Tips & Advice
Recommended Installation Procedure
1. Calculate or measure the needed lengths of the guys (the part of the “anchoring system” made
from the synthetic rope).
2. Add the length needed for proper end termination. For the standard terminations (thimble, clip,
knot) it is about 60-times the rope diameter for each end.
3. Cut the rope using hot edge (for example with a soldering iron). Melting temperature of polyester
is about 260 °C (500 °F), Dyneema 150 °C (300 °F).
4. Prepare appropriate thimble. If needed, you can open the thimble by pliers, thread on the
attaching subject and close it to original shape. Small shape distortion has no influence to total
strength.
5. Prepare appropriate clip – dismantle it.
6. The rope wraps around the thimble, place it to the clip and put the clip together (see Figure). The
open end of the rope should be left free, about
35-times the rope diameter (for the safety knot).
7. Place the clip as close as possible to the
thimble.
8. Tighten the screws of the clip very firmly
and make the knot (see Figure). Fix the free end
of the rope with a cable tie to stop it fraying.
9.
10. It is necessary to tighten the clips
repeatedly during tensioning the rope. Therefore
at the inaccessible end of the guy is necessary to
tighten before installing the guy. Attach the end of
the rope (the one with the thimble) to a solid
object and tighten the rope gradually. After each step (increase of tensioning force) tighten the
screws of the clip. Ideally, the final tightening is performed at maximum workload (30% of the
strength). With thicker ropes, however, this ideal is difficult to achieve – for example the
stretching could be performed by a rope stretched between two fixed points and loading the
rope perpendicular to the their axis with the required weight. Also we could use a car to pull on
the rope or create a temporary hoist for tensioning.
11. Place the guy where it will be used. Tension it gradually and tighten the clips (as described
above).
12. Visually check whether there has been slippage of the rope in the clip - if so, it means that we
have not chosen a suitable tensioning and tightening procedure, or that the terminal is defective.
13. For tensioning cables we can use threaded turnbuckles. For telescopic masts, we can do it
without a turnbuckle. Lower the mast slightly and tighten clamps then wind the mast back up
and retighten. The suitability of this procedure is, of course, different for each type of mast.
14. Optimal pre-tension of the rope (tension in idle) is dependent on a number of factors - the design
and strength of the mast, the type and strength of the rope, the distance from the base of the
mast to the anchor point. In most applications best suited force is 5-20% of the strength of the
rope. Do not guess! Calculate for your particular mast.
15. After final tensioning of the guys in "idle" the rope will for some time continue "settling". Check
the guys and, if necessary, tension them the next day after the installation and then about 3
times at intervals of about 1 week. We must always follow the correct procedure for tightening
clamps!
Most common mistakes and accident causes:
The anchor point is situated too near to the tower base and that is why the angle between the
guy rope and the tower equals much less than 45 degrees.
The clips weren’t re-tightened while the rope was under tension.
Behind the clips there is no safety element (second clip, knot).
The end of the rope is not terminated with a thimble, but tied directly to the construction.
The rope was chewed through by an animal or cut through.
From: https://www.mastrant.com/tips-advice/useful-tips-tricks-and-advice/12-recommended-installation-
procedure
Tips & Advice
Basic Instructions to Guy with Synthetic Ropes
When planning an “anchoring system” (guy-ropes with end termination, couplers and anchorage) there
are a number of facts that have to be taken into account:
1. The stability of the system is determined by its weakest link. That is why it is no use combining a
rope of 5000 kg of strength with a turnbuckle 500 kg strong.
2. Even the most excellent synthetic rope is elastic – when guyed it elongates. In the layout of the
tower and its anchorage (even when fixing elements of the antennas) you have to reckon with
this characteristic and always consider how the elongation of the anchoring system will affect the
overall construction. In certain cases it will be necessary to use a stronger rope (with a smaller
absolute extensibility), than for other constructions that are not negatively affected by the
elongation of the anchors. A problem occurs especially in such a case, when the ground anchor
point is situated too close to the tower base, or when dealing with a lattice tower with low
flexibility.
3. The rope must be screened against all kind of sharp edges. For this reason it is necessary to fix
the rope with a thimble or tie it to a coupler with a very smooth surface. Be aware of the fact that
inappropriate metallic materials corrode and therefore their surface roughens. Never should you
tie a rope to a concrete slope or to a stone! If you do want to use a stone, a rock or a concrete
slope as ground anchor point, we recommend using a loop from steel rope, which you can
connect to the guy rope with the help of a smooth coupler.
4. A great danger for any synthetic rope lies in friction against any object on its path. This can
cause the rope to be seriously damaged or cut through, and has to be avoided at all cost. Even a
guy rope on a tower can move enough to suffer friction damage if it touches anything along its
length, so please locate your guys carefully. Particularly to be avoided are trees and tree
branches. If you are using a tree support for a wire antenna you must ensure that no part of the
synthetic rope can get close enough to the tree to risk damage by rubbing. Always use steel rope
near or in a tree. You could use a pulley on the end of a steel rope to keep the synthetic rope well
clear.
5. The lower part of the anchoring system should consist of steel rope cord in 2-4 meters of length.
This ensures that the synthetic rope isn’t “chewed up” by an animal or gets damaged by some
human activity (intentionally or unintentionally).
A key element of safety is the end termination of the rope:
1. Guy ropes can be terminated with a thimble (permanent installation) or they can be tied to a
smooth object.
2. When fastening a rope by tying, we recommend making sure the rope does not move on the
object it is tied to (even though we are talking about smooth fastening points). This can be
achieved by tying the rope to a coupler – chain quick-acting coupler, spring hook or shackle – and
only then fix it to the fastening point.
3. Each thimble must be followed by a clip or swaged fitting. We
recommend duplex wire rope clips or first-grips. Behind the main clip
(the one that follows the thimble) the loose end of the rope must be
fixed by a safety element – another clip or several loops, similar to the so-called anchor-hitch.
Further, the end of the loose rope is insured
against uncurling for example with a cable tie.
4. Other
possibility is using crimped terminals (swaged “clips”). Those are only
practical on one end of the rope – otherwise it is not possible to
adjust the length. We sell them as “Ready-made" or “Terminated” guyropes - here.
5. When guyed, a rope’s diameter decreases and therefore
it loosens inside the clip. For this reason, clips must be drawn up
while the rope is guyed, that is “under pressure”.
6. Beware of classic bull-dog grips! These rope clips are constructed specially for steel ropes and
when under high tension they can “snip off” synthetic ropes. In no case do we recommend using
them as main clips for the end termination of ropes – they may be used as “safety clips” behind
the main clip, however.
7. We suggest considering wedge sockets. Although they are relatively expensive they have several
exceptional rope protecting properties, thanks to the "self-locking" system they tighten when
stretching and allow convenient changes in the length of the anchoring system.
Most common mistakes and accident
causes:
The anchor point is situated too near to the tower base and that is why the angle between the
guy rope and the tower equals much less than 45 degrees.
The clips weren’t re-tightened while the rope was under tension.
Behind the clips there is no safety element (second clip, knot).
The end of the rope is not terminated with a thimble, but tied directly to the construction.
The rope was chewed through by an animal or cut through.
In the following case there was used improper rope with high elongation.
From: https://www.mastrant.com/tips-advice/useful-tips-tricks-and-advice/11-basic-instructions-to-guy-
with-synthetic-ropes
Tips & Advice
Anchoring the masts and vertical antennas - 1
Martin Huml, OL5Y/OK1FUA, huml@mastrant.com
(note: all tables are available in Excel format)
During my radio amateur activities, I dedicate most of my time (probably like any one of us) to the
question of antennas. And one of the most important and maybe the most challenging task is to get the
antenna “into the air” and keep it there. Apparently this applies to all antennas, perhaps with the
exception of beverage antennas... I wrote about this subject in the article “How to build and anchor
simple antenna masts” (magazine “Radioamatér” 2 & 3/2004). At that time, I already felt that this issue is
so interesting, complicated and extensive that it would be appropriate to return to it.
Another motive for writing the following article was to include the questions asked either by my friends
or emerging on their own, e.g. “Why are you anchoring the vertical so low down?”, “Will this rope be
strong enough?”, “Will this mast be able to carry the antenna?” and so forth. Most of the time I couldn't
find a better answer than “because I think it's enough” or “because I saw it somewhere like that”. This
doesn't sound very scientific. Practice and experience are great and irreplaceable, but too much of it is
guesswork, so when my activities brought me to “anchoring” I decided to look into it from the theoretical
perspective as well. First, I would like to state that I am not an engineer; so, after studying some time, I
consulted Engineer Richard Beber, who, unlike me, has studied this issue. Here, I would like to thank him
- the article wouldn't have been written if it weren't for him.
Hence, as indicated by the name of this article, its main subject is focused on how to anchor antennas.
This doesn't mean that owners of the non-anchored masts won't find something interesting. For
instance, calculations of forces acting on the antenna in the wind or other matters might be useful.
Used terms and simplification
I ask the experts and linguists for leniency - I use these terms as I know them from amateur practice:
Place (point) of mounting = the place where the anchor rope is mounted on the mast
Height of mounting = the distance between the point of mounting and the mast bottom
Anchoring place (point) = the place where the anchor rope is attached to the ground (or other
fixed point)
Distance of anchoring = the distance between the point of anchoring and the mast bottom
The system = the mast with antenna
A vertical antenna is actually a mast
without the antenna. Therefore, where it is
not appropriate in the following text, I will
not distinguish between these two types of
antennas. In other words, e.g. the phrase
“anchoring in the middle of the mast” will
have to be understood as “anchoring in the
middle of the vertical”.
Unless stated otherwise, we assume that
the mast is built on a horizontal surface;
therefore, the anchoring points and the
mast bottom are at the same level,
perpendicular to the axis of the mast. This
is for simplicity - the reality definitely tends
to be different. Therefore, the following
text will indicate how to deal with the
reality.
In our considerations, we also do not deal
with the behaviour of the antenna itself - we assume that the antenna on the mast does not change.
And, finally, for those who are not friends with physics - we will talk a lot about force, whose unit is 1 N
(Newton). For instance, if you lift a weight of 1 kg, the acting force on you is approximately 10N.
The Antenna and the Mast
If we look at the simplified model of the anchored mast and the antenna at its top (fig. 1), the following
forces will affect the system:
gravity force (mass of the mast, ropes and antennas)
resistant wind force,
Tension force of the anchored ropes.
This set of forces will produce a reaction so that the resulting forces will be balanced. The reaction will
appear in the gripping of the mast bottom and in the places of mounting of the anchoring ropes. There
will also be a flexible deformation of the mast and the ropes. In this respect, we do not consider the
irreversible deformation or destruction of the material - it is these cases that we want to avoid and
therefore we will focus on the identification of all acting forces.
But forces do not represent all factors that will influence the behaviour of the system. We must not
forget about the structure of the mast (tube, lattice structure etc.) and the material of which it is made,
especially its physical properties such as density (specific gravity), flexibility and strength. Similarly, we
need to know the properties of the anchoring ropes - their strength and elongation. Let's summarise
what we need to know:
antenna - mass
antenna - shape (number, length and diameter elements)
mast - structure, material
anchoring rope - elongation (stretch at working load), strength
And the parameters with which we will be dealing are as follows:
total height (the height of the antenna above ground = the height of the mast)
the number of the anchoring directions (3 or 4)
the number of anchoring levels (at how many levels will the mast be anchored)
the height of the anchor mounting(s)
the distance of the anchoring from the base
The distance of the anchoring
The first question that we will address is the influence of the distance of anchoring on the size of the
forces (acting on the mast and the anchoring ropes). We will divide this task into the following marginal
situations - in the first case, the wind is blowing from the anchoring direction; in the second case, the
wind is blowing “in between the anchors”. (fig. 2)
If the wind is blowing from the point of anchoring direction, it is a simple composition of forces - the
case of a right triangle where one of the legs is the mast (h), the second one the distance between the
mast bottom and the point of anchoring (r), where the anchoring rope is the hypotenuse (l). The
proportion in which the individual legs of this triangle are is the proportion of forces acting in
individual directions. We know (can calculate) the force Fant caused by the wind acting on the antenna.
(Its specific value is not important at this moment; we will deal with it later - as we are now assessing the
influence of the distance of the point of anchoring.) So the force on the mast (in its axis) is Fst = F
and the force acting on the anchoring rope is Fko = F
* l / r. We will calculate the length of the rope by
ant
* h / r,
ant
the Pythagorean Theorem: l = √(h2 + r2).
When the wind is blowing from the direction of the axis between the anchors the situation is somewhat
more complicated, because we have to bear in mind the angle between the anchors - in other words, to
how many directions the mast is anchored.
Anchoring directions
For this purpose we look at the mast from the top and introduce a total of 3 points - the mast and 2
anchoring points. Further we will introduce the direction from which the wind is blowing - it is the axis
between the anchoring points going through the mast. The place where this axis intersects the
connecting line between both of our anchoring points is a point that represents the virtual anchoring
point for the calculation of acting forces. We see that it is much closer to the mast bottom than the
anchoring distance - the closer it is, the larger the angle between the anchors.
This is again a case of triangles, but not necessarily right angle triangles. If we apply the basic
goniometric functions we get to these relations:
For 4 anchors in 90°:
Fst = F
High of the fixation
10 m
Distance of anchoring points
10 m
* (h / r) * √2 = Fst = F
ant
* (h / r) * 1,414
ant
Fko = F
* (l / r) * (√2) / 2 = F
ant
* (l / )r * 0,707
ant
for 3 anchors 120° each:
Fst = F
Fko = F
* (h / r) / cos(60/180π) = F
ant
* (l / r) / cos(60/180π) = F
ant
* (h / r) / 0,5
ant
* (l / )r .
ant
At a first glance, an interesting feature might not be seen - when anchoring in 3 directions the force
acting on the anchoring rope is the same as with wind “from the anchor” as well as “in between the
anchors”.
How does this look in practice
From the theoretical perspective, which is
probably boring for most of us, we move
on to practical effects. (I promise that the
following text will be without formulas they would be much more complicated
...)
For illustration, I chose a simple example
- a mast 10 m high with a tribander
(10/15/20m) on top. I repeat again – it is
an example to show the impact of
anchoring distance and the number of directions to which the mast is anchored.
Therefore we are not interested in the mast or rope properties. So - we let the wind blow on the
tribander at 130 km/h. It can be approximately calculated that the wind's acting force is approximately
775N. How I got to this result will be explained in the next chapter; for now this result will do.
I will however mention a very important fact, i.e. that the force is proportional to square (squared)
velocity (e.g. half velocity = quarter force; the force in the case of 80 km/hour will thus be approx. 290 N).
However, the force grows at a similar pace – so you can then understand what a tornado with its wind
velocity reaching over 300 km/h in its centre can do, so please do not think that cars flying the air are a
mere invention of the American filmmakers.
But now back to anchoring. In the following tables you will see the force calculated for both versions of
anchoring (3 and 4 directions) and for the anchoring of 10 and 5 m. I think it is obvious that bringing the
anchoring points closer to the mast results in unnecessary increase of the acting forces. This is similar in
case of anchoring into 3 directions, which increases the load on the mast.
Speed of the wind
130 km/h
Direction of the wind
number
of
directions
Force [N] effecting:
guy-wire
mast
from direction of the guywire
4
1 095
775
between of the guy-wire
4
775
1 095
from direction of the guywire
3
1 095
775
between of the guy-wire
3
1 095
1 245
High of the fixation
10 m
Distance of anchoring points
5 m
Speed of the wind
130 km/h
Direction of the wind
number
of
directions
Force [N] effecting:
guy-wire
mast
from direction of the guywire
4
1 732
1 549
between of the guy-wire
4
1 224
2 191
from direction of the guywire
3
1 732
1 549
between of the guy-wire
3
1 732
3 098
As you can see, given a sensible layout, forces caused by such high wind are not so huge. In other words
- we do not need any extreme ropes for anchoring such an antenna. As can be found in a lot of places,
even a relatively weak rope will endure if it’s designated for this purpose. The weakest places are all
joints ... And in our conditions, we must not forget situations where the antenna is encased with frost...
But this is really a distraction here and we will return to it.
Just to complete, one more paragraph - observant readers have definitely noticed that it is not about
absolute height and distance - we will get the same results with mast of 20m and the distance of 20 and
10m. It is the angle formed between the anchoring rope and the mast. This should be acknowledged
especially in situations where the anchoring point cannot be placed at a level perpendicular to the mast
(it is on a slope). In such case, for example, if you had to place the anchoring point 3m lower than the
mast bottom and you want to keep the angle between the rope and the mast 45° you have to place the
anchoring point 13m from the axis of the mast (be careful, not from the mast bottom!). This can be
hardly calculated at times, that is why it is possible to calculate and measure the length of the anchoring
rope - in this case being 13*1,41 = 18.3m (1,41 = √2).
Wind force
If we place an object in the fluid stream, in our case the air, it will cause resistance by the friction and
pressure elements. This resistance is determined experimentally in aerodynamic wind tunnels and is
expressed in relation to the resistance force:
,
where FO is the resistance force [N], C is the resistance coefficient of the object (-), A is the area of the
Antenna
Wind
area
[m2]
Force of the wind [N]
at speed as [km/h]
50
130
180
HF - 3el. tribander ECO
0,82
116
765
1476
HF - 3el. tribander A3S
0,40
56
373
720
HF - 3el. tribander TH3JRS
0,32
45
299
576
HF - 7el. tribander TH7DX
0,88
124
821
1584
HF - 11el. 5-bander TH11DX
1,17
165
1092
2106
HF - 10el. LP 10-30m
LP1010
1,49
210
1390
2682
HF - 5el. for 6m F9FT
0,13
18
121
234
HF - 5el. for 10m LJ105CA
0,37
52
345
666
HF - 5el. for 15m LJ155CA
0,49
69
457
882
HF - 5el. for 20m LJ205CA
0,84
119
784
1512
HF - 6el. for 20m HD OWA
1,80
254
1680
3240
HF - vertical 6-20m R6000
0,14
20
131
252
HF - vertical 6-40m R8
0,24
34
224
432
HF - Inv.V full-size 20-160m
0,90
127
840
1620
2m - 9el. 2M9
0,12
17
112
216
2m - 11el. F9FT
0,18
25
168
324
2m - 12el. 2M12
0,14
20
131
252
2m - 17el. F9FT
0,29
41
271
522
2m - 18el. 2M18XXX
0,30
42
280
540
object perpendicular to the wind direction [m2], ρvz is the air density [kg/m3], &vvz is the wind velocity
[m/s].
The value of the resistance coefficient is not constant, but depends on the so-called Reynold's number non-dimensional criterion, expressing the ratio of inertial and viscous
Re = vvz * d / v ,
where d is the characteristic dimension [m] a v is the kinematic viscosity of the air.
If we simplify the antenna (in our case a tribander) to several cylinders, then the characteristic
dimension is the diameter and Reequals roughly 104 in normal conditions while the resistance coefficient
of the object C is approximately 1.2. By the resistance force acting on the antenna (tube diameter d = 35
mm, length l = 23.6 m, wind velocity vvz = 36 m/s = 130 km/h; air density 1.2 kg/m3) we can determine:
.
This force acts as a continuous load
on the whole antenna (if we simplify the actual
situation on the same velocity profile for the whole surface of the antenna). We can determine the
resistance force acting on the mast in a similar way.
The following table illustrates forces calculated for several typical antennas (I apologize to those who
can’t find their exact antenna in the table, please just extrapolate).
70cm - 18el. 440-18
0,08
11
75
144
70cm - 21el. 440-21ATV
0,12
17
112
216
70cm - 38el. 432-13WLA
0,24
34
224
432
23cm - 35el. 23CM35EZ
0,06
8
56
108
Design of element /boom
Multiplication of
weight with icing:
50%
100%
200%
Spar (all diameters)
1,2
1,5
2,4
Pipe ø 8 mm, wall 1 mm
1,5
2,2
4,3
Pipe ø 10 mm, wall 1 mm
1,6
2,5
5,0
Pipe ø 14 mm, wall 1 mm
1,8
3,0
6,4
Pipe ø 24 mm, wall 1 mm
2,4
4,4
9,9
Pipe ø 24 mm, wall 2 mm
1,7
2,8
5,7
Pipe ø 30 mm, wall 1 mm
2,7
5,2
12,1
Pipe ø 30 mm, wall 2 mm
1,9
3,2
6,7
What can be caused by frost?
The frost, which is a very important element in our calculations, affecting the function (as well as
survival) of the antenna, causes
increase of the surface the wind effects and
mass gain.
Because I do not have any personal experience with the frost I have consulted this issue with a few
friends who have their antennas on a variety of problematic places including those where the frost lasts
several months. Their experience indicates that frost on the components adds up to 50-100 % and in
extreme cases up to 200 % to their original diameter (the component then increases its diameter). Let’s
see how much this increases wind loading.
The previous chapter shows that the resistance force of the wind is directly proportional to the surface
of the antenna perpendicular to the wind direction and, therefore, to the diameter of its components. So
if the diameter of the components increases 2x, it doubles the wind force. These are very easy
calculations - if you wish to design an antenna system for extreme frost, multiply the forces by 3.
The mass issue is more complicated. For its calculation, we need to know not only the thickness of the
frost but also its density. Although the density of ice is 917 kg/m3, the density of frost stated in literature
and standards is considered 400-500 kg/m3 - let 's calculate preferably 500 kg/m3. Since we are
interested in the amount of increase of the mass of the standing antenna, we also need to know the
density of the material, which it is made from. This is usually some aluminium alloy whose density is
around 2800 kg/m3.
A brief remark about the calculation: for the sake of simplicity, we would again consider an antenna
consisting of tubes or rods. The mass of the object m = V * ρ, where V is the volume and ρ the density.
The volume of the cylinder is V = π * r2 * l, where r is the radius and l the length. If we substitute the
known values we will calculate the original mass and the mass of the frost. This is demonstrated below.
Pipe ø 50 mm, wall 1 mm
3,8
7,8
19,2
Pipe ø 50 mm, wall 2 mm
2,5
4,5
10,3
The facts shown in the table may be shocking for some people. It is not easy to admit that the antenna
consisting, for example, of tubes with 24mm in diameter with 1mm wall increases its mass in a 100%
frost by 4.4 times! On the other hand, it is necessary to consider that the conditions for creating
continuous frost on the entire perimeter of the tube, especially on those with larger diameters, are
relatively rare in ordinary QTHs.
As a matter of interest, Wikipedia states the following about frost:
The frost is an atmospheric phenomenon that develops by creating ice crystals on the surface of the object by
inflicting the following effects:
• freezing tiny droplets of the air's humidity (clouds, fog etc.) in it's contact with the surface of the ground,
object or other subjects at the temperature of 0°C and below;
• precipitation (sublimation) of air's humidity on a sufficiently cold surface of the ground or subjects and that
even without the presence of fog or clouds.
The highest probability of frost creation is with contact at a temperature (0 to -4 °C) between the surface of the
object and the moist airflow. With temperature below -4 °C the possibility of frost creation decreases and at
temperatures below -12 °C frost does not occur or is very weak.
The above data is interesting especially in the consideration of structure & design of the antenna - to
what extent the components and the boom should be dimensioned and reinforced to avoid bending.
That is again a completely different topic.
Next time, we will focus on anchoring a real mast, including considerations about its strength and other
influencing elements.
From: https://www.mastrant.com/tips-advice/useful-tips-tricks-and-advice/15-anchoring-the-masts-and-
vertical-antennas-1
Tips & Advice
Anchoring the masts and vertical antennas - 2
Martin Huml, OL5Y/OK1FUA, huml@mastrant.com
In the first part we talked about forces and the issues regarding anchoring in general; today we
will talk about the mast itself. Before I begin I would like to thank for all your feedback,
questions and other topics. I am glad that you were interested in the previous article and I will
try to keep it that way.
In this sequel we will focus on the most basic version – the tube mast anchored in one level below the
antenna. This situation is illustrated under figure 1. To simplify the calculations, we assume that the
entire mast is the same tube diameter and has the same properties throughout its length. We will also
assume that the wind velocity along the length of the mast is the same (in reality it is lower just above
the ground).
When analyzing quantities and properties
that affect the behavior of the system we
get to this list:
the total height of the mast, height
of the attached rope, distance of the anchor
from the mast bottom (to determine forces
affecting the system)
external and internal diameters of
the tube (to determine the strength and the
weight of the mast)
physical properties of the material
from which the tube is made from: density,
elastic modulus, strength limit, proportional
limit (to determine the strength and weight
of the mast)
area and weight of the antenna (to
determine the wind resistance force)
coefficient of the resistance of the
mast and the antenna (to determine the wind resistance force)
properties of the environment (air): kinetic viscosity, gravitation acceleration, air density
wind velocity
Outputs of the calculations we wish to obtain:
force in the axis of the mast bottom (action on the point of placement of the mast bottom)
force in the axis of the rope (for the selection of the suitable rope)
Quantity
Symbol
A B C D E F G
Unit
11m
duralumin
ECO
11m
duralumin
ECO
11m
steel
ECO
11m
duralumin
11el. 2m
11m
fibreglass11el.
2m
23m
duralumin
TH7DX
23m
steelTH7DX
mast - tube
total height
h
13
13
13
13
13
23
23
m
height of rope
attachment
h_ki
12
12
12
11 9 17
20
m
anchor
r_ki
10
10
10
10
10
15
15 m distance
However, we will be interested particularly in safety - if the mast will survive and to what degree of
safety.
But how to assess and compare safety if it has no unit and its expression in words is quite difficult and
above all subjective? We will be probably unable to measure it. Construction sectors use a unit
called safety coefficient. It is calculated differently for each type of structure, but its interpretation (sense)
is always the same: If it is greater than 1, “there is a theoretical guarantee that the structure will survive”.
The recommended minimum value is 1.4. If the safety of the structure involves several factors, the
coefficient is calculated for each factor separately and the total safety of the structure is the smallest one
of them. In our case, there are two critical factors: the strength of the material of which the mast is made
(i.e. the tension in it), and the mast buckling (so the mast will not bend). Our considerations will result in
the assessment of the total safety of the system.
From the foregoing, it is clear that there are a large number of quantities that are different for specific
situations. Everybody has a different antenna, different mast, different mast height ... For illustration I
have chosen several situations, that I find appropriate for demonstration and for which I calculated
different outputs. In each case I chose the height of the rope attachment so that the total safety is the
greatest. Individual variations are as follows:
The mast height of 13 m, on which an ECO antenna is placed (3el. tribander for 10/15/20m). This
version is calculated for 3 different masts: tube diameter 80 mm with 3 mm thick wall from an
average quality duralumin (ver. A), tube from the same material 100/4 mm (B) and steel tube
60/3 mm (C).
The mast height of 13 m with 11el. antenna for a 2 m band in two versions: average duralumin
60 mm in diameter with a 2 mm thick wall (D) and fiberglass 60 mm in diameter with a 5 mm
thick wall (E).
The last version is a 23 m mast with a bulky antenna TH7DX (7el. tribander for 10/15/20m) again
in 2 versions: high quality duralumin 100 mm in diameter with a 10 mm thick wall (F) and steel
100 mm in diameter with a 5 mm thick wall (G).
Other parameters used for calculations are: air density = 1.2 kg/m3, gravity acceleration = 9.82 m/s2, wind
velocity = 36 m/s = 130 km/h, coefficient of mast and antenna resistance C = 1.2. The results are shown
in table no. 1.
external
diameter
D_o
80
100
60
60
60
100
100
mm
internal
diameter
D_i
74
92
54
56
50
80
90
mm
mast density
ro_s
2700
2700
7850
2800
1200
2800
7850
kg/m3
elastic
modulus
E_s
60000
60000
200000
60000
18000
60000
200000
MPa
strength limit
sigma_t
300
300
320
300
220
350
320
MPa
proportional
limit
sigma_tu
200
200
120
200
200
200
120
MPa
rope reaction
F_ropex
1355
1486
1223
629
768
2446
2079
N
reaction in
mast bottom
F_forces
in the
axis of
the mast
2023
2346
2153
856
858
4951
5808
N
reaction in
mast bottom
perpendicular
F_axis
-381
-492
-270
-267
-128
-376
-743
N
force in rope
axis
F_rope
2116
2321
1911
934
1034
3697
3466
N
antenna
area of
antenna
S_ant
0,82
0,82
0,82
0,18
0,18
0,9
0,9
m2
weight of
antenna
m_ant
15
15
15
3,5
3,5
40
40
kg
assesing the safety
tension in the
mast
k_t
4,01
6,21
2,86
2,37
2,14
3,16
3,34
buckling
k_b
2,47
5,84
3,62
2,01
1,89
3,27
4,75
total safety
k
2,47
5,84
2,86
2,01
1,89
3,16
3,34
In version (A) I wanted to show that although a relatively thick tube is used the total safety is not as
material
density
elastic modulus
strength limit
proportional limit
kg/m3
MPa
MPa
MPa
duralumin
2800
60000
180-450
x
aluminum
2700
60000
60-150
x
steel
7850
200000
320-835
120-290
fiberglass
1200
18000
220
x
perfect as some might expect based on their experience. This is because the arrangement of the system
with a single anchor height is definitely not optimal and places high demands on the strength of the
mast material. We will talk about other versions next time, but I can disclose that the strength of the
system in dual anchoring is four times greater and even nine times greater in triple anchoring levels (of
course, if they are placed in optimal heights). I have also included version (E) because I have seen similar
masts being used by several radio amateurs.
Table no. 2: physical properties of the materials
In addition to its own safety system, it is also interesting to look at the distribution of some quantities
along the length of the mast. This is shown in figure 2 (for version C) and 3 (E). If the anchoring height is
chosen at a height to maximize safety, then the curve shapes are very similar - that is why I show only 2
typical examples.
From: https://www.mastrant.com/tips-advice/useful-tips-tricks-and-advice/16-anchoring-the-masts-and-
vertical-antennas-2
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