> > >> It seems, on the surface, that one could dip a small air variable in
> > >>(pure) water and have a high voltage part with 80x the capacity of the
> > >>original.
> >Or, if not water, some non-conductive liquid. Don't have a dielectric
> >chart handy, but there must be something suitable.
> Transformer oil (or nearly any mineral oil) would work quite well. The
> dielectric constant typically is just over 2.0, and the voltage insulating
> characteristics are excellent. A good application would be for the tune
> cap on 160 or 80 meters : a 150 or 200 pf, 1000V air variable would become
> a 300 or 400 pf HV variable cap.
When you look around and see the industry avoiding a method
there is almost always a good reason. In this case they are
probably concerned about loss of Q and heating of the component.
Dissipation factor is the ratio of energy dissipated to energy stored
per cycle. The dissipation factor would increase greatly if you pick
the wrong material.
As a second effect when you add a dielectric, energy is more
concentrated. There is more current in a smaller area. That also
can increase losses if you don't plan for it.
A third effect is drift. The component will change values with
temperature.
You need to look at more than capacitance.
Many materials also have an increase in dissipation factor with
temperature.
73, Tom W8JI
W8JI@contesting.com
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