[RFI] TV RFI - an update 2

[Tim Groat]

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 at 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.