Author Topic: Streamlining a transponder antenna  (Read 3739 times)

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Offline flyingwaldo

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Streamlining a transponder antenna
« on: December 08, 2013, 06:42:53 PM »
On another forum I read that building an aerodynamic structure around an antenna can or will change it's performance.  My (purchased) EZ has the transponder antenna directly in front of the P-51 scoop.  Given the known drag of a round wire I can't help but think it is causing undue disruption of the air flow to the engine cooling.  Anybody know about this subject?
Thanks

Offline Rick Hall

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    • Cozy MK-IV, plans # 1477
Re: Streamlining a transponder antenna
« Reply #1 on: December 08, 2013, 08:42:37 PM »
I remember a Yew-Toob vid where they put round/streamlined/square rods in a wind tunnel and measured the drag.

If I had to remake a transponder antenna, I'd look for a junk hunk of a Bruntons [type] streamlined 'flying wire', and use that.

Rick
Cozy MK-IV, plans #1477. 90% done, 70% to go!
Currently working on the canopy, side windows just installed.
My hobby at: http://zggtr.org My plane at: http://cozy.zggtr.org/

Offline srothert

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Re: Streamlining a transponder antenna
« Reply #2 on: December 09, 2013, 01:51:07 PM »
Another option would be to remove the existing external antenna and buy an internal one from Bob Archer, at his website or from Aircraft Spruce.  I've installed one when I was building. Center has never had a problem receiving my signal.

http://sportcraftantennas.wordpress.com/shop/

Steve

Offline flyingwaldo

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Re: Streamlining a transponder antenna
« Reply #3 on: December 10, 2013, 06:07:39 PM »
Thanks guys.  Will look into both suggestions.
Does that internal one from Archer have a vertical component? 

Offline dkreidel

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Re: Streamlining a transponder antenna
« Reply #4 on: December 10, 2013, 06:37:08 PM »
I've tried a blade antenna, Archer's and the simple "ball on rod", and I've found the cheap "ball on rod" with only the ball sticking out of the skin works best. Mine is forward of the rudder pedals with an irregular shaped .020" aluminum ground plane and some copper screen to extend the ground plane forward almost to the battery. Center always sees me, even in the radar sparse West. Having just the ball protruding from the skin minimizes drag and potential damage.
Another benefit of locating the TXP antenna in the nose shortens the antenna lead. Use RG400, not RG58. Ask me how I learned this :>/

Dick Kreidel
N888EZ
2,992 hours *** 8 hours more and I will have flown it as many hours as it took to build ***