Okay. I typed ‘lighting’. Everyone else knew that I was referring to ‘lightning’ but I guess someone will sue me over the grievous, fatal typo that invalidated the entire post.
I put "mission critical" in the first sentence for a reason. That means public safety matter-of-life-and-death systems. Systems that aren’t allowed to fail.
Ever.
Murphy was an optimist. A site will fail at 4:00 PM on the Friday before Labor Day weekend or your wife’s family reunion, or when your tower crew is out of town. That often means "mission critical" service may not be restored before noon the following Tuesday. Maybe as soon as mid-day Saturday IF overtime, overnight courier freight and a whole lot of time in the dark with cold rain pouring down fixing the problem at great expense isn't an issue. And there are a couple hundred feet of 1-1/4" LDF and all the Sure-grounds, connectors, hoisting grips and the rest of the required items cached locally ready to install.
The dark and stormy night fail could be avoided IF you had planned, budgeted and prepared for replacement a year in advance, and picked a mild sunny day during a low traffic period to do the preventive work.
I sweep "mission critical" coax and antenna systems several times a year. They're mission critical systems. Failure is not an option.
It’s called preventative maintenance. You can't assume a reliable system will stay that way without it. I replace backup generator batteries every three years. It is not a contest to see how long you can make them last. They are mission critical, must start 100% of the time and still fail. Do I use a still-okay-take-out generator battery in my lawn mower? Yep. I have a charger and the grass can wait. Car tires are legal as long as Lincoln’s head disappears into the tread. Do I run tires that long? Maybe for a while on the car I only drive in town to the grocery store on sunny dry days. Should a police agency? No. A failure during a high-speed run in the rain could be catastrophic.
Do you replace your tires before they are no longer legal? Why? They are legal and shouldn’t be a problem. Murphy’s Law is over-rated.
Several years ago issues were reported at a five-year-old public safety site. Everything installed and grounded to R-56, including lavish bend radius, secure attachment, Sure-grounds with exothermic welds at the top, bottom and every 50 feet down the structure. Everything on the ground was tight and dry as a bone. It was still working acceptably so we scheduled repairs with the agency. It was only five years old, so it must be a simple loose connector up-top. Wind and other problems delayed climbing for a week. That made me nervous.
The site worked until the monsoon rain hit (at 11:00 PM on a Friday night of course). The site went deaf as a post and the transmitters went into auto-protect. Degraded the law enforcement, fire and EMS comms for a part of the county on a busy holiday weekend.
At 3:00 AM I found water inside the bottom N-Connector. At daylight (with the antenna disconnected) I checked the coax with my megger. The jacket was perforated in several places and would pass 1,000 volts to the structure. My tower guy could hear the snapping when I applied megger test voltage.
When we pulled the coax down hairline cracks became apparent in the upper sections. They were not visible until the coax was flexed, something you keep to a minimum with 1-1/4’ Times Microwave® LDF6. All weather-proofing was intact and dry. Removing the jacket from around the perforated sections revealed old corrosion mid-run. A combination of black and green death. This was a long-term slow-motion failure that waited until the worst possible time to rear its ugly head.
Did I bill the agency for the late night overtime weekend work? Only for materials. I have a fixed-amount monthly contract to make sure their mission critical systems don’t fail.
Even the best UV-Resistant jacket is not forever. That’s why it is marketed as ‘UV-Resistant’ and not ‘UV-Proof-Forever’. I have seen much coax fail simply because of the weather. Water is evil and patient, and I can guarantee it is silently doing everything it can to ruin your day. How do I waterproof connectors and mid-run Sure-grounds? Glue-lined heat shrink under self-vulcanizing tape under two kinds of vinyl tape. Overkill? No. Not for mission critical. Why do radome fiberglass antennas have drain holes in the bottom? Because after years of sun and wind they will draw water right through the coating. It’s inevitable. Why do the weep holes get plugged? Because Japanese Beetles are evil too, and learned everything they could from water.
Another inherited older site was hit by lightning. An observer said it was impressive. The Sure-ground waterproofing had leaked and corroded, and the lightning found an easier path by jumping through the outer jacket and carbon tracking down the water tower leg to a crack in the paint. The lightning had already traveled many thousands of feet through air, so blowing open an imperfection in the 1/8” jacket and running down a few feet of wet steel was easier than following the original installer’s suggested path to ground. Another finger of lightning found its way through the wet foam at the bottom and exploded the lightning protector.
A case of not being a problem until it becomes one.
Do I replace my own coax at home on a schedule? No. It’s for a hobby, and not mission critical. Do I go out in the rain to fix it? No. I confess to being crazy, not stupid. Did I buy all of it new? Nope, not all of it. Some of my hobby coax is used, but still sweeps good. It’s ‘good enough’ since my hobby is not ‘mission critical’. Pain in the rear when it fails, but nobody is going to die because of it.
Mission critical is another kettle of fish. Do I re-install used coax on mission critical antenna systems? No.
Mission Critical means it can’t fail.
Ever.
(Composed using Microsoft Word®, and spell-checked, twice.)
</rant> Ooooohhhhhmmmmm.
