I have a problem with a 30m Moxon. It is a two element yagi with
aluminium elements & wire to make the rectangle. The wire is #16 silver
coated stranded with teflon jacket. The wire broke yesterday at the
element joints on one side of the rectangle. I assume one joint broke &
the wire was hanging vertical. The wind made the wire fatigue & the
second wire to element connection failed & the wire fell to the ground.
I used a Y or yoke arangement to tie the wire to the aluminium
elements.I didn't think the joint would fatigue in just 4 weeks but it
did. I might put in little eye bolts & hang the wire thru them with
the wire tip bonded to the element end. That might allow flexing & ease
the stress on the wire.
I have been reading my ARRL antenna book this AM. I built it using
Cebiks Moxgen formula. The boom is 12'10'' which was the software
spacing for the Moxon. I am thinking of going to a basic 2 ele yagi. I
can't change the boom length. I would just add aluminium to the
existing elements. It would be apx. 6' 6'' to each side of the
reflector & 5' 5'' to the driven element. The tips would probably be
3/8'' taper to 1/4''. A bit floppy in the wind but I think it would
survive OK.
My question is the spacing. I'm guessing the element spacing @ 12'
10'' is .23-.27 wave. It would be the minimum I could get away with &
still have gain & F/B. The impedance should be in the 40-60 ohm region.
That is also close enough.
Mosley markets a TW32XL 2 ele WARC beam [trapped] with a 12' boom. It
covers 30/17 & 12m. Commercial antenna makers of multi band trapped
antennas play with the element spacing & boom length to get a close to
50 ohm feedpoint impedance.
Anyone have any thoughts on my plan or at minimum how to releave the
stress on the wire /element connection?
K9IL
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