In a message dated 3/27/2001 13:32:42 Eastern Standard Time,
> Is it somehow possible that the mechanical resonances in the elements
> could feed through to the mounting bracket on the boom and cause some of
> the rivet failures F12 have had with some of their antennas? For those
> who don't know what I'm talking about, I'm referring to some of the
> failures in the rivets that hold the element brackets to the boom. I'm
> trying to figure out what caused this (so it can be prevented from
> happening again) and was wondering if resonances could have been a
> contributing factor (in addition to them using the wrong rivets)?
There have been discussions how good, beneficial and revolutionary rivets are
in the Force 12 antennas. I think this is wrong application for use of
rivets. Rivets should be used to hold two pieces together and be stressed on
compression, like squeezing two sheet metal plates (airplanes, bridges).
There is multitude of them squeezing the plates and connection is made by
friction between the plates. Using rivets as a pivot fastener (not sure about
English terminology) like in Force 12 elements, or element to boom clamps is
wrong. There, rivet holds two circular pieces of tubing together with room to
move. Being in soft aluminum and with all the wiggling and vibrations they
will eventually work themselves loose. The result is first bad connection and
eventual divorce. The same goes for element to boom clamps. Whenever there
are just few rivets and connection prone to some play, vibration or sheering
stress, sooner or later failure is in store. I bet that many riveted antennas
will sooner or later fly apart.
There is nothing better than good old hose clamp with slit tubing. You have
good all around compression fitting, good electrical contact and continuity
on the surface for RF to flow smoothly without being forced to go inside and
out of tubing joints :-)
Even the old Hygain clamps with screws are not so good, they bite into the
tubing, bitch to take apart years later and they do not provide full
circumference contact between two diameters.
If you see anything vibrating or singing in the wind, take the sucker down,
before is too late, or you will be looking for pieces in neighbors yards.
I had commercial antennas fly appart (except 3rd hand TH6), but none of the
home brewed Razor monsters did. I used tapered booms with only top strut,
home brewed element to boom clamps with muffler clamps and hose clamps for
element junctions. Rope inside of Yagi elements.
VE3BMV, VE1BY etc.
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