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GPS/WAAS antenna install help needed

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rparigoris

Joined: 24 Nov 2009
Posts: 792

Posted: Thu Sep 24, 2020 10:07 am Post subject: GPS/WAAS antenna install help needed

Hi Group To comply with ADS-B requirements we are installing a Garmin GDL-82 along with our Becker transponder. I have some questions about the install of the GA35 GPS/WAAS antenna. I want to mount it inside our Europa aft of the doors by 2 feet. Questions: 1) Garmin calls for a ground plane extending for minimum of 7.5" from edges of antenna, that equates to a circle of about 19", is a ground plane needed at all? If so could I make it out of a Brass base and perhaps 6 soldered copper tapes? Does it have to be the full 7.5" overhang? 2) I have both RG400 and RG142B cable, run is going to be about 6', is there a preference? (Garmin wants between 1.5dB and 6.5dB) 3) The connection to the bottom of the antenna is a screw on TNC, can I use a 90 degree connector? 4) If I wanted could I mount the antenna inside the top engine cowl? (fiberglass) 5) Garmin calls for antenna to be parallel with longitudinal axis, how critical is this? What sort of angle would begin to cause problems? If a ground plane is required, if I kept the antenna parallel with longitudinal axis, could I angle the antenna to the ground plane? 6) My Aeroelectric Connection (old) doesn't have any info on GPS antenna install, a note said that it will probably be added in future. Is there any Aeroelectric info on GPS antenna installation?  Thx. Ron P.

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recapen(at)earthlink.net
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Posted: Thu Sep 24, 2020 10:45 am Post subject: GPS/WAAS antenna install help needed

 	  Quote: 	
		  From what I have read about the Europa it is a composite airframe.  Based on that, you should install a ground plane....


	






--

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nuckolls.bob(at)aeroelect
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Posted: Thu Sep 24, 2020 5:29 pm Post subject: GPS/WAAS antenna install help needed

At 01:07 PM 9/24/2020, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "rparigoris" <rparigor(at)hotmail.com>



 Hi Group To comply with ADS-B requirements we are installing a Garmin GDL-82 along with our Becker transponder. I have some questions about the install of the GA35 GPS/WAAS antenna. I want to mount it inside our Europa aft of the doors by 2 feet. Questions: 1) Garmin calls for a ground plane extending for minimum of 7.5" from edges of antenna, that equates to a circle of about 19", is a ground plane needed at all? 	


  Yes . . . from the dimensions cited, it's

  not a 'tuned' ground plane . . . so the

  goal is to put as much conductor under the

  antenna base as practical. It doesn't have

  to be round. Rectangular of similar square

  area works.



  	  Quote: 	
		  If so could I make it out of a Brass base and perhaps 6 soldered copper tapes? Does it have to be the full 7.5" overhang? 	


  use single sheet thin aluminum . . . maybe 0.020"  Mechanical

  robustness doesn't get you anything here.



  2) I have both RG400 and RG142B cable, run is going to be about 6', is there a preference? (Garmin wants between 1.5dB and 6.5dB)



  Either is fine.



  3) The connection to the bottom of the antenna is a screw on TNC, can I use a 90 degree connector?



   Yes



  4) If I wanted could I mount the antenna inside the top engine cowl? (fiberglass)



   I'd stay away from the engine. Back in the empennage is best.



  5) Garmin calls for antenna to be parallel with longitudinal axis, how critical is this?

  What sort of angle would begin to cause problems? If a ground plane is required,

  if I kept the antenna parallel with longitudinal axis, could I angle the antenna

  to the ground plane?



  Ground plane arallel to upper/lower skin, antenna centrally

  located and perpendicular to ground plane.



  6) My Aeroelectric Connection (old) doesn't have any info on GPS antenna

  install, a note said that it will probably be added in future. Is there

  any Aeroelectric info on GPS antenna installation?  Thx. Ron P.



   GPS antennas need no ground plane. Just clearest

   practical view of sky above the horizon all around.



   Some folks have enjoyed satisfactory performance

   under the cowl . . . give it a try . . . but best

   is probably under upper surface of empennage.



 

   Bob . . .

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rparigoris

Joined: 24 Nov 2009
Posts: 792

Posted: Fri Sep 25, 2020 12:31 pm Post subject: Re: GPS/WAAS antenna install help needed

Hi Bob Thank you for your reply. I'm going to mount the antenna inside the airplane 2 feet aft of the doors. The ceiling at this section is a constant changing equation of compounded 3D curves. Making a single bent up piece of aluminium would be a bear of a job. Same holds true trying to layup a composite shelf. Keep in mind the ground plane is going to be the support for the antenna so it must be capable of supporting ~12 lbs. About 1/3rd of the circular ground plane will be bent against the ceiling. The front will be below the ceiling by 3".



Is it OK to make the ground plane out of a piece of .063 6061 aluminium? 



I would trace the shape of the antenna on a piece of aluminium and draw in eight 1" wide legs. Truly a spider shape. I can now easily bend the 1" legs to follow the shape of the ceiling. Where it's in contact with ceiling will use 6-32 click bonds, where the legs are below the ceiling will screw into a 1/4" G-10 tube stand off. To protect people from sharp edges will use a 1" wide plastic cap: https://www.mcmaster.com/caps/caps-4/rectangular-caps/ chances are that the antenna may be a little bouncyif just suspended by the ends of the spider. Can add 2 or 4 G-10 standoffs near the antenna if that's the case.



Aft part of spider would be just forward of green tape which would put the edge of spider just 2 feet from antenna:

http://www.europaowners.org/main.php?g2_itemId=31240



Ron P.

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