[Amps] construct ferrite "line isolator"

[Ward Silver]

> The Palomar data sheet says #6 is good for 2-30 MHz. 

Part of the problem is that what is "good" for use in an energy storage or transfer device (an inductor or transformer) is not the same as "good" for use in an RF suppression device.  If you are building an impedance transformer, you want complex permeability that results in very low loss.  If you are trying to soak up common-mode RF, you want complex permeability that results in dissipating energy.  Using a core designed to make good inductors can actually make RFI problems worse by creating a resonant circuit or by cancelling capacitive reactance already present.  (This is a far more complex subject, so to speak, than can be discussed in a short email.)  

You have to look at the complex permeability of the material to determine the characteristics of the resulting impedance. Most plots of impedance versus frequency for ferrite materials (including Fig 27.18 in the new Handbook) only show impedance magnitude without phase angle.  The result is that it's not clear why #31 material is much better for RF suppression than #43 material at lower HF frequencies - the magnitudes of the impedance simply aren't that different.  You have to look at the permeabilities, as is covered in the 2010 and 2011 Handbooks in Chapter 5.

We're trying to make this clearer, but it is relatively new information (to hams) and will take some time to "permeate" the amateur radio world.

73, Ward N0AX