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Getting the most from tower inspections
Tower inspection expenses are small compared to the financial consequences of not spending the money on one. However, make sure that this is actually a preventative measure that is worth the money spent. These inspections are designed to help broadcasters comply with government and safety regulations, catch present and potential problems that compromise the integrity of the tower and verify the accuracy of drawing plans on hand. The latter objective becomes particularly useful to tower upgrades as we install new digital antennas and their corresponding appurtenances. Accurate information as to tower-member dimensions and orientation at the level where the digital antenna will be installed will be required by the antenna manufacturer for side-mounting considerations.
Qualified tower inspectors
Inspections need to be performed by qualified tower inspectors. By qualified I mean someone with enough experience in tower installation and maintenance. The inspector should be skilled in the use of the dynamometer and surveying transit and knowledgeable with OSHA, TIA, FAA and FCC rules and standards. An inspector is definitely more than just a tower climber.
Engineers from other stations may be able to make recommendations from working experience with specific tower companies or individuals. It also helps to call and interview previous clientele of the tower company being considered. It is up to the owners and station engineers to make sure that the job gets done right and that the stations gets the most out of the company expense.
There are several questions that should be asked and details that should be defined from prospective inspectors during the request for quotation (RFQ) process.
Obtain a checklist of what is included in their inspection. It should include tests on the tower lighting to ensure that the remote monitoring and alarm actually work.
Require a detailed report be provided, complete with pictures and recommendations of actions to be done in order of priority.
For FM, have the tower inspector equipped with a personal RF radiation monitor when he goes up the tower. Broadcast time is costly, so minimize reduced power or off-the-air intervals to when the climber is in the RF hazard levels of the tower. AM towers will probably be cold when being climbed, but additional equipment may be installed.
Ask if the inspector will check for coaxial line leaks as part of the inspection. Some inspectors would even do minor touch ups on cold galvanizing for free as long as the work does not exceed the maximum two man-hours. Some pro-bono items may include replacement of obstruction lights as part of the inspection package.
When the work is awarded and the job is scheduled, ensure that driving directions to the site are communicated. Ask for the mobile phone number of the inspector who will do the work. Coordinate possible off-air times, and have the tower drawing plans ready for reference and review by the inspector. Be sure that the areas to be inspected are clear from bushes and are readily accessible.
Ensure that the inspector has hand-held transceivers for coordination. It's a good idea to have your own set of binoculars so you can observe the process and perhaps see for yourself whatever the climber wants to show you when he is up the tower.
Verifying this information ensures clear communication and will allow you to compare individual quotes on an equal basis.
General site conditions
RF warning and FCC tower registration signs need to be properly posted as per FCC and OSHA standards. The inspector should be able to spot this on entering the site premises and be able to recommend how to properly comply. In cases where there are gray areas with regards to compliance to rules, it is best to be at the safe extreme rather than risk being found deficient.
The inspector should also check the integrity and continuity of the security fence around the tower and guy anchors. Locks should be operational and chains used should be strong enough to provide protection. He should also be able to determine if tall trees around guy anchors can pose a hazard during inclement weather. Soil erosion due to drainage passing through guy anchors or tower base could possibly weaken the soil bearing. Excessive growth of vegetation can hinder visibility and prevent access to the tower base and anchors.
Corrosion due to rust is perhaps the biggest enemy of guy anchor components. Cotter pins, clips, turnbuckles, anchor rods and plates need to be inspected for signs of corrosion. Preformed guy grips should be prevented from unraveling with tie wires. Safety wires should be installed on turnbuckles to prevent them from turning. TIA/EIA 222F requires that these safety wires be in a figure-eight formation. A security fence should surround the guy anchor to protect it from grazing animals and as a visual warning to people operating farm equipment and other vehicles.
Tower structure and guying
Guyed towers need to be vertically plumb from top to bottom. The inspector uses a surveying transit on at least two observation points that are 90 degrees from each other with respect to the base of the tower as shown in Figure 1. The tower should be sighted at each guying level and approximate the deviation from vertical compared to the leg of the tower. The findings at each level should be recorded.
The results gathered above will give the inspector an idea of the tensions of the guy wires. A tower that is not plumb within the width of the leg of the tower must have a loose guy wire on one side and a tight guy wire on the other side. A dynamometer is used to determine the guy-wire tensions. The inspector should use the right correction factor for each guy wire size and type. He should also be able to verify and update the plan as to the type and size of guy wires used on the tower.
The inspector may also be the climber or another one who is trained to spot rusted bolts, members and girths of the structure. Signs of corrosion, bends or dents should be noted and photographed for your reference. Loose or missing hardware included in the report should be fixed with due diligence.
Lighting and grounding
The inspector should check the tower obstruction lighting system for FAA compliance and test the alarm system and monitoring. The flash head units on the tower should be checked for signs of lightning damage and corrosion. Painted towers should be checked for flaking and fading as compared with the FAA color chart. This includes coaxial cables if run on the outside of the tower.
Lightning prevention systems are only as good as their grounding. Ground rods should be inspected for electrical and mechanical integrity. There should be no sharp bends or discontinuity on the ground wire from top to bottom. All cables should be grounded on the tower with grounding kits as specified by the cable manufacturer. The inspector should take note of deficiencies should he find missing or faulty grounding apparatus on any cable, guy wire or fence.
All hardware attached to the tower should be secured and all bolts tightened. The inspector should take note of any signs of dents or bending or anything that may hinder the proper electrical performance of the antenna or transmission lines. He should check for weep holes on microwave dishes, leaks on connectors or antenna tuning slugs, signs of overheating or warping on any connector and presence of weather proofing on connectors. The inspector should also take note of the presence or integrity of ice shields.
Verify the location of lighting conduits and coaxial cables on the tower, especially if future antenna installations are planned. The inspector should be able to update or correct any documentation you need on the actual tower installation.
Frequency of inspections
It is beneficial to have a tower inspection after every winter or spring to check for possible damage due to ice or thunderstorms. Another general inspection before winter for preventative purposes is also useful. However, station engineers can conduct most of the inspections on the ground on a bi-monthly basis. This can form part of the preventive maintenance schedule done on-site by station personnel. With the help of a checklist, the job will not be as hard as it seems.
When the inspection report arrives, it should serve as a point of action to rectify whatever deficiencies has been found. Be sure to make good use of this inspection report.
Tower Inspection Checklist
General Site Conditions
Tower Structure and Guying
Obstruction Lighting System
Lightning and Grounding System
Antenna and Transmission Line System
Rolin Lintag is an RF engineer in Little Rock, AR.
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