How To Select Your Tensioner(s)

 

First…should you use just one Tensioner or two?  The answer is to use one Tensioner at each movable support tree.  If you have a tree supporting your antenna at one end and a rigid fixed support (utility pole, tower, building, etc) at the other end you need just one “Main” Tensioner. It can be mounted at either end of the span. If you have two support trees you should use two Tensioners, a “Main” and a “Reciprocal” …one at each end of the antenna. Two Tensioners will have twice the tree sway displacement of a single unit and will make a rugged and conservative installation.  Also allow 10' at the end of your antenna for each Tensioner.  This will allow it to expand when the tree sways.  If space is a problem, consider mounting the Tensioner(s) vertically at the base of the tree.

The suspended weight that is pulling down at the feed point determines the depth of sag and which of the two basic Tensioner models that you should use to control it.  Under 3 lbs, the 20-50 models are the correct Tensioners to use.  Over 3 lbs, the 30-100 models are the correct Tensioners.  This selection method will result in your antenna (and the Tensioners) being nicely tensioned and the antenna will have 5% or less center sag depth, a sound and achievable antenna design goal.  For borderline situations it’s always safe to use higher tension and the 30-100 model Tensioners.

To simplify the Tensioner selection process we have made this 3 pound weight threshold calculation for you based on the type of feed line that you will be using. We have also included an average weight allowance for a center balun and/or center insulator plus all of the suspended feed line needed to feed a flat top wire antenna that is up to 60’ high. The weight of the actual antenna wire does not need to be included.

If you know the exact weights of your suspended feedline, center insulator and balun and would like to do your own calculations we’ll guide you through the steps of the selection process in the “Calculating Center Weight” section below. Otherwise use the following guidelines to select your Tensioner(s).

If you use small diameter feed line:

Model 20-50 and 20-50-R are the correct Tensioners for flat top antennas that are up to 136’ long and up to 60’ high that are fed with small diameter coax equivalent to RG-8x, RG-58, RG-59 or 450 ohm ribbon window line. The center weight pulling down on the antenna, including the feed line, an average center insulator, balun, and/or line choke will usually be no more than 3 lbs. and the 20-50 Models are the correct choice.  These antennas include dipoles, OCF, Carolina Windom, G5RV, Zepp, etc.  Inverted L’s, loops, and long wires should also use the 20-50 Models.

If you use large diameter feedline:

Model 30-100 and 30-100-R are the correct Tensioners for flat top antennas up to 265’ long, and up to 60’ high that are fed with large diameter coax equivalent to RG-8, RG-11, LMR, or 600 ohm ladder line.  The center weight pulling down on the antenna, including an average center insulator and/or balun, will be over 3 lbs. and the 30-100 Models will be the correct choice. All flat top fan dipoles with parallel elements, trap dipoles and coaxial dipoles should use the 30-100 Models regardless of the feed line size.

NOTE

Center Supported Antennas   Inverted V dipoles and OCF’s that are hung from a tree at the balun feed point can be tensioned with a Model 20-50 or 20-50-R Tensioner at the bottom end of each wire.

160 M. Antennas   Because of overall weight and length, all 160m center fed flat top antennas, regardless of the size of the feedline, should be supported by Model 30-100 Tensioners.

Breaking Strength   Check to be sure that your antenna wire and all antenna components have a minimum breaking strength of 300 lbs. and halyards 700 lbs. minimum.  For breaking strength information go to Table 2 at the bottom of this page. 3/16” and larger diameter Dacron rope meets this requirement and has a breaking strength that exceeds 700 lbs.

 


CALCULATING CENTER WEIGHT

​STEP 1  Determine the weight of your feed line...just the part that is suspended from your antenna. If you have an end fed antenna or corner fed horizontal loop, consider the feed line weight to be zero. Go to Table 2 below and find the weight per foot of your feed line and calculate its total weight in pounds. (Wt/ft. x suspended length = total weight).

STEP 2  Determine or estimate the weight of your center insulator and/or balun.  This is usually small and just a fraction of the feed line weight.  Add this to the feed line weight to get the total weight suspended at the feed point.  Again, your answer will be zero if you have an end fed antenna or corner fed loop.

Step 3  Determine the total suspended weight from 1 & 2 above.  You do not need to include the weight of the antenna wire.

Step 4  Is the total weight under or over 3 pounds?

Under 3 pounds…Model 20-50 Tensioners are recommended. This will typically be 160m-10m antennas that are end fed or loops or are center fed 80-10m antennas with feed lines using window or ladder line or small diameter coax weighing less than 3 pounds including the center insulator/balun. Add a Model 20-50-R reciprocal Tensioner to the other end to make a very conservative and rugged installation that will have twice the tree sway displacement of a single unit.

Over 3 pounds…Model 30-100 Tensioners are recommended.  It is designed for larger center fed antennas with unsupported feed line weight over 3 pounds and all fan dipoles.  These are usually antennas fed with large diameter coax or 600 ohm ladder line and/or a center insulator/balun that is suspended on the wire.  Add a Model 30-100-R reciprocal Tensioner at the opposite end for a very conservative and rugged installation having twice the tree sway distance of a single unit.

Borderline situations....for borderline weight situations it is always safe to use higher tension and the 30-100 model Tensioners.

 

Refer to the "Data Tables, Wire Sag vs Tension" for estimating the amount of sag that your antenna will have when you vary the tension. The data applies to a one or two Tensioner installation.

 

 


 

 

Table 2

Wire breaking strength in pounds

Wire wt/ft

 

Feed line wt/ft

AWG

40%Cu clad steel

Hard drawn copper

Soft drawn

copper

Cu Flex Weave

7 strand

clad Cu

 

 

 

 

   RG-6

 

 

 .030

12

917

337

200

170

---

,0198

 

   RG-8    RG-213

.115

14

550

234

125

128

349

.0124

 

RG-8X

600 ohm

ladder line

.040

16

381

135

70

n/a

---

.0078

 

RG-11

.092

 18

280

85

50

n/a

---

.0049

 

450 ohm

.026

 

RG-58

.029

 

RG-59

.032