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Author Topic: 2el STEPPIR or HEXBEAM @ 36'???  (Read 1335 times)
VA3GVS
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Posts: 25




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« Reply #15 on: October 23, 2007, 07:55:51 AM »

In responce to a few posts and better explain set-up;
Penninger 6' Snap tube poles are made of 2" dia 6061 T6 Aluminium 1/8" wall thickness joined together with specially designed aluminium joiners. They are designed for this purpose. So mast is 2" dia from top to bottom.
1) Again would this modified arrangement work better? If instead of the use of 2 regular steel/teflon slip rings originally planned to attach guy lines, I modified the use of 2 thrust bearings such as the Yeasu GS-050. They would be installed so that the top part of bearing that rotates would be clamped onto the mast. The bottom part has 4 attachment tabs (normally to bolt to a plate I assume) that would serve to connect guy lines.
2) some have mentioned a thrust bearing just above the rotor to support weight of mast. I'm not sure how this would be mounted (All new to me, I had wire dipoles and vertical antennas in the past. That's why I'm asking for ELMER help). The Tipper base I'm using comes with a 2 1/2' long starter tube 2" dia, .250" wall thickness, attached to base. To this tube I install a Yeasu GC-038 Mast clamp connected to the G-1000DXA rotor. Another GC-038 Mast clamp attaches the upper mast to the rotor at top end of rotor. Where/How is the weight bearing Thrust Bearing installed. (thrust bearing attached to a small length of 6061-T6 AL tube coming up from top rotor clamp, then full mast connected to top of thrust bearing??) See I need help!!
As far as wind loads, this area of Canada is not subject to hurricane force winds. Our area is rated at 70 mph max. which is the lowest rating in North America.
Thanks again everyone
Gary  VA3GVS
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N3OX
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« Reply #16 on: October 23, 2007, 08:15:24 AM »

"Personally I'd never put a rotor below standard mast guying rings. Maybe below ball bearings or greased bronze bushing rings, but not a steel against steel mast ring.
"

These aren't standard guying rings.

http://penninger.com/new_page_5.htm

They look like nylon on nylon which is pretty good.

I'd prefer a metal outer ring of some kind so that the thing was fail-safe to failure of the plastic, but then again, some nylon grades are awfully strong.

I've used plastic bushings on steel and plastic bushings on aluminum for this sort of thing with good results.  I have mounted a few light fiberglass supported antennas on rotating masts simply because it makes it easy to walk the mast up.  My 20m Moxon rectangle only weighs a few pounds.  Putting even a TV rotator up there would probably triple the mast-head weight and make it hard to erect it without a fixture or a friend.

Agreed that standard guy rings would be terrible for this, but the Penninger slip rings look quite suitable.

Gary, Tom's right that you haven't given enough detail, but I think you're asking in the wrong place anyway.

When I was a teenager I built these things on the basis of two things:

1) It seems sturdy
2) If it falls, it falls only on me or my parents' property.

You can put up some pretty stupid stuff safely that way... safely in the sense that if it fails, the consequences are minor.  That said, I never had a thousand dollar antenna to put on top of anything I "engineered" myself before I knew anything.

Now I can do my own stress calculations, at least estimates, and that gives me a lot more ability to build things that need to be failure-free, like a mast in a neighborhood.

I think you need some engineering help.  I think you should get it from Penninger.  You're going to spend hundreds and hundreds of dollars on their mast equipment.

But I get the impression that they've already sent you to the internet forums.

So I don't know what to tell you.

You're unlikely to find a mechanical good Samaritan on the internet forums in the way you can find people to do calculations for you regarding electrical or electronic matters.

I think you can build a rotating mast from Penninger parts that will hold either a HexBeam or a 2el SteppIR (though the latter might be heavy duty) but without some engineering calculations from someone...

 I can advise that you should use their mast clamps instead of snap tubes and joiners.  If you use snap tubes and joiners, the joints will be weaker than the masts.  If you use those clamps with the three bolted ribs, the joints will be stronger than the masts.

This is the only thing I'm sure of.

I think the Penninger guy rings are probably OK.

But to assess the whole thing, you need to analyze the whole thing, antenna, mast, etc.

Penninger's not saving you any money over other options.  If they won't tell you what mast components you need to hold your antenna, take your dollars to someone who has done appropriate engineering analysis on their products and can make windload recommendations!

Otherwise you're on your own or at the mercy of people willing to give structural engineering advice over the internet.  It's too much of a liability issue for people to do it casually for free and give you a solid "yes" or a firm "no".  I'll do it for myself, but I'm not going to do it for anyone else.  I'm not an engineer.

Someone can design you a rotating mast that will hold your antennas but it takes time and work to do that and who better than the people you're already paying for the rotating mast?


Dan








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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
N3OX
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« Reply #17 on: October 23, 2007, 08:29:45 AM »

"See I need help!! "

Yes, you do, from someone you're paying.

This is not Elmer help, this is tower/mast engineer help.

Just to give you an example, using a thrust bearing to take the weight above the rotor is probably silly.  

The rotor IS a thrust bearing.  It's got a large ball bearing  race that can take 440lb vertical load continuously and 1320lb momentarily.

Weight of antenna + mast is probably about 60lb.  

Downward force from static guy tension is probably a couple hundred pounds at most.

Downward force from guys translating windload on the antenna and mast to compressive mast stress, probably another couple hundred pounds in massive gusts.

But I don't know for sure what guy wires you need, so I don't know what the guy wire static tension needs to be.  So I don't *really* know what the load on the rotator is.  

Do you really want some guy on the internet saying "yeah, that'll work" only to have your thousand dollar antenna hit the ground in January because you have a little ice storm?

Buy a mast from someone who will tell you if it will safely hold your antenna.

I bet the guys at Spiderbeam would tell you.  They have some nice telescoping aluminum masts.

http://www.spiderbeam.net/sb/product_info.php?info=p48_Aluminium%20Telescopic%20Mast%2015m%20(49ft).html

There are plenty of people who will sell you a mast and tell you where to guy it and how much windload the antenna can have.

Dan



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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
KT8K
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Posts: 1490




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« Reply #18 on: October 23, 2007, 12:03:50 PM »

From the information you've given, and the fact that you've talked with the Penninger folks, it sounds like you'll be OK.  Without more in-depth engineering analysis I'd probably go with the hexbeam to be safe.  Yes, it won't perform as well as the stepIR, but it will work better than the wires and verticals you (and I) are most used to, and that will be fun.

There is some good information among the previous posts, you just have to read through it carefully to get the best from it.  I've used a similar setup for portable ops - 40 ft. TV push up mast on a tail twister with a special homebrew ground mount, with some sizeable VHF antennas on it, with success, and will use it again from time to time.  

I'd say, just don't put it where it can fall on your neighbor or your car, and you'll be fine.  By next Spring you'll have learned a lot more about how it handles Winter ice and wind storms, and you'll be able to advise us on this type of setup.
Good luck & 73 de kt8k - Tim
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WE1X
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« Reply #19 on: October 23, 2007, 05:20:06 PM »

"Weight? What's all this stuff about weight? The biggest problem is almost always windload, almost never the weight. If something is so marginal you are worried about the weight it will NEVER be reiable in the wind."

Tom...think about it.  A G-1000DXA rotator is no small, light weight device.  Yes, wind loading is an issue. However, I will wager dollars to donuts 90% of the folks out there who place a rotator of that size and weight on top of a push up mast are going to be severely challenged installing and servicing (raise and lower) their mast/antenna.  Further, given the tapering of telescoping/push up masts mounting such a rotator while maintaining stability is going to be problematic.

As for my installation described earlier.  The guy rings allow for the free rotation of the mast with no binding or resistance.  And with the rotator (a G-1000DXA) mounted on the bottom there have been no performance or reliability issues as that rotator can easily withstand the vertical force from the combined 40 lbs of mast and antenna.

Bottom line: been there, done that, got the T-shirt.

Harry
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WE1X
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« Reply #20 on: October 23, 2007, 05:27:02 PM »

By the way, I purchased my 30 foot push up mast from Traffie Technology...with the hexbeam.  Believe specs may be availble on the website.

Harry
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W8JI
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« Reply #21 on: October 23, 2007, 06:19:21 PM »

2" diameter 1/8th inch wall 6061 aluminum is pretty strong.

Nylon on nylon bearing slip rings are probably pretty good if they are encased in metal. I'd never use nylon under tension or a sheering load, but as a flat bearing it is OK.

The Hex beam is pretty small too.

~30 feet, on the other hand, is a pretty tall 2" mast. For example my ten meter Yagi antennas are 36 foot long 1/8 inch thick 2 inch diameter 6061T6 booms. They have 18 feet each side of the tower with only three small ten meter elements on them, and only one element is at the very "tip".

At that span I would say the booms are "marginal", even though they are strutted with fiberglass guys. They are a bit "snakey" in 50-60 MPH gusts. But since they are the lowest antennas on my tower and they can't hit anything if they blow down, I'm taking a chance on them.

I have absolutely no idea what the wind speed rating of your mast system would be and that's what you really need to know.... unless you consider the system disposable and you don't care if it falls. But from my experience (and I have a lot of antennas) a 2 inch mast can get pretty wobbly when the height is a few hundred times the diameter.

I have no idea if it would break or not in reasonable winds. A great deal of the rating depends on the guying and how much twist the antenna would place on the mast. 2" is really a pretty small diameter and 1/8th inch isn't very thick, so I would be cautious.

But that's only because I see how my 2" boom antennas behave when they extend 15 feet or so from a very solid support.

73 Tom


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AD5VM
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Posts: 26




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« Reply #22 on: October 31, 2007, 07:12:39 AM »

Hi,
  I didnt go through all three pages of resposes so you may have already gotten your answer but I have the 30' mast from force 12, I bought an extra 6' section to make 36'. I think it's just about identical to the one youre talking about but the couplers on yours are for more of a permanent install.
I think your setup will work fine with the HexBeam on top and the rotator on the bottom. I can tell you that at 36' even the hexbeam is pushing the limit. I'm saying the limit for the 2el SteppIr on this type of mast would be 24'. Another option would be the TA-32Jr from Mosley.
How do you plan to erect the antenna? That was my biggest challenge on field day. I used the Hexbeam with a TV rotator at 30' and I thought the mast was going to snap in half when we were pushing it up! But it was fine and worked like a champ.
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