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Antennas

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frank.hinde(at)hp.com
Guest

Posted: Thu Apr 06, 2006 1:17 pm Post subject: Antennas

Hello Bob,



I must say the magic of antennas is a little lost on me so I was looking

at your COM and VOR antenna designs. I have a Bob Archer com antenna and

he talks about Vertial polarisation but your example shows both glued

down to a horizontal surface...Am I missing something?



I assume that one can't put both a VOR a COM antenna in the same

fiberglass wingtip?



Can one do the same with a much shorter (5"?) transponder antenna say on

the bottom of the rudder?



Us RV guys really don't like things hanging on the outside of fast

airplanes...



Thanks



Frank

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brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Thu Apr 06, 2006 1:51 pm Post subject: Antennas

Hinde, Frank George (Corvallis) wrote:

 	  Quote: 	
		   

 

 Hello Bob,

 

 I must say the magic of antennas is a little lost on me so I was looking

 at your COM and VOR antenna designs. I have a Bob Archer com antenna and

 he talks about Vertial polarisation but your example shows both glued

 down to a horizontal surface...Am I missing something?


	


The radiator part (the part of the antenna attached to the center

conductor of the coax feed line) should be as close to vertical as

possible. The VOR/LOC/GS antenna should be horizontal.

 	  Quote: 	
		   

 I assume that one can't put both a VOR a COM antenna in the same

 fiberglass wingtip?


	


It is not a good idea. You want as much isolation as possible between

the two.



 	  Quote: 	
		   Can one do the same with a much shorter (5"?) transponder antenna say on

 the bottom of the rudder?


	


The transponder antenna is actually 2.6" (6.5cm) long. That antenna you

do want to mount on the belly as it is prone to being shielded by other

things on the airplane. There should be nothing between the transponder

antenna and the RADAR site on the ground.

 	  Quote: 	
		   

 Us RV guys really don't like things hanging on the outside of fast

 airplanes...


	


The airflow on the belly is already turbulent from mixing outflow

cooling air with the undisturbed air so putting antennas on the belly is

not going to have any effect on maximum speed. You should definitely

mount your transponder antenna on the belly far enough away from the

gear legs and exhaust pipes so they do not constitute a shield for the

signal.



Brian Lloyd

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_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery

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