My planned antennas - w/ pics

[killmoles]

I am in the process of building a short but sturdy 25' Rohn 25G tower and this is what I plan to put on top off it. I'll share all of that later in the Pictures forum, but this post is just about what I'm pretty set on doing with the antennas. I just poured the tower base yesterday, so while I'm waiting for it to cure I loosely assembled the antennas in the garage today with the top section on sawhorses. Unfortunately, I will have to take it all apart and rebuild it up in the air once I put this last tower section on.

From left to right, DPD Omni-X, Diamond X-50NA, and Diamond D-130NJ. The mounting assembly for the side antennas is the Radio Shack 1.25" mast that was on clearance recently, all connected with Rohn double bend u-bolts. I also want to hang an inverted vee for 40 and 80 meters off the bottom of the vertical piece supporting the DPD. It's a little over 30" from each tower leg to each adjacent side antenna mast.

I wish the pictures were better but this is the best I could manage in my messy garage.

 

[ridgescan]

Oh NICE I am shocked nobody commented in here. That set is going to look very pro. Looking forward to the finished one

 

[davidgcet]

looks good, i would leave it on there and just lift the whole thing up.

 

[ScanWI]

I like it that gives me some more ideas for the future

 

[killmoles]

Thanks for the comments. I'd love to lift it in place all assembled like that, but I don't think I'd try it with a gin pole and a crane is out of the question.

 

[prcguy]

I would move the antennas farther apart if you can and raise the center one several more feet so there will be no interaction with the side mounted ones. It looks like your have a Rohn 25 tower and maybe 8ft long tubing for the horizontal mount. You should be able to use 10ft tubing for the lightweight antennas they are holding up.

I have a short Rohn 25 tower but used two 10ft sections at the top for holding an array of antennas. My spacing is only about 3ft between antennas but I carefully arranged VHF/UHF and 800/900 antennas for the least amount of interaction. I can also climb the tower and walk out on the horizontal section to service antennas.
Mike

 

[davidgcet]

do it whatever way feels safest to you, we send them up assembled all the time but we also use professional tower monkeys!

 

[kb2vxa]

I suspect the center one is a transmitting antenna, if such is the case it's imperative you raise it above the others to avoid burning out receiver front ends. In any case interaction and stray signals leaking back up the pipe from scanners, etc. should be avoided. A 10' section of Rat Shack steel antenna mast should do nicely, you'd be surprised how strong it is.

"...we also use professional tower monkeys!"
It's bad enough that monkeys fling poo as it is but I hope they're not unionized or it won't be long before they start demanding more bananas, shorter hours...

 

[davidgcet]

yeah, some of them can get pretty demanding. luckily they ain't unionized yet, if they do i will have to start buying bananas by the case!

 

[killmoles]

Okay, I got the top section up today with the help of a friend. Just the top section, I'll be building the rest again up there. Some pro tower monkeys would have been nice but it was just me and my friend. Also got to use my tower harness for the first time. Everything went well but I sure need some steel shank boots! Those of you who have worked on a Rohn 25 know what I'm talking about...

I've decided to raise the center transmit antenna up above the others as suggested. I was worried about the same thing, even though I rarely transmit. I've removed the short tubing that was going up from center in the pics and will be adding another 5' or so. I think I'll leave the horizontal distance as is. More would be better but I'd only gain another foot or so on each side and I don't want to increase the wind load any more than I am doing now by raising the transmit antenna.

 

[kb2vxa]

"Everything went well but I sure need some steel shank boots!"
Fairies wear boots but what about the Monkees? (If know what I'm talking about you're showing your age.) Eh, adding another section adds a weak point, you'd be better off using a single 10' section. That's quite enough and you don't want to go higher putting more wind load on the mast. As long as the transmit antenna is not in the same horizontal plane as the others it's quite OK.

 

[killmoles]

kb2vxa, you do know what you're talking about! I'm 46 and it's starting to show, but I never listened to the Monkees. I did listen to Black Sabbath though, which you may have referenced.

We're on the same page with the center mast too. I removed the short piece that fits in the top tower section and will replace it with a longer one. I'm not comfortable with a full 10' section there so I'll go with around 6' or so which will bring the bottom of the TX antenna above the top of the scanner antennas. The short center mast section kept everything low enough that I could service it while strapped to the top of the tower. With a taller center mast I'll just have to remove it from the tower before working on the top antenna. This is being built for max antennas with as high of a wind survivability as one can do with a non-guyed 25G. What I showed in the pictures is getting close to 4 sq ft according to my estimates. The tower and base met those specs, before I bracketed it to the house. I always overbuild everything...

 

[kb2vxa]

"kb2vxa, you do know what you're talking about!"
I'm glad SOMEONE appreciates me! (;->)

"I'll go with around 6' or so which will bring the bottom of the TX antenna above the top of the scanner antennas."
Good enough.
"The short center mast section kept everything low enough that I could service it while strapped to the top of the tower."
A picture is worth a thousand words.
"With a taller center mast I'll just have to remove it from the tower before working on the top antenna."
Nope, remove the bolt that supports it and slide it down inside the tower.
"I always overbuild everything."
OK then, add a cross brace to prevent the mast from falling down inside the tower when the bolt is removed. That's a whole lot easier than trying to retrieve it from its cage should you lose control.

You have an interesting user name, should the mast get out of control that's likely just what would happen. (;->)

 

[killmoles]

Warren, your sense of humor is amazing!

I think I'll buy a stick of 1" rigid conduit and cut it down to 7' for the top antenna mast. I'll probably regret not using the full 10' but I'm conservative that way. I need the 1.315" OD because the short heavy gauge fence top rail I had in there was 1.315" OD and it was a tight fit pressing it into the factory top bushing made for 1.25", which is just too loose there now... Is the rigid conduit overkill or too heavy for this application? I don't think I'd trust the extremely thin wall top rail that's available at the home improvement stores, but I could always call the fence companies and see if they have some heavy stuff they could sell.

My user name comes from the many moles in my yard. Even with this project I dug into a mole tunnel and one kept pushing dirt from the tunnel into the corner of my tower base hole. I even had to use the shop-vac to get the dirt out the day I poured concrete! More pics coming soon, my coax and other needs should arrive tomorrow.

 

[davidgcet]

how tall is this tower? that looks like a lot of concrete to fill the hole. unless the pic is deceiving, it is almost as much as on our 180' Rohn 25! for a 50' or so self supported but house bracketed towers we used to just stick 4-5' in the ground and fill with dirt, 30 years later thise are still standing straight even though it never was the "recommended" means of installing!

 

[wyomingmedic]

Looks great!! I am curious as well, how tall is that going to be?

I have an X50NA at 60 feet above my house which is about 50 feet over the rest of town (we're on a hill). It is an awesome performer and has been meeting my strict requirements.

As for tower climbing, I wear cowboy boots every day and they are the perfect thing for tower climbing. Get a real nice leather sole pair of heavy riding boots and you will feel great.

WM

 

[prcguy]

I'm with David on this one, the Rohn 25 is not self supporting and must be guyed if over about 20ft, what is all that concrete for?
prcguy

how tall is this tower? that looks like a lot of concrete to fill the hole. unless the pic is deceiving, it is almost as much as on our 180' Rohn 25! for a 50' or so self supported but house bracketed towers we used to just stick 4-5' in the ground and fill with dirt, 30 years later thise are still standing straight even though it never was the "recommended" means of installing!

 

[towerclimber37]

I suspect the center one is a transmitting antenna, if such is the case it's imperative you raise it above the others to avoid burning out receiver front ends. In any case interaction and stray signals leaking back up the pipe from scanners, etc. should be avoided. A 10' section of Rat Shack steel antenna mast should do nicely, you'd be surprised how strong it is.

"...we also use professional tower monkeys!"
It's bad enough that monkeys fling poo as it is but I hope they're not unionized or it won't be long before they start demanding more bananas, shorter hours...

ok, you can stop making fun of us now... *grin*

I've been one of those "professional poo-flingers" for about 11 years now. I doubt we'll ever unionize. Most of us hate unions and rarely like being told we have to give our money to some pen licking chair sissy so that he can tell an employer something that we can say well enough ourselves.

As for the tower. It looks good. I would make a small suggestion though. if you extend your booms out any farther, bolt yourself some round stock on, below the antenna booms so it will make it easier to walk out on and tie off to work on your antennas. Then some shorter round stock to the bottom of your boom at the ends. That way it'll be stable and give you a good work platform.
any farther than 3 feet off the tower and you're not going to be able to really reach it comfortably and those things are a pain in the huevos for us to climb up on and shimmy out to, especially when they're that rickety.
Keep in mind when you build these booms. they need to be able to take about 1000 pounds of weight on em as a safety factor if a person needs to get out on them.


also, if you feel uncomfortable flying the booms with antennas already built on them, fly everything except the antenna's themselves. they don't take too long to put up.,

Other than that? it's a great looking tower and boom! I hope that my suggestion will help you when it comes time to maintain it.
If you're doing your own climbing, I can only say be safe and keep a 100% tie off at all times.

73

 

[killmoles]

I'll try to answer the posted questions and detail the method to my madness.

I used many information sources to design this installation, with these two documents being the most important:

ROHN G-Series Self Supporting Tower -Low Cost Solution for Lightweight Antennas

ROHN Products, LLC

The tower itself is approximately 25' AGL.

I am located in a 90 MPH wind zone, but winds over 100 MPH are not all that uncommon. In 1998 we had winds over 110 MPH come through my neighborhood. Ice accumulation is not uncommon either. I am in a 3/4" ice at 40 MPH zone. There are many different ways to measure and describe wind, but you get the idea, it can get really windy here.

Rohn designs are for "normal" soil. My soil is not "normal". At the tower location there is less than 12" of topsoil, then 24 to 30" of sugar sand, then hard pan, which is very dense packed clay. I'm basically on the upslope leading out of an old glacial path and river flood plain.

I plan on attaching approx 4 sq ft wind load to the tower.

Basically, I wanted something designed and rated to support a minimum of three antennas totaling 4 sq ft, at a minimum of 90 MPH, and at reduced wind speeds with 3/4" radial ice accumulation.

Since I had been given a nearly new Rohn 25G tower, that choice was easy.

Rohn only gives a set of "typical" installations describing supported winds and loads, none of which were exactly what I needed to build. I'm not an engineer, but I was able to use their published information to come up with a solution for me that I felt was within their design tolerances. Way too much to go into here, but I think it was sound and prudent.

My 25' Rohn 25G in a self-supporting configuration will support approx 4.1 sq ft wind load at 90 MPH. That is in "normal" soil. The bracketed configurations aren't so easy to interpret, but for discussion let's say that a 25' bracketed 25G with the bracket at mid-point will support approx 4 sq ft at 90 MPH also, in normal soil.

The base for a self-supporting 25G is 4' x 4' x 4', or approximately 2.4 cu yards concrete. This is the base I used in my abnormal soil. I don't know if I built a free-standing tower that's bracketed to my house, or if I built a bracketed tower with a large base. Either way, I can sleep at night knowing it will likely take a tornado to seriously impact my tower, and at that point I'll probably have more important things to worry about.

I didn't want a guyed tower, just a sturdy place to put some VHF/UHF antennas. Keeping the tower at 25', spending a little more on extra concrete, and buying a heavy duty bracket was worth every penny to me. Peace of mind is priceless.

I'll try to get pics of the whole thing up later this weekend.

 

[davidgcet]

yeah, you DEFINITELY overbuild! like you said though, it ain't going anywhere on you.