David,
One question is which W6NL Moxon as there are three - original scratch
build, Cushcraft mod, and high strength Cushcraft mod? I've built two
of the original and own a third from another builder. Mine when up was
at 91ft with an 86ft 80m L loaded rotatable dipole above at 102ft. No
interactions noticed. SWR plots as expected. Performance as predicted.
My Moxon shows a measured resonance at 23-24Mhz (the only dip), I think
the loading tips are the cause, so would expect some interactions on 12m
with the 4L pattern/swr. I don't think which is the top Yagi will
matter for this. Beyond that, some modeling is appropriate, AC6LA has
all of the SteppIR models built for AutoEZ. With that software you
might find a 4L setting to minimize the pattern/swr issues. My bet is
any triband+17/12 antenna will behave the pretty much the same on 12m
but you wouldn't have the ease of tuning with the SteppIR.
I have the SteppIR 4L on another tower and am quite pleased with its
performance and reliability the last 8 years. A DB36 replaced the Moxon
to gain 30m, with 40m and the rest and it is a different story
altogether for high DB36 swr with the 80m dipole on 30 & 40, even with
the 80m boom parallel. I think this is due to interaction with the
effectively linear loading of the trombones to cover those frequencies.
Higher bands act like my 4L since the tape isn't looped in the trombones.
If I didn't want 30m, I wouldn't hesitate to put the Moxon and 4L on the
same mast. I think a pair of very good antennas.
have fun, stay safe, 73
Grant KZ1W
On 8/28/2020 15:32, David Aslin G3WGN wrote:
Consulting the TT hive mind. I'm sure someone has faced/modelled this question:
I have a 100ft tower with 16ft stub mast. The two antennas I plan to mount are
a W6NL 40m Moxon and a 4-el Ultrabeam (which is electrically identical to the
4-el Steppir). Both antennas have similar weights and similar wind areas and
will mount around 12ft apart on the mast.
My logic to date is that I'd want the Moxon to be the higher of the two, as
115ft is lower than ideal for the 40m band, but the best I can do. And that
the similar weights/areas suggest that there is no mechanical reason why one
particular antenna should be on top of the stack
But, I had not previously understood the possibility that the Moxon may screen
the 4-el and thereby reduce the performance of the 4-el (maybe the Moxon too?)
That might suggest the 4-el should be above the Moxon.
What does the hive mind say? Am I overthinking this or is there indeed a
preferred configuration dictated by experience and/or modelling?
73, David G3WGN M6O WJ6O
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