Hi All,
> All of those above frequencies are ONLY for reasonant circuits. For
> wideband use in baluns, etc. the frequencies are VERY different.
> For instance Ferrite Mix 43 is now 1-50MHz and 61 Mix is now 2-100MHz. It
> pays to read all the specs. Also note that any of those specs are not
> absolutes; they are suggested for optimum performance but are not cast in
> concrete.
To further complicate the problem, the type of transformer or balun
and the power level also affects core selection.
> When dealing with ferrite it is particularly important to consider the
> loss tangent of the material at the frequencie(s) of interest. That is
> why I KEEP stating that cores with a mu of 5000 and 10000 are no good for
> Beverage xfmrs unless you want them as a dummy load.
Carl is certainly correct, but another important fact is permeability
of all iron cores drop rapidly at some upper frequency.
Above that frequency, the core can actually DECREASE the coupling and
inductance of the winding. It's more like the transformer was wound
on a rusty nail than a proper core. The eddy currents in the core can
actually make the core DECREASE the coupling and inductance over
just plain old-fashioned air!
At 100 KHz the perm of the typical ui=10000 type cores begins
to drop, and is often less than 100 by the time 160 meters is
reached.
Why use a core providing an operating frequency permeability of 100
or less, when other materials with lower loss would easily be near
the 1000 area at the operating frequency? We aren't building
100 KHz antennas.
73, Tom W8JI
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