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Antenna Ground Plane

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Dennis.Kirby(at)kirtland.
Guest

Posted: Thu Dec 17, 2009 8:22 am Post subject: Antenna Ground Plane

(Note – subject line changed to reflect the new direction of this thread.)  

   

   

"Richard Pike" wrote: <<... you want a ground plane that radiates out from the antenna  

and ties into the airframe, assuming the airframe is steel. >>  

   

   

Hi, Richard –  

   

I copied your idea for a radio antenna ground plane while I was bulding my Kolb ten years ago, using an aluminum sheet on the belly (below the fuel tanks), spanned between the two bottom longerons and covered over with fabric.  My ground plane is grounded using a single wire attaching it to the common airframe ground, which ties into the gear leg and engine case.  But my antenna ground plane does not touch the metal cage directly – there is fabric in between.    

   

I have never considered my radio reception as “outstanding.”  Acceptable, but not great.  Could this be because the ground plane is not in direct contact with the frame?  Do you think my antenna would be more effective if the ground plane (approx 24 inches diameter hexagon shaped) were touching the metal cage?  

   

Dennis Kirby  

Mark-3, 912ul  

Sandia Park, NM  

   

   

   

      [quote][b]

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John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Thu Dec 17, 2009 11:40 am Post subject: Antenna Ground Plane

Dennis/Gang:

  

 Poor reception is usually caused by excessive RMI  and EMI interference.

  

 I don't think the ground increases reception  performance of the radio, only the transmit side.

  

 john h - 5 months until MV and  counting.

 mkIII

  

  

 [quote]    I have never considered my radio reception    as “outstanding.”  Acceptable, but not great.  Could this be because    the ground plane is not in direct contact with the frame?  Do you think    my antenna would be more effective if the ground plane (approx 24 inches    diameter hexagon shaped) were touching the metal cage?

      

    

Dennis Kirby   

 

[b]

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_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

kuffel(at)cyberport.net
Guest

Posted: Thu Dec 17, 2009 3:07 pm Post subject: Antenna Ground Plane

Dennis, 

<< I have never considered my radio reception as  “outstanding.”  Acceptable, but not great.  Could this be because the  ground plane is not in direct contact with the frame?  Do you think my  antenna would be more effective if the ground plane (approx 24 inches diameter  hexagon shaped) were touching the metal cage? >> 

Short answer, probably yes.  There are basically two  types of ground planes: Untuned = Infinity (or as close to it as one can manage)  and Tuned = 1/4 wavelength in *radius*.  For aircraft com frequencies this  would be a radius of about 22 inches or a diameter of 44 inches.  Thus  converting your badly tuned 1/8 wavelength ground plane into an "untuned" type  by grounding it to the airframe should improve your performance.  The  bonding between the ground plane sheet and the airframe should be a much as  possible, not just a single point or two. 

In addition, John Hauck's  statement 

<< I don't think the ground increases reception performance of the  radio, only the transmit side. >> 

is contrary to accepted  electronics theory.  The rule is an antenna works exactly the same for  transmit or receive except for the effects of heating and high voltage  associated with very high power transmissions.  For aircraft applications  these effects are undetectable. 

Tom Kuffel 

  

  

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    [quote][b]

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Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Thu Dec 17, 2009 4:53 pm Post subject: Re: Antenna Ground Plane

[quote="Dennis.Kirby(at)kirtland."](Note â€“ subject line changed to reflect the new direction of this thread.)     

   

"Richard Pike" wrote: <<you>>    

   

Hi, Richard â€“  

   

I copied your idea for a radio antenna ground plane while I was bulding my Kolb ten years ago, using an aluminum sheet on the belly (below the fuel tanks), spanned between the two bottom longerons and covered over with fabric.  My ground plane is grounded using a single wire attaching it to the common airframe ground, which ties into the gear leg and engine case.  But my antenna ground plane does not touch the metal cage directly â€“ there is fabric in between.    

   

I have never considered my radio reception as â€œoutstanding.â€  Acceptable, but not great.  Could this be because the ground plane is not in direct contact with the frame?  Do you think my antenna would be more effective if the ground plane (approx 24 inches diameter hexagon shaped) were touching the metal cage?  

   

Dennis Kirby  

Mark-3, 912ul  

Sandia Park, NM     

       	  Quote: 	
		  [b] 	




Hi Dennis, I got my info from this page - http://www.biplaneforum.com/forum_posts.asp?TID=1882



Don't know if the guy knows what he is talking about or not, but since he is in the business of selling antennas, I decided he probably knows more than I do - anyway, this is what he said on the page:



 "The steel tube structure can be used as a ground plane but to work properly the antenna ground must be tied electrically into the tubing. Remember, a ground plane at these frequencies should be about 48 inches in diameter at least to work properly. Larger is better. An antenna mounted to a smaller plate and the plate then attached to the tubing will be OK but the plate must be electrically attached to the tubing and I do not mean with a ground wire. Ideally the ground currents should go into the ground plane in a radial manner in several places but do the best you can. If the antenna ground is not done properly the VSWR of the antenna can be very high."



So the skinny little tube had the paint ground off it from moving it around the garage, I stretched the two strip of aluminum across it to for a six sided spoke arrangement, and riveted the crossing strips to the longerons. So it ought to be tied in all around, and if it doesn't work right  I can always try and persuade Ed that he doesn't really need a transponder in a FSII anyway... not to mention that we don't know yet if the transponder still works after the crash.



Richard Pike

MKIII N420P (420ldPoops)

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rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Thu Dec 17, 2009 4:56 pm Post subject: Antenna Ground Plane

Dennis, Tom, Actually, probably not. RF grounding and electrical grounding

are common in name only. Another of the great hangar myths teaches that

tying every piece of metal in the airplane together electrically helps radio

performance. It doesn't matter, what does is metal in the transmission path

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