[TowerTalk] "Roll your own" tower/mast.

Sun Jan 24 07:50:36 PST 2010

Hello John,
	Thanks for your response. My intention is to use the masts/towers as
the supports for LF wire antenna systems; I already have a Strumech P60 for
my HF array and a Hilomast tubular aluminium crank up mast for VHF arrays. I
plan to suspend a horizontal wire LF antenna/array from a catenary support
which would be attached to the top of each proposed masts. There would be a
considerable compressive force being applied to each mast/tower, as both the
catenary and the antenna system were being tensioned. The mast guying
tension would be yet another consideration. 

	The use of tubular aluminium is my plan B. In fact, adjacent to the
site I have available, and in the surrounding countryside, a number of the
farm fields have gates supported on 5 foot sections of about 7 inch diameter
aluminium tube, which I am told, used to be 100ft masts, previously located
in the area, which were felled and then cut up by the farmers! Looking at
those cut sections, with tears in my eyes, I think that the tube may have
been rolled and welded, specifically for the job, rather than "drawn" from
softer stock aluminium. I found the remains of the masts, in cut 5ft
lengths, being stored in a barn! The metal appears to be what I knew as
"Dural" which was a very hard aluminium and dates from the late 50's. I am
told that aluminium, or rather one of its many alloys, such as the
structural variety, can be stronger than steel of an equivalent dimension,
however this does depend on the aluminium being processed in the correct way
by the manufacturer. 

	My only concern might be that more guys will be required to keep a
smaller diameter tubular mast of that height, stable during the lifting
process, as smaller diameter tube will probably "sag" between the guy
points. I suppose that is why those I used whilst in the RAF, were cigar
shaped sections, which did not appear to flex that much during the lifting
process. By the way, the one we "dropped" must have flexed because it
sheared at a flange joint.

	Getting the specialist coupling sections machined would be no
problem, because I have the necessary machine tooling and equipment already,
my number 2 hobby being model engineering.

	Sincerely John. G3JVC.

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of John Lemay
Sent: 24 January 2010 13:29
To: 'Tower and HF antenna construction topics.'
Subject: Re: [TowerTalk] "Roll your own" tower/mast.

Hello again

John, you haven't mentioned (unless I missed it) what you want to put on top
of these masts. However, since you have considered not only lattice masts
but also poles and timber construction, I'm thinking the head load may not
be large.

You could "roll your own" using tubular sections. Take a look at Aluminium
Warehouse. Their prices are very competitive and tube up to 5 inch diameter
is available in 5m lengths. You would need to find someone with a lathe to
turn up some coupling pieces, which could also form the guy attachment
points. By stepping down a diameter for each ascending length you could for
example have a mast 4 inches diameter at the base and 2 inches diameter at
the top, which would provide the strength where you need it and save weight
and windage where you don't.

Use the gin pole method to raise it.

Looks like you should be able to get two suitable masts like this for les
than £1k.

Regards

John G4ZTR

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of John E. Cleeve
Sent: 24 January 2010 12:52
To: towertalk at contesting.com
Subject: [TowerTalk] "Roll your own" tower/mast.

I thank everyone who took the time to consider my request and provided
useful information. I have used "Alumast" sections in the past, whilst
working in Sweden, where they were manufactured, however, they do not come
cheap, a bit like Volvo's I suppose, especially when you consider the
"middle man" importer involvement. Although I do have a mechanical
engineering background, I spent all my working life in electronic
engineering, because the working conditions and pay were better! However, I
take the point raised about the various structural and manufacturing
stresses which are involved, and the need for professional engineering
advice and the reference to a computer program is very helpful. 

With regard to a wooden structure, at the beginning of WWII, the early radar
experiments carried out, and subsequently used to provide early warning of
the enemy fighters/bombers approaching the UK from mainland Europe had the
antenna systems held aloft on groups of wooden towers, from memory, I think
that they were 200 ft plus, in fact, several are still in place overlooking
the English Channel, and probably visible using Google Earth. The radar
site, near Dover, is now a museum dedicated to that work. I do not think
that local authority planners these days, would be very keen on the idea of
using wood for such a tall structure, probably because we are not now "under
attack" and we have a "health and safety" regime in place, and I am sure
that it would be considered an intrusion into my neighbours "visual amenity"
even though the proposed location of my masts is about a quarter of a mile
from the neighbours!

Whilst serving in the RAF, the signals branch, and stationed in Germany
during the early 1950's, I recall using 90 foot tubular masts to support
wire antenna systems.  Each mast consisted of three 30 ft cigar shaped
sections, which were about six inches or more, in diameter at the centre,
each section had a flanges at the ends, for guy attachment and also so that
sections could be bolted together on the ground, then the four sets of
guys/anchorages would be attached, laid out and prepared. The sections were
quite lightweight; one mast section could be carried around by two 19 year
olds! The mast sections were painted military dark grey/green, I assumed
that they must have been of USA manufacture, probably shipped to the UK for
the "D day" event of WWII, but there were no manufacturer plates visible,
but they could have fallen off during extended use. The completed mast would
then be raised by using a "gin pole" method, with the gin pole set
vertically and attached at right angles to the base of the mast as it lay on
the ground, the gin pole would then pivot to the horizontal, with the mast,
as the mast rose up to the vertical. The gin pole had a complete set of
"taught" guys attached to the top, which also took the weight of the mast as
it was raised. The "9 oclock and 3 oclock" sets of guys would be laid out
and pulled "taught" whilst the mast lay on the ground, which left the 12
oclock set of guys (back guys) to be finally adjusted as the mast came up to
the vertical . The top of the "gin pole" was brought down to ground level (6
oclock") by means of a vehicle mounted winch and guy anchorage pulley
system, and secured to the ground. 

The erection of the mast took a team of six men about an hour at most, two
stationed at some distance from the mast, (3 oclock/12 oclock positions)
with plum lines set on small "gallows" to visually align the mast with their
weighted vertical bit of string, if things were getting out of hand, these
men had warning whistles! One man controlled the vehicle winch, whilst the
others had to rush around adjusting the three sets of guys, especially the
"back" guys as the mast went up, all great fun, when you were around 19
years of age, and there was about three feet of snow on the ground. During
my involvement, we only "dropped" one mast, from about 45 degrees during the
course of erection! But, if I could find a source, then two of these units
would certainly solve my present problem.

I appreciate your help and comments, and continue with my quest, spreading
the word of my needs, but I think that any metal structure being scrapped
today, will be earmarked by the bean counters for maximum return, and the
scrap man wins, but I live in hope. Thank you all once again, sincerely,
John. G3JVC.  

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