Digging hole concrete cement for high-wind (120mph) WiFi antenna

I've never done this before so I merely ask advice.
Googling, I find that this seems to be the set of steps to install a combination TV WiFi (WISP) antenna pole (mast?) in the San Francisco bay area San Franciscian sediments (mostly chert) where it rarely freezes for more than a couple of hours but the wind can easily top 100 mph.
I'd like it to be removable (not sure why ... but it just seems like that's a better way to do it than installing it permanently).
Critique requested on the initial plan:
1. Go to Home Depot and buy large thick steel pipe for the support, maybe two or three feet long (1.5" ID?); also buy a 15 or 20 foot long steel pipe (1" OD?) for the mast. 2. Drill & tap a series of set-bolt holes in the top 6 inches of the large pipe 3. Dig a two-foot deep hole in the soil, about a foot in diameter. 4. Fill the bottom of the hole to the 18 inch deep mark with gravel. 5. Mix concrete and pour the concrete around the large pipe to ground level with the large pipe sticking up at least six or so inches 6. When set, lower a 15 or 20 foot one-inch OD steel pipe into the larger pipe, and tighten the set bolts.
Anyone have experience in this type of endeavor that I may learn from before I do this job?
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No experience and little knowledge here, but I suspect there's not much point in worrying too much about your footing if you're going to use such a flimsy mast... At the very least you'll need a few hard- points to guy it. Think much large diameter, in which case the "pipe" you'll find at HD will be pointlessly thick (and expensive).
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Agree. 1" is going to be way to flimsy for 15 or 20 ft. I'd be looking at 1 1/2 or 2" for the mast. I'd also go a lot deeper than 2ft with only 18" of concrete. I'd probably go 4 ft deep using a large sona tube.
I never tried tapping a pipe like that for set bolts. The pipe wall is not very thick and I wonder what holding power it will have. Ideally, I'd weld a nut on it and skip the tapping.
Alternatively, some googling might find a ready made kit with all the components.
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wrote:

check with local amatuer group for advice.....
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On Sat, 12 Nov 2011 09:42:03 -0800, snipped-for-privacy@optonline.net wrote:

That's good advice (which others also suggested). So I'll go deeper (I may need a hole digger corkscrew for that deep of a hole).

Makes sense. It would have stronger threads and can be welded onto both sides of the pipe hole.
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On Sat, 12 Nov 2011 09:25:17 -0800, Larry Fishel wrote:

I'm ok with a thicker & deeper mast if that's what it takes.
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worker bee wrote:

The wifi antenna will not be any significant wind load.
You'd have to specify what TV antenna you're looking at. It's either going to be a pure UHF antenna ("bow-tie" / Gray-hoverman or Yagi) or a combination UHF / VHF. This will depend on what TV channels (real or RF channels, not virtual channels) you want to receive, and how far away they are.
Go to the website "tvfool.com" and enter your address (or somewhere relatively close if don't want to give it your exact street address) and you'll get a map diagram and chart showing what TV stations are around you (up to about 100 miles away) and your likelyhood of receiving them.
A UHF or combination UHF-VHF-hi antenna can present a moderately large wind load.
If you're really going to build for a 100 mph wind event, a single mast (even if it's 2.5" OD steel pipe) will not take that wind if it's more than 20 feet high with a medium-sized antenna.
You haven't said if this mast is free-standing (in the middle of your back yard or some other relatively open space) or if it's running up along the side of your house (or some other structure) where it can be supported (tied) to the structure somewhere higher above ground.
There's also the possibility of supporting the mast with guy wires.
Do you intend to have an antenna rotor? Again, the map diagram that TVfool gives you will tell you if the antenna can be fixed in one direction to receive the desired (or the majority) of available channels.
As others have mentioned, 18" worth of concrete is not enough.
I would use a 1 or 2-man gas-powered post-hole driller to drill an 8" or 10" diameter hole, 4 feet deep (or even 5 feet using a drill extension). Then set a sono-tube into the hole and your pipe and pour in the concrete. You won't need a 12" diameter hole (it's a bitch to drill a hole that size compared to 8" or 10"). You can throw some re-bar into the hole before you pour in the concrete.
Mixing concrete is not exactly a science, but with a little bit of care and extra preparation you can make a very strong concrete mix yourself, instead of the pre-packaged garbage you get from the big-box stores.
And as others have mentioned, a 1-inch pipe is way too small, even for a 10' mast. You want a minimum 2.5" pipe if you're going to 20-feet, and even I wouldn't want to do that without some support guy-wires attached to it somewhere.
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On Sat, 12 Nov 2011 14:10:02 -0500, Home Guy wrote:

Interesting. I would have figured the parabolic dish (even if it's a wire mesh) would catch the wind more so than the standard protruding Y-shaped TV antennas I see on people's houses.

Nice web site. It looks like, at 10 feet antenna height, I'm "green" for: Analog channel 6 @ 38.7 dbM Digital channel 32(46.1) CBS @ 39.7 dbM
And, I'm "yellow" for: Analog channel 2 @ 30.7 dbM Digital channels 19,38,39,22,8,13 @ a minimum of 21.5 dbM

The intent is to be free standing on a hillock in the back yard.

Yuck.
ancillary TV antenna to the one or two stations that are best.

I see. Looks like I'll be going 3 or 4 feet deep (I had thought concrete was stronger).

I need to rent one of these babies.

Will do!
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worker bee wrote:

Some thoughts. You can buy high strength steel pipe that can do this job, but probably want it somewhat larger than 1". This is NOT water pipe you get at Home Depot. You don't want it bending in the breeze.
Make sure neither pipe is closed at the bottom. Gravel is good until you let the pipe work its way thru and plug up with dirt during installation.
You want a lump on the outside of the pipe in the concrete. Smooth pipe risks working loose and rotating when the antenna applies torque. Once the pipe starts moving in the concrete, the support will deteriorate rapidly.
I'd worry about corrosion that near to the ocean. The pipes need to be a snug fit. But, it won't be long before they're rusted together and your pipe won't be removable any more.
If the pipes are not a snug fit, you're hozed. You need at least two solid mounting points as far apart as possible. The pips banging around in the wind will drive you nuts while the mounts grind their way thru the metal.
The usual solution is to put the pipe at the end of the house and support it at the apex of the roof. That turns your iffy project into a no-brainer. You won't need any concrete at all. Guy wires can help a lot.
120MPH IS A LOT OF WIND.
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better plan....
Take a look at mast / antenna combos online. The mast / antenna combo that suits your requirements will have a footing suggestion for you.
A 1" or even a 1.5" pipe will be way too flexible for your application at a 20' height.
Antenna masts are very often three sided frames made of triangular elements much stiffer than a flag pole pipe.
Even an school yard tetherball pole will have 2" pipe and it's only ~8' tall.
cheers Bob
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On Sat, 12 Nov 2011 17:02:41 +0000 (UTC), worker bee

Get some six inch well casing. Dig a hole at least 30 feet deep and set the pipe with 70 yards of concrete, being sure the pad is at least 10 ft. x 10 ft. and 14 feet deep. Attach your antenna and watch tv for 100 years or more.
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If your TV antenna has any size to it you should not use what you stated.
There are all kinds of pipe available but for best results you should use hardened light weight pipe. This type of pipe is specifically made for use as a mast pipe. Standard water pipe is just to heavy. It will use its own weight to help bend itself when rocking in heavy wind. Use guy wires if practical.
Use this page as a guide http://www.texastowers.com/towerhardware.htm
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wrote:

just a minor curiousity, but what requirements do the planning commission/building department require...it is SF and I can't imagine you'd get away doing this without an approved set of plans
OTOH, i'd consider buying a surplus telephone pole and digging a hole about 25% the length of the pole to place it in
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Malcom \"Mal\" Reynolds wrote:

I think a lot of this thread is bull crap.
I'd like to know where in the SF-bay area the OP lives in. Then run that city through tvfool.com to see what TV stations are in the area.
My gut feeling is that you won't need a 20'+ mast to pick up what-ever stations are available in the area.
A larger yagi, or a double-bay or quad-bay bowtie, either one with a good amplifier, can be mounted closer to the ground to compensate for not having a taller mast.
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Home Guy wrote:

multipath than signal strength. I've got lots of signal but poor reception. Might have something to do with the metal pole building 50 feet away. Height can make a big difference in a hilly area with lots of reflections.
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He did say WiFi, not TV, which means the above is irrelevant. But even if it were TV, it's not all that unusual to find a location that needs a 15 or 20ft mast to pick up TV. Most places you wouldn't need it. But that doesn't make it BS for someone that does.
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On Sun, 13 Nov 2011 13:49:36 -0800, "Malcom \"Mal\" Reynolds"

They dont have "telephone poles" anymore. Many years ago they had the phone up on the pole, and to make a call, you would have to climb the pole. I recall seeing this on "Green Acres". But those days are long gone. Now we have cell phones. Ya know, those annoying things in your pocket that demand your attention at the worst possible moment, like when you are 40 feet up on an electrical power pole connecting a 275lb triplex cable, or under your car lifting an automatic transmission into place. Then after you fall off the pole, or you drop the tranny on your forehead, you find your cell phone has no signal. Ahhhh, yes, bring back the good old days, where all we had to do was climb the telephone pole to make a call!
And, regarding the person who suggested using "guy wires", what if you would rather have GAL wires. You know, the female variety. Why are those wires always made just for the guys? That's kind of sexist if you ask me.
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