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Re: coil form questions
From: Bert Hickman[SMTP:bert.hickman-at-aquila-dot-com]
Reply To: bert.hickman-at-aquila-dot-com
Sent: Sunday, November 16, 1997 11:02 AM
To: Tesla List
Subject: Re: coil form questions
Tesla List wrote:
>
> From: randy-at-gte-dot-net[SMTP:randy-at-gte-dot-net]
> Reply To: randy-at-gte-dot-net
> Sent: Sunday, November 16, 1997 2:34 AM
> To: tesla-at-pupman-dot-com
> Cc: rwall-at-ix-dot-netcom-dot-net.pupman-dot-com
> Subject: coil form questions
>
> I tried to post some of these questions previously, but either the
> post didn't make it or the replies never made it to me.
>
> 1.What about fiberglass? If properly sealed, would this make a suitable
> form material? They do make helical-wound 'glass antennas for HF use.
> 2.What about tapered coil forms; any problems here?
> 3.What about those orange "road cones" for traffic control. The usual
> variety that I see are one-piece semi-rigid or rather floppy, but I
> have seen 2-piece (base,cone) type that are somewhat stiffer.
>
> Any thoughts would be appreciated,
> Randy Venable
Randy,
1. Should work fine, but you may want to seal it after baking it a bit
to prevent any absorbtion of water during humid days. The material's
dielectric loss is significanly less than PVC, but it's dielectric
strength is lower.
2. No major problems here, except that you won't have as efficient a
coil. The "Q" of a tapered coil is lower since it doesn't have as
"sharp" of a resonant frequency as a cylindrically-wound coil. The other
potential (npi) problem is that you may get premature breakout at the
top of the winding due to its reduced radius of curvature. As long as
the top is not "too" small a diameter, and you use a large enough toroid
to shield it, you should be OK. Finally, the taper may cause the coil
windings to want to "slide off", particularly if you're using a slippery
LDPE or HDPE form.
3. Depends on the variety. I've seen some that seem to be about 15" at
the base, tapering to maybe a foot at the top - these should work very
well. The others seem like smaller cones but scaled up top be about 3'
high - these may suffer more from the effects above.
Try it out and let us know how it works!
-- Bert --