A three-sided mast is used for taller construction projects, and it's considerably more involved than a simple pole antenna for a Dish TV receiver. You may be putting one up to extend cell phone coverage over a remote area or as part of a weather-monitoring station in which the mast will hold an anemometer at a specific altitude. Because this type of mast entails a more robust and detailed construction job, a number of practical engineering considerations must be factored in.
1Location and Ground Condition: The first step in setting up an antenna mast of this variety is a survey. You'll want to look for local obstructions that could block your signal, check for power lines that may cause electromagnetic interference, examine the ground, and consider soil conditions. You can make a three-sided mast that compensates for uneven terrain, but it adds to the complexity of assembly and raising it to its final height. Your tower must be designed by a qualified engineer and meet the standards of EIA-222, including variations for your intended location.
2Legal Considerations: Consult with your local building department to determine what permits are required to put up an antenna mast, and be sure to explain that you're making one that's free standing -- it may require a building permit. Your permitting authority will probably be accessible through your local Blue Stake center, where you can also obtain information about buried cables and right-of-ways for power lines. No tower may be constructed in such a manner that it could touch power lines, even if it falls.
3Foundation: Your first task in assembling the tower mast is laying the concrete base, and you'll need to factor in the soil survey you did earlier. Make sure that you've anchored the footings of all three trusses of the mast. Your assembly crew will need to lift each truss individually and then bolt the trusses together. Someone should be on the tower's guy lines while another worker is up in the trusses doing assembly work. At the end of each day's work – and large masts will require multiple days of work – make sure to double-check and secure the guy wires.
4Final Assembly and Maintenance: Each segment of the mast needs to be carried up by a person secured with a guy line and bolted into place on the parts below. Each height component is typically done in three parts – one for each "side" of the mast. Once the mast is assembled, you'll need to run the power lead up to the top, making sure that the power is grounded appropriately and that anti-lightning grounding materials are in place. Once power is confirmed, hoist the transmitter into place. Secure all aspects of the mast with appropriate guy wires, and put the appropriate barricades in place to prevent unauthorized persons from climbing the mast. Inspect the mast every month or so for weathering or signs of wear and tear. Properly constructed, a three-sided mast should be as sturdy as a well-built bridge.