calculator for measuring the permeability of ferrite rods?

[coppercone2]

Torroids I found:
http://coil32.net/online-calculators/determine-toroid-core-permeability.html
http://zpostbox.ru/how_to_determine_permeability_of_unknown_cores_online_calculator.html

How about rods? Have any of you used a formula and compared it to the manufacturers specification so I can get an idea of how accurate a proposed method would be? I am only interested in signal level behavior.

Is there anything to watch out for, especially with long ferrite rods (like antennas?).. Like coil length in relation to the length of the rod?

This  table looks useful for determining effective permeability:
http://www.magneticsgroup.com/pdf/erods.pdf

But how about material permeability?
This is the best I found:
http://www.sklaic.info/forum/index.php?topic=175.0

Accuracy is kind of cryptic. Does anyone have more insight? And his graph disappeared.

[T3sl4co1l]

It's mostly air gap, so the best you can say is it's "good enough".

See:



Note that the curves cut off at higher mu, where they go asymptotically vertical (air gap dominates over core reluctance).

I would be surprised if you found any ferrite rods that were low enough permeability for this to matter.  Powder rods maybe, but those must be pretty rare, I've not seen any that I know of (I'm sure they're out there, though!).

Tim