Roy Lewallen wrote:
Bear in mind that the impedance of multiple turns is proportional to the
square of the number of turns. So 5 turns, for example, through a single
core gives you the same impedance as 25 cores strung along the line.

Something that fooled me is the way Amidon specifies
"one-turn" impedance for beads in their brochure. Their
"one-turn" for beads is a wire running through the center
hole, wrapped around the outside, and back through the
center hole. (I would count that as two turns and
would say one-turn is just a wire running straight
through the core.)

As a result, for their FB-77-5621 bead, for instance,
they specify 270 ohms per turn. If one simply threads
these beads over RG-58, the impedance is about 1/4
of that amount, i.e. about 67 ohms per bead, requiring
about 15 of them to get to 1000 ohms.

As Roy says, ten turns of coax on an FT-240-77 core
is roughly equivalent to 100 FB-77-5621 beads strung
over coax.

Interestingly enough, Amidon specifies "one-turn" on
an FT-240-77 core to be 76 ohms, obviously a different
kind of "one-turn" than that of the 270 ohms for an
FB-77-5621.
--
73, Cecil http://www.w5dxp.com