[Amps] Edge wound inductors

[Tom W8JI]

> Isn't it mostly about being able to make a really good 
> sliding contact
> to the two flat sides?

The factors that affect optimum form factor of an inductor 
would fill a good sized book, but the edge wound tape does 
two good things besides the obvious mechanical tap 
attachment advantage.

First, the turn-to-turn center spacing can be smaller 
without increasing turn-to-turn capacitance to the value of 
tubing. Turn-to-turn capacitance kills Q in high reactance 
inductors. A more compact length increases mutual coupling 
from end-to-end and reduces inductor physical length for a 
given inductance and current rating.

Second, eddy currents decrease. This also increases 
inductance for a given size and reduces heat and loss 
resistance.

Measuring edge wounds and tubing or round wire in a good 
test fixture with good gear at HF, I find edge wounds have 
about the highest Q of any inductor I've ever 
tested...generally up in the area of Q=1000.

While we can do very well with tubing in low or moderate 
reactance inductors and we might not need the additional 
component Q when the operating Q of the system is low, there 
isn't much bad about them and they are easy to find and easy 
to work with. They even work well in the rain.

73 Tom