I might add, I suspect one could adjust the matching point to 50 ohms
bye using a delta connection running out on both sides from the center
of the driven element provided the center point would give you something
less then 50 ohms. Just seems there should be a better MOXON program
then MOXON Utility. I'm also thinking one could increase bandwidth bye
wrapping the fiberglass tubing with aluminum foil. Fiberglass intrigues
me as it is lighter then aluminum tubing. (Wrapping it before the
helical loading coils.)
Lee, w0vt
On 2/5/2017 10:33 AM, Lee wrote:
Some time ago I decided I wanted to build a full size 40 meter Moxon
Yagi beam. It never happened. Right now I've gotten Cold Feet to
the project. I'm beginning to think the beam would be just too heavy
for my situation. I'm now considering building a 40 meter Mini MOXON
beam as built by W7XA. This rendition uses fiberglass tubing instead
of aluminum tubing and is inductively loaded making it close to a 26
foot x 16 foot rectangle. Has anyone on here built one? I'd like to
hear from you if you indeed have one up and running. Since fiberglass
tubing is shipped in 8 foot lengths, the two elements would be made up
of 4 eight foot lengths. The design has an element length of 26
feet. That means I'd have to discard 3 foot off two pieces. I looked
at the MOXGEN UTILITY Software and for 7.1 Mhz, the program shows you
all the other beam dimensions. They were as W7XA described except for
he shortened the two elements and made up for it with loading coils.
What I don't know is if I make the two elements longer to make use of
the full fiberglass tubing and then if I reduce the size of the
inductors to maintain resonance, will I upset the feed point
impedance? I'm thinking this will be the case. But, by altering the
length will I be able to find a 1:1 SWR at 7.1 Mhz ? The bottom line
to all this is, will I screw up the feed point impedance by making
the elements longer and have smaller loading coils? Then too, I'm not
sure W7XA actually saw 50 ohms at his feed point with his design in
the first place. Looking at the MOXGEN software, it does not appear
you can alter element spacing with it's program. It just gives you
all the dimensions without loading coils for a specific frequency.
(The only thing I see you can do with the program is put in the
desired frequency and you give the element diameter. Also, what
happens to the impedance if I use a longer boom like 20 foot instead
of 16 foot? I think the impedance would then change too. The MOXGEN
software doesn't allow you to pick different length booms. Anyone on
here brighter then me on this subject? Is there a better software
program for designing a Moxon Yagi beam then MOXGEN UTILITY?
Lee, w0vt
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