On Fri, 09 Apr 2004 11:31:16 0700, Jack Twilley
wrote:
the
transceiver has three turns of coax through three large rare earth
magnets. How does one model those with NEC2?
Hi Jack,
Magnets do not play any particular role in chokes. Magnetic cores
perhaps, but being magnetic is not in and of itself a remarkable
indicator of efficient choking potential.
Research the archives for ferrites, amidon, type 43 or 75 or 77 (there
are others), beads, and so on as terms.
As for modeling them, they are resistors. You can rate them at about
a Watt to 5 Watts (I've never tested one to destruction). Again, you
need the characteristics to know how much. The typical bead exhibits
about 20 Ohms in the mid to high HF region. The shape of its curve
(the resistance vs. frequency) is variable for any particular type.
Some increase through HF, others decrease, some don't even begin until
VHF.
Beads are additive. Two beads, 40 Ohms, three beads, 60 Ohms and so
on. Passes through a larger core (same material) sees a square law
effect X1, X4, X9 and so on.
73's
Richard Clark, KB7QHC
