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Re: [TowerTalk] Vertical vs Beam

To: "'Michael Tope'" <W4EF@dellroy.com>, <towertalk@contesting.com>
Subject: Re: [TowerTalk] Vertical vs Beam
From: "Joe Subich, W4TV" <lists@subich.com>
Reply-to: lists@subich.com
Date: Tue, 7 Apr 2009 00:37:11 -0400
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>

> My vague recollection was that W8JI had pointed this out in a 
> Towertalk post a number of years ago, but I couldn't recall if 
> it was WWV or WWVH that used radials under their 1/2 wave 
> vertical dipoles.

This goes back more than 10 years and was probably on topband 
rather than Towertalk.  

> It makes sense that there will be ground lossess even with a 
> 1/2 wave vertical dipole. Any antenna in close proximity to 
> ground will couple some energy to the lossy ground and induce some 
> current there.

About the same time as the information on the WWVH radials, N7CL 
provided data from some of his work for the DOD that indicated 
the losses were a function of height.  Losses were very high 
when the e-field was intense at the ground surface and decreased  
with separation.  Most of the improvement occurred with the first 
1/8 wave of height.  However, "radials" needed to be 1/4 wave 
above ground before the losses approached that of an FCC ground 
system and even then losses were still measurable up to and beyond 
1/2 wave!  Sloping the wires, like those in the WWV/WWVH verticals 
concentrated the e-field at the end of the skirt and increased the 
losses (unless the feed point was further elevated). 

73, 

   ... Joe, W4TV 
 





> -----Original Message-----
> From: towertalk-bounces@contesting.com 
> [mailto:towertalk-bounces@contesting.com] On Behalf Of Michael Tope
> Sent: Tuesday, April 07, 2009 12:02 AM
> To: lists@subich.com
> Cc: towertalk@contesting.com; 'Bill Aycock'
> Subject: Re: [TowerTalk] Vertical vs Beam
> 
> 
> Joe Subich, W4TV wrote:
> 
> >  
> >
> >>Thanks, much. It is interesting that, as far as I can recall,
> >>yours is the first reference (Directly) to the QST article. I 
> >>had forgotten it (Senior moment?) I must go back and re-read.
> >>    
> >>
> >
> >The radials were added at WWVH after field strength testing showed
> >that the half wave verticals failed to produce the expected field 
> >strength due to e-field losses in the ground below the bottom end 
> >of the antenna.  While the radials did not effect the feed point 
> >impedance they provided a significant improvement in field strength. 
> >
> >  
> >
> Thanks for that clarification, Joe. My vague recollection was 
> that W8JI 
> had pointed this out in a Towertalk post a number of years ago, but I 
> couldn't recall if it was WWV or WWVH that used radials under 
> their 1/2 
> wave vertical dipoles. It makes sense that there will be 
> ground lossess 
> even with a 1/2 wave vertical dipole. Any antenna in close 
> proximity to 
> ground will couple some energy to the lossy ground and induce some 
> current there. The hard questions to answer are whether these ground 
> losses are small enough to ignore and whether the additional field 
> strength to be gained is worth the effort and expense of a ground 
> screen. The suspect the answer to those questions will vary 
> depending on 
> the ground characteristics and the requirements/motivation of 
> the user 
> (i.e. do I just want something with decent performance or do 
> I want to 
> squeeze out every last dB?).
> 
> 73, Mike W4EF............. 
> _______________________________________________
> 
> 
> 
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