Hi Carl,
Here's another case where mixing models can mislead us.
> >Series resistive losses (such as winding the coil from a lossy
> >material) in the coil have greater effect as the frequency is
> >lowered, while parallel resistances (the kind most people use) have
> >less effect at low frequencies.
>
> There I must disagree. Pure resistive losses due to skin effect become
> more pronounced as frequency is raised, not lowered. The same reasoning
> that is used in wire sizing for the tank coil should follow thru from
> anode to the output connector.
I'm talking about changing the material in the inductor, and the
effect on VHF impedance of the entire L/C combination when viewed as
a "black box". It appears to me you appear to be talking about a
non-coiled conductor with no parallel lumped resistance.
Is that correct?
The second confusion seems to be mixing in the effects of plating.
Plating changes losses very high in frequency a large amount, but
plating affects low frequencies very little. That's why silver
plating a copper LF tank coil only reduces corrosion,you might as
well just spray it with a good clear coat dielectric. Yet silver
plating a strip line greatly reduces VHF losses.
If we aren't talking about plating, if we are talking about changing
the base metal....
Changing the base metal to a lossy type has the largest effect on the
lowest frequency. As frequency is increased, LOSSY material have a
larger cross sectional area that carries current. Lossy materials
have a slower increase in resistance with frequency than very good
conductors. (That's why a carbon comp resistor is almost free of
skin effect resistance changes from DC to VHF, but a conductive
material is not. The less conductive carbon supports few eddy
currents and so has little skin effect. A conductive material looks
much "thinner" as frequency is increased).
I guess it becomes a question of what the goals are. If you want
less of a loss difference between HF and VHF, a more resistive
conductor makes sense. If you want more loss at VHF with less
disturbance at HF, use a thin resistive plating over a good
conductor would be better.
73, Tom W8JI
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