[Towertalk] F12 40M antenna near 10-20M antennas

[Guy Olinger, K2AV]

Hi Mel,

If you have modeled a Cal-Av, you should be able to model the basic
form of an F12 N element, with the linear loading folding outward,
etc. Since you've done the one model, you've already crossed the
bridge of accepting antenna evaluation in virtual space.

For most modeling programs, you can get the 95% accurate model of N
element behavior by the following:

1) define ALL conductors as 1" aluminum tubing. This and the steps in
3) avoid documented weaknesses in various modeling programs.
Physically speaking this is not a practical configuration, but you
don't have to manufacture it.

2) keep the physical length of the inner (unparalleled) portion, and
the length of the linear loaded section the same as the physical F12 N
element.

3) in the linear loaded section, keep the parallel conductors 8 inches
apart from each other. The end view of the elements forms a triangle.
For each element half the conductors are:

  a) conductor out from the center to the outer end of the LL area,
  b) perpendicular 8" connection,
  c) conductor back toward center to inner end of LL area,
  d) perpendicular 8" connection,
  e) conductor out from inner end of LL area to the end of the
element.

Although it really doesn't matter what way you lay out the triangle,
do this consistently everywhere in the antenna, and one half of an
element must be a mirror image of the other.

4) adjust the outer end of the e) conductors to get the required
primary resonant frequency of the element(s).

5) add your favorite triband model at whatever separation you wish.
Carefully record interactions, and current distributions.

6) Remove the folded N design and do the same with a full size 40 m
antenna at the same separation. Carefully record interaction, etc.

7) Compare results from 5) and 6).

You will need to get the LL area placement, and the resonant
frequencies from F12.

As you observe the induced currents you will see certain non-intuitive
behaviors of the N element design which are responsible for it's
performance in proximity to tribanders. It will not be necessary to
get involved in a Dodge vs. Ford vs. Chevy discussion. You will know
WHY they work. From there it is a small mental leap to a real element
with the same effect optimized in a practical physical element.

It is this WHY that is always missing from the Dodge/Ford/Chevy style
arguments. You might even figure out a good way to explain it to the
skeptics (I never have).

Prepare for a good time.

73, Guy.


----- Original Message -----
From: "Mel Martin" <ve2dc@rac.ca>
To: <towertalk@contesting.com>
Sent: Friday, April 26, 2002 4:05 PM
Subject: [Towertalk] F12 40M antenna near 10-20M antennas


> Looking for opinions on this setup.
> Force 12 claims that their 2 and 3 el 40M beams (240M 340M) can be
> mounted within 7' of their C31.
>
> I modeled the Cal-Av 40M, and various 2el and 3el 40M beams within
10 ft
> of a C31XR and various other 10-20M beams, (using EZNEC 3.0) and the
> result always seems to be serious loss of gain and destruction of
the
> 10-20M pattern. So I'm skeptical about this "within 7 ft" claim.
OTOH, I
> had a TH7 10 ft over a 3 el Hy-gain (until the Ice Storm of '98) and
it
> seemed to work fine.
>
> Has anyone actually used the 240N or 340N in close proximity to a
higher
> frequency antenna, and how were the results?
>
> BTW, I'm looking at the Optibeam Tribander (perhaps over a 240M)...
> anyone have experience with the Optibeam antennas?
>
> Thanks...
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