wrote:
Hi,

It seems that my location boasts 60 to 110 mph winds on a regular
basis. I had put up a 1/4 wavelength 20m vertical with 1/8 wavelength
radials elevated at 7 feet, with rope guys... and the wind blew it
apart like so much tin foil!

Same kind of location here, wide open to the Irish Sea.... but that
wasn't a big antenna, and with the guys it certainly should have stayed
up.

You're missing something here. Typical ham antenna structures are a
mixture of over-design and weak spots, so maybe you should look at the
wreckage in more detail and try to learn something from it.

OK, I just read your second posting and pulled this back from the
outbox. From the top downwards...

* Fishing rod good. Carbon fibre not good (possibility of losses and
detuning compared with plain fibreglass; definite loss of money compared
with plain fg).

* Copper pipe not good in these long lengths. Ask yourself why everyone
else uses aluminium.

* PVC pipe coupler not good... well, that you know.

* Again, copper pipes not good for radials. Copper pipe tees not good
for supports. If the top part hadn't fallen down, those pipe tees would
probably have been next to go.

* 3/4-in copper for your main support mast is a big mistake. The heavy
radials flopping up and down create a huge leverage at this point, so
that copper will be rapidly work-hardening and well on its way to
breaking (may well have done so by your morning).

* In your wind conditions, 1-in galvanized pipe is way too small for the
lower part of your mast. The only thing that kept it from snapping is
that something else broke first.

* Were your guys helping to reduce the bending forces at the point where
the coupling snapped... or helping to concentrate them? In your
particular case, I'd bet the latter.

The big lesson is that the construction of a copper J-pole for 2m will
not scale up to 20m wavelengths... basically because copper tubing is a
poor structural material, and as the model-makers say, "You can't scale
Nature." When you increase the scale by 10x, you have to use different
structural materials and techniques.

Again, ask yourself why everyone else uses larger tubing for masts; uses
aluminium, not copper; and doesn't use small, soft plastic plumbing
fittings. Have a look at HF antenna construction in the antenna
handbooks and catalogues, and do what they do... because there's a
reason for it.


Does anyone know of a decent commercial design for less than $1000 for

Hang on now - that would be spending money to *avoid* learning
something.

a free standing 30 to 40 foot support that can take this darn wind???

One option that's surviving very strong winds here is a tapering
fibreglass pole. I'm using a Spiderbeam telescopic pole that is almost
40ft high and strongly made:
www.spiderbeam.net/english/pole.php

The pole is tied to a very solid clothes-line post at about 7ft, and
also guyed at about the 30ft level to prevent the worst of the swaying.
In very strong winds it bends into an alarming S-shape, but by the
nature of fibreglass it also springs back again.



--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek