"The grapevine of the communications tower industry"

 

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They are actually pretty neat.

On February 21, 2002 my company replaced a standard incandescent beacon with a Dialight LED (light emitting diode) beacon on the WKDF tower in Brentwood Tennessee at 1140 feet. From the outset the new beacon worked quite well and continues to do so ten months later.

The old H & P L-864 beacon was replaced because the broadcast engineer in charge of the tower was convinced that lightning was responsible for frequent failures of the top beacon. When we removed and lowered the top beacon I found evidence of water getting into the housing and the lamps had shattered without the usual evidence of a surge, a powdery residue inside the glass envelope. Flash Technologies personnel had been replacing the lamps up until then and they always use GE lamps. We tend to use the Weatherex lamps for the broadcasters which are made, unlike the GE, with Pyrex glass. They withstand a little cold water much better than the GE's.

The Dialight L-864 beacon is supposed to be a direct replacement for any other L-864. It turns out that the Dialight is a bit wider than the H&P or TWR about six inches above the standard mounting plate. When we attempted to lower the Dialight into place it moved to within six inches of the mounting plate and stopped, held in check by the four lightning rods that were affixed to the top of the tower.

The lightning rod assembly that came with the tower looks like an upside down, four legged, bar stool. It is held in place by the four bolts that hold the beacon in place. The distance between the rods at the mounting plate (bottom) was less than the width of the Dialight beacon so the new assembly wouldn't fit. We had to back up and remove the new beacon, secure it, and then remove the lightning rod assembly before we could bolt the Dialight down to the tower's beacon mounting plate. We then lowered the lightning rod assembly to the ground where it remains to this day. The engineer had ERI fabricate a new assembly designed to clear the Dialight beacon and to clamp to the pylon supporting one of the FM transmitting antennas. The new assembly was shipped in about a month later and remains in my shop. The reason the new assembly hasn't been installed on the tower is due to the fact that one of the occupants of this community broadcast tower was in the middle of changing out a transmitter when the new assembly came in and a year later has yet to get his transmitter up and running. The crux of the matter is that they cannot go to a standby antenna until they finish their transmitter install. The tower's manager is upset because he doesn't want the lightning rod installation to have to be a midnight job and realizes that we won't be able to work around hot antennas. Yet he has not been able to get this other engineer to finish his transmitter install. The tower's engineer has feared lightning damaging his $4000 beacon but fortunately his fears have not been realized.

Just after we installed the LED beacon without the lightning rods, quite a few spring (2002) storms marched through the area. Strike after strike took out fuses in the red light controller that serves the LED beacon and the remaining incandescent beacons but there were no problems with the Dialight beacon whatsoever. We installed a set of LED markers at about 1000 feet during the beacon install and then came back several months latter and installed another set of LED markers at about 800 feet.

The LED Markers came configured for a bottom, rather than side, conduit entry. We had to do some conduit modifications on the ground in order to be able to remove the old incandescent markers and install the new. The engineer's plan is to have the entire tower lit by LED beacons and markers before too long.

Very reliable and apparently impervious to most lightning stirkes, the Dialight LED L-864 beacon seems to be a quality product. It's a good thing too since it doesn't look to be repairable on the tower top. I spoke with Doug Woehler, the beacon's designer today.

 

He indicates that the life of the beacon should be around seven to ten years. The assembly which gets its power from a simple 120 volt AC circuit contains two internal power supplies that run in parallel and is designed so that if one power supply fails, the other will also fail. Since the beacon draws more current than any one power supply is fused for, the remaining supply's fuse will blow. The beacon will then be dark but to run less than total current would cause the beacon to be out of FAA/ICAO specifications so in this case "dark" is better. The LEDs are arranged in blocks of eighteen to a module. There are thirty-six modules nested within the housing which is divided into two hemispheres, making a total of six hundred forty-eight individual LEDs. If the beacon is to be "re-lamped" an entire hemisphere and power supply assembly must be replaced. Since by nature of its design the beacon would be dark at the time of such maintenance, it would be prudent, if not necessary, to replace both hemispheres. Doug couldn't tell me what the hemisphere assemblies weigh but that they should fit onto a pack rack for transport up the stick. The entire beacon weigh eighty-four pounds and most of that weight is concentrated in the hemispheres containing LEDs, power supplies and a large heat sink. Therefore the hemispheres could easily weigh thirty-five to forty pounds each. It appears the question at the time when it was necessary to replace parts would be to rig, or not to rig. When you consider that tall towers, like the WKDF tower in Brentwood, Tennessee require a minimum of 3000 feet of rope to remove the assembly the cost of a service call to the tower's owner will be significant. On the tower owner is supposed to be able to avoid seven to ten years worth of relamping of the tower.

We spent some time on the ground inspecting the beacon and trying to get an idea of what a service call might entail. Access to the beacon is rather simple, the only question being what would a service technician do once inside, especially at 1000 feet or so. The beacon we installed disassembles differently than the current model. I'm going to try and get detailed pictures of the latest iteration of this beacon.

In any event, the Dialight L-864 beacon seems reliable and capable of putting out a good deal of light. It is controlled by the user's existing red light controller and consumes a little more than one amp where the standard beacon consumes around ten amps. There is quite an electricity savings but also a problem for present day current monitors and alarm systems. I'm sure Dialight has a monitoring solution though I didn't have the presence of mind to ask while I had Doug on the telephone.

 

 

 

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