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It has to be twisted with its return line to make a controlled impedance. The twisting itself does nothing at the frequencies of interest. By your reasoning, just twisting a wire on a plastic rod would decrease the inductance.
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Two loose wires makes an open loop, in this case an open loop laying on a steel chassis--an iron-core inductor.
Twisting the supply and return wires ensures that the two wires carrying opposite currents are magnetically coupled (to each other, not the iron), and that their fields can substantially cancel.
-- Cheers, James Arthur
=A0That's
=A0----> =A0 |
| =A0 =A0 | =A0- =A0switched
| I =A0 | | |
=A0| =A0f =A0| | | load
=A0 | =A0 =A0 | =A0-
=A0 =A0. =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 =A0| =A0 =A0| =A0 = =A0 =A0 =A0 =A0 =A0|
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ssible at RF.
The actual equivalent circuit is a lot messier, with a spider web of stray 'L's everywhere, but yes, point taken--I can take a lot of heat off the load return wire if I can cram in a decent cap. If I'm allowed to revise the layout, there might be room for 10uF. Better than nothing.
That was a pre-existing bug, well outside my assignment. When doing a limited upgrade in other areas, with a limited charter to do just and only that, one just doesn't imagine a system so widely fielded would have these sorts of deficiencies, or look for them a priori. This one bit me.
-- Cheers, James Arthur
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Having written that, I'm not sure it's really an iron-core inductor if the core isn't passing through the loop. Part of my sleep-deprived brain thinks the iron actually couples the two parallel conductors' fields, canceling, just not as well as directly twisting them.
--James
It doesn't have to be twisted to make a controlled impedance--viz
300-ohm TV twin lead. Twisting is a convenient way to make two wires stay at a constant distance.And making a solenoid has nothing to do with what I'm talking about. Do the math, it isn't difficult--in the magnetostatic limit, it obeys Laplace's equation, which is about the simplest PDE going. It even works in 2D if you consider only the field--try it.
Cheers
Phil Hobbs
You mean they configured in such a way to create a common mode choke?
I don't see how that really effects L other than canceling. UNless I am not following something here ?
Jamie
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