Radials on the ground do not have a magic length. Worrying about resonance
for them is not necessary.
If you tune a quarter wave wire up in the air - then lay it onto the ground
- it couples to the ground and is no longer a distinct single piece of
wire. Just make them an easy length to deal with and put as many of them
down as you can.
Tree N6TR
On Fri, Dec 19, 2014 at 2:28 AM, Doug Turnbull <turnbull@net1.ie> wrote:
> Brian,
> I understand that the VF varies with soil type. One could just
> compensate by being conservative but who wants to use 30/40% more wire than
> needed. Why does the ON4UN book ignore VF when doing the example
> problems?
> Should I shorten to take into account VF?
>
> 73 Doug EI2CN
>
> -----Original Message-----
> From: k8bhz@hughes.net [mailto:k8bhz@hughes.net]
> Sent: 19 December 2014 00:08
> To: Doug Turnbull; Topband@contesting.com
> Subject: Re: Topband: Confusion in ON4UN's Low Band DXing radial
> lengthcalculations.
>
> Hello Doug,
>
> The 50-60% figure depends on your soil conditions, so may vary quite a bit.
> With my poor, sandy soil, the Vf is 67.7% with the radials laying on the
> ground. When I buried them 6", the Vf was 39.8%. Using these shortened
> radials, there wasn't much improvement going beyond 16 radials.
>
> To find out your soil conditions, simply lay a temporary dipole on the
> ground and use an analyzer to find it's resonance. Then trim to length. Now
> you have your first two radials!
>
> Good luck
>
> Brian K8BHZ
>
> -----Original Message-----
> From: Doug Turnbull
> Sent: Thursday, December 18, 2014 4:18 PM
> To: topband@contesting.com
> Subject: Topband: Confusion in ON4UN's Low Band DXing radial
> lengthcalculations.
>
> Dear OMs and Yls,
>
> I am replacing raised radials for 160M inverted L with ground mounted
> radials mostly because I could not readily get the raised radials up high
> enough in my wood and also because of maintenance problems.
>
>
>
> This inverted L goes up 100 feet at its top before levelling out for
> the final 32' or so. It should I believe have a strong vertical element.
>
>
>
> ON4UN's book Low-Band DXing 56th edition is generally excellent but
> I
> do find the coverage of ground radials both confusing and somewhat
> contradictory. This surprises me for what is pretty much considered the
> bible.
>
>
>
> On page 9-14 the text states that the velocity factor falls for
> ground mounted radials to the "the order of 50-60%, which means that a
> radial that is physically 20 meters long is actually a half-wave long
> electrically!" This example is for 80M not 160M. However in the
> examples
> found on page 9-15 the velocity factor change is ignored. I understand
> the velocity factor change and have always accepted this. It generally
> did
> not pay to try and cut radials precisely to a given wavelength. I accept
> the radial length vs. radial number charts but is this an electrical length
> in free space or a length considerably reduced due to velocity factory
> change? Example 3 ignores velocity factor correction and from what I can
> see this correction is ignore in most of the text concerning ground
> radials.
> What does one do? Who does one believe.
>
>
>
> While I am talking about a 160M inverted L; I did reference the
> SteppIR BigIR vertical manual, page 18. Lengths should be scalable. I
> find no mention of velocity factor and the shortening effect which is
> experienced. The recommendations are not very different from those in
> ON4UNs book. So does this mean one ignores the change in velocity factor?
>
>
>
> I appreciate some guidance with this matter. I would like a
> radial field which would take me to within 0.5/1 dB of the maximum
> achievable for reducing near field losses.
>
>
>
> 73 Doug EI2CN
>
>
>
>
>
>
>
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