Topics For Technicians!
In your planning stage you have looked over your proposed tower or mast site and found the ideal place in which to "plant" it in the ground and you know how high it will be when it is installed.
Now you ask yourself where to put the guy wires for it on the ground...you walk around the area and pick some good locations for each of them hopefully conforming to recommended safe installation procedures. In your observations, you realize that each guy wire will have to be a different length due to obstructions and Murphey's Law getting in the way. It never fails, Murphy is always looking over our shoulders and picking on us as ham radio operators!
Ok now, stand back Murphey...each guy wire has to go in a specific location whether "Murphey" likes it or not and you know how high the tower or support mast, pole, etc is so then it hits you... and you ask yourself....how long will the guys have to be for the locations I have picked out? I don't want to have to buy more guy wire than I need. After all, my wife says I am cheap!
You look at the tower, pole, mast etc and your location for the guy wire at ground level and say....well the mast is 50 feet tall, so the length at the location of my first guy has to be at least as long as the mast is high but a bit longer...but how much longer will it have to be due to the angle of the guy coming off of the tower if it is 70 feet away? See the example drawing below for our proposed setup and to get the answer to our question in our fictitious installation.
Back to our school days!
Get your calculator out, the simple one with 4 functions plus square root. No, you don't need a scientific calculator...get the one that you use to balance your checkbook. If you don't have a calculator, use the one at the top of this page when the guy gets done with it! GRIN!
Leg C (the hypothenuse) is the unknown guy wire length that we are looking for.
Here is the formula:
We will be using the first formula above in this example to figure out how long our guy wire "C" needs to be in the drawing above since "C" is the unknown in our situation. We already know what "A" and "B" are in length.
Using the formula:
C squared = A squared plus B squared so we insert our known numbers, 50 and 70.
C squared = 50 squared plus 70 squared. (in case you have forgotten, "squared" means multiplying by itself)
So.... C squared = 50 times 50 equals 2500 + 70 times 70 equals 4900...adding together 2500 + 4900 we get 7400.
So.....C squared = 7400
Now since C is squared, we need to take the square root of 7400. Here is where your handheld calculator comes in handy unless you are Einstein. Plug in the 7400 in the calculator and get the square root......
Our answer is the square root of 7400.......86.02 feet!
So....."C" in the drawing above, which represents our unknown guy wire length, is now known to us as 86.02 feet! Don't forget to add a few inches or so for the wrapping of the guy wire points, tying off, etc on each end.
Now for the other guys required for your installation use the same formula above making sure you know how high the guy attachment point is for each set of guys and the distance out from the tower or mast to tie off the guy wire...then just plug in the numbers into the formula like in the example above. This method works for any tower, mast, etc as long as it forms a "right triangle" with the earth below it. We are simply using math to represent the installation in this example.
Your mast is 30 feet tall. The mast will be guyed at it's top and then extend outward to the ground. The distance from the base of the mast to the guy point is 35 feet...how long will this unknown guy wire be?
Using the first formula given above:
C squared = A squared + B squared.
C squard = 30 squared + 35 squared.
C squared = 900 + 1225
C squared = 2125
Taking the square root of 2125 =46.09 feet!
Always use the recommended tower or mast mfg's guying specifications for your height, wind load, etc for your particular installation. Be safe, not sorry. Never install a tower or mast near power lines. Murphey says that one or the other will fall.
More good reading on tower and mast installations and the Pythagorean theorem:
Pythagorean theorem calculators: (off site)
If you know of another method of determining the unknown guy wire length that is simple to use, please give us your input! n4ujw AT hamuniverse.com...thanks!