Re: NEC-LIST: Hi-Q inductors

Eric,

The only issue I take with your approach is your use of
PVC in high power RF applications. PVC supports fire
if ignited by any source, such as an arc from any
component in a high power RF amplifier.

PVC is a particularly bad choice for any use in a high
power amplifier. I recommend that you rewind your
coil on a form that cannot support fire, such as
ceramic or porcelean.

Another example of bad RF engineering is the use of
combustible materials on antennas, particularly at
high power. There have been many cases where
cheap plastic insulators and traps with plastic housings
or coil forms have ignited. Can you imagine flaming
plastic dropping onto a wood roof or into a tinder
dry forest during a drought?

There's more to good RF engineering than high Q...

73!
Frank
W3LPL
donovanf_at_erols.com

<EVonvaltie_at_aol.com> writes:
> 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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