The selection, routing, and length of coaxial cable are extremely important in the installation. If there is a
3 dB line loss in the cable between your unit’s output and the transmitting antenna, the unit will only
deliver half power. Buy the best cable you can obtain, route it via the shortest way to the antenna, and
keep it straight. Do not form it into sharp bends on its way. Do not use any more cable fittings for the
installation than absolutely necessary. All cautions here apply equally to all coaxial cables in the system
- input and output.
Pay attention to radial ice accumulation when designing the transmission system. It is not uncommon for
at least an inch of ice to build up on a tower or antenna in some locations. This in turn significantly
increases the weight, cross section, and wind loading of the system, not to mention creating issues from
reflective power.
Attaching the transmission line to the tower is crucial to maintain a safe and reliable operation. Nylon wire
ties and electrical tape will breakdown in the sunlight and ultimately fail, creating a potentially dangerous
situation. It is important to use proper clamps and hoisting grips and also ensure that the transmission
line is grounded to the tower in several locations. When high currents flow through the tower in the event
of lightning strikes, some of that current will flow through the outer conductors of the transmission lines.
Due to the resistance difference between the steel tower and copper transmission line, a significant
voltage can be developed, often resulting in arcing between the outer jacket and outer conductor, thus
pitting the conductor.
Preventative maintenance is crucial in ensuring that safety is maintained. Specifically, check that
transmission line grounds are tight and are not missing any hardware. Frequently inspect support clamps
or spring hangers. Consider investing in an ice break, if you haven’t already done so, as shards of falling
ice can damage the transmission line – and if it is going to happen, it will happen at an important time.
Check the tower light photocells and conduit.
The better-known tower manufacturers offer complete technical and safety documentation with their
towers. Be sure that you have this information as it regards wind loading, guying, etc. The best-designed
antenna system will function poorly if shortcuts and compromises are used during installation. Follow the
manufacturer’s instructions exactly, along with any engineering data prepared for the site. Be absolutely
safe and certain about this aspect as human lives may be at stake.
12.4. Shelter Security
The FCC requires that the equipment be secure from entry or control by unauthorized persons, and that
any hazardous voltages or other dangers (including most tower bases) be protected by locks or fences
as necessary to protect personnel and prevent unauthorized tampering or operation. Security of the
building further implies that it be secure from wildlife. Use sturdy construction materials, including sheet
metal if necessary. Holes around conduit, cable, and other similar entry points should be stuffed with
steel wool and caulked to prevent entry of wildlife. Other features of security for your shelter may include
its location with respect to the prevailing wind conditions. Locations leeward of some natural
topographical feature will prevent wind damage and snowdrifts. Check the soil runoff conditions that may
slow or hasten wind or water erosion and other concerns that may be unique to your location.
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