Re: Topband: 80m rotatable dipole load coil questions

[Bob K6UJ]

Ray,

I made a 40M rotary dipole and followed Force 12's Tornado loading coil 
design.  They issued a study
on the evolution of their loading coils from Tom Schiller's original 
design. They first went to  a smaller diameter (less efficient) coil and 
later back to a larger diameter final version they call their Tornado 
coil.  It is interesting
to note that with their new Tornado coil they went back to the larger 
diameter coil as Tom Schiller used.
The Tornado design coils are now used on all their coil loaded antennas. 
 I thought this might be interesting to you on designing the 80M coils.


http://www.force12inc.com/content/Application%20Note%20-%2040m%20Delta%20Coils%20Overview%20DRAFT%202.pdf


Bob
K6UJ







On 10/10/16 9:03 PM, Ray Benny wrote:

I am building a 90 ft, 80m rotatable dipole. I am near the point of fabricating 
the inductors/coils that will go about 23 ft out on the element. I am guying 
the element just before the inductor. I have several questions:
1. Does the size of the gap between the center element and element tip make 
much difference? Is one inch enough, or should it be almost the same size as 
the coil length?
2. Is there advantage of winding the coils of copper vs. aluminum? Is it worth 
silver plating the copper windings? I'm most likely planning to use 1/4" tubing 
either way.
3. Once I figure out the total length of the element, a friend is going to run 
EZNEC and tell me the inductor valve I need. I will use a calculator to compute 
the physical dimensions of the coils. What is the advantage of building the 
coils on either 3 inch vs. a 4 inch form?
Is there anything else to consider in the construction of this antenna?
Tnx for your thoughts,
Ray,N6VRLocated in central AZ

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Re: Topband: 80m rotatable dipole load coil questions

[Grant Saviers]

From a coil loaded 80m 2L yagi (bought JKantennas) and 80m rotatable 
dipole I built and reading here are some thoughts.


My rotatable 80m Tornado loaded 86' dipole at 100' doesn't have much of 
a pattern,  height is everything and at about 130' or so they really 
start to play.  The beam is at 157'.


Element gap isn't too important - wide enough to stand the voltage, 
strong, and UV durable. 2" is ok.   A fiberglass solid rod with paint 
would work, or a UV resistant plastic sleeve over the FG.  No steel or 
SS near the coil if possible.


IMO, there is very little loss difference with 1/4" tubing Cu vs Al.  
Good electrical joints are probably more important.  Coil L/D ratio 
about 1 and turns spaced tubing diameter seems to be about optimal for 
highest Q.  Any form will reduce Q, so best to avoid them and make the 
coil self supporting.  I use 
http://hamwaves.com/antennas/inductance.html for a coil calculator, it 
gives you every value you might want.


Many other issues - truss connections,  3 way truss per Lesson's 
designs, wind load calcs, etc.  My dipole truss is 2 phillystrans up to 
a 5' wide crossbar 5' up the mast.  So far no problems, but in a treed 
area with modest wind loads.  YagiMech predicts 85 mph survival w/o truss.


I'll send a coil picture offline.

Grant KZ1W

On 10/10/2016 21:03 PM, Ray Benny wrote:

I am building a 90 ft, 80m rotatable dipole. I am near the point of fabricating 
the inductors/coils that will go about 23 ft out on the element. I am guying 
the element just before the inductor. I have several questions:
1. Does the size of the gap between the center element and element tip make 
much difference? Is one inch enough, or should it be almost the same size as 
the coil length?
2. Is there advantage of winding the coils of copper vs. aluminum? Is it worth 
silver plating the copper windings? I'm most likely planning to use 1/4" tubing 
either way.
3. Once I figure out the total length of the element, a friend is going to run 
EZNEC and tell me the inductor valve I need. I will use a calculator to compute 
the physical dimensions of the coils. What is the advantage of building the 
coils on either 3 inch vs. a 4 inch form?
Is there anything else to consider in the construction of this antenna?
Tnx for your thoughts,
Ray,N6VRLocated in central AZ
  
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Re: Topband: 80m rotatable dipole load coil questions

[GALE STEWARD via Topband]

Here's a link to a 80M yagi designed and built by VE6WZ.
Some good loading coil info.
73, Stew K3ND

80m 2-el Yagi

  
|  
|   |  
80m 2-el Yagi
   |  |

  |

 


  From: Grant Saviers 
 To: Ray Benny ; "topband@contesting.com" 
 
 Sent: Tuesday, October 11, 2016 11:35 AM
 Subject: Re: Topband: 80m rotatable dipole load coil questions
   
 From a coil loaded 80m 2L yagi (bought JKantennas) and 80m rotatable 
dipole I built and reading here are some thoughts.

My rotatable 80m Tornado loaded 86' dipole at 100' doesn't have much of 
a pattern,  height is everything and at about 130' or so they really 
start to play.  The beam is at 157'.

Element gap isn't too important - wide enough to stand the voltage, 
strong, and UV durable. 2" is ok.  A fiberglass solid rod with paint 
would work, or a UV resistant plastic sleeve over the FG.  No steel or 
SS near the coil if possible.

IMO, there is very little loss difference with 1/4" tubing Cu vs Al.  
Good electrical joints are probably more important.  Coil L/D ratio 
about 1 and turns spaced tubing diameter seems to be about optimal for 
highest Q.  Any form will reduce Q, so best to avoid them and make the 
coil self supporting.  I use 
http://hamwaves.com/antennas/inductance.html for a coil calculator, it 
gives you every value you might want.

Many other issues - truss connections,  3 way truss per Lesson's 
designs, wind load calcs, etc.  My dipole truss is 2 phillystrans up to 
a 5' wide crossbar 5' up the mast.  So far no problems, but in a treed 
area with modest wind loads.  YagiMech predicts 85 mph survival w/o truss.

I'll send a coil picture offline.

Grant KZ1W


   
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Re: Topband: 80m rotatable dipole load coil questions

[AB2E Darrell]

Ray,

There is a lot of interesting info (possibly useful to you) at VE6WZ's website 
http://www.qsl.net/ve6wz/intro.htm

In his case, he designed a short boom 2 el 80m yagi, and designed his own 
coils. He used the Brian Beezley design program.


73 and best of luck with your antenna project,

Darrell AB2E



From: Topband  on behalf of Bob K6UJ 

Sent: Tuesday, October 11, 2016 11:16 AM
To: topband@contesting.com
Subject: Re: Topband: 80m rotatable dipole load coil questions

Ray,

I made a 40M rotary dipole and followed Force 12's Tornado loading coil
design.  They issued a study
on the evolution of their loading coils from Tom Schiller's original
design. They first went to  a smaller diameter (less efficient) coil and
later back to a larger diameter final version they call their Tornado
coil.  It is interesting
to note that with their new Tornado coil they went back to the larger
diameter coil as Tom Schiller used.
The Tornado design coils are now used on all their coil loaded antennas.
  I thought this might be interesting to you on designing the 80M coils.

http://www.force12inc.com/content/Application%20Note%20-%2040m%20Delta%20Coils%20Overview%20DRAFT%202.pdf
APPLICATION NOTE - Force 12 / InnovAntennas 
Superstore
www.force12inc.com
APPLICATION NOTE 40 Meter Delta Coil Overview Including Tip Dimensions For 
Using 3rd Generation 'Tornado Delta' Coils Introduced In 2014




Bob
K6UJ







On 10/10/16 9:03 PM, Ray Benny wrote:
> I am building a 90 ft, 80m rotatable dipole. I am near the point of 
> fabricating the inductors/coils that will go about 23 ft out on the element. 
> I am guying the element just before the inductor. I have several questions:
> 1. Does the size of the gap between the center element and element tip make 
> much difference? Is one inch enough, or should it be almost the same size as 
> the coil length?
> 2. Is there advantage of winding the coils of copper vs. aluminum? Is it 
> worth silver plating the copper windings? I'm most likely planning to use 
> 1/4" tubing either way.
> 3. Once I figure out the total length of the element, a friend is going to 
> run EZNEC and tell me the inductor valve I need. I will use a calculator to 
> compute the physical dimensions of the coils. What is the advantage of 
> building the coils on either 3 inch vs. a 4 inch form?
> Is there anything else to consider in the construction of this antenna?
> Tnx for your thoughts,
> Ray,N6VRLocated in central AZ
>
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>

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Re: Topband: 80m rotatable dipole load coil questions

[GALE STEWARD via Topband]

Hmm, the link didn't take! The info is on QRZ.com/VE6WZ
73, Stew K3ND

  From: GALE STEWARD via Topband 
 To: "topband@contesting.com"  
 Sent: Tuesday, October 11, 2016 11:59 AM
 Subject: Re: Topband: 80m rotatable dipole load coil questions
   
Here's a link to a 80M yagi designed and built by VE6WZ.
Some good loading coil info.
73, Stew K3ND

80m 2-el Yagi

  
|  
|  |  
80m 2-el Yagi
  |  |

  |

 


      From: Grant Saviers 
 To: Ray Benny ; "topband@contesting.com" 
 
 Sent: Tuesday, October 11, 2016 11:35 AM
 Subject: Re: Topband: 80m rotatable dipole load coil questions
  
 From a coil loaded 80m 2L yagi (bought JKantennas) and 80m rotatable 
dipole I built and reading here are some thoughts.

My rotatable 80m Tornado loaded 86' dipole at 100' doesn't have much of 
a pattern,  height is everything and at about 130' or so they really 
start to play.  The beam is at 157'.

Element gap isn't too important - wide enough to stand the voltage, 
strong, and UV durable. 2" is ok.  A fiberglass solid rod with paint 
would work, or a UV resistant plastic sleeve over the FG.  No steel or 
SS near the coil if possible.

IMO, there is very little loss difference with 1/4" tubing Cu vs Al.  
Good electrical joints are probably more important.  Coil L/D ratio 
about 1 and turns spaced tubing diameter seems to be about optimal for 
highest Q.  Any form will reduce Q, so best to avoid them and make the 
coil self supporting.  I use 
http://hamwaves.com/antennas/inductance.html for a coil calculator, it 
gives you every value you might want.

Many other issues - truss connections,  3 way truss per Lesson's 
designs, wind load calcs, etc.  My dipole truss is 2 phillystrans up to 
a 5' wide crossbar 5' up the mast.  So far no problems, but in a treed 
area with modest wind loads.  YagiMech predicts 85 mph survival w/o truss.

I'll send a coil picture offline.

Grant KZ1W


  
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Re: Topband: 80m rotatable dipole load coil questions

[Wes Stewart]

On 10/10/2016 9:03 PM, Ray Benny wrote:

I am building a 90 ft, 80m rotatable dipole. I am near the point of fabricating 
the inductors/coils that will go about 23 ft out on the element. I am guying 
the element just before the inductor. I have several questions:
1. Does the size of the gap between the center element and element tip make 
much difference? Is one inch enough, or should it be almost the same size as 
the coil length?
I suppose it depends on how you mount the inductor; concentric or offset.  I 
suggest making the gap at least the length of the inductor.

2. Is there advantage of winding the coils of copper vs. aluminum? Is it worth 
silver plating the copper windings? I'm most likely planning to use 1/4" tubing 
either way.
Both materials will tarnish (oxidize).  Since aluminum is already oxidized, I 
would go with it, since we are both in AZ where, until the big one, we are 
removed from salt air.  Silver plating is a waste, IMHO, and not necessarily of 
any benefit. See: http://k6mhe.com/n7ws/Plating.pdf
  
3. Once I figure out the total length of the element, a friend is going to run EZNEC and tell me the inductor valve I need. I will use a calculator to compute the physical dimensions of the coils. What is the advantage of building the coils on either 3 inch vs. a 4 inch form?

Is there anything else to consider in the construction of this antenna?
Tnx for your thoughts,
I "built" your proposal in AutoEZ (http://www.ac6la.com/autoez.html) and EZNEC.  
I assumed your 90' overall length, inductors at 23' from center.  The inner 
tubing 1.5" diameter; a 1' length to hold the inductor, 1" diameter and the 
remaining length also 1" diameter.  I modeled in free space to avoid unknown 
ground and height effects.


AutoEZ is too cool for words (I was an early beta tester) and has a built-in 
resonating function.  I let it set the reactance of the inductor to resonate the 
element.  I used 3.55 MHz for this and came up with +jX = 413 (18.5 uH).  Now 
the fun part is to sweep the inductor Q (X/R), by using a swept variable "R".  I 
can then plot (or tabulate) the gain v. Q.  The point of this is to question the 
wild claims about the superiority of coil X (no pun intended) to coil Y.  I 
don't know whether the following table will make it through the list filter but 
here it is:


FQR X  SWRGAIN
3.550   50  

55.02   -0.71   1.101   0.67
3.550   75  

50.41   -0.37   1.011   1.05
3.550   100 

48.11   -0.22   1.040   1.25
3.550   125 

46.73   -0.13   1.070   1.38
3.550   150 

45.81   -0.08   1.092   1.47
3.550   175 

45.15   -0.04   1.107   1.53
3.550   200 

44.65   -0.01   1.120   1.58
3.550   225 

44.27   0.011.129   1.62
3.550   250 

43.96   0.031.137   1.65
3.550   275 

43.71   0.041.144   1.67
3.550   300 

43.50   0.061.149   1.69
3.550   325 

43.32   0.071.154   1.71
3.550   350 

43.17   0.071.158   1.73
3.550   375 

43.04   0.081.162   1.74
3.550   400 

42.93   0.091.165   1.75
3.550   425 

42.82   0.091.168   1.76
3.550   450 

42.73   0.101.170   1.77


IMHO, what this shows is that an inductor Q of 200 or so is good enough and 
heroic efforts to increase it are met with rapidly diminishing returns, as well 
as increased cost, wind loading, etc.


Using K7MEM's calculator 
(http://www.k7mem.com/Electronic_Notebook/inductors/coildsgn.html) which 
implements Terman's formulas, also, the late Charlie Michaels, W7XC, simplified 
some of Terman's tables to determine the AC resistance of a coil. ("Loading 
Coils for 160-Meter Antennas", QST, April 1990) Using these references, I did 
some playing.


Arbitrarily, I selected 12 AWG bare wire and a 1:1 length to diameter ratio.  
Skipping some of the arithmetic and assuming I did it correctly, for 18.5 uH the 
program calculates among other things that 18 turns requires ~174" of wire on a 
3" dia form.  The DC resistance is therefore ~0.11 Ohm.  From Michaels, the AC 
resistance ~1.62 Ohm @ 3.55 MHz. So Q ~ 250.  Good enough.


What your design has going for it is that it's not too heavily loaded.  Shorter 
lengths would require much more loading.


FWIW,

Wes  N7WS


Ray,N6VRLocated in central AZ
  
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