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The inductance of a single loop of wire will increase in inverse proportion to its diameter. Are there exceptions to this rule when applied to multi stranded wire (not litz wire). I should make it clear that the diameter refers to the wire used to form the loop.

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    \$\begingroup\$ huh? are you saying that smaller loops have higher inductance? \$\endgroup\$ – Jasen Jan 14 '16 at 9:01
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For a notionally thin wire, you can say that the magnetic flux produced by any part of the flow of current couples to flux produced by all other parts of the flow of current. This maximizes the wire's inductance.

When the effective cross sectional area of a wire gets larger, current flowing on one edge of the wire can produce a small amount of magnetic flux that does not couple entirely with current flow on the opposite edge. This begins to degrade the overall inductance of the wire.

In an extreme scenario, you could imagine a wire being cut down the centre so that the current splits into two distinct and separate paths. If these two half-wires are at some distance to each other, very little magnetic flux will couple from one half-wire to the other and the net inductance will tend to become 50% of when those two half-wires were united as a whole.

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  • \$\begingroup\$ In the experiment in which 17 ft. of 44/030 was used as a transmitting loop at 7 mhz the r.f resistance(0.900 ohms) and the inductance(9 uh) were much greater than predicted by formula which does indicate that the effective diameter is much less than stated . \$\endgroup\$ – maurice murphy Jan 15 '16 at 9:11
  • \$\begingroup\$ Well, that's nice to know but I neither know what formulas you used nor have I any idea how you physically constucted the loop. Neither do I know if there were any ferrous objects in the vicinity of the loop and neither have you said how much bigger the inductance actually measured was. I don't understand your measurement method either. A lot of uncertainties here dude. \$\endgroup\$ – Andy aka Jan 15 '16 at 10:07
  • \$\begingroup\$ I will also add this. 7MHz has a quarter wavelength of about 11 metres. 17 foot is 5.2 metres. Because of the relative closeness of these two numbers you will be beginning to see a good few percent error due to standing waves i.e. the electric field and magnetic field will be starting to form a true electromagnetic wave (radio transmission) and this will certainly affect your resistance and inductance more than you might expect or have considered. Add to the is the feed wire length that you may have used (and the mismatch to a quarter wave) and strange things can start to happen. \$\endgroup\$ – Andy aka Jan 15 '16 at 10:14
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the answer is that when calculating the inductance of a multi stranded wire it is the effective diameter that is relevant to formula.

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