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

[k8bhz at hughes.net]

I can’t agree with this “conventional” thinking. Why does a piece of wire magically lose it’s length just because you lay it on the ground? The electrical length changes because of Vf, and it’s resistance changes because of the lossy ground, but it’s still a piece of wire. I’m going to try to attach a posting I did back in 2006. If it doesn’t work, I will follow with a separate posting.

Brian  K8BHZ

From: Tree 
Sent: Friday, December 19, 2014 10:07 AM
To: Doug Turnbull 
Cc: k8bhz at hughes.net ; 160 
Subject: Re: Topband: Confusion in ON4UN's Low Band DXing radial length calculations.

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 at 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 at hughes.net [mailto:k8bhz at hughes.net]
  Sent: 19 December 2014 00:08
  To: Doug Turnbull; Topband at 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 at 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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