Topband: GAP Vertical Question

[Lew Sayre]

Yo,
    Tom, et. al.  please do keep taking this seriously!  Most of us on this
reflector do not have
engineering degrees involving the physics of RF. However we do greatly
enjoy developing systems
to receive and fling RF energy into the ether and try desperately to follow
the discussion here in order
to improve both our hardware and the understanding of how it works.
     Exercising the little grey cells in disciplines where I am minimally
competent is enjoyable and adds to the
operating experience in radio. Minimizing the magic in radio by showing how
the tricks are done makes me a better magician..
    Thanks to all those who contribute! I hope you all continue to do so in
a professional manner.
    73 and I remain,
    Lew      W7EW

On Mon, Dec 17, 2012 at 10:21 AM, Lennart M
<lennart.michaelsson at telia.com>wrote:

> Tom et al,'this a hobby, pse dont take it that seriously
> 73
> Len
> SM7BIC
>
> -----Ursprungligt meddelande-----
> Från: Topband [mailto:topband-bounces at contesting.com] För Tom W8JI
> Skickat: den 17 december 2012 18:55
> Till: topband at contesting.com
> Ämne: Re: Topband: GAP Vertical Question
>
> > To work at its maximum efficiency a vertical needs a real ground
> > system and the image is its fictitious counterpart to isotropic. Im
> > oversimplyfing here so no need to pick nits.
>
> Besides being untrue, that is confusing or misleading.
>
> 1.) Some verticals need no ground. What would also be true is that end-fed
> antennas always require a counterpoise of some sort, because there always
> has to be a second terminal of some type for the feedline to "push
> against".
>
> 2.) The image is a shortcut tool used to allow longhand pattern
> calculations. It is not used for efficiency, antenna descripition, or
> actual
> operation.
>
> 3.) dBi, on the other hand, is a reference condition for a field strength
> ratio.
>
> > According to Kraus that image, mirror, or whatever you care to call it
> > occurs at a distance from the base and at a mathematical relationship
> > to where the current peak is on the vertical radiator.
> >
> > In the case of this half wave discussion the reflection occurs around
> > .35 wave out unless you, or others, want to try and discredit Kraus.
> > Thus radials do work with a 1/2 wave and "system" efficiency is
> > dependent upon the actual ground and how well the radials perform.
> > Since this forum is predominantly DX oriented I prefer to qualify the
> > "system" efficiency by how well the main lobe extends between its peak
> > and the ground. IOW those low angles needed for DX.
>
> There is not wrong with what Kraus teaches. The problem comes when we
> misunderstand or misapply what he teaches.
>
> > Using modeling it is easy to realize that significant degradation of
> > the radiated field at the lower angles is very real.
>
> I'm not sure models we use are all that meaningful at low angles on low
> bands. They are OK on extended groundwave, and probably OK on upper HF.
> They are, however, all we have.
>
> > Various verticals (mostly VHF/UHF) on tall buildings or towers are not
> > subjected to those ground losses and place a strong signal at the
> horizon.
>
> I'm not going to touch that one, other than to say ground losses for a
> given
> soil and condition are dependent of intensity of the electric, magnetic,
> and
> electromagnetic fields in a given volume of lossy media.
>
> This is why we can have moonbounce, even though losses in the moon's
> surface
> are horrible, and why moving an antenna up away from earth or distributing
> the fields over a wider area by using more radials reduces loss.
>
> Where we create a misunderstanding or problem is when we ignore how it
> works, and pretend all field intensities in a given volume of lossy media
> are equal at all distances with all antennas.  When we do that, we get
> false
> ideas................such as half wave verticals have high loss without
> large radial fields. If that was true, our horizontal half-wave dipoles 1/4
> wave or more high would have poor efficiency without large counterpoise
> fields below the dipole.
>
> 73 Tom
>
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