tom wrote in
t:

I am getting answers that aren't quite for the question I thought I
asked, and that's a good thing.


I wrote something long, then deleted it, but one core idea persists...
Instead of going for rigidity and mass, you could try flexibility and minimal
mass, like a reed, feather or twig in principle. I made a 35 foot 'mast' for
an FM reception 1/4 wave dipole, from scrap. It lasted 15 years so far, and
might go on a lot further yet. It flexes to absorb wind blasts of up to 80
mph at times, or bird impacts, and is guyed (by its own coax plus a couple of
lengths of burglar alarm cable) at a 'static' node like that of a plucked
string, to minimise stress on guy wires. If any part gets hit, the whole of
it takes the strain. It looks like crap but it works and even though we don't
get heavy ice it would just crack and fall off it periodically if it got any.
Natural motion and flexing would see to that. I got the idea from seeing how
well reeds will stand long after winter hits them, and from realising that
the dynamics in the aluminium were similar. Its height is several hundreds of
times its width, and even if I'd had to scale that up to something much
taller, intended to bear more load, I think it might still work better than a
rigid tower. But it would be useless for strongly directional antennae.

Lostgallifreyan wrote in
:

tom wrote in
t:

I am getting answers that aren't quite for the question I thought I
asked, and that's a good thing.


... I got the idea from seeing how well reeds
will stand long after winter hits them, and from realising that the
dynamics in the aluminium were similar.

Crucial detail that did not survive the long reply I did not send, or get in
the one I did send: The aluminium was angle-sectioned, and used torsion as
well as bending to absorb force.

The insulated spacer and mount (crudely hacksawed hardwood from an old chair)
for the vertical dipole would damp the oscillations like a kind of 'anchor'
against the wind. The only time anything broke on it was a guy wire when mast
torsion made it bend and fatigue at the attachment point, but the mast never
fell even during the wind that did this to it, and this weakness can be
easily designed out. The metal mast never fatigues because it never flexes
beyond its natural spring tension at any point. If it did, it would have
fallen in weeks instead of lasting many years. The load at the top is only
about a half-pound, but the rest of the mast is less than double that, so
it's very efficient and cheap.