Topband: Confusion in ON4UN's Low Band DXing radial length calculations.

[Eddy Swynar]

Hi Doug,

As I understand it, the velocity factor of 50% applies for radial wires that are simply laid atop the ground, & not buried in any way...

But of course, I COULD stand to be corrected..!

~73~ de Eddy VE3CUI - VE3XZ









On 2014-12-18, at 4:18 PM, Doug Turnbull wrote:

> 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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