale explained. As you push the gas out, you create a vacuum inside that contracts as it gets cold and sucks gas or air inside.

"As the air gets sucked in, it's cold air that has a higher humidity," he said. "When the sun comes out again the next day, that humidity then forms drops of water."

If water migrates down to the feedline and gets cold, it can freeze and split the outer jacket on the feedline.

"If you're in a climate where you get below-freezing temps, whenever moisture gets in somewhere and freezes, it expands and thaws out," Miller said. "The next time water gets in there and freezes, it expands a little more."

Wind vibration presents another water problem.

"If you haven't tightened the coupling nut properly on the connector, the vibration causes the connector to come away from the antenna, which then allows water to get in," Hale said. He added that areas with consistently high winds face the most problems.

When any amount of water gets into critical areas of your cable and connectors, you'll see problems instantly.

Water can cause a corona arc, which would take the power from the center conductor to the outer conductor, destroying the dielectric and damaging the cable permanently.

According to Bruce Holsted, Holsted Company owner & contractor, water that enters a connector creates a direct short, preventing the transmitter from radiating and shutting down equipment. A system's diagnostics usually will pick up the problem and send an alarm back to the switch, but not for the receive side.

"(Water in a connector) makes the cell site deaf, and not everyone has the ability to diagnose the receive antenna remotely," he said.

Most carriers contract out cable installation and maintenance work. If an unqualified person installs your cables and connectors, you're asking for trouble.

Hale said one cellular carrier that installed cables and connectors incorrectly got a thermal cycle up in the antenna at more than 100 feet. Water traveled down the center conductor and into the radio room, which is dangerous because electrical elements are located there.

"Antennas have holes in them for the thermal cycle, and they blocked them," Hale explained.

This mistake resulted in poor system performance and expensive repairs.

KEEPING 'EM DRYAlthough manufacturers may claim that cables are weatherproof, most carriers need to take extra waterproofing precautions.

"If you don't get a good weatherproof connector, water can get down into the connectors, and it will affect the performance of the antenna," Swing said.

All connector junctions on the transmission-line system, including jumper-cable connections, base-station-to-antenna interfaces, external surge arrestors and splices, need environmental protection. According to Swing, at-risk points include the jumpers between the equipment and to the main line, the jumper at the antenna and the actual ground end of the coax.

The connection to the equipment itself is usually inside the cabinet, which provides connector protection. But there may be small, half-inch jumpers that connect outside the cabinet and then reconnect in the main line.

"At that connection we have exposure to water," Swing said. "Also, we ground all of the coax, and at that point we also have exposure to water."

Connector designs that use O-ring and watertight press-fit seals at critical junctions can provide the required waterproofing for connector interfaces. O-rings keep water out, but sometimes the grease that's used to keep them from drying out will get into connectors, Swing said.

Butyl tape is one form of secondary weatherproofing, but according to Hale, it will dry and crack in the sun.

"You have to put some kind of UV protector on top of the butyl tape," he said.

In addition, UV rays accelerate aging in the tape, and if you don't install it properly and water is underneath it, you can trap the water and make the problem worse.

"The sun will definitely deteriorate the tape and cause it to peel back, and eventually water will get in there, and it will peel back even more," Miller said. "But (the life of the tape) depends on a combination of the weather and how well it was installed."

If you wrap the tape upside down, water may get caught, Hale explained. You have to wrap in spirals so that water flows down like on a roof tile. He suggested starting at the bottom and wrapping up so the tape overlaps.

Miller said Sprint PCS' field contractors install butyl tape as extra weather protection. Contractors wrap butyl over one layer of electrical tape over the coax and then wrap electrical tape over that three more times. Third-party contractors inspect the weatherproofing on Sprint PCS' tower tops and provide the carrier with detailed information and digital pictures.

"It can be pretty obvious if you have a poor weatherproofing job," he said. "If you look at a connector and you've got butyl poking out in between the tape, then it's obvious that we didn't get three good wraps of tape on the connector."

According to Holsted, cold shrink has become a more popular option among carriers.

"Butyl is messy, it's a pain in the neck, and nobody likes to do it," he said. "The cold shrink's cleaner and easier to service -- you don't have to cut all the yucky, icky, sticky (butyl) away."

Cold shrink resembles a sleeve and uses a compression method; you pull the inside out, and it shrinks down to cover the places prone to leakage. To prevent installation mistakes, make sure the feedline is turned horizontal out to the antenna.

Without such preventive measures, water can ruin cables. To fix frozen water in cables, for example, Miller said sometimes you just can cut off six inches to a foot of the cable and reconnect it. But if you get moisture from the top of the antenna, and you take off a connector at the bottom, and water pours in and out, then there's a good chance you will have to replace an entire cable line.

There are no alarms to alert operators that water has invaded cables, but Miller said sweep tests can catch problems. If enough water gets into the connectors, he said, it would cause an arc, which would show up as a flat line on a sweep test.

"Whenever a coax is installed, we do a sweep test on it," he said. "If there's anything wrong with the coax when it's installed, you can find it out on the sweep test."

Sprint PCS re-sweeps coax and checks for degradation once a year, but problems may come up more frequently.

"If someone's constantly getting dropped calls in a certain area, they'll call customer care, a ticket will be written up and then the techs will check into the problem, pin it down to a sector and sweep the coax," he said.

PREVENTION BETTER THAN CUREAccording to RFS Cablewave, three preventive measures will stop water migration in new and existing systems before it begins: installing watertight connectors within the main feedline; waterproofing the antenna bulkhead termination properly; and avoiding leak-prone braided jumper cables at the antenna input.

Holsted said the most important thing you can do is develop a systematic test and measurement program for your antenna network.

"(Carriers) do maintenance on cell sites, on the ground, on everything except the most important thing that makes the phone work -- the antenna," he said. "You've got to do periodic maintenance of your antenna network."

Holsted also suggested equipping your technicians with test equipment so they can test the antenna networks as part of routine site maintenance. Another thing to consider is using air dielectric feedline, as opposed to foam dielectric feedline.

"Air line is pressurized, usually with a dehydrator or CO2 gas bottle, and having positive air pressure on the lines prevents contaminants from entering because if there's a leak, it just blows air out of the leak," Holsted said.

Protecting your cable and connectors from water is an important task that you can't ignore. Taking preventive steps now will keep your system dry and prevent you from having to install new cable lines later.