Suggestions Appreciated

Thanks for taking the time to read this post. I’ll make it as short and sweet as possible, I’m just looking to see if what I’m planning will work and not give any issues.

I have 40’ of Rohn 25G tower, and intend on getting an additional 30’ to add. My antenna selections will be an imax 2000, as well as a Maco BA-1 and a MFJ-1768 both on a small rotator. My concern is with my tower base. I will be running guys at 32’ and at 65’, my county wind rating is 70mph. The base will be 4x4 at 3’ deep, with 1’ above grade for a total depth of 4’. I’m situated in the thick north east Texas clay, just below 3’ I hit extremely hard pack. I did get enough depth to make the sand and gravel pack a full 6”.

Should I be concerned about the depth of my base? I don’t have any neighbors nearby nor will it be near my house, the feed line is all 1/2” heliax except the dual band, that is 1/4”. I don’t foresee it being overloaded, or anywhere near it.

I’ve put up towers for commercial use, but I’ve not dealt with the concrete work before. I myself am more of the tower dog, not the engineer.

Any opinions or advice is greatly appreciated.

I would look at the mfg spec's on the tower base.
Also is it new or used tower any rust .
A quick thought you have more coax loss at 440mhz
Than at 26mhz - 30 mhz

From what I’ve gathered it needs a 4x4x4 base with all but 6” below grade, this is on a self supporting to 40’ though. I will be guyed as stated at 32’ and 65’ per manufacturer specs. I’ve been over the Rohn site trying to make sure I get the base right numerous timesover the course of the last two weeks.

It is a used tower, no rust in or out. All of it is straight and I have new hardware for it as well. Understanding the coax loss in UHF is the main reason for hardline. Reviewing I will likely swap the dual banded and the omni feedlines. Thanks for reminding me, that late at night my brain is fried.

Once you go that height the next thing you will want is a larger antenna and then we'll let's go larger again Lol
Let's try uhf and vhf ssb it all grows from here .That East Texas Soil is good for Antenna farms.

Sounds like you got this under control Sir.

lol, well I’ve already talked to the wife and she’s agreed to another tower in the future. That one I’ll be getting equipment for to dig the holes, and 150’ of Rohn 45 is readily available here. But that will be a little while away. I don’t foresee much more than a 3 element and omni for 11meters and going into vhf/uhf ssb. Possibly going with a scanner and listening to shortwave. I figure I can do it all with the current build, but eventually I’ll want the extra height.

On another note, I am probably the only one in my area, or anywhere, that has already painted my tower and is lighting it with obstruction lighting. Not necessary for this tower and I’m nowhere near an airport, but I like a painted tower, and there’s something calming about the red lights at night lol.

I'd just throw in a reminder that coax and hardline don't weigh 0 pounds. They also increase wind area on the leg supporting them. I don't know of a good resource that can tell you how to factor them into any calculation, just reminding that they should be taken into account. Your current deployment description doesn't sound like anything close to an overload. KC5AKB makes a good point above that it's possible to end up with more than originally part of the calculation. I am aware of a certain local Rohn 25 install when making these comments.

Sounds like alot of trouble for just 30 feet.
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And higher doesn't always mean better..
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I've seen plenty of antennas raised more than that and signals actually got worse.

suggestion

A few guy wires and extra cement at the base is cheap insurance.

Just a,thought if you have some noise it could be you're lighting.

Think about stacking a few antennas with a ring rotor and a few mono band antennas

I did see a set of tennadyne log-periodic antennas stacked mainly for 20m as a test
And the second set stacked for 15m
Even a 10 or 11 meter stack of 3 would give you somthing to think about like
Www.k0xg.com
Depends on what the final goal and outcome you are looking for.

A tower foundation design is site specific as it depends on the soil. The main issue is how much side pressure the soil can take. Basically. the tower always has some side loading which is 'trying' to push the base sideways. the foundation has to have enough sidewall so the soil can 'take' it. I would ask around and see what the 'locals' do or better yet check with a local civil engineer. The side loading can be quite large -especially when wind is considered. Worse yet, if it starts moving it takes a lot less force for it to keep moving.

Not knowing the consistency and horizontal loading of the soil you are dealing with, any advise is going to be based on 'typical' values or guesses. For the most part, most foundation designs are based on overloads of 300-500% to cover the uncertainties.

Hope this helps

If the tower had only one set of guy cables then there would be some sideways forces on the foundation but most of the energy pushing sideways on the tower would be converted into a downward force. You can get away with very little foundation on a guyed tower compared to free standing. Since there will be two sets of guy cables at different heights there should be virtually no sideways pressure on the foundation, only downward force.

I agree the best solution is an engineered foundation or factory recommended size.
prcguy

wyShack said:

A tower foundation design is site specific as it depends on the soil. The main issue is how much side pressure the soil can take. Basically. the tower always has some side loading which is 'trying' to push the base sideways. the foundation has to have enough sidewall so the soil can 'take' it. I would ask around and see what the 'locals' do or better yet check with a local civil engineer. The side loading can be quite large -especially when wind is considered. Worse yet, if it starts moving it takes a lot less force for it to keep moving.

Not knowing the consistency and horizontal loading of the soil you are dealing with, any advise is going to be based on 'typical' values or guesses. For the most part, most foundation designs are based on overloads of 300-500% to cover the uncertainties.

Hope this helps

Click to expand...

Thanks for the help guys, all the extra info is helpful.

I’ll have to get pictures of it all once it gets going and the weather is right.