Topband: Toroidal common mode choke

[Tom W8JI]

> Also the difference between Mix 31 and 43 is not great and was used for 
> decades successfully before 31 was introduced.


For a non-critical application like this almost anything would work with 
enough core depth and/or turns, but they are not nearly the same. There is a 
large difference between 43 and 31 material.

31 has an initial perm of 1500 and slopes down with increasing frequency, 
with a Q of unity at around 3 MHz.

43 has an initial perm of 900 and slopes down at 1 MHz, with a Q of 1 at 
around 15 MHz.

Both have a curie temp of around 130 C.

About half the permeability is not the same, and the Q=1 being five times 
higher in frequency is certainly not the same.     31, with lower Q across 
HF, is a significantly better suppression material.