Don raises interesting points. A couple of minor addenda. First, keep
in mind that "skin depth," iwhich is the tendency of an AC current to
flow near a conductor surface, is frequency dependent. The skin depth
approaches infinity at zero frequency, which means DC currents are
pretty much uniform throughout the cross section of a uniform wire.
On 160m the skin depth is about 50 microns.
Second, lines of current tend to repel each other (I.e., spread out)
because the magnetic field of the moving charges repel each other. In
an edge-wound inductor, the current density will be highest along the
outer thin side of of the inductor. IMHO there is an insignificant
performance difference between it and a traditional inductor.
73,
Jim w8zr
Sent from my iPhone
> On Sep 6, 2018, at 10:49 AM, Donald Chester <k4kyv@hotmail.com> wrote:
>
> Sat Sep 1 21:21:26 EDT 2018 Mike www.w0btu.com wrote:
>> It may very well be true that tank coils made from round copper have some
>> slight advantages over edge-wound. But after all is said and done, does
>> this really make a great deal of difference? :-)
>> I have an edge-wound roller inductor in my homebrew amplifier.
>> http://www.w0btu.com/833C_linear_amplifier.html
>> It's reliable, doesn't arc, and doesn't get warm. Isn't that what's really
>> important?
>
> I recently ran across this discussion on another radio forum, claiming that
> edge wound is inferior in terms of Q to round wire. It was said that on a
> flat strip, the current tends to crowd to the two edges for the same reasons
> that cause skin effect, thereby wasting much of the copper. Round wires would
> be less prone to this "crowding effect" because they have no edges.
>
> I checked out a few on-line sites, but they quickly get bogged down in long
> series of long, tedious mathematical equations, and I was not able to come to
> any clear conclusions. Some suggest that the subject is not well understood,
> even suggesting Terman's textbook is wrong, or that the effect is negligible
> if the radius of curvature at the edges of the strip is much greater than the
> skin depth. The skin-effect proposition makes some sense, although I had
> never thought of this. The closest I could come to a conclusion from the
> texts is in regard to the "proximity effect" of closely spaced parallel round
> conductors, in which the rf current density in each conductor crowds in the
> direction away from the adjacent conductor. The rectangular conductor could
> be thought of as approximating a large number of closely-spaced round
> conductors, so the current density would tend to crowd towards the edges of
> the conductor. I would like to see/hear some opinions on the subject.
>
> I can understand that primary advantage of edge-wound would be for mechanical
> reasons, for example for a rotary inductor where an effective sliding contact
> is more difficult with round wire. Slip-on coil clips like the ones EF
> Johnson used to make are designed to work with edge-wound coils. I would add
> that the spacing between turns with edge-wound can be decrease compared to
> the same amount of copper in round stock, thus increasing the number of turns
> per inch with edge-wound, resulting in more rigidity for a given thickness of
> conductor. Most broadcast transmitters, phasors and ATU units use edge-wound
> stock, so there must be a good reason.
>
> I threw together a prototype for the matching unit for my 160m vertical,
> using some badly corroded round-wire coil stock from the junkbox, with
> deteriorated plastic supporting strips. Once the final design of the coils
> was determined by trial-and-error, I built a permanent version, using
> like-new silver-plated edgewound coil stock, with the same coil diameter and
> turns spacing. I had anticipated slightly better efficiency with the final
> version, but as it turned out, the prototype and final version performed
> equally well, neither one any better or any worse than the other. With the
> same DC input to the final, the rf ammeter reading at the base of the
> vertical was exactly the same with either set of matching coils.
>
> Don k4kyv
>
>
>
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