NEC-LIST: Hi-Q inductors

I have personally built and tested many inductors, usually aimed at Hi-Q for
RF applications.I have found it difficult to get above 250-300 using the best
materials and winding techniques.

For applications to antenna loading coils and PI-Network coils in xmitters,
I would like to pass along a technique which I have developed within just the
past year, which is easy and works consistently well.

I utilize a coil form of ordinary PVC pipe, with diameter of 1-4 inches,
which is a home depot items. An additional, but not necessary, addition is the
PVC end caps, which make a nice device for retaining the wire. Also, this
material is very easy to work with and allows you to fabricate mounting hardware,
holes for exiting the wire, etc.

The winding is done with #12 or 14 TFE stranded teflon hookup wire. This wire
is silver plated and the insulation is thick enough to provide almost all of
the benefit that comes from spaced winding. To eliminate the "proximity
effect" from close wound turns, it is only necessary to allow a gap of several
skin-depths between turns. The 20 or 30 mil teflon insulation does this quite
nicely and the teflon has minimal loss in the small electric field of the winding.

I have wound many coils, and for the last year I have used this technique
exclusively. The results are coils that CONSISTENTLY measure within 10-15% of the
common inductance formula, which I will repeat here for reference, and
measured Q's in the range of 200-300. As further proof, I offer the example of the
tank coil in my 160M. amplifier. It is wound on 2.5" PVC with about 25 turns
of #12 TFE, and when run at 1.5KW OUTPUT, the coil is just slightly warm to the
touch. A little calculation shows that this implies a very high Q(unloaded)
of the coil.

A convenient form of the inductance formula is as follows, where N=#turns,
d=diameter (inch) and l=length(inch):

L(uH)=N(squared)xd/(18+40l/d)

73
Eric von Valtier K8LV

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