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1/2 Wave Ring Antenna

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user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Thu Apr 15, 2010 8:02 am Post subject: 1/2 Wave Ring Antenna

Has anyone ever experimented with a 1/2 Wave Ring Antenna?  It is described here: http://www.slvrc.org/902band/902antennas.htm

It could be mounted on a metal turtle deck and covered with non-conductive fabric or fiberglass for streamlining.  Its low profile would have less drag than a quarter wave antenna at high speeds.

Joe

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_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Apr 15, 2010 9:05 am Post subject: 1/2 Wave Ring Antenna

At 11:02 AM 4/15/2010, you wrote:

 	  Quote: 	
		  



Has anyone ever experimented with a 1/2 Wave Ring Antenna?  It is 

described here:


	




 	  Quote: 	
		  http://www.slvrc.org/902band/902antennas.htm


	


 	  Quote: 	
		  It could be mounted on a metal turtle deck and covered with 

non-conductive fabric or fiberglass for streamlining.  Its low 

profile would have less drag than a quarter wave antenna at high speeds.


	




   I'm planning on building a cousin to this antenna for

   my 2M storm watch transceiver. See:



http://www.antennex.com/preview/2mddrr.htm



   This is the 1/4 wave version. Given that both the

   1/4 and 1/2 wave antennas are vertically polarized

   says that all the magic happens in that short vertical

   mast that goes to ground. This becomes the same thing

   as a short vertical with a strong top-hat loading

   scheme. So whether the "top hat" is 1/4 or 1/2 wave

   in circumference probably offers little difference in

   performance.



   Given the lengthening effect of so severe a

   "rake angle" on this antenna, the physical length

   of a 1/4-wave will be shorter than the classic

   22" whip.  22" bent around in a circle would give

   us less than 6" diameter and about 2" tall for VHF

   Comm frequencies. This cross section, even if well

   faired, could offer much more drag than the simple

   whip stuck out in the breeze.



   However, this form of antenna might perform well

   inside a composite fuselage.



   The biggest problem with heavily loaded antennas

   is loss of band-width.  They tend to be sharply

   tuned at the design frequency with efficiency

   falling off rapidly either side. The extreme example

   of this phenomenon is demonstrated by small diameter

   loop antennas for lower ham frequencies. They

   have to be fitted with motor driven capacitors to

   allow remote tuning to the frequency of interest.

   Circulating currents tend to be very high, voltage

   across the tuning capacitor is quite high. To keep

   the losses low at such high currents, the antenna

   is made from 3" DWV copper!



   The DDRR antenna needs a high conductivity ground

   plane that's at least 2x the antenna diameter. So

   a 6" DDRR might be built on a 12" square piece of

   copper clad that could become a "shelf" of sorts

   in the tailcone. Further, that same sheet might

   also be a good mounting location for the transponder

   antenna.  Food for thought.



   Bob . . .

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FisherPaulA(at)johndeere.
Guest

Posted: Thu Apr 15, 2010 9:56 am Post subject: 1/2 Wave Ring Antenna

There has been some discussion about a ring antenna here: http://www.vansairforce.com/community/showthread.php?t=52676



The discussion was specifically about APRS which uses 144.39MHz in the ham bands, but it's close enough to aviation frequencies that it might give you some ideas.  The biggest issue on this thread is where do you mount such an antenna in an all metal airframe.  Obviously, the problem becomes much simpler if you eliminate that! 



Paul A. Fisher 

Q-200, N17PF - copper foil dipole embedded in the vertical tail

RV-7A, N18PF - 1/4 wave sticking out in the wind! 

--

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tshankland(at)sbcglobal.n
Guest

Posted: Thu Apr 15, 2010 6:51 pm Post subject: 1/2 Wave Ring Antenna

Boy that brings back memories I had a two meter halo antenna on the back 

of my car in the the 1960's, the principle advantage was that it was 

horizontally polarized like most of  the other hams base station's. By 

the way a much younger version of myself is the middle one of the group.

Tim Shankland 601HD flying ( no halo antenna)

Robert L. Nuckolls, III wrote:

 	  Quote: 	

 <nuckolls.bob(at)aeroelectric.com>

 At 11:02 AM 4/15/2010, you wrote:

> 

> <fran4sew(at)banyanol.com>

>

> Has anyone ever experimented with a 1/2 Wave Ring Antenna?  It is 

> described here:

> http://www.slvrc.org/902band/902antennas.htm

> It could be mounted on a metal turtle deck and covered with 

> non-conductive fabric or fiberglass for streamlining.  Its low 

> profile would have less drag than a quarter wave antenna at high speeds.

   I'm planning on building a cousin to this antenna for

   my 2M storm watch transceiver. See:

 http://www.antennex.com/preview/2mddrr.htm

   This is the 1/4 wave version. Given that both the

   1/4 and 1/2 wave antennas are vertically polarized

   says that all the magic happens in that short vertical

   mast that goes to ground. This becomes the same thing

   as a short vertical with a strong top-hat loading

   scheme. So whether the "top hat" is 1/4 or 1/2 wave

   in circumference probably offers little difference in

   performance.

   Given the lengthening effect of so severe a

   "rake angle" on this antenna, the physical length

   of a 1/4-wave will be shorter than the classic

   22" whip.  22" bent around in a circle would give

   us less than 6" diameter and about 2" tall for VHF

   Comm frequencies. This cross section, even if well

   faired, could offer much more drag than the simple

   whip stuck out in the breeze.

   However, this form of antenna might perform well

   inside a composite fuselage.

   The biggest problem with heavily loaded antennas

   is loss of band-width.  They tend to be sharply

   tuned at the design frequency with efficiency

   falling off rapidly either side. The extreme example

   of this phenomenon is demonstrated by small diameter

   loop antennas for lower ham frequencies. They

   have to be fitted with motor driven capacitors to

   allow remote tuning to the frequency of interest.

   Circulating currents tend to be very high, voltage

   across the tuning capacitor is quite high. To keep

   the losses low at such high currents, the antenna

   is made from 3" DWV copper!

   The DDRR antenna needs a high conductivity ground

   plane that's at least 2x the antenna diameter. So

   a 6" DDRR might be built on a 12" square piece of

   copper clad that could become a "shelf" of sorts

   in the tailcone. Further, that same sheet might

   also be a good mounting location for the transponder

   antenna.  Food for thought.

   Bob . . .

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