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Author Topic: Antenna Foundation / Mast Question  (Read 4097 times)
KD2CJJ
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Posts: 368




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« on: June 27, 2012, 11:08:22 AM »

After a few discussions I have started to gather the various parts to get me on the air.

The last piece is the antenna foundation.

I am putting up my 3 band dipole antenna on the side of my house held up by a mast attached to a wall mount support - it will be up around 25 feet.

I want to do it right the first time planning a small Hex beam OR Vertical later on...


I want to run the support mast (foundation as I call it) from the top most bracket down to the ground, with around 4 - 6 feet burred with the top most section either having a small end off the bracket OR even if mast piping allows no more then 5 feet above the top bracket.  Top to bottom 10 foot sections coupled together (some how)

I have two options that I can see.

Option 1 - LDR Industries 1-1/2 in. x 10 ft. Galvanized Steel Pipe at my local home depothttp://www.homedepot.com/Plumbing-Pipes-Fittings-Valves-Galvanized-Pipe-Fittings/h_d1/N-5yc1vZbuu8/R-100536541/h_d2/ProductDisplay?catalogId=10053&langId=-1&storeId=10051

with LDR Industries 1-1/2 in. Galvanized Iron FPT Coupling http://www.homedepot.com/Plumbing-Pipes-Fittings-Valves-Galvanized-Pipe-Fittings/h_d1/N-5yc1vZbuu8/R-202310548/h_d2/ProductDisplay?catalogId=10053&langId=-1&storeId=10051


Concerns:  Very heavy, Couplings could give way..  Is it strong enough?

OR

Option 2
 
From radio shack Antennacraft® 10-Ft. 16-Gauge Mast http://www.radioshack.com/product/index.jsp?productId=3739599

Concerns:  Is it strong enough?


Which option should I choose?  Is there another option?
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73

Mike
KD2CJJ
K2DC
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Posts: 1343


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« Reply #1 on: June 27, 2012, 11:48:56 AM »

The Radio Shack mast would be insane to try.  16 Guage aluminum is only 0.051" thick, and it would fold like a house of cards.  The galvanized steel sounds like it might be promising.  I would recommend more than just the one bracket at the top, perhaps adding one or two additional brackets if you can.  That should add quite a bit of rigidity and take strain off the couplings.

I would also recommend the small hex beam (or a very small yagi like an MA5-B) over a vertical.  An elevated vertical requires tuned radials for each band (best with more than one per band), and at that height it also might beg to be guyed.  That's an awful lot of stuff hanging off the house.

73,

Don, K2DC
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WX7G
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Posts: 5917




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« Reply #2 on: June 27, 2012, 11:56:55 AM »

The Radio ShackTM mast is steel and is pretty strong. I've used it in Colorado for just such an antenna and it held up fine in winds exceeding 70 mph. For the dipoles it would be fine extending 10' above the roof line and anchored at the roof line. This is how I used it. The bottom of the mast does not need to be deep in the ground as the bending moment on it is small. A foot or so should work.

As for the Hex Beam I would want to run calculations unless it was mounted just a couple of feet above the anchor point.
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KQ6Q
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« Reply #3 on: June 27, 2012, 12:36:40 PM »

I've got the Radio Shack steel mast setup - a 10' mast on the side of the mobile home with 3 brackets for rigidity - it doesn't touch the ground. At roof level, a 5 foor steel mast section, then a rotator, then another 5' mast with a 6m 3 el, and a 2m14CP. It's been up for about 10 years, with the winds here in SoCalif. I'm starting to get a bit nervous, with the weight - a lot of mass starting 5' above the roofline - am seriously considering taking down the beams and rotator, and going with horizontal loops for 6m and 2m. But the masts are plenty strong - but starting to show some rust. I'm 6 miles from the ocean.
I have another setup done with galvanized fence topline tubing - it's got a discone on top, and a hamstick dipole. No rust, and with less mass and area, no issues with the wind.
With both, I have lovely bird perches, with the resultant ground cleanup needed a couple of times a week!
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VE1IDX
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Posts: 141




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« Reply #4 on: June 27, 2012, 12:53:18 PM »

Agreed with the last two posters. The RS mast is adequate for what you want. The only stress on it will be from what is above the topmost support bracket. It's not like you are running 10 or 15 feet of it unsupported. Many folks up here use a 10 foot length of it in the top of their towers to support light duty antennas like large TV antennas, dipoles. VHF/UHF yagis, and even CB antennas and small tribanders. The thing is to not have too much unsupported mast and you will be fine. Like someone above said about the base, there is not that much bending moment at the bottom of the mast so it will only need to be a foot or preferably two in the ground.; Best to dig a hole, set the mast it it and then add some concrete mix. That will give the mast an even larger diameter and keep it from wanting to move at all.
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K5LXP
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« Reply #5 on: June 27, 2012, 02:20:54 PM »

I want to run the support mast (foundation as I call it) from the top most bracket down to the ground,

There is no value to having all of that mast from the rooftop to the ground.

Use ~10 feet of mast, with either eave brackets or standoffs.  Put a pulley at the top of the mast so you can hoist your antenna up and down at will.  Don't make this thing any more expensive and complicated than it has to be.

http://www.dennysantennaservice.com/1476678.html
http://www.dennysantennaservice.com/1079227.html


Mark K5LXP
Albuquerque, NM
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AA4PB
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Posts: 12672




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« Reply #6 on: June 27, 2012, 02:49:41 PM »

The value of having the mast run all the way to the ground is that it eliminates the downward pressure on the house support brackets. The mast doesn't have to be deep into the ground, but you may want to pour a concrete piller of some type of support below the frost line - depending on your local weather. The mast can then be easily grounded at the base rather than having to run a ground wire down the house for lightning protection.

You might also want to consider putting a slightly larger (than the mast) pipe into the ground and sliding the mast into it so that you can remove it from the support if need be. I added a flexible plumbing boot over the junction so that water doesn't run down the mast and into the support pipe where it could freeze and damage the pipe.
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WB6BYU
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« Reply #7 on: June 27, 2012, 04:56:43 PM »

The base serves two purposes:  to support the downward pressure of the mast and
keep it from sinking into the ground, and to keep the base from moving sideways.

Sinking a significant length of pipe into the ground isn't necessary:  it won't help
with the first one, and is way more than needed for the second.  A couple feet of
rebar or angle iron driven into the ground with the mast slipped over it will prevent
it from moving.  A 6" square metal plate or other flat object with a hold through
it (to pass the stake) will support the mast (unless the soil gets very wet.)  You
just want to spread out the weight over a larger surface area.

That assumes that the mast is bracketed to the edge of the roof, of course, which
provides the side-to-side rigidity for the upper part.  Sinking a mast into the ground
as you proposed might be useful if you were trying to make it self-supporting without
the benefit of being attached to the house.
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K5KNE
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Posts: 65




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« Reply #8 on: July 04, 2012, 07:44:18 PM »


The "footing" is not a big deal. When you get your house bracket in place drop a plumb bob or just a weight on a piece of string to center the hole in the ground. Just dig a little depression like the start of a fence post and put the butt of the pipe in it - backfill it.  The attachment to the house is of much more importance - like some of the above posts have said.  A good house bracket for a mast will do the job - be sure you are screwing or bolting into a 2x or something more than just the facia board.

Good luck on your project.

Walter   K5KNE
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