Dennis OConnor wrote:
> The word picture (and diagrams) of the 'missing half 'of a dipole antenna
> going down into the ground is a device to help visualization of how the
> induced ground currents act to complete the return current flow for a quarter
> wave monopole (vertical)... It is not what is actually happening in the
> generated EM field underneath the vertical... I can assure you that a 160
> meter quarter wave monopole does not have an image 130 feet down into the
> dirt and rocks,...
> An elevated ground plane antenna also has radials just like a ground mounted
> vertical yet we do not see authors repeatedly claiming that there is an image
> of half a dipole forming below the radials - though some do, must be what
> they are smoking...
>
> Next, the 'poor performance' of vertical antennas is grounded in the lack of
> knowledge of those making such claims...
> Lets us discuss two antennas for 40 meters... A half wave DIPOLE hung
> horizontally a quarter wave above ground - and a quarter wave MONOPOLE
> (vertical), ground mounted...
> Now, the dipole has that wonderful 4dB of reflection gain (or whatever your
> favorite fantasy dB number is) giving is something in the 6dBi range......
> And the poor, tired vertical has a ground loss of xxx dB (pick your favorite
> fantasy dB number) and no reflection gain so it is struggling along at 1.25
> dBi (or some such - you pick it)...
> So now, Joe Ham wants to talk to his friend Bob, 175 miles away.... On the
> dipole Joe is booming in at Bob's qth, and on the vertical Bob can barely
> hear him... Yup, it just proves that verticals radiate equally poorly on all
> directions...
> Later that day Joe hears a DX station on a tiny rock in the middle of that
> antarctic ocean exactly half way around the world from his shack (the
> antipode)...
> He calls on the dipole... The DX goes CQ back in his face... He calls and
> calls and calls... No joy... Finally, in frustration and about to give up he
> switches to the inferior, radiates equally poorly in all directions, vertical
> - and gets an answer on his first call...
>
> So, which antenna is inferior?
>
I kinds like to think of it like the serious DXer who has 3 or 4 stacked
Yagis using the lowest one for close in and the higher for longer
distance. Actually which ever one gives the best signal at any given
time. IOW which ever one has the best angle of radiation for the
conditions.
Using the criteria for the vertical we've been reading we'd be asking
which of the 3 or 4 Yagis is inferior when they are all the same, yet
may have quite different performance based on the height/radiation angle.
73
Roger (K8RI)
> denny / k8do
>
>
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