A couple of thoughts on these verticals:
Is there a specific reason for going with the short sections of tubing? You
can purchase aviation grade Aluminum tubing in lengths up to around the 20
to 24 foot range. Using fewer lengths of tubing will make the mast far more
sturdy. Going to the expense of renting a bucket truck means freight for the
longer lengths should not be a problem (they'd have to come by truck unless
you have a local supplier). Use a large enough diameter and hardness to keep
the "springiness" to a minimum.
Guying: Guying a mast like this is a different proposition than a tower.
The guys only need to be snug, not tight or stressed as they are for towers.
All they are doing in this case is keeping a relatively light weight mast
from falling over. It also has a relatively small wind area. Using
relatively small Kevlar or Phillistran I'd not exceed 50# tension or what
ever you could pull by hand. Pull 'em tight and tie 'em off. No turnbuckles.
The stretch in these guys is minimal and not worth worrying about. Pull
every thing tight by hand and then go over and "shake" the mast. You'll
know right away if there are any resonances or if the guys are not tight
enough.
Don't put the guys at evenly spaced intervals. This can prevent resonance,
may result in not needing as may guy levels and reduces the stress on the
bottom sections.
Speaking of vibrations...I once built one of the wood masts shown in the
older hand books. We had a pretty strong wind and I noticed a "humming"
sound. I looked out to see that wood mast oscillating with the guys at the
nulls. It was the perfect picture of a standing wave with peaks and nulls.
The problem was that mast appeared to be about a foot and a half across at
the widest point. Then it literally exploded with a bang as loud as a 12 Ga
shotgun. The largest piece left was no more than 3 feet long and that
thing had been constructed of 2 X 4 laminations.
Cost wise I wonder how the high grade tubing would compare to a relatively
inexpensive/light weight Aluminum tower?
I'd like to put up a pair of light weight Aluminum towers for 75 near the
back of the lot. I'd settle for one, but the problem of putting the tower(s)
near the back of the lot is it is all old woods behind our lot and I'd not
want either a tower of guys near those old trees.
Last winter we had one go down into our yard and it extended at least 60 to
70 feet into the yard. Two summers back we had two of them get dumped into
the yard during a storm. They are mostly trash and birch trees which are
rather fragile.
Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
www.rogerhalstead.com (Use return address from home page)
----- Original Message -----
From: "Tom McAlee" <tom@klient.com>
To: <towertalk@contesting.com>
Sent: Saturday, October 28, 2006 4:06 PM
Subject: Re: [TowerTalk] 80m vertical: reality check
>I have 2 full-size 80m verticals using tubing from Texas Towers. The
> current versions have been up for 1.5 years with no problems. But, they
> are
> the third version. The first 2 attempts didn't go so well!
>
> As they are now, they start at 2.125" and telescope to 1.25". They are 6'
> sections with several of the first 3 sizes doubled up. They are guyed at
> 5
> levels (every 12') with Phyllistran to posts 43' out, guys attached to the
> top of the posts that extend 3' out of the ground (makes mowing the yard
> easier)
>
> These verticals cannot be "walked up" as you would do with a smaller
> vertical. I used a 60' bucket truck to build them 12' at a time. I found
> a
> local sign company that charges $55/hour and it took about 1/2 hour per
> vertical.
>
> Mistakes made in the first two versions that were destroyed on windy days:
> - telescoping up to too small a size that couldn't withstand the vibration
> in the wind and broke off
> - not having enough guy levels (without enough of them, you can't tighten
> them much because tightening them will buckle the tubing without more guys
> below to prevent that)
> - not having the guys out far enough (tried to be cheap on the
> Phyllistran,
> bad idea)
>
> 73,
> Tom, NI1N
>
> ----- Original Message ----- > From: towertalk-bounces@contesting.com on
> behalf of Yo3ctk
>> Sent: Fri 27/10/2006 12:40
>> To: towertalk@contesting.com
>> Subject: [TowerTalk] 80m vertical: reality check
>>
>>
>>
>> I am trying to design an 80m lambda/4 vertical for a 4-square. My plan is
>> to use 6 ft sections of AL tubing, 0.058" wall, as advertised on Texas
>> Tower website:
>> http://www.texastowers.com/aluminum.htm
>>
>> Starting with biggest O.D of 2.125", twelve (12) more 6 ft sections of
>> progressively smaller O.D. will be telescoping with 1 ft overlap at each
>> joint. Joints will be fastened with AL rivets. The entire vertical will
>> have an (adjustable) height of 66 ft (20m) and a total weight of about 22
>> pounds (10 kg).
>>
>> Unfortunately I have no expertise in calculating if such a structure is
>> mechanically sound, hence following questions for the experts on the
>> list:
>>
>> 1. Is the vertical expected to break at the lower joints in stiff winds
>> (say no more than 65mi/100km/h)?
>> 2. Must the vertical be guyed? Where?
>> 3. Is it feasible to raise the vertical from the ground, by fixing the
>> largest section to the base and telescoping sections starting with the
>> smallest diameter, and riveting as we go?
>>
>> Thank you all for any comment.
>>
>> 73 de Mike, YO3CTK
>> YR7M stationmaster
>> _______________________________________________
>>
>>
>>
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>>
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>>
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>
>
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