Topband: Air Wound Coil

[Donald Chester]

Besides the advantage in roller inductors, edge wound more easily accommodates adjustable taps, using slide-on clips.  It also makes the coil more mechanically stiff, for a given number of turns per inch than does round  wire.  That's probably the reason that edge-wound stock is more often used in AM broadcast transmitters and ATUs, than round conductors.

I threw together a prototype for the matching unit with my quarter-wave 160m vertical, using pieced-together corroded scrap coil stock from the junkbox.  After the design was completed, largely by trial-and-error,  using shiny new edge-wound coil stock, I built the final permanent version, with each coil the same diameter and length, and same number of turns per inch.  The final version behaved precisely the same with the same efficiency as the prototype using the junk coil stock.  No better, no worse.

Don k4kyv
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From: Richard (Rick) Karlquist <richard at karlquist.com>
 
Edge wound is inferior in terms of Q to round wire.
It only makes sense for a rotary coil, where it needs to be edge
wound for mechanical reasons.  On a flat strip, the current
crowds to the two edges for the same reasons that cause skin
effect, thereby wasting most of the copper.  Round wires are
immune from this because they have no edges.

73
Rick N6RK