The following article was written by Steve Morris, K7LXC, of Champion Radio Products. The original can be found Here. He is well known amongst the international Ham Community as the owner and moderator of the popular 'Towertalk' ham-forum.
The Ten Most Common Tower Building Mistakes
- After working on over 150 amateur radio tower and antenna systems
over the last 15 years, I have seen many problems and failures that
could have, and should have, been avoided. By avoiding making these
mistakes, you can make your tower and antenna system safer and more
reliable. It'll even let you sleep nights better when that big storm
- 1. Not following the manufacturer's specifications
- Commercially manufactured towers have to comply with current
standards for wind loading and structural integrity. Licensed
Professional Engineers (PE's) design the towers and make the
calculations to make them safe. If you don't follow their specs at a
minimum, the tower will not take the stresses and loads that it is
subject to. In other words, it'll probably fail.
- One of the immutable laws of antenna and tower construction is the
LXC Prime Directive - "DO what the manufacturer says". Violation of this
rule could be catastrophic.
- The inverse of this law is DON'T DO what the manufacturer DOESN'T
SAY. In other words, don't invent something that the manufacturer hasn't
intended. Here are a couple of examples. A ham was installing a KLM
antenna that used the Lexan element brackets. After final assembly, he
spray-painted the whole antenna with clear Krylon spray paint. Why?
Because he always did that to protect his antennas. Unfortunately the
Krylon reacted with the Lexan in the boom-to-element brackets and
cracked all of them. Did the manufacturer say to do that? No.
- Here's another. Another amateur taped the bottom of the turnbuckles
on the anchor end of his tower guy wires. Over time, the tape trapped
water that eventually rusted the turnbuckle and he couldn't see it
because it was covered up by the tape. All it took was a medium-sized
windstorm to break the turnbuckle and have the tower fail. Did the
manufacturer say to tape the turnbuckles? No. Not only did he do
something the manufacturer didn't specify, but he also violated Mistake
#8 below - Not doing an annual inspection.
- 2. Overloading
- This is the most common reason for amateur tower failure. The first
thing you need to know to plan and build a tower and antenna system is
what the wind speed rating for your county is. Next, you need the
manufacturer's specifications for that wind speed. Then you must not
exceed the wind load rating based on those factors. This is even more
important for crank-up towers. Refer also to number 1.
- Let's face it, many amateurs overload their towers and get away with
it. I've seen tower installations that have violated just about every
one of the ten mistakes and their installation has been up for 20 years.
Why is that? First of all the manufacturers have built in some amount of
engineering overhead - sometimes 30 to 50%. And sometimes the tower is
actually stronger than the engineer's specs. This over-engineering is
done to increase long-term reliability, not to let you put more antennas
on it. Another reason is that it might be sheer luck - after all, every
time you speed you don't get a speeding ticket do you?
- Whatever the reason, it's NEVER a good idea to overload anything. If
in doubt, err on the side of conservatism - you'll never regret it.
- 3. Underestimating wind forces
- Wind pressure on a tower and antenna system can be tremendous.
Unless you've been up on a tower during a windstorm to feel the pressure
and the forces, it's difficult to appreciate how significant they are.
Increases in wind pressure are not linear; wind loading goes up as the
CUBE of wind speed. An increase of 10 MPH in wind speed can increase the
wind force by almost 50% in some cases (see Chart 1).
- 4. Not building to the wind speed rating for the county
- While many counties, and even whole states, in the US are only rated
for 70 MPH winds (the minimum rating), many other counties have ratings
much higher, up to 115 MPH for Dade and Broward in Florida for example.
Find out what the wind speed rating is for your county, or your specific
location and use that as the minimum design parameter for your tower and
- County wind speeds for all 3076 counties in the US from the TIA-222
Tower Standard are online at www.championradio.com under Tech
Notes. Remember these are the minimums and some building departments
might use a slightly higher figure for their building permits.
- 5. Using the wrong mast for the job
- This is an all too common failure. Stacks of medium to large sized
HF beams can put huge stresses on your mast. There are two materials
available - pipe and tubing. Pipe is designed to transport liquids and
is not rated for strength. It's fine for small installations where you
don't have much wind speed or loading or when there is only one antenna
at the top of the tower. Tubing is carbon alloy steel, IS rated for
strength and is the preferred material.
- What you're interested in is the yield strength. For instance, with
a Cushcraft 402CD 10 feet up the mast, a TH11DX 6 inches above the top
of the tower and a 70 MPH wind speed, the bending moment is 18,218
in-lbs and you'll need a 2" mast with a yield strength of 42,000 psi and
a wall thickness of 0.188 inches. An aluminum mast of 6061-T6 isn't
suitable because its yield strength is only 35,000 psi so you need to
look at something like SAE 1026 tubing that has a yield of approximately
65,000 psi. Obviously for taller masts, bigger loads or higher wind
speeds you'll need a bigger mast. Talk to your local steel supplier and
they can provide you with the specs for different materials.
- By the way, the above figures were determined by my MARC
(Mast, Antenna and Rotator Calculator) Program. It's also available
from Champion Radio Products. For more information on masts, Dave
Leeson, W6NL, ex-W6QHS's book, "Physical Design of Yagi Antennas" has a
great chapter on this topic.
- 6. Not having the guy wires tensioned properly
- Proper guy wire tension is a critical part of a tower's ability to
handle wind stresses. Having the wrong tension can be like driving your
car with over or under-inflated tires; it is potentially dangerous and
is not the proper specification from the manufacturer. Having too little
tension can result in wind slamming of the tower and guys as the tower
is blown back and forth. Too much tension puts too much preload on the
guys and lowers the safety margin significantly.
- Probably 90% of ham towers use 3/16" EHS steel guy wires. Guy wire
tension is typically 10% of the breaking strength - in the case of 3/16"
EHS that would be 400 pounds. The only inexpensive and accurate way to
measure this is to use a Loos Tensioner. I devoted three columns to guy
wire topics that included reviews of the Loos so you've probably already
seen the info. If not, the Loos
PT-2, which does 3/16" and 1/4" wire rope sizes, is available from
Champion Radio Products.
- 7. Not having a proper ground system
- A good ground system is necessary not only for lightning protection
but also for minimizing RFI to adjacent electronic devices. A ground
system will protect your equipment, your home and your life.
- Whole books have been written on this topic so it's something that
will be covered in a future column. If you're interested in more
information, Champion carries the book "The
'Grounds' for Lightning & EMP Protection" from the Polyphaser
Company, a leading manufacturer of lightning protection hardware.
- 8. Not doing an annual inspection
- Your tower and antennas system is in a constant state of
deterioration. While it may be a slow process, it is going on
continually. The best way to find and fix small problems before they
grow into big problems and potential calamities is by doing an annual
- You want to look at everything and push and pull on the hardware.
You also want to put a wrench to 10% or more of the tower nuts for
tightness as well as all of the nuts on appurtenances (antennas, mounts,
- 9. Not fitting the tower sections on the ground
- Tower sections, new or used, may not fit easily together. It's much
easier to correct alignment problems on the ground than up on the tower.
- A handy tool for doing this is the Tower*Jack
Combo that combines a leg aligner along with a jack for pulling
sections together or pushing them apart. It's available from Champion
- 10. Using the wrong hardware
- Since tower and antenna materials are in a constant state of
deterioration, you should only use hardware that minimizes corrosion.
Galvanized or stainless steel materials are the only ones that will
survive outdoor use reliably.
- While corrosion is a big problem, using the wrong hardware also
includes substituting the wrong hardware, i.e. using general hardware
store-type bolts for tower legs when they call for SAE Graded ones;
using hardware totally unsuited for the task, i.e. installing the WRONG
type of 'screw-in' anchor (see Photo 1) or anchor rods; use of
non-closed-eye eyebolts (use only welded or forged ones); use of the
wrong guy material (EHS only!); and many more. Using the wrong hardware
can be disastrous.