Good morning, Dan.
Yes, the Create 80/75 mtr elements can be modeled with some care for the
capacity hats. The KLM linear loaded 40 mtr elements are probably not possible.
Having interlaced many different types of elements, perhaps I can offer a
suggestion or two.
Normally, the elements that will be most negatively affected are the high
frequency ones. It is possible to do some informative tests using garden
variety
equipment. If you have a sensitive antenna mesuring device, such as a good
noise
bridge, add a VU meter output (you might need a small amplifier) and it will be
possible to "see" the influence of the adjacent lower frequency element(s).
This
was an idea from the late Ron Ciappari, N6AUV, back in about 1983 and we did a
lot of interesting projects using it.
For example, set up a 40 mtr element at some workable height, in the clear (I
use about 8' for this type of basic test) and very carefully measure its
resonant frequency, which will be zero noise on the bridge and no indication on
the VU meter. It is important to maintain the test environment, so be sure
there
is nothing moving around, including yourself. We mark spots on the ground for
each person to stand. You can test the sensitivity of the setup by moving close
to the element and watching the meter, or listening to the noise. One reason
for
using a VU meter is it will move before noise is audible. It will also be
interesting to move your hand along the element and note where your body
capacitance has the most affect. Now that you have the 40 mtr element in place,
carefully move an 80/75 element into proximity to it. It is not necessary to
use
a boom, but it might be the easiest. You can start with it close enough to
probably cause interaction and then move it away, or far enough away to not
have
any and move it closer until there is interaction. Each time you move the
80/75,
it is necessary to move (you and assistants) to your designated spots to
maintain the test area and then read the meter.
Some results that might be of interest are that the KLM can co-exist (in round
numbers) within 4' of a full size 20 mtr element, which led to my first large
20/40, a 5 element 20 and 3el 40 using a HyGain 205B as the core, which Ron and
I built shortly after our first tests. Since that time, I have built many
versions of 20/40's. We have used this knowledge at Force 12 and have also
added
80/40 interlaced antennas. The one I have used for almost 5 years uses 2
elements on 40 (similar in length to the KLM) and 2 elements on 80/75 (68'
long), all being linear loaded. At a horizontal spacing of 4'11", the 80 mtr
elements detune the 40's by 10 kHz, which is a good guide to making a useful
antenna. One word of caution: I always will build the higher frequency antenna
completely and test it before adding the lower frequency elements - just to
make
sure! I often will also build the lower frequency antenna separately, too -
just
to make sure - then make the composite product. For a "one-off" design project,
you might need to go to that effort, as the initial proximity measurements have
been tracked the final product in most cases.
The only exception I can recall is where I was working on interlacing 30 mtr
elements (shortened) and they did not appear to disturb anything, but in actual
practice, they did. Apparently, the feedpoint was not changed by the 30 mtr
elements. After realizing the situation, I used a different design on the 30
mtr
element. This is similar to adding a 15 mtr Yagi above a 20 and not seeing any
change in the 15 mtr VSWR curve; however, upon using it, the F/B will have gone
down the tubes!
Have a great day & 73,
Tom Schiller, N6BT
President, Force 12, Inc.
Amateur Antennas, Commercial Towers & Antennas
P.O. Box 1349 Paso Robles, CA 93447
Phone: 805.227.1680 FAX 805.227.1684
Web Site: http://www.QTH.com/force12
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