That sounds like a powdered iron core. It's good for high-Q inductors at
lower HF frequencies, such as for tuned circuits or transmitter output
filters. It's not so effective for common-mode RFI chokes because the
permeability is quite low.
Ferrite materials have much higher permeability, but also much lower Q.
On the higher HF bands, RFI suppression ferrites (#31 and #43) provide
an impedance that's more resistive than inductive: Q < 1. That's fine
for an RFI choke, but not for a tuned circuit.
To get the same impedance on the 160M band, you need about ten times as
many turns with #2 powdered iron (mu = 10) as you would with #31 ferrite
(mu = 1000), or about eight times as many as with #43 ferrite (mu =
600)--all for the same size core.
The technical data is available online:
<http://www.fair-rite.com/cgibin/catalog.pgm>
<http://www.micrometals.com/materials_index.html>
73,
Tim (KR0U)
rrath@charter.net:
The torroids I bought from Palomar were the T-200 model 120. This is
their mix 2, which is for .25 to 10 MHz.
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