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Copper Foil width for VOR antenna
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p32gxy

Joined: 06 Aug 2013
Posts: 16

Posted: Tue Oct 15, 2013 6:50 am Post subject: Copper Foil width for VOR antenna

Hello all,



I am installing a Jim Weir style copper tape antenna in the wing of my composite aircraft. I have the choice of 3/8 or 1/2 inch wide copper tape... will going with one or the other make any real difference for a VOR antenna?



Thx,

M

kuffel(at)cyberport.net
Guest

Posted: Tue Oct 15, 2013 9:37 am Post subject: Copper Foil width for VOR antenna

<<  I am installing a Jim Weir style copper tape antenna in the wing of my 

composite aircraft. I have the choice of 3/8 or 1/2 inch wide copper tape... 

will going with one or the other make any real difference for a VOR antenna? 

 >>



Real difference?  No.  The wider tape will give you in theory a wider 

bandwidth antenna but the performance difference is hard to detect.  But if 

I had the wider tape available anyway, I would use it.  Besides, the wider 

tape is marginally more mechanically robust.  The foil tapes have a history 

of breaking when installed in flexing locations such as landing gear.



Tom Kuffel

p32gxy

Joined: 06 Aug 2013
Posts: 16

Posted: Tue Oct 15, 2013 11:38 am Post subject: Re: Copper Foil width for VOR antenna

Ok... got the bandwidth angle... as planned now it would be installed in tension mostly...



my other option is to use part of the coax itself as the legs of the V shaped dipole 



any thoughts?

kuffel(at)cyberport.net
Guest

Posted: Tue Oct 15, 2013 12:34 pm Post subject: Copper Foil width for VOR antenna

<<  part of the coax itself as the legs of the V shaped dipole  >>



This has been done often in composite fuselages.  It certainly is more 

physically robust than the foil tapes.  The difference in bandwidth between 

the thin center conductor and the foil tape versions is measurable with less 

than lab quality equipment but the difference in performance is still not 

perceptible.  Be sure to seal the end of the cable where the shield and the 

center conductor split to form the legs of the antenna with something like 

Performix Liquid Tape (Walmart Auto Section).  Also seal the end of the 

center conductor.  If water gets into the coax you will detect lower 

performance.



Tom Kuffel

p32gxy

Joined: 06 Aug 2013
Posts: 16

Posted: Tue Oct 15, 2013 1:26 pm Post subject: Re: Copper Foil width for VOR antenna

Thx... I am actually thinking of using the braid only as the antenna material... as part of making a proper balun one would only use the braid to connect to the antenna elements  anyway while the center cnnductor is not connected... this should avoid the problem you are describing... as long as i can successfully slide about a 16" long undisturbed braid-external shielding up on the stripped coax to avoid the large resulting gap.



Water will not get into this setup as it will be saturated with epoxy.

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Oct 15, 2013 7:22 pm Post subject: Copper Foil width for VOR antenna

At 04:26 PM 10/15/2013, you wrote:

 	  Quote: 	
		  



Thx... I am actually thinking of using the braid only as the antenna 

material... as part of making a proper balun one would only use the 

braid to connect to the antenna elements  anyway while the center 

cnnductor is not connected... this should avoid the problem you are 

describing... as long as i can successfully slide about a 16" long 

undisturbed braid-external shielding up on the stripped coax to 

avoid the large resulting gap.



Water will not get into this setup as it will be saturated with epoxy.


	


   The problem with embedded antennas is the potential for

   fatigue failure of the conductors if the composite

   structure flexes. This can produce hairline fractures

   in foil or wire antennas bonded to a composite surface. It can

   make your antenna conductors look like the wires in a strain

   guage . . . that stretch and compress as the surface responds

   to structure flexing.



   RF bandwidth of the wider foil is attractive but as mentioned

   here, insignificant with respect to performance. Consider an

   ALL COAX antenna assembly. Balun is optional . . . cool

   but performance difference is very small. Making the

   antenna elements from coax braid FLOATING INSIDE a piece of 1/4"

   Nylon tubing will get you a simple antenna material,

   adequate performance and the tubing isolates the antenna

   from structure so that flexing doesn't mechanically irritate

   the elements.

   Bob . . .

FisherPaulA(at)johndeere.
Guest

Posted: Wed Oct 16, 2013 4:12 am Post subject: Copper Foil width for VOR antenna

Just another data point.  I used Mr. Weir's antennas in my Q-200 (fully composite structure).  The vertically polarized comm antenna in the tail and the horizontally polarized VOR antenna in the main wing.  Both were installed exactly as Mr. Weir describes using his kit including the copper foil. Both antennas have given satisfactory performance for 23+ years and ~1,500 flight hours.  



Paul A. Fisher

Q-200 N17PF

--

p32gxy

Joined: 06 Aug 2013
Posts: 16

Posted: Wed Oct 16, 2013 3:27 pm Post subject: Re: Copper Foil width for VOR antenna

I am loving the idea of a protective sheath/tube to achieve mechanical isolation... 

Unfortunately, i don't see how I can make use of this approach without either drilling holes in the spar or messing up the wing's shape/airflow



The VOR antenna I can install has to be flat so that it integrates into the wing surface. Don't want to be compromising the wing skin... moving the antenna is also not an option because the only place I can keep the tips away from "metal" antennae like structures is in the outboard 1/3 of the wing.



I am all open to suggestions and will consider anything and everything including novel designs and unusual shapes as I am finding that the 22.8" per leg of the V shaped antennae is hard to place without interference.... please keep them comming.



Thx.



 	  nuckolls.bob(at)aeroelect wrote: 	
		  At 04:26 PM 10/15/2013, you wrote

   The problem with embedded antennas is the potential for

   fatigue failure of the conductors if the composite

   structure flexes. This can produce hairline fractures

   in foil or wire antennas bonded to a composite surface. It can

   make your antenna conductors look like the wires in a strain

   guage . . . that stretch and compress as the surface responds

   to structure flexing.



   RF bandwidth of the wider foil is attractive but as mentioned

   here, insignificant with respect to performance. Consider an

   ALL COAX antenna assembly. Balun is optional . . . cool

   but performance difference is very small. Making the

   antenna elements from coax braid FLOATING INSIDE a piece of 1/4"

   Nylon tubing will get you a simple antenna material,

   adequate performance and the tubing isolates the antenna

   from structure so that flexing doesn't mechanically irritate

   the elements.

   Bob . . .

raymondj(at)frontiernet.n
Guest

Posted: Wed Oct 16, 2013 4:38 pm Post subject: Copper Foil width for VOR antenna

A technique used by         some boat builders to form pillow blocks for prop shafts is to         coat the shaft with wax of sufficient thickness to assure         clearance between the block and the shaft when the wax is         removed.  

         

         WARNING, I HAVE NOT TRIED THE TECHNIQUE DISCUSSED BELOW. IT IS         ONLY SPECULATION!!!!!

         

         A similar approach might be applied to the copper strip in the         matrix.  Coat it with several layers of wax or mold release         before imbeding it in the matrix.  The theory is that the wax         will prevent the matrix from bonding to the copper, effectively         creating a space on either side of the copper allowing it to         move slightly to avoid being stressed when the matrix is         deformed.  The downside is that it is functionally a         delamination.  Whether or not that is acceptable would have to         be decided by the builder.

               	  Quote: 	
		  Raymond Julian

Kettle River, MN.



"And you know that I could have me a million more friends,

and all I'd have to lose is my point of view." - John Prine 	
       On 10/16/2013 06:27 PM, p32gxy wrote:

     

     [quote]        	  Quote: 	
		  --> AeroElectric-List message posted by: "p32gxy" <p32gxy(at)gmail.com> (p32gxy(at)gmail.com)



I am loving the idea of a protective sheath/tube to achieve mechanical isolation... 

Unfortunately, i don't see how I can make use of this approach without either drilling holes in the spar or messing up the wing's shape/airflow



The VOR antenna I can install has to be flat so that it integrates into the wing surface. Don't want to be compromising the wing skin... moving the antenna is also not an option because the only place I can keep the tips away from "metal" antennae like structures is in the outboard 1/3 of the wing.



I am all open to suggestions and will consider anything and everything including novel designs and unusual shapes as I am finding that the 22.8" per leg of the V shaped antennae is hard to place without interference.... please keep them comming.



Thx.

nuckolls.bob(at)aeroelect wrote:

          	  Quote: 	
		  At 04:26 PM 10/15/2013, you wrote

   The problem with embedded antennas is the potential for

   fatigue failure of the conductors if the composite

   structure flexes. This can produce hairline fractures

   in foil or wire antennas bonded to a composite surface. It can

   make your antenna conductors look like the wires in a strain

   guage . . . that stretch and compress as the surface responds

   to structure flexing.



   RF bandwidth of the wider foil is attractive but as mentioned

   here, insignificant with respect to performance. Consider an

   ALL COAX antenna assembly. Balun is optional . . . cool

   but performance difference is very small. Making the

   antenna elements from coax braid FLOATING INSIDE a piece of 1/4"

   Nylon tubing will get you a simple antenna material,

   adequate performance and the tubing isolates the antenna

   from structure so that flexing doesn't mechanically irritate

   the elements.

   Bob . . .

	
       





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=410717#410717



	
     [b]

p32gxy

Joined: 06 Aug 2013
Posts: 16

Posted: Wed Oct 16, 2013 7:15 pm Post subject: Re: Copper Foil width for VOR antenna

 	  raymondj(at)frontiernet.n wrote: 	
		  A technique used by         some boat builders to form pillow blocks for prop shafts is to         coat the shaft with wax of sufficient thickness to assure         clearance between the block and the shaft when the wax is         removed..

	
       



Well... I have been thinking of something similar... except using copper foils such as http://www.mcmaster.com/#9053k12/=oyvy3i and putting it between 2 layers of PTFE tape such as http://www.mcmaster.com/#76475a43/=oyw325 before covering the thing with 1 ply of 3oz glass.



This approach, I think, would create a non-stick copper foil 'assembly' to which epoxy would not stick... effectively the copper tape would not be bound to the wing skin. The push-pull on the copper foil should be much reduced...



The "de-lamination" should not be an issue as the covering fiberglass layer only has the purpose of keeping the tape in place... no structural impact as i understand it.



The only place to be fixed would be where the coax attaches as the leads would have to penetrate the wing skin through very small holes.



I don't mind spending a bit more money upfront rather than fixing broken VOR antennae later

raymondj(at)frontiernet.n
Guest

Posted: Wed Oct 16, 2013 8:03 pm Post subject: Copper Foil width for VOR antenna

The only potential         problem I see with that is that the epoxy might be drawn in         between the 2 pieces of plastic by capillary action or if it's         vacuum bagged, and then bond to the copper.  You might be able         to get some thin wall HDPE tubing that will pull down flat if         you vacuum bag it.  I wonder if you could just put some grease         on it.  I suppose a couple of test layups will answer most of         the questions.

         

         I just had another thought.  Could you lay a thin piece of         styrofoam in and then dissolve it and slide the foil in?  Then         just fill the slot, leaving the copper anchored at one end.

         

         Good luck, I look forward to hearing what your solution is.

               	  Quote: 	
		  Raymond Julian

Kettle River, MN.



"And you know that I could have me a million more friends,

and all I'd have to lose is my point of view." - John Prine 	
       On 10/16/2013 10:15 PM, p32gxy wrote:

     

     [quote]        	  Quote: 	
		  --> AeroElectric-List message posted by: "p32gxy" <p32gxy(at)gmail.com> (p32gxy(at)gmail.com)

raymondj(at)frontiernet.n wrote:

          	  Quote: 	
		  A technique used by         some boat builders to form pillow blocks for prop shafts is to         coat the shaft with wax of sufficient thickness to assure         clearance between the block and the shaft when the wax is         removed..



	
              



Well... I have been thinking of something similar... except using copper foils such as http://www.mcmaster.com/#9053k12/=oyvy3i and putting it between 2 layers of PTFE tape such as http://www.mcmaster.com/#76475a43/=oyw325 before covering the thing with 1 ply of 3oz glass.



This approach, I think, would create a non-stick copper foil 'assembly' to which epoxy would not stick... effectively the copper tape would not be bound to the wing skin. The push-pull on the copper foil should be much reduced...



The "de-lamination" should not be an issue as the covering fiberglass layer only has the purpose of keeping the tape in place... no structural impact as i understand it.



The only place to be fixed would be where the coax attaches as the leads would have to penetrate the wing skin through very small holes.



I don't mind spending a bit more money upfront rather than fixing broken VOR antennae later 





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=410726#410726



	
     [b]

kuffel(at)cyberport.net
Guest

Posted: Thu Oct 17, 2013 7:59 am Post subject: Copper Foil width for VOR antenna

<<  don't see how I can make use of this approach without either drilling 

holes in the spar or messing up the wing's shape/airflow  >>



We have reached the point where we need more information.  Are you talking 

Rutan moldless composite construction or premolded skins a la 

Lancair/Glasair?



In the case of the former and you have not laminated the wing skins yet, 

there is no problem.  Do what you would have to do with the coax anyway, cut 

a groove in the foam for the tubes with the braids inside.   Make the 

grooves deeper than needed and cover with microbaloon slurry and a temporary 

layer of peelply.  This forms a surface for glassing with no delamination 

areas or profile distortion.



With premolded wing panels you glue the tubes to the undersurface.  With 

braid as my antenna elements, I would have no qualms about just ShoGooing 

them to the panel undersurface.  The ShoGoo remains flexible enough to not 

stress the wires.  For routing the feedline, structural theory says there is 

little problem drilling a small hole in the middle of the vertical shear 

web, particularly outboard.  But don't get too compulsive about routing the 

end of the coax/balun directly away from the Vee.  Even bent 90 degrees to 

the Vee you won't see much, if any, difference.



<<  22.8" per leg of the V shaped antennae is hard to place without 

interference  >>



The purpose of making the legs Vee shaped is to remove the null reception 

points off the ends of a straight dipole.  But you don't need  45 degree 

bends to do this.  A much shallower angle will still give adequate 

performance.  And there is no problem with curlling the tips somewhat near 

the leading edge.



Understand we don't need the last db of signal strength in this application. 

In a composite fuselage a 23" length of wire dangling from the center 

conductor on the back of the radio would still give "adequate performance".



Tom Kuffel

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Thu Oct 17, 2013 9:42 am Post subject: Re: Copper Foil width for VOR antenna

When the wires at each end of 300 ohm TV antenna twin lead are connected together, the twin lead will have the same bandwidth as copper tape.  Jim Weir has used twin lead for some of his antennas.

Joe

_________________
Joe Gores

p32gxy

Joined: 06 Aug 2013
Posts: 16

Posted: Thu Oct 17, 2013 1:14 pm Post subject: Re: Copper Foil width for VOR antenna

 	  kuffel(at)cyberport.net wrote: 	
		  

We have reached the point where we need more information.  Are you talking Rutan moldless composite construction or premolded skins a la 

Lancair/Glasair?

	


The wing is all finished, using premolded skins. This is a retrofit as the original builder did not see the need to put in a VOR antenna. I only have access to the inside of the wing through the pitot service door (small)... not a lot of room to work with... which is the reason why I have been attracted to the copper foil antenna which can be mounted on the "outer" surface of the wing.



Theory notwithstanding, I don't like to drill holes in structural elements... call me crazy... unless there is absolutely no other way. For me, this thread is about finding the other way 



I am even considering the Dave Morris Loop antenna (http://www.davemorris.com/MorrisComLoop.cfm), adapted to the NAV band I calculate a 29.5" diameter for the loop... I could fit such a loop on the underside of the fuselage and avoid the complications of wing based antennae...placement supposedly is not so critical as with the "V" shaped when it comes to proximity to other metal elements... then again this is all theory for me as I have no experience with loop antennae.



 	  kuffel(at)cyberport.net wrote: 	
		  

The purpose of making the legs Vee shaped is to remove the null reception points off the ends of a straight dipole.  But you don't need  45 degree bends to do this.  A much shallower angle will still give adequate 

performance.  And there is no problem with curlling the tips somewhat near the leading edge.



	


The location and available space is less than ideal... I do try to avoid curling the tips or getting them within 1/4 wave length of metallic wires/tubes, etc. due to the tips being more the sensitive end of the assembly from a placement standpoint... the best angle I'll be able to do is 120 deg between the legs.



 	  kuffel(at)cyberport.net wrote: 	
		  

Understand we don't need the last db of signal strength in this application. 

In a composite fuselage a 23" length of wire dangling from the center 

conductor on the back of the radio would still give "adequate performance".

	


I am not sure i agree with the basic principle inherent in this statement (I keep hearing a lot). While i agree that some of the "optimizations" don't have an adequate reward ratio, I still try to do the best job I can under the circumstances. If and when I cut corners, I want to do so fully understanding the tradeoffs (and risks if any) so that i can make informed decisions.



Coax is a typical example... I am spending x6 the $$ to get RG400 rather than RG58U being fully aware of all the arguments that from a sheer dB loss standpoint, the difference will not be practically noticeable... the extra shielding however is not just a matter of dB loss (in my eyes)... interference from strobes, etc. comes to mind.



Thanks for all the posts... keep them coming !!!

p32gxy

Joined: 06 Aug 2013
Posts: 16

Posted: Thu Oct 17, 2013 1:53 pm Post subject: Re: Copper Foil width for VOR antenna

 	  user9253 wrote: 	
		  When the wires at each end of 300 ohm TV antenna twin lead are connected together, the twin lead will have the same bandwidth as copper tape.  Jim Weir has used twin lead for some of his antennas.

Joe 	


Not familiar with this technique... theorizing here... the effective performance depends on distance between leads, dielectric type, etc... this type of antenna would have to be seriously tuned post installation...

kuffel(at)cyberport.net
Guest

Posted: Thu Oct 17, 2013 2:01 pm Post subject: Copper Foil width for VOR antenna

<<  copper foil antenna which can be mounted on the "outer" surface of the 

wing... don't like to drill holes in structural elements  >>



So the plan would be to drill 2 tiny holes in the wing skin and feed 

pigtails through them for connection to the coax/balun?  Or is it to have 

the center of the Vee even with the rear edge with the cable in the aileron 

slot for feeding to the wing interior perhaps via an existing gap?



<< Dave Morris Loop antenna >>



This is an excellent antenna, best if mounted horizontally as you propose. 

RG-59 will work for the matching line.  Depending on conditions you might 

need to replace the tuning section every 10 to 15 years or so.  The local 

amateur radio club (see ARRL.org) can get you access to an antenna analyzer 

which will tell you the condition of the antenna.



The effects of the rudder cables and elevator control are unknown.  Not as 

visually hidden but the top of the fuselage might work better electrically.



<<  > In a composite fuselage a 23" length of wire dangling from the center

 	  Quote: 	
		   conductor on the back of the radio would still give "adequate 

 performance".


	


I am not sure i agree with the basic principle inherent in this statement >>



Try it, it is a simple, easy experiment.



<<  RG400 rather than RG58U >>



For me the RG400 is worth the cost.  Besides the lower loss and much better 

shielding which you mention, RG400 is much more stable over time.  I've seen 

some really ratty RG58 come out of older airplanes over the years.  Shocking 

the radio still worked at all (see 23" dangling wire above).



Tom Kuffel

p32gxy

Joined: 06 Aug 2013
Posts: 16

Posted: Thu Oct 17, 2013 2:51 pm Post subject: Re: Copper Foil width for VOR antenna

 	  kuffel(at)cyberport.net wrote: 	
		  

So the plan would be to drill 2 tiny holes in the wing skin and feed 

pigtails through them for connection to the coax/balun?  Or is it to have 

the center of the Vee even with the rear edge with the cable in the aileron 

slot for feeding to the wing interior perhaps via an existing gap?

	


2 tiny holes and feed pigtails to the balun which will be coiled up in an inside space.



 	  kuffel(at)cyberport.net wrote: 	
		  

<<Dave>>

This is an excellent antenna, best if mounted horizontally as you propose. 

RG-59 will work for the matching line.  Depending on conditions you might need to replace the tuning section every 10 to 15 years or so.  The local amateur radio club (see ARRL.org) can get you access to an antenna analyzer which will tell you the condition of the antenna.

	




I have been researching loop antennas as I do like the small footprint, omni-directionality, etc. What I am finding so far sounds very good... I am looking for the gotcha... why are they not popular if they are so good? 



The only answer I am able to come up with thus far is that impedance matching seems too complicated for most people, you do need to invest in an SWR meter for proper tuning! In other words you do need some background/experience in RF engineering.



 	  kuffel(at)cyberport.net wrote: 	
		  

The effects of the rudder cables and elevator control are unknown.  Not as visually hidden but the top of the fuselage might work better electrically.

	




As i understand this particular challenge... any long conductor near the loop should theoretically act as a reflector, which means in that direction the reception will be affected. Worst case, one may have a dead spot if the conductive element (rudder cable/elevator controls) are near the antenna's plane. Loop antenna or not, the effects are the same ... am I missing something?



The top of the fuselage is indeed further removed from most elements which would interfere with the antenna (except for the salty water in my head). Considering that a loop antenna in that location is full wavelength with a minimum of 1dB of gain... I believe I will investigate the possibility of placing the loop antenna there. For the loop antenna, I could use regular Tefzel wire and mount the whole thing on the inside 



I will have to curve the whole antenna downward to match the curvature of the fuselage, but this should have minimal effect on performance, especially if using a Delta Loop (3 sided triangular loop) as this would allow me to angle the tip backwards with the widest part of the loop placed in the widest section of the fuselage.



 	  kuffel(at)cyberport.net wrote: 	
		  

In a composite fuselage a 23" length of wire dangling from the center conductor on the back of the radio would still give "adequate performance".



Try it, it is a simple, easy experiment.

	




Technically a wet string would work... that doesn't mean I want to use wet strings in my airplane ... I do find the irony in it though... millions are spent on antenna design... when wet noodles would do the trick

LynnCole(at)foxvalley.net
Guest

Posted: Fri Oct 18, 2013 8:12 am Post subject: Copper Foil width for VOR antenna

Why not  use some fiberglas to laminate the sheath into the wing in the position where you want it?

 -----

Lynn Cole

LynnCole(at)foxvalley.net (LynnCole(at)foxvalley.net)



 

 

On Oct 16, 2013, at 6:27 PM, p32gxy wrote:

[quote]--> AeroElectric-List message posted by: "p32gxy" <p32gxy(at)gmail.com (p32gxy(at)gmail.com)>



I am loving the idea of a protective sheath/tube to achieve mechanical isolation... 

Unfortunately, i don't see how I can make use of this approach without either drilling holes in the spar or messing up the wing's shape/airflow



The VOR antenna I can install has to be flat so that it integrates into the wing surface. Don't want to be compromising the wing skin... moving the antenna is also not an option because the only place I can keep the tips away from "metal" antennae like structures is in the outboard 1/3 of the wing.



I am all open to suggestions and will consider anything and everything including novel designs and unusual shapes as I am finding that the 22.8" per leg of the V shaped antennae is hard to place without interference.... please keep them comming.



Thx.

nuckolls.bob(at)aeroelect wrote:

 	  Quote: 	
		  At 04:26 PM 10/15/2013, you wrote

   The problem with embedded antennas is the potential for

   fatigue failure of the conductors if the composite

   structure flexes. This can produce hairline fractures

   in foil or wire antennas bonded to a composite surface. It can

   make your antenna conductors look like the wires in a strain

   guage . . . that stretch and compress as the surface responds

   to structure flexing.



   RF bandwidth of the wider foil is attractive but as mentioned

   here, insignificant with respect to performance. Consider an

   ALL COAX antenna assembly. Balun is optional . . . cool

   but performance difference is very small. Making the

   antenna elements from coax braid FLOATING INSIDE a piece of 1/4"

   Nylon tubing will get you a simple antenna material,

   adequate performance and the tubing isolates the antenna

   from structure so that flexing doesn't mechanically irritate

   the elements.

   Bob . . .

	






Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=410717#410717



         - The   -->             &n========================

p32gxy

Joined: 06 Aug 2013
Posts: 16

Posted: Tue Oct 22, 2013 6:22 am Post subject: Re: Copper Foil width for VOR antenna

Just an update... I am currently pursuing a loop antenna made out of Coax which allows me to reduce it's size somewhat. I am looking at placing this antenna inside the fuselage tailcone (all composite) and avoid the complications associated with placing the VOR antenna in the wing.



I've ordered an VHF/UHF Vector Antenna Analyzer to tune this guy in place. I am hoping that this "experiment" will go well.



Thanks everyone for your suggestions/comments.

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Oct 22, 2013 7:41 am Post subject: Copper Foil width for VOR antenna

At 09:22 AM 10/22/2013, you wrote:




Just an update... I am currently pursuing a loop antenna made out of 

Coax which allows me to reduce it's size somewhat. I am looking at 

placing this antenna inside the fuselage tailcone (all composite) and 

avoid the complications associated with placing the VOR antenna in the wing.



I've ordered an VHF/UHF Vector Antenna Analyzer to tune this guy in 

place. I am hoping that this "experiment" will go well.



Thanks everyone for your suggestions/comments.



    Look up loop antennas in the forums, websites

    and journals for amateur radio enthusiasts.

    Loop antennas can be adequate if not stellar

    performers. But as Robert Heinlein once penned,

    "their ain't no such thing as a free lunch".



    Generally, any physical shortening of an antenna

    requires some "tuning" reactances in the form of

    inductors as loading coils or capacitors at

    the ends as tuning devices. These added devices

    alter the distribution of currents along your antenna's

    conductors is ways that are almost never beneficial.



    I recall that halo antennas for 2m were rather

    narrow banded . . . on a ham band that was 4/146

    or +/- 1.5% wide. Your VOR 'halo' range of interest

    has a bandwidth of 113/10 or +/- 4.5% a bit

    worse.



    Fortunately, antennas for aviation are exceedingly

    forgiving . . . especially receiving antennas that

    watch 100W transmitters from line of sight distances.

    So getting your antenna centered on the range of

    interest for frequencies is task one. After that,

    making quantitative measurements of performance

    is at least tedious if not tricky. The analyzer

    will measure impedances that can be plotted over

    the range of interest but will be of no value

    for predicting performance.



    Probably the best thing a shade-tree pilot

    cum antenna designer can do is install the

    experiment. Go fly it. Then report performance

    based on experience with other antennas in

    rather broad terms of "works fine" or perhaps

    not.



    The time and effort that takes you from as

    assessment of "adequate" to a quantified

    plotting of one antenna against another is

    a really big jump.



    Please share your experiments and findings

    with us. Pictures are good too.



   Bob . . .

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