OK, so I arrived somewhat in the middle of this thread re:
40M yagi construction, but here's my experience since 2009.
I bought a second hand Mosley (criticize the design if you
must) PRO 67C3. This integrated tri-bander has 3el's on 40. No doubt
Mosley's designs are dated and can be improved upon electrically, but
mechanically, so far, my experience is that they are nearly indestructible.
Upon receiving the antenna from the seller, I put it
through a through clean-up and refurbishment knowing that once hung at
70' I probably would have very limited access to it in the future. This
antenna has the benefit of a 3" boom which, rather than truss the
elements, I decided to truss the boom to reduce sag and to stabilize the
structure when in motion. The 40M elements are conventionally loaded and
so are slightly shortened, but they are HEAVY and create a LARGE turning
moment when in motion. This has proven, over time, to be the secret to
keeping this antenna in service. The elements are well enough double
sleeved, strong yet flexible, the boom, even the 3" option, needs
stiffening. A mast to boom truss made from coated wire rope, (criticize
that choice if you must), really gives this HEAVY antenna the super
strength it needs. As a testament to this set up, the PRO67C3 has broken
more rotors (ask W2GD) than any parts of the antenna itself.
Bill, W2ZKX
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