W8IO
Rooftowers LLC
Ham Radio Roof Tower Mast Options
(updated 19 Dec 2016)
Aluminum Masts:
Aluminum
masts can be used safely with caution. I would not use an aluminum mast
with a wall thickness of 0.090" or less. Common wall thicknesses of
0.120" and 0.150" are common and work well with OD's of 1.90" and 2.0".
6061T6 is a good, strong aluminum alloy and has a yeild strength of
35,000 psi. Normally, I would use a 1.9" OD x 0.150" wall 6061T6 mast
with the HF beam mounted just above the thrust bearing. If the wind
load of the HF beam is 2 to 5 sq. ft. less than the tower's limit, then
you can also stack a small or medium sized VHF beam or omni a couple
feet above the HF beam. If the HF beam is 0.5 to 1 sq. ft. less than
the tower's limit, then you can only stack a short VHF or UHF omni just
above the HF beam.
Galvanized
Steel Masts:
Beware
of ordinary steel water pipe! Unless you know the grade of
material and it's yeild and tensile properties, it may be weaker than
aluminum and will rust if not galvanized. In fact, the
galvanized
steel pipe at Home Depot is ASTM A53 seamless, which has a yeild
strength comparable to aluminum: 30,000 to 35,000 psi. Most galvanized
steel
mast material sold by Ham Dealers have a yeild strength of 80,000 psi
or higher. With this type of mast, you can stack a medium sized VHF or
UHF beam 5 to 6 feet above an HF beam. However, the moment
produced by the VHF or UHF beam will be amplified by the distance to
the top of the tower, so you cannot just add the wind areas together.
This extra moment places more stress on the bottom of the tower legs
near where the feet attach. If you are going to stack at this distance,
make sure that the total wind area is 5 to 7 sq. ft. less than the
tower's limit OR do the calculations.
Here are some places to find tower masts:
Texas Towers  Texcom
Steel masts, galvanized, 87,000 psi typical. A 10
foot long 2" OD x 0.120" wall mast is about $129. Other lengths
available.
HRO  US
Tower M10, galvanized, reinforced, 10 foot steel mast, 2" OD
x 0.120" wall is about $129. Other lengths available.
Array Solutions  Mast 2" OD x 0.22 wall x 22 to 24 ft  1026 DOM Tube 87 k psi
Array Solutions  Mast 2" OD x 1/4" wall x 20 to 24 ft 4130 Chrome Moly 112118 k psi
DX Engineering  HeavyDuty 4130 Chromoly Steel Masts

Texas Towers  Universal
Tower AM216, 16 foot long 6061T6 aluminum 2" OD x 0.120"
wall mast is about $109.
Penninger Radio  6061T6
Aluminum 2" OD x 0.250" wall x 10 feet long is about $100.
Other lengths available.
Penninger Radio  6061T6
Aluminum 2" OD x 0.125" wall x 10 feet long is about
$62. Other lengths available.
Online Metals  6061T6
Aluminum Schedule 80, 1.9" OD x 0.200" wall x 8 feet long is
about $47. Shorter lengths and other wall thicknesses available.
Helpful
References:
"Match your
Antenna to your Tower", Roger Cox WB0DGF, Ham Radio Magazine, June 1984
"Practical
Application of WindLoad Standards to Yagi Antennas: Part 1", Stuart E.
Bonney K5PB, QEX Jan/Feb 1999, pp 4650
"Practical
Application of WindLoad Standards to Yagi Antennas: Part 2", Stuart E.
Bonney K5PB, QEX Mar/Apr 1999, pp 4449
"Tower and
Antenna Wind Loading as a Function of Height", Frank Javanty
W9JCC, QEX July/August 2001, pp 2333
"Tower
Tips" a compilation of many tower tips from various authors
K7NV's
Windload equations
EIA/TIA222G
Explained
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contact
Roger: email to
rgcox2
(at) gmail.com
Roger Cox, W8IO (exWB0DGF)
 Spring
Lake, MI 49456