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IS a COM ANTENNA GROUND PLANE NECESSARY

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nuckolls.bob(at)aeroelect
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Posted: Wed Jul 01, 2020 10:27 am Post subject: IS a COM ANTENNA GROUND PLANE NECESSARY

At 12:54 PM 7/1/2020, you wrote:

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



 Yes, the antenna is a simple 1/4 wave whip.  The antenna base is mounted in

 a wood rib.  The antenna base does not touch the steel tube airframe but is 

 3/4 inch away from a horizontal steel tube and about 6 inches away from a

 vertical steel tube, not good I know. 	


   3/4 inch away from an airframe conductor and NOT

   electrically attached to it?



   So it's all covered up and painted over?



   I think an SWR check would be pointless but

   perhaps interesting . . . on second thought

   maybe important. Hard data on the down-side

   of installing an antenna the wrong way is

   a teaching moment opportunity.



   He's between a rock and a hard place. If

   there are builders flying this configuration

   and reporting satisfactory performance, it's

   going to be difficult/disappointing to wrap

   his arms around the next stage. Plan B is an

   antenna mounted to a tab which is electrically

   common with structure. Try mounting it inside

   the fuselage with widest practical separation

   from structure/cables. 



   An SWR check is still a good idea . . . you may

   find that proximity effects to the structure

   have electrically lengthened the antenna . . .

   SWR will minimize at some point below band-center.

   If it's under 3:1 overall, leave it alone. If

   over 3:1 at the lower edge, you can consider

   trimming the tip off in little bits (1/4"

   at a time) to bring antenna resonance up

   a bit.



   I'm noticing that handy little digital VHF/UHF

   swr meters are sorta drying up on eBay, et. als.

   This is one of my favorites



  https://tinyurl.com/ybfyl9fo



   it used to be offered by 20 or more suppliers,

   could only find a handful of offers



   Here's another which would suit our purposes

 

  https://tinyurl.com/ydy327v7



   It would be useful for you to track this

   builder's experience . . . perhaps we could

   craft a 'shop notes' article for archiving

   on aeroelectric.com



   If getting your own SWR meter is not practical,

   I can loan you mine.



 

 

   Bob . . .

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user9253

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

Posted: Wed Jul 01, 2020 4:42 pm Post subject: Re: IS a COM ANTENNA GROUND PLANE NECESSARY

Yes, the antenna base is very close to an airframe steel tube but not attached

electrically or physically.  The base of the antenna is mounted to a wood rib.  

The builder does not know much about electricity or antennas. 

And yes, the vertical stabilizer is all covered and painted.  The builder will not 

want to tear the airplane apart to get that antenna out.

  I had forgotten about that Red Dot SWR meter that I had purchased several 

years ago and only used once.  I found it in my workshop and discovered that 

all 3 AAA batteries had leaked.  Have you checked your SWR batteries lately?  

Luckily the battery holder is mounted with double sided foam tape which 

protected the circuit board.  I cleaned out the corrosion and installed new 

batteries.  Luckily the SWR meter still works.  I will test my friend's antenna 

SWR whenever he gets the RG-58 terminated.

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_________________
Joe Gores

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