Minor correction, the calculated relative permeability should be about
500, I made a mistake in the initial calculation. I just discover why
they call it initial permeability (bad joke) :-)

73, Dimitris VK2COW

Στις Σάβ, 12 Ιαν 2019 στις 2:48 μ.μ., ο/η Dimitrios Tsifakis
<[email protected]> έγραψε:
>
> Hi LF group,
>
> I have managed to acquire a few very large ferrite rods (36 cm x 10 cm
> x 2 cm). The material is unknown but I managed to form a square
> 'toroid' with four of them (they are heavy so gravity was enough to
> keep everything in place for a measurement) and I measured about 15 uH
> for 4 turns at 0.1 MHz, which if I have done the calculations
> correctly implies a relative permeability of about 1000.
>
> The R of the impedance of the square loop was low (<0.2 ohm) at 0.1
> MHz and it increased fast with frequency (170 ohm at 5 MHz!).
>
> The question is, what LF/VLF experiment would you do if you had half a
> dozen of these rods?
>
> 73, Dimitris VK2COW