> Where can I buy a couple 12" or 15" Ferrite Rods, without mortagaging
> the house? Sure would like a coupla big ones to experiment with..!!
Have I got a deal for you.
Though the material isn't quite as good as that designed
specifically for antenna use, you can easily glue long form
factor beads, available in several materials, to construct
large and quite usable ferrite rods.
For instance, Digikey carries three kinds of beads from
Steward. There is a low frequency material that has flat
permeability in the thousands, out to about 100kHz, a medium
frequency material that has flat permeability in the mid
hundreds out to a megahertz or so, and a high frequency
material that has flat permeability of about 100 out to
several megahertz. You can buy beads that are about a half
inch in diameter for about a dollar an inch. I like the
15.88 mm O.D. by 28.58 mm long ones (5/8 in by 1 1/8).
If you want to take a look,
Go to http://www.digikey.com/
type bead in the search box.
under Filters, select "Ferrite Cores for Cables & Wiring,
under series, the LFB choice is the low frequency bead
material, 28B is the medium frequency material, and HF is
the high frequency material. (If you filter on the Steward
brand, these are the only choices that show up).
Pick any one of these series and click on "Apply Filters".
You will see all the choices of size and price for that
Once you have selected a possibility, you can take the
Steward part number to:
and look up the detailed specifications.
I have made several rods from each type by epoxying them
together, end to end, or clamping them together with a
length of nylon all-thread, though it doesn't matter much if
you use a metal bolt, because the flux stays in the bead,
and does not really have to pass through the bolt. Just
don't use large metal washers and nuts on the ends, because
they will intercept the flux passing through the rod end.
Use a nylon nut, if you can find them.
The high permeability, low frequency material may benefit
from having the ends lapped to a smooth and flat surface to
reduce the small gap between each pair. However, in some
cases, the rod may actually perform better (higher Q) if
there are small gaps between the beads. It is a trade off
between permeability and loss.