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Re: [TCML] air core

As long as the form is clean and dry enough that there isn't any discharge along the surface the performance will be pretty much independent of the material. I've experimented quite a bit with making coils for receivers using various forms of PVC tubing, ordinary mailing tubes with or without drying and sealing, and even a piece of wood and couldn't tell any difference in the Q at 4 MHz, well above the frequency of most TC's. The purpose of these particular tests was a report that some forms of black and grey PVC pipe were quite lossy when used for coil forms and that sure wasn't true for my cases. I certainly agree about the 'art and appearance' business. A neatly wound coil on a 'good looking' form can be a real thing of beauty!


Jim Lux wrote:

On 11/10/12 3:32 PM, JJR+weluvlucy.com wrote:

Hello to the list,
Has anyone ever built a secondary coil without a coil-form. Wouldn't air
be the ideal coil-form because it has a dielectric constant of 1?

the dielectric constant doesn't necessarily change much in the way of performance .. what you worry about is loss (disspation factor, loss tangent, etc.)

I suppose that having a different Cself for the secondary might change things a bit.. However, I think from a "spark generating" standpoint, my gut feel is that topload C is more important, because it can feed the growing streamer.


how would one wind a secondary of lets say 20 gauge wire with an end
result of no plastic, paper, wood, etc. coil-form?

You could use an insulation that sticks to itself (perhaps by heating).

Greg Leyh did something similar to this for Electrum...I think he wound the secondary on a cardboard form, coated it with resin, then pressure washed the form out after it was done.

I think that performance isn't the reason you do these things, it's art and appearance.

Certainly there are things you could use for structural support that are better or worse.. you want something with decent dielectric strength, but that has low dissipation. Fused silica or sapphire?

 Is it possible to

wind the coil then remove the core that it was wound on. Also, doesn't
coating the coil with some form of urethane etc. add capacitance to the
coil which is undesirable?

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