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recapen(at)earthlink.net
Guest

Posted: Wed Sep 28, 2011 6:16 am Post subject: AeroElectric-List:

IIRC the Lancair is not metal-skinned....



The ground-plane should be electrically connected to the shield of the coax - which should also be electrically connected to the ground-side of the electrical system via the radio.

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BGray(at)glasair.org
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Posted: Wed Sep 28, 2011 6:47 am Post subject: AeroElectric-List:

Then why do some radio manufacturers require a ground plane of a minimum

diameter? If the ground plane was connected to the aircraft ground, size

would not matter. (no puns please)



Bruce

WWW.Glasair.org 



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recapen(at)earthlink.net
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Posted: Wed Sep 28, 2011 7:33 am Post subject: AeroElectric-List:

The ground plane of minimum diameter provides for the reflection of the RF energy at the antenna - specifically for non metallic airframes.  I think there is at least one Berkut out there that is set up this way.



In my case, I have my transponder antenna mounted inside my engine cowl pointing downward with an aluminum circle providing the ground plane.  It is isolated from physical grounding by the mount and is electrically 'bonded' to the ground system.



Bob could probably explain the theory better - I took it in to practice and it works well for me.

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grosseair(at)comcast.net
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Posted: Wed Sep 28, 2011 7:44 am Post subject: AeroElectric-List:

I believe that the minimum size of the ground plane is related to the 

wave length of the radio.

John Grosse



Bruce wrote:

 	  Quote: 	
		   



 Then why do some radio manufacturers require a ground plane of a minimum

 diameter? If the ground plane was connected to the aircraft ground, size

 would not matter. (no puns please)



 Bruce

 WWW.Glasair.org

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BGray(at)glasair.org
Guest

Posted: Wed Sep 28, 2011 8:28 am Post subject: AeroElectric-List:

Then why does my WX-500 require a 12 inch ground plane? It only receives

RF.



Bruce

WWW.Glasair.org 



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tiethoff

Joined: 02 Sep 2008
Posts: 23

Posted: Wed Sep 28, 2011 9:23 am Post subject: AeroElectric-List:

Try it without the groundplane and you will find out why you need the thing... 

Met vriendelijke groet en

 verzonden vanaf de bijna

 illegale Samsung Galaxy S2,

 Eric Tiethoff. Op 28 sep. 2011 18:36 schreef "Bruce" <BGray(at)glasair.org (BGray(at)glasair.org)> het volgende:> --> AeroElectric-List message posted by: "Bruce" <BGray(at)glasair.org (BGray(at)glasair.org)>

 > 

[quote] Then why does my WX-500 require a 12 inch ground plane? It only receives

 RF.

 

 Bruce

 WWW.Glasair.org 

 

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recapen(at)earthlink.net
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Posted: Wed Sep 28, 2011 10:28 am Post subject: AeroElectric-List:

Not the expert on the theory - but I think RF exhibits the same behaviour relative to the antenna regardless of being transmitted or received.

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nuckolls.bob(at)aeroelect
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Posted: Wed Sep 28, 2011 8:28 pm Post subject: AeroElectric-List:

At 09:13 AM 9/28/2011, you wrote:

 	  Quote: 	
		  

<recapen(at)earthlink.net>



IIRC the Lancair is not metal-skinned....



The ground-plane should be electrically connected to the shield of 

the coax - which should also be electrically connected to the 

ground-side of the electrical system via the radio.


	


    I think he was asking if the ground plane needed

    some extra conductor from the metal over to

    the electrical system ground.



    There is no value in adding such wires from

    an RF perspective. I've seen such bonding

    conductors added for lightning strike issues

    on composite aircraft.

   Bob . . .

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nuckolls.bob(at)aeroelect
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Posted: Wed Sep 28, 2011 8:34 pm Post subject: AeroElectric-List:

At 09:43 AM 9/28/2011, you wrote:

 	  Quote: 	
		  



Then why do some radio manufacturers require a ground plane of a minimum

diameter? If the ground plane was connected to the aircraft ground, size

would not matter. (no puns please)


	


   The ideal ground plane is an infinite number

   of radial conductors having the same length

   as the antenna itself. In other words, a 22"

   comm antenna would ideally sit on a 44" diameter

   disk.



   The 2.6" transponder antenna sits on a 5.2" disk.



   Since the ideal, 'tuned' disk is impractical

   for most aircraft installations, the next best

   thing is to have 4-8, 22" radials fan out from the

   base of the comm antenna and conform to the inside

   surface of the aircraft.



   Aircraft power ground and antenna RF ground are

   completely separate, unrelated systems. See chapter

   on antennas and feedlines in the 'Connection.

   Bob . . .

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