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N81JG(at)aol.com
Guest

Posted: Sun Jun 06, 2010 5:23 pm Post subject: Com antenna

Hi Bob,

  

  I have been flying a Rutan VariEze for many years with several changes in  com antennas. All have been suboptimal. I am planning on mounting a dipole in  the wing-winglet with ferrite donuts at the coax as used with the copper tape  antennas. The plan is to use a length of copper tubing for each leg of the  dipole and thread it up the leading edge of the winglet in the underlying  styrafoam and horizontally in the leading edge of the wing foam. The  center coax lead will be connected to the vertical winglet pole and the shield  to the horizontal wing pole. I was planning on using 1/8 inch copper tubing.  Would that size tubing give me adequate bandwidth? Do you see any other pitfalls  in this plan? I want to make sure it will work before I cut the 2-3 inch hole in  the wingtip-lower winglet junction in order to thread the tubing in and connect  the coax.

  

 John Greaves

 VariEze N81JG

 Redding, CA



  [quote][b]

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nuckolls.bob(at)aeroelect
Guest

Posted: Sun Jun 06, 2010 7:44 pm Post subject: Com antenna

At 08:17 PM 6/6/2010, you wrote:

  	  Quote: 	
		   Hi Bob,

  

 I have been flying a Rutan VariEze for many years with several changes in com antennas. All have been suboptimal. I am planning on mounting a dipole in the wing-winglet with ferrite donuts at the coax as used with the copper tape antennas. The plan is to use a length of copper tubing for each leg of the dipole and thread it up the leading edge of the winglet in the underlying styrafoam and horizontally in the leading edge of the wing foam. The center coax lead will be connected to the vertical winglet pole and the shield to the horizontal wing pole. I was planning on using 1/8 inch copper tubing. Would that size tubing give me adequate bandwidth? Do you see any other pitfalls in this plan? I want to make sure it will work before I cut the 2-3 inch hole in the wingtip-lower winglet junction in order to thread the tubing in and connect the coax. 	


   What kinds of antennas have you tried so far?

   What's your criteria for judging them sub-optimal?

   Are there other VariEze builders who have already

   built the antenna you propose? Have THEY made any

   Antenna A versus Antenna B comparisons that would

   encourage you to carry out this surgery on the

   airplane?



   What is the height of the winglet? Can you get

   a half-wave radiator up the winglet? There's

   a unique center-fed half-wave that runs a

   feedline up the center of the lower element.

   See:



  http://www.miracleantenna.com/AirWhip.htm



   This might be easier to install. But

   before you start carving on the airplane,

   it would be useful to calibrate your

   expectations against the physics of

   contemporary airborne antenna performance.



 

   Bob . . .    [quote][b]

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N81JG(at)aol.com
Guest

Posted: Sun Jun 06, 2010 9:00 pm Post subject: Com antenna

Hi Bob,

  

 I originally had a foil dipole with 20.3 inch limbs and 3 ferrite donuts on  the coax that worked reasonably well until I had to change my brake lines from  Nyloseal to aluminum. That detuned and ruined the antenna. Next I had a similar  tape dipole on the seat back, but my body detuned that. Now I have the Miracle  Whip inside the front fuselage that works within a few 10's of miles(OK only for  inside airport areas), but is too directional probably due to metal and my legs  nearby. Other VE's have had these wing-winglet dipole antennas and I think they  have been satisfactory and I think superior to all other buried  antennas, but I am waiting for reply on the canard aviators site. The  surgery on the plane is minimal since I have a wire conduit in the foam wing  from root to the tip just under the fiberglass tip that I can access easily and  also thread the copper tubing in the foam from.

  

 The winglet height is adequate for the 20.3 inch vertical limb. I would use  the Miracle Whip, but it is too long for the winglet height. I considered  extending it along the outer wing foam with the last 1/2 of the tip in the  vertical part of the winglet, but that would require quite a bit of surgery to  bury the base load box in the wing foam near the center of the wing and might  compromise the foam-skin stress structure of the wing( a definite no go there  option).

  

 I could go to an external whip antenna with a ground plane of wire or  aluminum, but I would prefer not to add parasitic drag. The wingtip idea is less  invasive surgery.

  

 Thanks for your reply. I hope I have answered you questions.

  

 John Greaves

  

  

  

  In a message dated 6/6/2010 8:45:31 P.M. Pacific Daylight Time,  nuckolls.bob(at)aeroelectric.com writes:

  	  Quote: 	
		  At 08:17    PM 6/6/2010, you wrote:

    	  Quote: 	
		  Hi Bob,

 

I have been flying a Rutan VariEze for many      years with several changes in com antennas. All have been suboptimal. I am      planning on mounting a dipole in the wing-winglet with ferrite donuts at the      coax as used with the copper tape antennas. The plan is to use a length of      copper tubing for each leg of the dipole and thread it up the leading edge      of the winglet in the underlying styrafoam and horizontally in the leading      edge of the wing foam. The center coax lead will be connected to the      vertical winglet pole and the shield to the horizontal wing pole. I was      planning on using 1/8 inch copper tubing. Would that size tubing give me      adequate bandwidth? Do you see any other pitfalls in this plan? I want to      make sure it will work before I cut the 2-3 inch hole in the wingtip-lower      winglet junction in order to thread the tubing in and connect the      coax. 	


  What kinds of antennas have you tried so    far?

  What's your criteria for judging them sub-optimal?

     Are there other VariEze builders who have already

  built the antenna    you propose? Have THEY made any

  Antenna A versus Antenna B    comparisons that would

  encourage you to carry out this surgery on    the

  airplane?



  What is the height of the winglet? Can    you get

  a half-wave radiator up the winglet? There's

  a    unique center-fed half-wave that runs a

  feedline up the center of    the lower element.

  See:



http://www.miracleantenna.com/AirWhip.htm



     This might be easier to install. But

  before you start carving on the    airplane,

  it would be useful to calibrate your

     expectations against the physics of

  contemporary airborne antenna    performance.



   

  Bob . . .  	  Quote: 	
		  



====================================

List href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.matronics.com/Navigator?AeroElectric-List

====================================

ms.matronics.com/">http://forums.matronics.com

====================================

tp://www.matronics.com/contribution">http://www.matronics.com/contribution

====================================



	
	


  [quote][b]

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jun 07, 2010 8:48 pm Post subject: Com antenna

The winglet height is adequate for the 20.3 inch vertical limb. I 

would use the Miracle Whip, but it is too long for the winglet height.



I considered extending it along the outer wing foam with the last 1/2 

of the tip in the vertical part of the winglet, but that would 

require quite a bit of surgery to bury the base load box in the wing 

foam near the center of the wing and might compromise the foam-skin 

stress structure of the wing( a definite no go there option).



    Agreed.

I could go to an external whip antenna with a ground plane of wire or 

aluminum, but I would prefer not to add parasitic drag. The wingtip 

idea is less invasive surgery.



    Okay. How about a 1/4 wave with 'half' a ground

    plane?  Run a 21 inch piece of copper up the winglet

    and two to five radials into the foam toward the

    fuselage. Connect all the radials together at the

    coax shield, center conductor to the winglet radiator

    and ditch the donuts.



    Don't worry about bandwidth. Proximity effects

    of conductors for de-tuning and/or pattern

    modification are profoundly more hazardous to

    performance than SWR.

   Bob . . .

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sportav8r(at)gmail.com
Guest

Posted: Tue Jun 08, 2010 5:12 am Post subject: Com antenna

Yeah, until the transmitter power amp stage folds-back at higher SWR to protect the output transistor - that's a performance-killer, sometimes.  Bandwidth can matter...



 	  Quote: 	
		  >Don't worry about bandwidth. Proximity effects

   of conductors for de-tuning and/or pattern
	


  modification are profoundly more hazardous to

  performance than SWR.<<



On Tue, Jun 8, 2010 at 12:50 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

 [quote]--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>

  

 

 The winglet height is adequate for the 20.3 inch vertical limb. I would use the Miracle Whip, but it is too long for the winglet height.

 

 I considered extending it along the outer wing foam with the last 1/2 of the tip in the vertical part of the winglet, but that would require quite a bit of surgery to bury the base load box in the wing foam near the center of the wing and might compromise the foam-skin stress structure of the wing( a definite no go there option).

  

    Agreed.

 

 

 I could go to an external whip antenna with a ground plane of wire or aluminum, but I would prefer not to add parasitic drag. The wingtip idea is less invasive surgery.

 

    Okay. How about a 1/4 wave with 'half' a ground

    plane?  Run a 21 inch piece of copper up the winglet

    and two to five radials into the foam toward the

    fuselage. Connect all the radials together at the

    coax shield, center conductor to the winglet radiator

    and ditch the donuts.

 

    Don't worry about bandwidth. Proximity effects

    of conductors for de-tuning and/or pattern

    modification are profoundly more hazardous to

    performance than SWR.

 

 

   Bob . . . 

 

 ===========

 "im">

 -List" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List



 ===========

 http://forums.matronics.com

 ===========

 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

 ===========

 

 

 

 



[b]

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N81JG(at)aol.com
Guest

Posted: Wed Jun 09, 2010 9:10 am Post subject: Com antenna

HI Bob, 

  

 Thanks for your replies. I have one question on the dipole with several  radial base wires. That would be easy to set up, but I don't understand why I  could ditch the toroids at the end of the coax. Does the balance of the coax and  dipole work out due to many ground radials or does the arrangement turn the  antenna into a simple base loaded 1/4 wave whip? I assume the latter is what  happens. Would the base on only the wing side of the vertical element make it  quite directional or not significantly directional?

  

 John Greaves

  

  

  In a message dated 6/7/2010 9:49:28 P.M. Pacific Daylight Time,  nuckolls.bob(at)aeroelectric.com writes:

  	  Quote: 	
		  -->    AeroElectric-List message posted by: "Robert L. Nuckolls, III"    <nuckolls.bob(at)aeroelectric.com>

The winglet height is    adequate for the 20.3 inch vertical limb. I 

would use the Miracle Whip,    but it is too long for the winglet height.



I considered extending it    along the outer wing foam with the last 1/2 

of the tip in the vertical    part of the winglet, but that would 

require quite a bit of surgery to bury    the base load box in the wing 

foam near the center of the wing and might    compromise the foam-skin 

stress structure of the wing( a definite no go    there option).



    Agreed.

I could go to an    external whip antenna with a ground plane of wire or 

aluminum, but I would    prefer not to add parasitic drag. The wingtip 

idea is less invasive    surgery.



    Okay. How about a 1/4 wave with 'half' a    ground

    plane?  Run a 21 inch piece of copper up the    winglet

    and two to five radials into the foam toward    the

    fuselage. Connect all the radials together at    the

    coax shield, center conductor to the winglet    radiator

    and ditch the donuts.



    Don't    worry about bandwidth. Proximity effects

    of conductors for    de-tuning and/or pattern

    modification are profoundly more    hazardous to

    performance than SWR.

      Bob . . .  ========================= Use   utilities  Day  ================================================               - MATRONICS WEB FORUMS  ================================================             - List Contribution Web Site  sp;                             ===================================================



	


  [quote][b]

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nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jun 09, 2010 8:24 pm Post subject: Com antenna

At 11:17 AM 6/9/2010, you wrote:

  	  Quote: 	
		   HI Bob, 

  

 Thanks for your replies. I have one question on the dipole with several radial base wires. That would be easy to set up, but I don't understand why I could ditch the toroids at the end of the coax. 	


    They don't really do much unless they're of a material

    appropriate to the operating frequency and then only

    when they add significant inductance to the currents

    flowing in the shield.



    Since inductance is proportional to the square of

    the turns, you need 9 toroids on the coax (nine

    series connected inductors of 1-turn each) to equal

    1 toroid with three turns of coax wound through

    the center. Take the miracle whip "can" apart

    and you'll find a single core with multiple turns

    through it.



    The idea was to improve the interface between an

    unbalanced feeder (coax) and  a balanced antenna (dipole)

    but it takes quite a few of the RIGHT toroid to do

    the best job . . . and tens of thousands of airplanes

    have successfully fed balanced VOR cat-whiskers 

    at the top of the vertical fin with coax and NO

    toroids for decades.

   

    Does the balance of the coax and dipole work out due to many ground radials or does the arrangement turn the antenna into a simple base loaded 1/4 wave whip? I assume the latter is what happens. Would the base on only the wing side of the vertical element make it quite directional or not significantly directional?

     

    Correct. Adding radials to the "base" of a single

    vertical makes it an unbalanced antenna that more

    closely approximates a ground plane. And yes,

    it's radiation patter will not be 'round' but

    if it's more efficient, a few bumps in the radiation

    plot may not matter. Having say 4 radials at the

    base make the sum total of their radiation resistance

    1/4th that of the vertical radiator. This makes

    the radiator do it's magic with the majority of

    energy arriving at the end of the feedline.



    Further, the antenna is now decidedly unbalanced

    and the toroids are no longer suggested . . .

    although they were of limited value in the first

    place. A coax balun does a better job but also narrows

    the bandwidth of the system. A broadband balun has

    a wider bandwidth but adds its own losses.



    1/4 wave comm antennas over ground planes have

    been doing a really good job on viritually EVERY

    radio equipped airplane since the Lear LTRA6

    and Narco VT1 radios gave voice to little GA

    aircraft in the 50's.



    I think you the highest probability for success

    lies in getting as close to that configuration

    as the layout of your winglet allows. The more

    radials the better. 4 is enough and 8 is

    probably not practical.



    Bob . . .

     [quote][b]

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N81JG(at)aol.com
Guest

Posted: Thu Jun 10, 2010 2:38 pm Post subject: Com antenna

Thanks much Bob for the explanation. It looks like the radial base may be  my best bet for coming close to a standard aircraft cats-whisker antenna. I will  try that first and I can lay it out on the outer skin and measure the SWR for  confirmation of the efficiency before I install it in the foam. I will also see  how different the SWR will be between the outer surface and inside the foam. I  will report back.

  

 John Greaves

  

  In a message dated 6/9/2010 9:25:27 P.M. Pacific Daylight Time,  nuckolls.bob(at)aeroelectric.com writes:

  	  Quote: 	
		  At 11:17    AM 6/9/2010, you wrote:

    	  Quote: 	
		  HI Bob, 

 

Thanks for your replies. I have one question on      the dipole with several radial base wires. That would be easy to set up, but      I don't understand why I could ditch the toroids at the end of the      coax. 	


   They don't really do much unless    they're of a material

   appropriate to the operating frequency    and then only

   when they add significant inductance to the    currents

   flowing in the shield.



   Since    inductance is proportional to the square of

   the turns, you    need 9 toroids on the coax (nine

   series connected inductors of    1-turn each) to equal

   1 toroid with three turns of coax wound    through

   the center. Take the miracle whip "can"    apart

   and you'll find a single core with multiple    turns

   through it.



   The idea was to improve    the interface between an

   unbalanced feeder (coax) and  a    balanced antenna (dipole)

   but it takes quite a few of the    RIGHT toroid to do

   the best job . . . and tens of thousands of    airplanes

   have successfully fed balanced VOR cat-whiskers    

   at the top of the vertical fin with coax and    NO

   toroids for decades.

  

  Does the balance of the coax and dipole work    out due to many ground radials or does the arrangement turn the antenna into a    simple base loaded 1/4 wave whip? I assume the latter is what happens. Would    the base on only the wing side of the vertical element make it quite    directional or not significantly directional?

       

   Correct. Adding radials to the "base" of a    single

   vertical makes it an unbalanced antenna that    more

   closely approximates a ground plane. And    yes,

   it's radiation patter will not be 'round'    but

   if it's more efficient, a few bumps in the    radiation

   plot may not matter. Having say 4 radials at    the

   base make the sum total of their radiation    resistance

   1/4th that of the vertical radiator. This    makes

   the radiator do it's magic with the majority    of

   energy arriving at the end of the    feedline.



   Further, the antenna is now decidedly    unbalanced

   and the toroids are no longer suggested . .    .

   although they were of limited value in the    first

   place. A coax balun does a better job but also    narrows

   the bandwidth of the system. A broadband balun    has

   a wider bandwidth but adds its own    losses.



   1/4 wave comm antennas over ground planes    have

   been doing a really good job on viritually    EVERY

   radio equipped airplane since the Lear    LTRA6

   and Narco VT1 radios gave voice to little    GA

   aircraft in the 50's.



   I think you the    highest probability for success

   lies in getting as close to    that configuration

   as the layout of your winglet allows. The    more

   radials the better. 4 is enough and 8 is

      probably not practical.



   Bob . . .

 	  Quote: 	
		  



====================================

List href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.matronics.com/Navigator?AeroElectric-List

====================================

ms.matronics.com/">http://forums.matronics.com

====================================

tp://www.matronics.com/contribution">http://www.matronics.com/contribution

====================================



	
	


  [quote][b]

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jun 10, 2010 4:38 pm Post subject: Com antenna

At 05:31 PM 6/10/2010, you wrote:

  	  Quote: 	
		   Thanks much Bob for the explanation. It looks like the radial base may be my best bet for coming close to a standard aircraft cats-whisker antenna. I will try that first and I can lay it out on the outer skin and measure the SWR for confirmation of the efficiency before I install it in the foam. I will also see how different the SWR will be between the outer surface and inside the foam. I will report back. 	


   Good show!  Inquiring minds want to know . . .

  

   Get a plot over the whole comm range.



 

   Bob . . .    [quote][b]

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