[TowerTalk] 40 Meter MOXON Yagi

[Lee]

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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