This article reports measurement of two ‘FT240-43’ cores (actually Fair-rite 5943003801 ‘inductive’ toroids, ie not suppression product) purchased together around 2019, so quite likely from the same manufacturing batch. IIRC, the country of origin was given as China, it is so for product ordered today from element14. The measurements are of 1t on the core, with very short connections to a nanoVNA OSL calibrated from 1-50MHz.
Above, the measurement fixture is simply a short piece of 0.5mm solid copper wire (from data cable) zip tied to the external thread of the SMA jack, and the other end wrapped around the core and just long enough to insert into the inner female pin of the SMA jack.
Based on the datasheet, we can calculate the expected impedance at 1MHz.
So, around 0.5+j6Ω is the expectation.
The two cores I measured are 0.16+j5.34Ω and 0.53+j6.32Ω, not a lot of departure though the first has quite a lot less core loss (the R component).
Above is a wider range prediction based on the published data. At the cross over frequency of 14MHz R=X=24Ω.
Now to the two sample cores that I measured.
Above from the first sample, the R curve is quite similar to expectation, but the X curve is quite different, it does not roll off nearly to the extent predicted above. As a result, the cross over frequency (R=X) is well above the expected 14MHz, around 46MHz in this case.
Above from the second sample, the R curve is quite similar to expectation, but the X curve is quite different, it does not roll off nearly to the extent predicted above. As a result, the cross over frequency (R=X) is well above expectation, greater than 50MHz.
So, in summary, the tested cores exhibited X, and therefore µ’, quite similar to the datasheet at 1MHz, but at higher frequencies X and µ’ were quite higher than expected.
I have tested a lot of #43 material in various shapes and sizes of cores, and this is the first time I have observed this effect. Ferrite products have wide tolerances, and certain characteristics are controlled, I could not say whether these meet the controlled parameters.
Such variation certainly makes identification of core material, designs and prototype measurements more challenging.
I might mention that Fair-rite issued a new table of permeability characteristics for type #43 in Feb 2020. The results measured here for two year old purchases are even further from the ‘new’ #43.