I have two 204BA's about to "go up the tower" - they include a modification
which I feel is worthy of mentioning here.
No matter what the yagi, except for Telrex', we have ALWAYS had element
rotation problems. There always are more birds on one side of the element
than the other, etc. etc.......bottom line, be it the HyGain plates, or
Cushcraft U-Bolts...whatever....they all will slowly deform the aluminum to
the point that the element can rotate.....bummer.
Standard operating procedurew for us now is to use inserts into the boom
which will allow you to pass a bolt through the boom, and tighten it down
WITHOUT having the tubing deform and losing its structural qualities....
How do we do this.....funny you should ask!
Plastic Lumber.....aka ReCycled 2 litre soda bottles mixed with a lil wood
fibre. We used to use wooden pieces turned down on the lathe but the rotted
and weathered and becam worthless over time.
For the two 204BA's under construction, I had the local full service lumber
yard rip a 3 X 6 piece of Trex (one brand name of plastic lumber) into 3 X 3
pieces....
Take the 3 X 3 pieces and on one end find the center (draw an X from corner
to corner) and at that point drill a small hole which serves as the location
for you to put a Lag Bolt (wood screw with a Six Sided Head) into it - sock
it down to the hilt with your socket wrench.....on the other end, mark the
center and just hit it with the center punch once or twice.....
You have just prepped the piece for turning on a metal cutting lathe. The
six sided head of the lag bolt goes into the three jawed chuck....and the
dimple on th other end goes on the rotating center.
This stuff turns quickly and easily....don't get carried away.........check
with the calipers and hen make sure it is an easy fit into the boom tubing.
With the boom plugs turned, insert them into the boom so that they are
centered at the element locations ( a turned block six or 8 inches long is
plenty).
For the 204BA's we first monted the boom to mast clamp onto a piece of pipe
and made sure the pipe was plumb......then:
We mounted the two piece element holding clamshells and elements onto the
boom.....checking they were level at the center of the element with the
bubble level (and rechecking the pipe mast to be sure it was still "on"
bubble.
With an element level, we then proceeded to drill through the tapped holes on
the clamshell plates (remove those nasty steel four sided nuts first). Slide
a 3" long stainless steel bolt through the holes in the clamshells and the
boom with its plastic lumber insert....tighten it down with a stainless
ny-lock stop nut....and you know what....that bad boy ain't gonna rotate no
more!
The mechanical engineers on this reflector will be quick to point out that
any time you put a hole into the side of a tube (aka our pinning bolts) you
will weaken the tubes inherent strength....this is true.........however:
The inner slug of plastic lumber keeps the boom from crushing, which
inevitably is what happens with any other method of trying to grip onto the
boom, and any time you make the boom NOT a perfect cylinder the strength goes
to hell anyhow......be it from dents that the u-bolts or clamshells create,
or whatever.....
MY PERSONAL OPINION is that this is a better way to go, rotation is no longer
possible, period....nope, nada, zilch! Since I truss all my booms I doubt I
will ever even think about a boom failure.....
It works for me!
Now to get those two up in the air before "the season" - tic toc tic toc
k4oj
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