[allowed] [TowerTalk] Re: Antenna element vibration damping -How

[David Robbins K1TTT]

> 
> Note: in the US, many cars come with a straight piece of stiff wire as

> an antenna. These "sing" when the car is at speed. This is the same 
> phenomenon as the beam antenna elements vibrating, because the wire is

> much smaller, the vibrations are at a much higher frequency. To 
> eliminate the singing, someone patented an idea: wrap a wire in loose 
> turns around the antenna wire
> (like 10 to 15 cm pitch). That kills the vibration. Now, all the US
> manufacturers have patented that design. This is not very practical
for a
> beam antenna, as the "wire" that would be used would have to be almost
as
> large as the element tube itself..

electric utilities use the same idea on hv lines.  Either a metal or
plastic spiral that goes around the wire is used to break up the
vortices.  On a large diameter wire (1.5-2" diameter) the spiral piece
is about .5" thick  with a pitch of 10-14" or so if I remember right.  A
smaller piece, maybe .25" or so might work on antenna elements up to
about 1"... unfortunately they would add to the wind load and also the
surface area for ice to accumulate.  It might be interesting to see
someone try it on a troublesome beam and see if it helps though.

Electric utilities also have vibration dampeners that look like little
lead dumbbells that they usually attach to the wire near the insulators
on towers.  These are actually lead or steel weights on a springy
support that absorbs the vibrations near the insulators.  I'm not sure
that something like this would work for an antenna though as the
oscillation mode is probably different than what those are designed for.

David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
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