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Author Topic: PVC pipe for antenna mast  (Read 9755 times)
KB3IBV
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Posts: 9




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« on: January 21, 2003, 05:33:48 PM »

I would like any and all information, plans, material lists, experiences, etc.... for using PVC or electrical conduit (metal) as an antenna mast. I'm not planning on building the Eiffel Tower, but I am interested in mobile to semi-permanent applications. Ease of set-up and strength are my primary concerns. I have priced what I believe is a good variety of prices for all the materials that I should need. Thanks! Kb3IBV
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K9PO
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« Reply #1 on: January 21, 2003, 05:52:58 PM »

PVC will break down from uV exposure so be sure to paint it dark black. I use metal conduit (1.5") as my antenna mast for my R5 vertical and satellite antennas and it has been up for 8 years and still shows no sign of age.
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WB2WIK
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« Reply #2 on: January 21, 2003, 06:04:36 PM »

The question is really too vague.

I wouldn't use PVC for any sort of antenna mast; this is not its intended application, and even Schedule 80 PVC of larger diameters (2.00") is not very strong.  As a temporary, short, light-duty antenna support: Sure.  I've used bamboo, tent poles, swimming pool net handles, all sorts of things.  But for anything "permanent?"  Nah.

Most electrical conduit like EMT and also fence post and rail material associated with chain link fence construction is weak.  Wrong alloy, and too-thin walls, for use as antenna mast.  In fact, most of this tubing is intended to be bent and formed using conduit and tubing benders...obviously, if it's designed to be formed in the field, this is not the material to use to support an antenna in a high wind.

For antenna mast, high carbon steel, chromolly steel alloy, and thick wall extruded aluminum hollowbar are the appropriate materials and are specifically sold as antenna mast materials.

WB2WIK/6
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AD6JN
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« Reply #3 on: January 21, 2003, 07:00:24 PM »

If you do use un-guyed tubing, pipe or conduit for a mast the main failure mode is buckling from wind loading.  For safety it is best to plan for this and make sure the antenna will not slap the side of your house or the neighbors.  

For this reason I mounted my vertical in the center of the roof.  If the winds should buckle the mast the antenna will come to rest on the roof.

If you do see a partial buckling occur replace the mast as the next mode of failure is separation from low cycle fatique as it flexes in the wind.

Bob AD6JN

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WY3X
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Posts: 768




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« Reply #4 on: January 21, 2003, 07:38:21 PM »

You can use it if you build a stress harness around it. Use four eye bolts
90 degrees apart at the top, the center, and the bottom. For the ones in
the center, use a "four-way" adapter, and add pipe with caps on the ends
to space it away from the center about a foot. Install turnbuckles near the
bottom so you can tighten the stress harness as needed. You should have
steel wires run from top to bottom through the center eyebolts. Have to run
do something else will finish this post later....
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VE7AOP
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Posts: 32




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« Reply #5 on: January 22, 2003, 01:02:35 AM »

I was seriously considering a PVC mast to support the apex of an inverted V - but dropped the idea in favor of using fibreglass tubes. (15 feet on flat roof top.) Fibreglass is much stronger and more elastic in its flex then PVC as well as being a better RF insulator. Also I wanted to make a telescoping tapered mast for strength and easy take down. Tapered masts are stronger because of the lower centroid (center of mass more or less).  Available PVC pipe diameters do not allow for neat, snug sleaves. I found a supplier of fibreglass tubing dimensioned so that a segments can be snugly sleaved together.  (Max-Gain Systems out of Marietta,GA www.mgs4u.com )  I have ordered some and will try it out.  If you like I can let you know how it works out.  (Given time constraints this project is goiing to take a few weeks - probably longer!)  
73, Ralph VE7AOP  
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VE7AOP
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« Reply #6 on: January 22, 2003, 01:02:52 AM »

I was seriously considering a PVC mast to support the apex of an inverted V - but dropped the idea in favor of using fibreglass tubes. (15 feet on flat roof top.) Fibreglass is much stronger and more elastic in its flex then PVC as well as being a better RF insulator. Also I wanted to make a telescoping tapered mast for strength and easy take down. Tapered masts are stronger because of the lower centroid (center of mass more or less).  Available PVC pipe diameters do not allow for neat, snug sleaves. I found a supplier of fibreglass tubing dimensioned so that a segments can be snugly sleaved together.  (Max-Gain Systems out of Marietta,GA www.mgs4u.com )  I have ordered some and will try it out.  If you like I can let you know how it works out.  (Given time constraints this project is goiing to take a few weeks - probably longer!)  
73, Ralph VE7AOP  
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KE4MOB
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« Reply #7 on: January 22, 2003, 10:13:23 AM »

Here's one from the "what in the h**l was I thinking"  department.  5 or 6 years ago (right after I got my ticket) me and my buddy decided we needed a field erectable mast for a dipole on field day.  We decided on 40 feet of 1.5 inch PVC pipe.  We immediately ditched the idea of using couplers.  Instead, we took 2 foot sections of 1.5 inch angle iron and "sandwiched" the pipe joints together, in essence bolting the joints together much like rails are joined together on the railroad.  We drove a long piece of construction rebar into the ground and left about 4 inches sticking up to use as a base pin.  Two sets of hemp (!!) rope guys were added at 20 and 40 feet to provide support.  The whole mess was assembled on the ground.  One person positioned the bottom over the pin while another tugged on the guy at the top.  The conclusion?  PVC is amazingly flexible.  At one point the bottom of the mast was on the pin, the top of the mast was on the ground, and the whole thing bent much like the shape of a rainbow.  It was like trying to work with sphagetti.  We finally did get it up (and it worked), but the bottom 10 foot section was not rigid enough to maintain the weight of the sections above and still remain "in column".  In retrospect, we probably should have only went to 30 feet and used metal instead....but we still laugh about the "sphagetti dipole" to this day....
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NZ5L
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Posts: 220




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« Reply #8 on: January 22, 2003, 10:25:04 AM »

I would like to pass on one idea I have used concerning the use of PVC as an  antenna mast.  First, I would recommend the dark colored variety if you can get it.  Use a 10'  length of schedule #40, and wind about 66' of insulated wire in an evenly spaced spiral from bottom to top.  At the top, fasten the wire to a short whip antenna - about 12-14" (not critical).  This correspons to a 1/4 wavelength vertical for 40 Meters (you will need a few radials).  A Simple wood bracket with large U-bolts is used to attach to eave, etc.  Performance was better than any short mobile whip, and can also be used on 15 and the SWR is not too bad.  This idea is from the old ARRL  handbook, for a usable, cheap, and short 40 Meter antenna.  (I scrapped mine when I got my firsr Butternut antenna, but it worked OK.)  P.S.- Use with a tuner is recommended.  GL.
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WB6BYU
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« Reply #9 on: January 22, 2003, 03:23:55 PM »

As others have noted, PVC pipe is quite flexible, and
will require guying to keep it reasonably straight.  I
also find the thicker wall types are comparatively
heavy, which increases the problems with bending.
However, you probably can get it to work up to a height
of 20'/6m or so.

Personally I'd check the black ABS pipe used for sewer
lines and vents:  it is lighter than PVC of the same
diameter and stiffer.

I looked at the metal EMT conduit and it seems rather
heavy for this application.  It probably would work,
but you may want a better splice between sections than
the standard connector.

Another material you might look into is downspouts,
either metal or plastic.  They tend to be larger
diameter with thin walls, giving a reasonable tradeoff
between weight and stiffness.

For portable use, I've found that mast sections about
4' ( 120cm ) seem to be a good length.  Instead of
assembling the mast horizontally and trying to raise
it upright, I set the top section vertical with the
guy ropes attached, then pick it up and insert the
next section underneath it.  This avoids a lot of the
lateral stresses that can turn PVC pipe into an arch
(and TV push-up masts into a pretzel on Field Day.) By
leaning the mast against two of the guys, I've put up
a 40' mast by myself in less than 15 minutes.  I find
the 5' sections are just too tall for me to comfortably
hold the mast in the air while inserting the next one,
though a step ladder might help.
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WA9SVD
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Posts: 2198




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« Reply #10 on: January 22, 2003, 10:07:35 PM »

I wouldn't recommend going much over 20' with PVC for a mast, and NEVER without guy lines.  It's NOT my original idea, but there IS w good way to join two sections of PVC pipe.  
    You need two sections (use three sections at your own risk, but this may work with the larger diameter pipe, I've ised it with two sections of 1.5" PVC...)
   
    To join the two sections, you need a 18-24" section of the next larger size pipe, the kind that won't quite  fit over the smaller size.  You use a hacksaw to split the larger size pipe, clean up the burrs, and it will JUST fit over the smaller pipe.  Now, use three or four hose clamps, evenly spaced, to secure this "splice."  And it IS really "flexxy."  Make sure you support while erecting it, and make sure to guy it!  But it WILL work, especially for temporary operations.  (And if you use it to support the center of a dipole or inverted "V", all you need are an additional guys, as the dipole elements serve as guy wires themselves.
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