The VK1SV toroid calculator

This is a toroid flux density (B) calculator that helps with the selection of a suitable toroid used in RF applications. For both ferrite and iron powder toroids, Amidon recomends not to exceed the values in the following table. Small variations of these values may exist for the various materials available.

Note: The value of such calculation using Amidon's method is questionable when one takes into account the specific properties of the materials used (relative permeability) at the frequency of interest, as reported in VK2OMD's article. In this article, an example is given for two same physical dimension toroids, one made with -61 material and one with -43. It is shown that the -43 material would result in too much heat being dissipated in the ferrite while the -61 would be fine, if operated at the 'safe' voltage indicated by Amidon's calculation...

The formula suggested by Amidon is the following:

The crossections Ae in square centimetres of some popular toroid dimensions are:

Enter E in volts RMS: Enter Ae in square centimetres

Enter number of turns N: Enter frequency in MHz:

The calculated flux density Bmax in gauss is:

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