[TowerTalk] Vertical Pattern of a yagi

[Jim Miller]

I have exactly that situation where my Butternut vertical in mounted on a
fairly steep slope and I wondered what that would do to my pattern.  The
method I used with EZNEC was to "tilt my head".  I modeled as if the ground
was flat and the antenna was tilted.    I also did this with a dipole I plan
to install in the same area.  Then with the entire model tilted, you have to
tilt the patterns back the other way "in your head".  What I found was that
it did cause a pattern shift but it was much less that I expected and there
isn't anything I can do about it anyway.  I was glad to se that it didn't
create any nulls; it will vary the radiation angles once you tilt your head
to bring it back to reality but in my case, it helps in the right
directions.

73, de Jim KG0KP

----- Original Message ----- 
From: "K4SAV" <RadioIR at charter.net>
To: <towertalk at contesting.com>
Sent: Monday, April 24, 2006 6:24 PM
Subject: Re: [TowerTalk] Vertical Pattern of a yagi


> EZNEC does display the pattern in free space, but it also gives the
> pattern over ground (of any characteristics) at any height, but only for
> flat ground.  EZNEC cannot handle arbitrary terrains.  For this you need
> HFTA. However HFTA cannot handle arbitrary antenna designs.  HFTA works
> with single half wave elements or multiples thereof (2, 3, 4, etc...
> element yagis, or stacks).
>
> So you need both.
>
> Jerry, K4SAV
>
> Bill Tippett wrote:
>
> >N6KJ"
> >
> > >I'll be happy with a model of the 3 element SteppIR tuned to 28MHz.
> >This isn't the first time I've used EZNEC, but typically I start with
> >something similar to what I want then just modify as necessary.  I
> >didn't find a 3 element yagi example in my batch of models from the
> >ARRL Antenna Book.  I may have missed it if it is there.
> >
> >         There is a standard model of a 3 elementNBS Yagi for 50 MHz
> >included with EZNEC.  You
> >could re-scale it for 28 MHz, but...
> >
> >         EZNEC displays the pattern in free space,
> >which is not very useful.  You really need to
> >look at vertical patterns over ground to see
> >the effect of ground reflection vs antenna
> >height using a program like YT (included with
> >the 18th and 19th editions of ARRL's Antenna
> >Book) or its successor HFTA in the 20th edition.
> >The vertical pattern over real ground differs
> >dramatically depending on height above ground.
> >
> >                                         73,  Bill W4ZV
> >
> >
> >
> >
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