On Fri, 15 Oct 2010 14:35:53 -0400, Mike Coslo wrote:

Back when we had more designers writing here, instead of Xerox junkies
and home-spun Platocrats, the discussion of shorted coils made them
apoplectic where those turns became huge losses. This is different
from the screwdriver approach which shields those turns.

I'm wondering where the issue comes from. As I look at it, the shorting
is making the bottom part of the mast slightly longer. I have to imagine
that not shorting it would be worse. Dunno, though.

Hi Mike,

That, too, was part of the raging debate. I have long forgotten the
particulars, but I will hazard their argument. That is, in these
highly reactive designs there are large potentials and high currents.
With those circulating currents (the usual province of these
considerations are in the tuner) AND the proximity of a shorted turn,
you have a transformer relationship feeding the loss of the small
diameter wire and/or the resistive short (rarely do switches offer
optimal solutions in the face of truly enormous currents).

Screwdriver designs pre-empt this through the coil being nested inside
of the conductive cylinder - no transformer action, or at least so
goes the argument.

Reggie entered into these issues with his own observations about coil
length, diameter, winding pitch, and placement to summarize his
optimal design. You may want to look into that insofar as your base
loading goes.

73's
Richard Clark, KB7QHC