>>> Jim Brown K9YC wrote:
>>>
>>> "There is a MAJOR advantage to using a ferrite core -- it makes the
>>> choke RESISTIVE rather than inductive."
>>>
>> With respect, I don't believe this to be correct. >>
>> 73 Roger
>> VE3ZI
>
> This depends on the type of ferrite material. Some are designed for very
> low loss for use in transformer and inductors. Others are designed to
> have significant loss characteristics for use as RF absorbers and
> common-mode chokes. > 73, Ward N0AX
_____
We're not quite to the answer yet...
Yes, ferrites like 31 material maintain resistive characteristics down to
lower frequencies than most ferrites. This is extremely valuable for general
purpose EMI suppression, but it does not improve performance of a choke
balun.
As with any transmission line transformer, a balun's "choking action"
depends on total impedance -- the vector sum of the reactance and
resistance. It does not matter whether L or R is dominant, as long as the
total value is high enough to effectively eliminate common mode current
flow. [For a high power balun, low R is desirable for minimum heating.] At
low frequencies, high inductance is readily achieved with high permeability,
but resistive loss is harder to get since all ferrites, including 31
material, have peak resistive (absorption) properties in the VHF range.
73, Gary
K9AY
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160 meters is a serious band, it should be treated with respect. - TF4M
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