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Transmission Line Maintenance
Transmission line is one of the unsung heroes of any broadcast facility. Without it, the signal goes nowhere. Although line is typically of a robust construction, like anything it requires a certain degree of maintenance. In some cases, a simple visual inspection combined with a little old-fashioned common sense may be sufficient, while in others a more detailed approach may be required. Either way, staying on top of inspections and maintenance tends to allow for better outage planning.
Buried transmission lines such as those utilized in an AM directional array, if properly installed, tend to require a minimal amount of maintenance. As long as they are buried at a sufficient depth to avoid erosion and damage from implements, they will typically function properly for many years. With an intact outer jacket, the tendency for galvanic corrosion and dielectric contamination, in the case of foam designs, is virtually non-existent. Nevertheless there is no downside to an occasional sweep of such lines to be sure.
Rigorous maintenance can reduce the impacts of potential damage, but elimination of all risk is likely not possible. Supporting structures for above ground transmission lines should be well maintained and replaced if necessary. Places where lines enter structures or the ground should be such that small movements in the line will not result in damage. Increase visibility and review such areas with all personnel involved at the site. To identify problem areas on the tower, use a competent crew. For significant construction projects, an inspection by a different crew may be worthwhile.
Correct each of the problems identified in a timely fashion. Common sense should tell you that when the transmission line is heard slapping against the tower in wind, an issue may be present. In that true case, the cost in rectifying a year later was considerably more expensive than if the problem had been addressed when initially identified.
Beyond the visual
There is also an electrical component to maintenance. The easiest method of examining the condition of a transmission line run is through the use of a network analyzer. Any such analyzer used for this purpose must be a vector analyzer with time domain options. A scalar analyzer simply will not provide the necessary information to accurately diagnose a run of line. In a pinch, or in cases where a network analyzer is not available, other pieces of equipment such as a time domain reflectometer or return loss bridge may provide sufficient information to identify the presence of a problem or be satisfactorily used for occasional incremental measurements.
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