The backup plan (Blan B?)Part II

Last month I discussed the evolution of fire detection and communications systems within the South Carolina Forestry Commission (SCFC). The move from the old to the new was not without pain, and the new has not been the great panacea that some might have expected. Our whole way of doing business, both with our external customers (John Q. Public) and internal customers (SCFC employees), has changed, and we haven’t stopped evolving yet. Change leads to more change.

When our simple (simplex) radio system was in place, each lookout tower had a base station, as shown in Photo 1 at the right. The tower attendant usually lived in a house on the same premises with the lookout tower. It was far more than a job-it was a way of life. At least one of those sites was on an isolated mountain top with only the lookout tower and the log cabin for the attendant’s residence. The attendant was snowed in for as much as six weeks in winter.

Anyway, no lightning protection was provided for the radio system-unless you call a simple ground rod a lightning protection system. The tower attendants, themselves, were our lightning protection system. When any electrical storms approached the area, the attendant was required to open the radio box and physically disconnect each external connection to the radio set. This meant unplugging the coaxial line, the control cable and the power line to the radio set and placing the cables as far from the radio set as physically possible within the small space of the radio box, shown in Photo 2 at the right. What better lightning protection could there be?

This system worked well when the attendants disconnected the radio before the storm got too close, but too often a lightning strike some distance away could zap the radio before any warning of an impending storm. It wasn’t unusual to replace 20 or more discrete components to restore the radio set to service. The base station that we used did not contain a single IC-only discrete component transistors.

So, when the towers were removed from service and a repeater system was installed, it would not be possible to have anyone go to the repeater site and physically unplug the radio set during a storm. It had to remain on, and in service, during a storm and (we hoped) survive the storm. Obviously, we had to get serious about lightning and surge protection on our repeaters as well as the dispatch center, control stations and area office base stations.

First, we had to come up with a plan. This meant researching the subject to learn all we could about the theory, products and how to apply them to our particular needs. We soon found that it wasn’t going to be cheap and easy. We looked at buying everything commercially and found that approach too expensive. Then we considered how much of the hardware fabrication we could do ourselves. This was possible because we have a good metal fabrication shop at our central headquarters at the state capital.

We bought ground rods in bulk by the hundreds. We bought copper sheets and rolls of copper flashing. We bought copper tubing. (If the law of supply and demand really works, then we must have caused the price of copper to rise in this area. And the conductivity of the earth in South Carolina must have risen dramatically after we finished the project.)

Much work went into laying ground radials, driving ground rods, installing bulkheads and mounting surge protection devices. This is hard work: digging trenches, pounding ground rods and tying the copper radials to the ground rods. We soon found that a pneumatic jack hammer was the best way to drive in those eight-foot rods.

Photo 3 on page 53 shows a homemade bulkhead panel with lightning/surge protectors mounted on it. The homemade bulkhead consists of a copper plate and four stainless steel, all-thread rods to mount the plate to the wall. The plates were spaced six inches from the wall to allow access to the back of the panel so that antenna connectors and other hardware could be attached as needed. Two six-inch strips (cut from copper flashing) were attached to the copper panel and run down the outside wall to a common ground point.

Photo 4 below shows how the copper radials were attached to the individual ground rods along the radial. Four-inch sections of copper tubing were split in half and then used along with stainless steel clamps to secure the 1 1/2-inch copper radials to the ground rods. The photo shows how the radials are attached along with one of the split sections of copper pipe used to attach the radials.

Photo 5 at the right shows how copper flashing is attached to a wall at the dispatch center where many surge protection devices had to be mounted. The copper flashing is not as thick as the bulkhead copper, but remember the skin-effect rule. We have learned from our experiences (good and bad) that money spent on lightning and surge suppression is money well-spent.

So, what about the “backup plan” or “Plan B”? Well, the idea here is to make “Plan A” so solid that Plan B is rarely needed. Yes, I remember-the best-laid plans…. A few of our repeaters are located at sites where backup power is available. We have several power generators on hand that can be hauled to communication sites if necessary. At the dispatch center, we have a base station that can be used with the on-site radio tower to communicate over a fairly large area and can “hit” any of the repeaters in our forestry region. Most of the repeater sites are equipped with a table that can be used by a ranger to set up temporary emergency communications by using a mobile radio.

In the event of a power loss at the site, the battery from the ranger’s truck can be used with extension cables to supply power. All of our control stations and simplex base stations are powered by 12V power supplies. Thus, by making the necessary wiring arrangements, these stations can be powered from a vehicle’s 12V battery by simply moving a vehicle into place near the building and attaching cables from the vehicle to the base station(s).

In Part I last month, I discussed replacing our plastic surge protectors with better-grade devices. Photo 6 below shows a couple of the plastic-encased surge devices. Photo 7 below shows a series-mode surge protector that we used as a replacement in the dispatch center. The series-mode devices are not MOV-based devices. They are Grade A, Class 1, Mode 1 devices as defined in the Underwriters Laboratories UL-1449. They are heavy-weight devices and enclosed in metal. They are not cheap-you won’t find them at the local hardware store.

The backup options available to us with our communication system are many and varied. The option we use will, of course, be dictated by the events and what resources are needed and what resources are available. Although our main thrust is forest fire control and suppression we also find ourselves lending communications support in times of natural disasters such as hurricanes. At the time of this writing a hurricane named Bonnie is gathering strength in the Caribbean and could be our next test. It keeps us on our toes and keeps life interesting!

Until next time-stay tuned!