Bill Ogden wrote:
One ARRL stand (at Dayton) handed out small, black foam balls that are
intended to be stuck on the end of a whip antenna. Stops corona (maybe --
let us skip that discussion).

I do not normally have a transmitter in my truck, so I stuck the ball on my
standard truck radio antenna. (It is a 2003 Ford Ranger.) Since doing this
I have noticed that the antenna almost always vibrates a little -- even
after sitting stopped (engine off) in the garage for many minutes. The ball
on the top moves at least 1/8 inch; it is easily seen if I focus on it.

It appears I have a good resonant antenna to sustain this motion for long
periods, across an almost 3:1 range (the AM broadcast band) and a bonus VHF
range (the FM broadcast band). I assume that Hooke's law (if I remembered
the right name for it) applies instead of the
break-from-metal-fatigue-or-metal-work-hardening-law will apply such that
the antenna does not snap off sometime.

The principle behind Hooke's Law is only one element in determining the
resonant frequecies of vibrating bodies. Oops . . yeah, I know, that
could be taken . . ah, never mind. Moving along there is no such thing
as a "work hardening law".

What you have is a simple fully restrained fixed end cantiliver beam
with a point mass on it's far end. Your "system" when excited by random
forces like wind impingement loads vibrates *mechanically* at it's
natural freq and it's harmonics which can cover any number of octaves.

Your "system" won't crap out due to vibration unless the skin stresses
in the rod exceed the specific (published) endurance limit of the
material.

"The rest is left as an exercise for the student to bumble thru."

None of which of course has a friggin' thing to do it's characteristics
as an antenna. Which you already knew. Tnx for the troll, gave me
something delightfully useless to do while I finished off this double
magnum scotch 'n water.


Perhaps I should patent this
resonant antenna that is almost frequency independent!

Go for it William, you can't miss, the patent office hangs numbers on
any brainfart which comes down the road these days. At worst you'll be
able to claim that you're an "inventor" of record. Brag points are
where you find 'em.

Ditty dah dit dah.


Bill
W2WO

w3rv