[ARDF] fibreglass/kevlar yagis

[Matthew Robbins]

Dick Arnett wrote:

<<I do not know how you tell the difference between fibreglass or kevlar but 
in any case DO NOT handle the stiffener without gloves.  One of the 
installers was complaining of fibers in his hand weeks after touching the 
stiffener.  The ends of the optical fibers are even more dangerous.  Be sure 
to tape them up.>>

It's funny how someone can mention something and it makes you remember a 
whole bunch of stuff:

I know of two sources of fiberglass or other composite materials that might 
be useful for making antennas in small quantities.  (I say that because you 
pay enormous markup on these two, but if you're just making a few antennas, 
you might save it in postage.  If you only need small quantities, these 
might work.)

Source 1:  Sail Battens.  These are fiberglass strips that make sails in 
sailboards and sailboats hold a curved shape.  They are inserted in a 
"batten pocket" in the sail and the sails takes on a curved airfoil shape.  
Here's a picture.  I had a really hard time finding a source for these 
things, even using google.  I bought a few from a sailboat store here in 
Cincinnati, but West Marine seems to have them.  They go down to 1/2 inch 
wide.  The cross section is either tapered like a diamond <> or rectangular 
with rounded edges: (          ):

http://www.westmarine.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10001&langId=-1&catalogId=10001&productId=753

Source 2: Model Aircraft Pushrods.  These are used between the servos and 
the control surfaces.  The kind I'm talking about are these carbon fiber (I 
think) rods a little over 1/4 inch in diameter.  I couldn't find these at 
chain hobby shops---I had to go to a specially store that caters to Model 
Airplanes only.  I've forgotten the brand name.  (You also might find black 
fiberglass painted to look like CF.)

Here's a link that is *not* what I have:

http://www.nyblimp.com/superior/carbon.htm

At the very bottom of the next page is Carbon Fiber Rod.  I'd definitely 
call and check whether these are solid rods or hollow tubes.  (The tubes I 
have are almost solid with a small hole down the middle for gluing in the 
airplane hardware.)

http://www.nesail.com/composite.html

I'm not sure if either of these will work, and remember that carbon fiber is 
quite conductive (I've damaged NiCad batteries that were shorted with Carbon 
Fiber).

Back to what made me remember both of these: They have fibers that will 
embed in your skin and hurt for days.  The battens were the worst.  Run your 
finger along the batten, and you're wounded.  Once I hurt myself on the 
battens, I didn't take any chances with the CF pushrods.  I'd almost 
recommend painting them before you work with them, and to use heat shrink or 
something more protective than paint when you get it built.  Latex gloves 
might be good, if you don't slide your fingers along the material.

Last winter I had to work around some carbon fiber composite that had 
burned.  The epoxy had completely burned away, and all that was left looked 
like hair, except that when you moved it there was a cloud of tiny little 
carbon fibers.  I was wearing a tyvek bunny suit and a respirator, because I 
was focused on the respiratory hazard, and I forgot about wearing goggles.  
I didn't go to the hospital, but I had something in my eye for about four 
days.  It was very low level irritation, and on the fourth day, I said, "If 
this hurts tomorrow, I'm going to a doctor."  The next day it was okay, but 
mostly because I had been sitting in the hotel room pulling my eyelid out 
and blinking a lot.  If you cut this stuff, do it outside with the wind 
blowing (downwind from your house and from you) or have a pro do it for you.

One last idea.  You might go to the plumbing section and look at the plastic 
tubes for sinks and toilets.  They're 3/8in tubes, and available in lengths 
up to 24 or 36 inches.  They aren't perfect, but you should check them out.  
A thin fiberglass rod  near the middle of the span might make these useable. 
  The one I have is 3/8 by 30 inches and says "100psi 180F SDR 9".  I cut it 
with a PVC cutter and use it as standoffs for circuit cards in project 
boxes.  I think it's what Dale Hunt uses for 80m loops.  If you bend it, it 
will hold that shape, but if you can store it straight, it stays straight.  
When you bend it by hand, it holds the bend, but you can reshape it.  Just a 
thought.

Matthew Robbins
AA9YH
Cincinnati,OH

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