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Transponder antenna

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Steve Kelly

Joined: 08 Jul 2016
Posts: 18

Posted: Fri Jul 15, 2016 8:09 am Post subject: Transponder antenna

I'm at that point where I need to install a transponder antenna on the bottom of my fiberglass fuselage.  Research shows differing opinions on several issues.

  -Location, For a number of reasons I am limited to the area below the pilot/ copilot seats.  Some say thats too close to your body. Some say it doesn't matter.  I have read that the radiation pattern from the antenna is horizontal and in the shape of a donut.  If this is true then under seat would seem to be a good location.  Also, since I need to add a ground plane, would this serve to reflect any radiation?

  -Ground plane, I have room for up to a 16" square ground plane.  I am unsure as to the size and shape.  I have read that if it's round it has to be a certain size, But don't know what that size is.  It seems that size doesn't matter as much if its square or octagonal.  Also, should I make ground plane as large as I have room for?

  The antenna is just the standard post and ball from B&C.

  Would appreciate any feedback, Steve

_________________
Steve

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Jul 15, 2016 8:40 am Post subject: Transponder antenna

At 11:09 AM 7/15/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Steve Kelly" <amsk22(at)gmail.com>



 I'm at that point where I need to install a transponder antenna on the bottom of my fiberglass fuselage.  Research shows differing opinions on several issues.

   -Location, For a number of reasons I am limited to the area below the pilot/ copilot seats.  Some say thats too close to your body. Some say it doesn't matter. 	


    It doesn't . . . there are no biological hazards associated

    with proximity to the transponder antenna.



  	  Quote: 	
		   I have read that the radiation pattern from the antenna is horizontal and in the shape of a donut. 	


    Sort of . . . it's 'half a donut' . . .



 [img]cid:.0[/img]



 

  If this is true then under seat would seem to be a good location.  Also, since I need to add a ground plane, would this serve to reflect any radiation?

    

    The ground plane is essential to antenna performance.



    It it isn't provided by 'very large' surface areas

    like the skin of a metal aircraft, . . .



  	  Quote: 	
		    -Ground plane, I have room for up to a 16" square ground plane.  I am unsure as to the size and shape.  I have read that if it's round it has to be a certain size, But don't know what that size is.  It seems that size doesn't matter as much if its square or octagonal.  Also, should I make ground plane as large as I have room for? 	


     The RADIUS of a minimal ground plane is equal to the

     seated height of the associated antenna. For a transpoder,

     this is 5.3" in diameter.



 

  	  Quote: 	
		    The antenna is just the standard post and ball from B&C.

   Would appreciate any feedback, Steve 	


    That would be my choice. See chapter 13 of



     http://tinyurl.com/pt97pha



 

 

   Bob . . .

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Peter(at)sportingaero.com
Guest

Posted: Fri Jul 15, 2016 12:46 pm Post subject: Transponder antenna

The maths to figure the size of the ground plane are quite straight forward

when you know that speed of light = frequency x wavelength.

For a transponder 3 x 10^8 m/s = 1090 x 10^6 x wavelength

Wavelength = 3/10.9 = 0.275m (or 10.84")

Most antennas we use are 1/4 wave dipoles, the ground plane should be tuned

to the antenna, so the radius should 69mm, diameter 138mm (5.42").



Peter



--

Steve Kelly

Joined: 08 Jul 2016
Posts: 18

Posted: Fri Jul 15, 2016 5:56 pm Post subject: Re: Transponder antenna

Thank you.  Those are the answers I was looking for.

Steve

_________________
Steve

donjohnston

Joined: 13 Dec 2009
Posts: 232

Posted: Sat Jul 16, 2016 7:15 am Post subject: Re: Transponder antenna

Take this with a grain of salt...



I was told that because there are two frequencies involved with the transponder that a ground plane of two different sizes is best.  So following that logic, I created an octagon shaped ground plane. I may have misinterpreted the RST document, but it works fine.



http://www.velocity-xl.com/blog/2013/11/07/13-99-transponder-antenna-ground-plane/

 	  Steve Kelly wrote: 	
		  -Ground plane, I have room for up to a 16" square ground plane.  I am unsure as to the size and shape.  I have read that if it's round it has to be a certain size, But don't know what that size is.  It seems that size doesn't matter as much if its square or octagonal.  Also, should I make ground plane as large as I have room for?

  The antenna is just the standard post and ball from B&C.

  Would appreciate any feedback, Steve

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jul 16, 2016 8:49 am Post subject: Transponder antenna

At 10:15 AM 7/16/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "donjohnston" <don(at)velocity-xl.com>



 Take this with a grain of salt...



 I was told that because there are two frequencies involved with the transponder that a ground plane of two different sizes is best.  So following that logic, I created an octagon shaped ground plane. I may have misinterpreted the RST document, but it works fine.



  http://www.velocity-xl.com/blog/2013/11/07/13-99-transponder-antenna-ground-plane/ 	


    This is REALLY fine hair-splitting.  The signals using

    the transponder antenna are not that far apart. Even

    if you had access to a %million$ antenna test range

    and equipment, you would be hard pressed to detect

    and quantify any improvement in performance for having

    crafted an 'optimized' ground plane . . . after all,

    the real magic in broader bandwidth performance

    has more to do with the shape of the antenna as opposed

    to its ground plane.



    There are much more expensive transponder antennas

    out there that do offer wider band width . . . but

    if you bought one and installed it, you wouldn't

    observe any difference in system performance. I've

    offered similar arguments about going with $higher$

    batteries to save weight by asking just how much

    the expense will shorten your take-off run, increase

    your rate of climb, increase your service ceiling?

    One might calculate the differences . . . John Q.

    OBAM airplane pilot would be hard pressed to fly

    two otherwise identical airplanes and tell us

    which one has the super-cool battery installed.



 

    Tony Levere was once known to run stripes of Scotch

    Tape over the lines of rivet heads on the skins of

    his p-38 race plane . . . with a notion of getting

    a few more knots out of the machine . . . intuitively

    one can 'see' how this might be useful but the

    difference would be hard to go measure. Tony did wins lots

    of races with his pride and joy . . . but was Scotch Tape

    really the tipping force . . . or did more powerful

    influences make the difference? We'll nver know.



 

   Bob . . .

ashleysc(at)broadstripe.n
Guest

Posted: Sat Jul 16, 2016 9:06 am Post subject: Transponder antenna

Hi All;



 I'll pose this as a philosophical point, as I am no expert: It would seem, considering no ground plane is required on a metal aircraft, that the only consideration is how small can they be made and still function adequately. In other words, there is no "too big," only "too small." If this is correct so far, it would behoove us to err to the large side.

 Cheers!   Stu.

 



   From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

To: aeroelectric-list(at)matronics.com

Sent: Saturday, July 16, 2016 9:47:11 AM

Subject: Re: Re: Transponder antenna

 



At 10:15 AM 7/16/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "donjohnston" <don(at)velocity-xl.com>

 



Take this with a grain of salt...

 



I was told that because there are two frequencies involved with the transponder that a ground plane of two different sizes is best.  So following that logic, I created an octagon shaped ground plane. I may have misinterpreted the RST document, but it works fine.

 



http://www.velocity-xl.com/blog/2013/11/07/13-99-transponder-antenna-ground-plane/ 	


   This is REALLY fine hair-splitting.  The signals using

   the transponder antenna are not that far apart. Even

   if you had access to a %million$ antenna test range

   and equipment, you would be hard pressed to detect

   and quantify any improvement in performance for having

   crafted an 'optimized' ground plane . . . after all,

   the real magic in broader bandwidth performance

   has more to do with the shape of the antenna as opposed

   to its ground plane.

 



   There are much more expensive transponder antennas

   out there that do offer wider band width . . . but

   if you bought one and installed it, you wouldn't

   observe any difference in system performance. I've

   offered similar arguments about going with $higher$

   batteries to save weight by asking just how much

   the expense will shorten your take-off run, increase

   your rate of climb, increase your service ceiling?

   One might calculate the differences . . . John Q.

   OBAM airplane pilot would be hard pressed to fly

   two otherwise identical airplanes and tell us

   which one has the super-cool battery installed.

 

   Tony Levere was once known to run stripes of Scotch

   Tape over the lines of rivet heads on the skins of

   his p-38 race plane . . . with a notion of getting

   a few more knots out of the machine . . . intuitively

   one can 'see' how this might be useful but the

   difference would be hard to go measure. Tony did wins lots

   of races with his pride and joy . . . but was Scotch Tape

   really the tipping force . . . or did more powerful

   influences make the difference? We'll nver know.

 



 

  Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jul 16, 2016 9:21 am Post subject: Transponder antenna

At 12:05 PM 7/16/2016, you wrote:

  	  Quote: 	
		  Hi All;

 I'll pose this as a philosophical point, as I am no expert: It would seem, considering no ground plane is required on a metal aircraft 	


    A ground plane IS required . . . but the airplane IS the ground plane.



  	  Quote: 	
		  , that the only consideration is how small can they be made and still function adequately. In other words, there is no "too big," only "too small." If this is correct so far, it would behoove us to err to the large side. 	


    The resonant ground plane on a composite aircraft

    is the electrical equivalent of an infinite number

    of 'antennas' surrounding the base of the radiating

    element. Hence, the minimal ground plane is 'tuned'

    to the operating frequency.



    Either fabricate a tuned ground plane or go with

    metal many times larger than the tuned ground plane.

    Erring to the 'large' side by smaller factors

    is counter productive.



 

   Bob . . .

billhuntersemail(at)gmail
Guest

Posted: Sat Jul 16, 2016 9:36 am Post subject: Transponder antenna

The belly of a Boeing id a rather large ground plane.  

The Dynon Installation Manual was extremely specific about the size of the ground plane being a minimum size and then increments above that... but the increments above the minimum were not defined 

 

Bill Hunter 

  

On Jul 16, 2016 10:11 AM,  <ashleysc(at)broadstripe.net (ashleysc(at)broadstripe.net)> wrote: 	  Quote: 	
		  Hi All;



 I'll pose this as a philosophical point, as I am no expert: It would seem, considering no ground plane is required on a metal aircraft, that the only consideration is how small can they be made and still function adequately. In other words, there is no "too big," only "too small." If this is correct so far, it would behoove us to err to the large side.

 Cheers!   Stu.

 



   From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>

To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)

Sent: Saturday, July 16, 2016 9:47:11 AM

Subject: Re: Re: Transponder antenna

 



At 10:15 AM 7/16/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "donjohnston" <don(at)velocity-xl.com (don(at)velocity-xl.com)>

 



Take this with a grain of salt...

 



I was told that because there are two frequencies involved with the transponder that a ground plane of two different sizes is best.  So following that logic, I created an octagon shaped ground plane. I may have misinterpreted the RST document, but it works fine.

 



http://www.velocity-xl.com/blog/2013/11/07/13-99-transponder-antenna-ground-plane/ 	


   This is REALLY fine hair-splitting.  The signals using

   the transponder antenna are not that far apart. Even

   if you had access to a %million$ antenna test range

   and equipment, you would be hard pressed to detect

   and quantify any improvement in performance for having

   crafted an 'optimized' ground plane . . . after all,

   the real magic in broader bandwidth performance

   has more to do with the shape of the antenna as opposed

   to its ground plane.

 



   There are much more expensive transponder antennas

   out there that do offer wider band width . . . but

   if you bought one and installed it, you wouldn't

   observe any difference in system performance. I've

   offered similar arguments about going with $higher$

   batteries to save weight by asking just how much

   the expense will shorten your take-off run, increase

   your rate of climb, increase your service ceiling?

   One might calculate the differences . . . John Q.

   OBAM airplane pilot would be hard pressed to fly

   two otherwise identical airplanes and tell us

   which one has the super-cool battery installed.

 

   Tony Levere was once known to run stripes of Scotch

   Tape over the lines of rivet heads on the skins of

   his p-38 race plane . . . with a notion of getting

   a few more knots out of the machine . . . intuitively

   one can 'see' how this might be useful but the

   difference would be hard to go measure. Tony did wins lots

   of races with his pride and joy . . . but was Scotch Tape

   really the tipping force . . . or did more powerful

   influences make the difference? We'll nver know.

 



 

  Bob . . .

ashleysc(at)broadstripe.n
Guest

Posted: Sat Jul 16, 2016 10:53 am Post subject: Transponder antenna

Hi Bob;



 Possibly I should have said no additional ground plane is required. I expect most understood what I meant. For those who didn't, I offer my apologies.

 Concerning the second portion of your comment, I appreciate the distinction you have made. Either use a tuned ground plane, or one much larger.

 Cheers!   Stu.

 PS: I have your manual, and it is invaluable.



   From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

To: aeroelectric-list(at)matronics.com

Sent: Saturday, July 16, 2016 10:20:22 AM

Subject: Re: Re: Transponder antenna

 



At 12:05 PM 7/16/2016, you wrote:

  	  Quote: 	
		  Hi All;

I'll pose this as a philosophical point, as I am no expert: It would seem, considering no ground plane is required on a metal aircraft 	


   A ground plane IS required . . . but the airplane IS the ground plane.

 



  	  Quote: 	
		  , that the only consideration is how small can they be made and still function adequately. In other words, there is no "too big," only "too small." If this is correct so far, it would behoove us to err to the large side. 	


   The resonant ground plane on a composite aircraft

   is the electrical equivalent of an infinite number

   of 'antennas' surrounding the base of the radiating

   element. Hence, the minimal ground plane is 'tuned'

   to the operating frequency.

 



   Either fabricate a tuned ground plane or go with

   metal many times larger than the tuned ground plane.

   Erring to the 'large' side by smaller factors

   is counter productive.

 



 

  Bob . . .

donjohnston

Joined: 13 Dec 2009
Posts: 232

Posted: Sat Jul 16, 2016 2:56 pm Post subject: Re: Transponder antenna

It cost exactly zero pennies more to create that octagon shaped antenna as opposed to a round one.  And it was significantly easier to cut eight straight lines as opposed to a single circle.  And it works just fine.



So in this particular case, splitting hairs turned out easier, cheaper (time is money, right?) and maybe a half a hair better.



 	  nuckolls.bob(at)aeroelect wrote: 	
		  At 10:15 AM 7/16/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "donjohnston" <don>



 Take this with a grain of salt...



 I was told that because there are two frequencies involved with the transponder that a ground plane of two different sizes is best.  So following that logic, I created an octagon shaped ground plane. I may have misinterpreted the RST document, but it works fine.



  http://www.velocity-xl.com/blog/2013/11/07/13-99-transponder-antenna-ground-plane/ 	


    This is REALLY fine hair-splitting.  The signals using

    the transponder antenna are not that far apart. Even

    if you had access to a %million$ antenna test range

    and equipment, you would be hard pressed to detect

    and quantify any improvement in performance for having

    crafted an 'optimized' ground plane . . . after all,

    the real magic in broader bandwidth performance

    has more to do with the shape of the antenna as opposed

    to its ground plane.

wrmaxwell(at)bigpond.com
Guest

Posted: Sat Jul 16, 2016 4:01 pm Post subject: Transponder antenna

While it probably           only a matter of academic interest, unlikely to produce any           meaningful differences in daily operation, the 2-different           size argument should also apply to the vertical radiating           element too.     

Bill

              



          

     On 17/07/2016 1:15 AM, donjohnston       wrote:

     

      	  Quote: 	
		          	  Quote: 	
		  --> AeroElectric-List message posted by: "donjohnston" <don(at)velocity-xl.com> (don(at)velocity-xl.com)



Take this with a grain of salt...



I was told that because there are two frequencies involved with the transponder that a ground plane of two different sizes is best.  So following that logic, I created an octagon shaped ground plane. I may have misinterpreted the RST document, but it works fine.



http://www.velocity-xl.com/blog/2013/11/07/13-99-transponder-antenna-ground-plane/



Steve Kelly wrote:

          	  Quote: 	
		  -Ground plane, I have room for up to a 16" square ground plane.  I am unsure as to the size and shape.  I have read that if it's round it has to be a certain size, But don't know what that size is.  It seems that size doesn't matter as much if its square or octagonal.  Also, should I make ground plane as large as I have room for?

  The antenna is just the standard post and ball from B&C.

  Would appreciate any feedback, Steve

	
       





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=458238#458238

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jul 16, 2016 4:12 pm Post subject: Transponder antenna

At 05:56 PM 7/16/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "donjohnston" <don(at)velocity-xl.com>



 It cost exactly zero pennies more to create that octagon shaped antenna as opposed to a round one.  And it was significantly easier to cut eight straight lines as opposed to a single circle.  And it works just fine.



 So in this particular case, splitting hairs turned out easier, cheaper (time is money, right?) and maybe a half a hair better.  	




   A brilliant deduction. Thank you. Let's go

   8-sided per the article's suggestion . . . even

   if it does not produce the supposed performance

   gain. Reduce cost of ownership is a demonstrable

   benefit.



 

 

   Bob . . .

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