> 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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