In a recent online thread, a ‘new’ online calculator was touted: https://miguelvaca.github.io/vk3cpu/toroid.html .
References without any qualification surely imply a recommendation.
Above, his calculation reconciles well with measurement at 3.6MHz.
Above is the same scenario calculated with VK3CPU’s calculator. An impressive GUI, if you like that sort of thing… and people do. Note the values at 3.6MHz in the cursor callout.
The value L is 7.06µH and it varies with frequency, but what does L mean. The notes state:
Tapping on a data point will display the parameters for a single frequency.
L(μH) : Inductance in microhenries.
Roger’s measured impedance @ 3.6MHz implies an equivalent series inductance (Ls in my calculators) of 3.965µH.
Though several posters to the thread have discussed VK3CPU’s calculator and the merits of it, it seems no one tried to reconcile it with Roger’s or any other measurements.
Wait a minute, v0.8 just released gives different values (including data for old #43 mix).
Now L=4.09µH which reconciles with Roger’s measurement.