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Author Topic: Optimum Turn-To-Turn Spacing for a Flat Wire Coil  (Read 787 times)
AA5WG
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Posts: 498




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« on: May 08, 2013, 04:36:58 AM »

Hi to all,

I read the optimum turn-to turn spacing for a coil is about the diameter of the wire.

What about flat wire that is wound broadside to the coil form?

Thank you,

Chuck
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N3QE
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Posts: 2303




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« Reply #1 on: May 08, 2013, 05:41:00 AM »

Generally having a diameter about the same to the length will result in the highest Q.

But there's a lot more to high-power antenna tuners than just raw unloaded "Q".

Many times other physical constraints (especially if you have nested or tapped coils like in a link-coupled tuners) result in different form factors. Multiband matching networks covering all of HF bands have by necessity many inter-related limitations meaning that they are not optimal in any one sense (like Q) but are optimal when all the constraints are applied. Single-band matching networks can be much closer to optimal.

e.g. in high-impedance systems - like the tank circuit in a link coupled tuner, or other places in other antenna matching networks - you want to reduce stray capacitance between the windings, and this is generally done with a longer, skinnier coil.

W8JI has pictures of some common inductor geometries with different possibilities, including edge-would coils like you ask about, at http://www.w8ji.com/loading_inductors.htm

And like I point out above, there are some additional physical constraints if you are building a link-coupled circuit or have a coil with taps to cover a broad bandwidth. In which case the coupling between link and tank coils is part of the design, and the coupling constant is very closely related to the inter-relationship between link and tank geometries. Look at Cebik's examples, or other designs on the web, or the pictures of tuners in shacks in old issues of QST (like the 30's through the 60's).
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