Tower Foundation

[W9WD]

I have 29' of 25G and plan to get another section making 39'. I want a "no guy wire" setup so I need to pour a large foundation block.
Has anyone done this with this size?

I'm thinking 4' square and 3' deep. That would be just shy of 2 cubic yards.
Is this enough concrete?

I got some 1-1/8 stainless rod and plan to drill it so it will slide into the bottom of each of the legs. Each SS piece is about 30" long. I plan to weld some chunks of stainless plate on each leg so it won't pull out of the concrete or rotate etc.

The tower will mostly be protected from wind by some Doug Firs and we rarely get extreme winds. I think I will only put the yagi on the tower and leave the 5/8 where it is. I think the wind load of the antenna is about 5'

Ideas?

 

[W5LZ]

That's close to the right amount of concrete. Instead of the dimensions you gave, I think I'd turn them around, 3' x 3' x 4' deep. Deeper wouldn't hurt a bit, maybe even 'bell' shaping that hole a bit. Especially for a free standing tower, you really do want a good pier under it. It's been too long, I don't remember the Rohn installation specs anymore. I think that 40 feet is pushing it though, without some mid-level bracing (eave of roof, whatever). If you ever plan to climb the thing, not fold it down, then you really do need to guy it. It's your neck though, treat it like you thing it ought'a be treated.
Instead of just three rods in that concrete to hold the tower, think about bracing those rods into some form of framework the full depth of that hole.
I know it sounds like a lot of 'over-kill' but it really isn't.
- 'Doc

 

[W9WD]

Thank you.
I don't mind overkill. I practice it regularly.
I'm going to try to figure a way to use a bucket truck (etc) instead of climbing the tower. Heights have been bothering me more as time goes by. Hopefully it will make the install easier (and safer)

 

[kd-5-bgt]

You shouldnt have any trouble with the 3 by 3 by 4 feet deep pad and the way you plan to tie the tower to the pad should work fine,and maybe guying it for anything unforseen wouldnt be a bad idea either.

I live in Missouri and if you dont practice overkill chances are good you will find your antennas on the ground :blink:

 

[HiDef]

As you probably know, 25G is 25G because the G means guyed. The stuff is supposed to be guyed every 30 feet. It isn't designed to be self supporting. Self supporting towers are completely different than 25G. You could put it up on the side of your house and bracket it to the house to get around the problem. A good house bracketing setup is plenty of work and can transmit noise to your home.

Concrete tower bases need reinforcement rod A.K.A. rebar in the concrete for strength. Rebar needs no welding. Welding rebar is a lot of work and has questionable value as rebar alloys vary. Rebar can be tied together with tiewire. Most large metal suppliers will sell prefab J bolts for tower bases. US Tower's website has engineering drawings for tower bases that you can peruse. Towerbase pours should be made against undisturbed soil. That means no forms below grade. You pour against the excavated dirt. This can be a real problem with sandy soil. In colder climes the tower base pour should not stick up above grade either. That contributes to frost heaving.

Make sure water has a way out of your tower where it meets ground. It can freeze and expand. This will crack the pipe.

Also check out towertalk on the WWW. Plenty of good info there.

Best of luck.

 

[W9WD]

Over the weekend I sort of decided to wait until I get it to New Mexico. There I can attach the tower to the radio shack at 10-12 feet leaving less than 30 feet unsupported.
I also thought about getting a short tilt up section as a base.
If I put up the tower at one end of the shack and a "gin-pole" attached to the other end I could use an electric winch to pull the tower up and down. It would also lower the total length. My goal is to get 1 wave length of tower at 10m. Having a tilt up is very appealing.

 

[74IN]

HiDef said alot, he seems to know his stuff.

The bell shape Doc said is also good, the large base helps against the leverage of the tower.

Call the concrete company you intend to use, most have a small load fee. Might want to form a sidewalk or any other project you might have at the same time to avoid it.

 

[W9WD]

Call the concrete company you intend to use, most have a small load fee. Might want to form a sidewalk or any other project you might have at the same time to avoid it.

I'll say
They are currently charging delivery fees of $4 per mile. Socorro is about 80+ miles away

 

[Captain Kilowatt]

Check the Rohn website for specs. They state that 40 feet of 25G should have no more than 1.5 sq. ft. of antenna surface area in a 70 Mph wind with zero ice loading. Not reccommended at all for 80 Mph.I would not want to install it as you have proposed.

As for the base,I agree with Doc. Going 3 X 3 X 4 feet deep is the better idea. As for the rebar,almost nobody I know of installs rebar in their own ham tower bases except the rich guy that install commercial towers and have professional riggers do thge job for them. I have had a 4.5 X 4.5 X 5 foot base with no rebar in it for almost 20 years and no problem at all.It even extends above grade about 6 inches as well. It does not affect frost heaving and trust me we get frost up here. All commercial towers are installed this way as well.Frost heaving comes from frost getting under the base if it is not deep enough.

 

[kevin IB/379 Stringbean]

My 51 footer three section freestanding hole was 4x4x6 deep.definately needs to be deeper than the width to prevent it from being able to fall to the side.Almost 4 yards of concrete.$110.00 a yard where I live.A buddy of mine ties re bar for a living and tied me up a bitchen cage for the hole.You can check it out in my pics.Send me rour e mail and I'll shoot you some pics of mine as I did it from beginning to end if you want.PM me.

 

[74IN]

Rebar can't hurt and it's cheap. #4(1/2 inch) is low cost peace of mind.

The frost thing is correct. Here in North West IN, the frost footing is 42" by code.

Isn't Nova Scotia decent in winter due to the ocean, or do you get the typical bitter cold we Yanks think of Canada getting?

 

[Captain Kilowatt]

Rebar can't hurt and it's cheap. #4(1/2 inch) is low cost peace of mind.

The frost thing is correct. Here in North West IN, the frost footing is 42" by code.

Isn't Nova Scotia decent in winter due to the ocean, or do you get the typical bitter cold we Yanks think of Canada getting?

We don't get as cold as the midwest does that's for sure but it does drop to 0º F here quite regularily at night in Jan. and Feb.The record low in my time was -32º F and that was the winter of '91/'92. It stayed below -10º F for almost two weeks even in the daytime. Normal nighttime lows are around the low teens to single digit temps for Jan. and Feb. which are the coldest months.The summers are nice as we rarely ever get above 85º F but the humidity starts to become pretty bad then.

 

[airplane1]

My tower is the 2 hole american, you know the old style tower with the straight bars instead of zig zag rohn style. I have on a 3x3x2.2 ft base with about 4 inches sticing out of ground level and used 4000lb concreate.

The tower is up through winter and all kinds of storms including 60+ gusts and it is 36 ft to the base of my maco 5/8 free standing. So far so good. I think you would be OK with 36-40 ft free standing with a small antenna but I would put it close to the house or other structure and bracket it. I am going to braket mine this summer as soon as I get the time just for good measure.

I sen a web site a while back where they tested rohn 25g and the old american 2 hole per leg tower on saw horses and adding sandbags till it failed, the american was much stronger which surprised me as it is old tower. I do know on the american web site it says the 2 hole tower is HD and self supporting.

Hope this helps