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AdventureD

Joined: 13 Jan 2021
Posts: 16

Posted: Fri Jan 15, 2021 7:53 pm Post subject: Antenna Ground Planes

Here is a dumb question about ground planes.  Does the ground plane serve to direct the signal to the antenna irrespective of whether the antenna is "connected" to the ground plane, or must the antenna itself be electrically connected to the ground plane?



I am asking because the tech says the best approach to the ground plane in my e-glass composite is conductive paint on the belly.  what I am wondering is how, after the conductive paint is painted over, one ensures that the antenna is "grounded" to the conductive paint ground plane.  I think it may be the case that the ground plane has nothing to do with "grounding" the antenna to the ground plane, but rather that the purpose of the ground plane is to absorb signal for the antenna located in the middle of it (whether or not the antenna "touches" the ground plane.



As you can see, I obviously don't know how antenna ground planes work.



Appreciate your help,

Dan

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Fri Jan 15, 2021 8:33 pm Post subject: Re: Antenna Ground Planes

The ground plane does not have to be connected to the aircraft ground.

But it does have to be connected to the coax shield at the antenna base.

I doubt very much that conductive paint will work.  Test the paint with an ohmmeter.

Consider an internal antenna:

http://www.aeroelectric.com/articles/Antennas/Morris_Com_Loop_Antenna.pdf

There are other designs for internal antennas on fiberglass aircraft.

Bob's book has a chapter on antennas.

http://www.aeroelectric.com/Books/Connection/

_________________
Joe Gores

bob.verwey(at)gmail.com
Guest

Posted: Fri Jan 15, 2021 11:34 pm Post subject: Antenna Ground Planes

Dan there are no dumb questions...even though i dont know the answer to your question...lol



On Sat, 16 Jan 2021, 06:05 AdventureD, <dobrien(at)microfoundations.com (dobrien(at)microfoundations.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "AdventureD" <dobrien(at)microfoundations.com (dobrien(at)microfoundations.com)>

 

 Here is a dumb question about ground planes.  Does the ground plane serve to direct the signal to the antenna irrespective of whether the antenna is "connected" to the ground plane, or must the antenna itself be electrically connected to the ground plane?

 

 I am asking because the tech says the best approach to the ground plane in my e-glass composite is conductive paint on the belly.  what I am wondering is how, after the conductive paint is painted over, one ensures that the antenna is "grounded" to the conductive paint ground plane.  I think it may be the case that the ground plane has nothing to do with "grounding" the antenna to the ground plane, but rather that the purpose of the ground plane is to absorb signal for the antenna located in the middle of it (whether or not the antenna "touches" the ground plane.

 

 As you can see, I obviously don't know how antenna ground planes work.

 

 Appreciate your help,

 Dan

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=500260#500260

 

 

 

 

 

 

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alec(at)alecmyers.com
Guest

Posted: Sat Jan 16, 2021 4:10 am Post subject: Antenna Ground Planes

A ground plane works the same way as a mirror: the boundary condition for the electric field at the surface of an infinite (or ground connected) ground plane is that no electric field component can exist parallel to the surface of the ground plane. To enforce this electric currents are induced in the ground plane to produce a cancelling field - equivalent to a reflected antenna mirrored in the plane. If the ground plane is small or not connected to the transmitter circuit then those currents are impeded to a greater or lesser extent. 

The effectiveness of a ground plane is improved if it is electrically connected to the circuit that’s connected to the antenna so those currents flow more easily. But it will still have some effect even if it’s not.

The higher the frequency the more effective a floating ground plane will be: at light frequencies a smooth metal surface is an almost perfect ground plane (mirror) even when not electrically connected to anything else.

Bob - how did I do?



On Jan 16, 2021, at 02:35, Bob Verwey <bob.verwey(at)gmail.com> wrote:

Dan there are no dumb questions...even though i dont know the answer to your question...lol



On Sat, 16 Jan 2021, 06:05 AdventureD, <dobrien(at)microfoundations.com (dobrien(at)microfoundations.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "AdventureD" <dobrien(at)microfoundations.com (dobrien(at)microfoundations.com)>

 

 Here is a dumb question about ground planes.  Does the ground plane serve to direct the signal to the antenna irrespective of whether the antenna is "connected" to the ground plane, or must the antenna itself be electrically connected to the ground plane?

 

 I am asking because the tech says the best approach to the ground plane in my e-glass composite is conductive paint on the belly.  what I am wondering is how, after the conductive paint is painted over, one ensures that the antenna is "grounded" to the conductive paint ground plane.  I think it may be the case that the ground plane has nothing to do with "grounding" the antenna to the ground plane, but rather that the purpose of the ground plane is to absorb signal for the antenna located in the middle of it (whether or not the antenna "touches" the ground plane.

 

 As you can see, I obviously don't know how antenna ground planes work.

 

 Appreciate your help,

 Dan

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=500260#500260

 

 

 

 

 

 

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

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 eferrer noreferrer" target="_blank">http://forums.matronics.com

 ===========

 WIKI -

 errer noreferrer" target="_blank">http://wiki.matronics.com

 ===========

 b Site -

           -Matt Dralle, List Admin.

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

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AdventureD

Joined: 13 Jan 2021
Posts: 16

Posted: Sat Jan 16, 2021 9:00 am Post subject: Re: Antenna Ground Planes

I think you’re saying that around an antenna will work to some degree even if it is not electrically connected to the antenna.  If that is true, conductive paint will work to some degree even if sealed over by actual paint.  To make it even better, should the inside of the hole drilled to accept the antenna be coated with the conductive paint so there is a connection between the ground plane and the antenna.  From what you are saying, it appears that that would make the ground plane work even better.

Ceengland

Joined: 11 Oct 2020
Posts: 391
Location: MS

Posted: Sat Jan 16, 2021 9:47 am Post subject: Antenna Ground Planes

On Sat, Jan 16, 2021 at 11:10 AM AdventureD <dobrien(at)microfoundations.com>

wrote:



[quote] 

 dobrien(at)microfoundations.com>



 I think you’re saying that around an antenna will work to some degree even

 if it is not electrically connected to the antenna.  If that is true,

 conductive paint will work to some degree even if sealed over by actual

 paint.  To make it even better, should the inside of the hole drilled to

 accept the antenna be coated with the conductive paint so there is a

 connection between the ground plane and the antenna.  From what you are

 saying, it appears that that would make the ground plane work even better

_________________
Charlie

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jan 16, 2021 10:11 am Post subject: Antenna Ground Planes

At 06:06 AM 1/16/2021, you wrote:



 <snip>

 If the ground plane is small or not connected to the transmitter circuit then those currents are impeded to a greater or lesser extent. 



 <snip>



 The higher the frequency the more effective a floating ground plane will be: at light frequencies a smooth metal surface is an almost perfect ground plane (mirror) even when not electrically connected to anything else.



 Bob - how did I do?



    Very good!



    At a hammer-n-tongs level I like to envision

    ground planes from two perspectives. The common

    terrestrial version utilizes what I would

    call a 'resonant' ground plane.



    The goal of a ground plane is to 

    provide a minimal loss (lowest practical

    metallic resistance) non-radiating

    conductor to concentrate radiation

    energy in the vertical element.



    Consider a vertical dipole antenna with

    a feedline attached to the center. You

    have two elements in the same plane

    that share energy management tasks for

    emitting and receiving energy.



    Now, fold the bottom element 90 degrees

    to horizontal. Intuitively, one can see

    that this element is now in vigorous argument

    with the vertical element for squirting

    energy off into the ether.



    Each element has a load impedance on the order

    of 30 ohms. Suppose we added a second horizontal

    element opposite the first. Now we have TWO

    radiating elements with a combined load impedance

    of 15 ohms . . . now we can calculate that

    energy fed to the base will have a 15:30 division

    ratio with most of energy going to the 'good

    guy'.



    Okay, let's add two more radials elements disposed

    90 degrees from the first two. Now we have a

    load impedance of 30/4 or 7.5 ohms for the

    combination of bad guys . . . and 80% of the

    energy at the end of the feedline goes to the

    'good guy'. 4-radials is a practical place to

    stop adding . . . the difference between 80

    and 100% of energy going to the 'good guy' is

    not observable in practice.



    But we don't need to stop there. If you droop

    the radials at about 45 degrees, you increase

    the theoretical feed point impedance of 30

    ohms (close but not quite 1:1 swr for 50

    ohm feedline) the match is a bit better and

    one of several potential losses in the system

    is reduced. Drooping also reduces the radiation

    angle of the antenna so as to focus more attention

    at the horizon as opposed to the Andromeda 

    galaxy.



    On the other hand, you can add an infinite number

    of radials forming a solid disk. Now the theoretical

    load impedance of the plane approaches zero

    ohms . . .  a good thing you can do to improve

    performance.



    Now, here comes those pesky machines known as

    airplanes . . . with envelopes and structures

    that are not very friendly for seeking an

    optimal antenna installation.



    In a plastic airplane, you can choose to go the

    enhanced or optimized route for achieving a

    suitable ground plane. At ADSB/XPNDR frequencies

    the optimized route is pretty easy. The disk

    is relatively small. At VHF frequencies, the disk

    is unmanageably larger so optimization with

    4 or more 'radials' becomes the technique of

    choice.



    The short answer is that mounting antennas

    on the outside of a metal airplane offers

    a perfectly satisfactory ground plane although

    the infinite number of radials are not resonant.

    No big deal. In a plastic airplane, the ground

    plane needs to be fabricated and going the

    resonant mode with either a disk (optimal)

    or radials (enhanced) works good, last a long time.



    The native conductive qualities of materials

    in composite airplanes whether carbon-fiber,

    paint or any spray on coatings don't even

    begin to approach the much-desired quest

    for close-to-zero-ohms qualities of the

    optimized ground plane.



 

 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

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user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Sat Jan 16, 2021 11:10 am Post subject: Re: Antenna Ground Planes

 	  Quote: 	
		  I think you’re saying that around an antenna will work to some degree even if it is not electrically connected to the antenna. If that is true, conductive paint will work to some degree even if sealed over by actual paint. To make it even better, should the inside of the hole drilled to accept the antenna be coated with the conductive paint so there is a connection between the ground plane and the antenna. From what you are saying, it appears that that would make the ground plane work even better. 	




Nobody above said that conductive paint will work as an antenna ground plane

except the OP's misinformed tech.  Yes, conductive paint does have some conductive properties.

It also has high resistance, too high to make an effective ground plane.

After installing the com antenna, check its SWR with a meter.

_________________
Joe Gores

AdventureD

Joined: 13 Jan 2021
Posts: 16

Posted: Sat Jan 16, 2021 5:05 pm Post subject: Re: Antenna Ground Planes

 	  Quote: 	
		  Nobody above said that conductive paint will work as an antenna ground plane except the OP's misinformed tech.  Yes, conductive paint does have some conductive properties. It also has high resistance, too high to make an effective ground plane. After installing the com antenna, check its SWR with a meter. 	




Funny thing is a bunch of Lancair guys believe (and say they have experienced) that conductive paint works.



Let's suppose it doesn't work.  Does the existence of the conductive paint over e-glass do any harm when the antenna is put on the outside of the plane?  If one put 4 or 6 or 8 copper strips radiating out from the coax attach point on the inside of the eglass plane, that would still work as well as if the conductive paint weren't there, would it not? On the other hand, if I wanted to put a strikefinder antenna on the bottom of the inside of the fuselage, I assume that conductive paint could interfere with the signal to the strikefinder antenna on the inside of the plane, yes?  In that sense, would the conductive paint actually do harm?  [/quote]

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Sat Jan 16, 2021 6:37 pm Post subject: Re: Antenna Ground Planes

An antenna will work without a ground plane.  But how well?  The opinion of others is subjective.

The best way to know how well an antenna works is with a SWR meter.

Conductive paint will not do any harm at all to the performance of an exterior antenna.

It will not do much good either.  Use whatever paint looks good.

Use a ground plane consisting of 4 wires or copper strips inside of the fuselage.

I am not knowledgeable about a strikefinder.

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Jan 17, 2021 12:34 pm Post subject: Antenna Ground Planes

At 08:37 PM 1/16/2021, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>



 An antenna will work without a ground plane.  But how well?

 The opinion of others is subjective. 	


   Antenna's come in a variety of flavors that

   have different demands for optimal performance.



   Some antennas do not require nor do they

   have provisions for including a ground plane.

  

   Such antennas include dipole glideslope, vor and

   Archer transponder antennas for composite aircraft.

   Loran are e-field 'probes' of exceedingly small

   length/frequency ratio . . . like the AM radio antenna

   for automobiles.



   Bottom line calls for following the manufacturers

   recommendations closely . . . just 'cause it's

   a radio-gizmo on the far end of a piece of

   coax does not automatically give it broad

   commonality with other antennas.



  	  Quote: 	
		  The best way to know how well an antenna works is with a SWR meter. 	


   Yeah . . . kind of. SWR is a measurement

   of the complex impedance peeking into the feed point

   of an antenna . . . or looking at an antenna at

   the other end of a feedline. It's the first

   place to start when you looking for a gross

   failure of a previously working antenna.



   With respect to performance, the qualities that

   affect radiation efficiency and pattern have

   an equal if not greater effect on performance

   and cannot be quantified by evaluating impedance

   of the power feed path (SWR).



   These qualities need analysis by computer prediction

   at least . . . or at best, measurements on the

   antenna test range. Fortunately, our antenna

   needs are simple and most designs and installations

   have been demonstrated for decades. When in doubt,

   check with someone who's been-there-done-that. 



  	  Quote: 	
		  Conductive paint will not do any harm at all to the performance of an exterior antenna.

 It will not do much good either.  Use whatever paint looks good.

 Use a ground plane consisting of 4 wires or copper strips inside of the fuselage. 	


   Exactly. Greg Richter and I had some discussion

   about spray-on conductors about 17 years ago.

   See page 24 of  https://tinyurl.com/y6ejr33s



   I worked a custom black box design for LearJet

   that was housed in a vacuum formed, plastic

   housing. We THOUGHT we'd mitigate a slight

   sensitivity to radiated RF by spraying the

   inside surface of the cover. That idea was

   one of several in my career that blew current

   accumulation of "ataboys" away and delayed

   delivery by a month or so.



   The spray on coating had only the slightest

   benefit to the shielding task. Retooling

   the enclosure in metal was out of the question.

   Had to beef up robustness of the electronics.



  	  Quote: 	
		  I am not knowledgeable about a strikefinder. 	


   StrikeFinder antennas are H-field receptors but they

   do perform best working against a ground plane. In this

   case, the ground plane carries no RF current but

   acts more like the 'mirror' alluded to earlier in this

   thread. The conductive plane under a StrikeFinder

   antenna serves to smooth the azimuth variations in

   reception pattern.



 

   Bob . . .



   Un impeachable logic: George Carlin asked, "If black boxes

   survive crashes, why don't they make the whole airplane

   out of that stuff?"

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Sun Jan 17, 2021 12:51 pm Post subject: Re: Antenna Ground Planes

AdventureD,

Read these two threads about the necessity of a ground plane:

http://forums.matronics.com/viewtopic.php?t=16775765

http://forums.matronics.com/viewtopic.php?t=16775667

My friend was in the same situation as you are.

Someone told him that their radio worked fine without a ground plane in the tail of their Kitfox.

And it probably did as far as the pilot could tell.  He probably did not try transmitting a long distance.

And the pilot was not aware of the reflected power which was not doing his radio any good.

The SWR in my friend's Kitfox was 3.8 without a ground plane.  After installing another antenna in

a better location and installing ground plane wires, the SWR improved to an average of 1.57

_________________
Joe Gores

AdventureD

Joined: 13 Jan 2021
Posts: 16

Posted: Fri Jan 22, 2021 6:30 pm Post subject: Re: Antenna Ground Planes

Thank you Bob, Joe, all, for all this advice. Happy and safe flying, Dan

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