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RE: Flat Ribbon Conductors
>For my next coil I want to use a ribbon conductor for the primary to
>greatly increase efficiency (reduce the damped wave in the tank).
I don't think that losses would be significantly lower by using a ribbon
conductor. Most of the benefit would be that the resulting primary would be
smaller in diameter than a similar coil wound from tubing. By "the damped
wave", do you mean the primary ringdown? That has to be there. The
decaying amplitude means that the primary energy is being transferred to the
secondary circuit.
>Obviously copper would be the best (well, who can afford gold!),
Bringing your copper tubing to a plating shop to silver plate would probably
be the best thing in terms of reducing primary losses, and I'm guessing, it
may not be too expensive. You'd certainly have the best looking primary
around, and least lossy!
>but I am
>having problems locating any. I am a college kid, so I can't afford to go
>to an expensive custom sheet metal shop. I have heard that you can buy
>copper roof flashing (haven't ever seen any though)
It appears to be a regional thing. In the Northeast, all Home Depot stores
carry rolls of copper flashing in various (1-3 foot) widths (beautiful
stuff!) in their roofing departments. You can buy it by the foot.
>or you can use
>aluminum roof flashing. Has anyone out there tried to use aluminum roof
>flashing in this manner? Is there a recommended width that is best.
I've personally not tried aluminum but others with more experience have
pointed out that aluminum has a very high resistance oxide coating that
makes its resistance at RF frequencies undesirable. Others still have used
it and it worked, but probably not as well as any good copper primary.
>I suppose a wider strip would be more efficient, but it would also have a
>higher coupling co-efficient, so you'd have to raise the secondary up out
>of the field.
The width has nothing to do with the coupling. I suspect that the coupling
may actually decrease with increasing ribbon width, as the centerline of the
ribbon gets further away from the secondary with increasing ribbon widths.
>Suggestions anyone?
>Dan
If you're striving for a more compact primary, try a two layer copper tubing
primary - two flat pancakes, wound in opposite directions, joined at the
inside, with a layer of plastic between. This will be more compact, use
fewer feet of tubing with comparably lower primary losses, and will have a
higher coupling coefficient than a single layer coil of the same inductance.
Just don't expect to see miracles from lower primary losses, as the gap
(and capacitor) is where almost all losses occur, and is the thing that
improvements upon are most worthwhile.
Regards, Gary Lau
Waltham, MA USA