> I presume you're talking about a condition where there is so much
> shunting capacitance that the self-resonant frequency is approaching
> the actual operating frequency.
I haven't looked at this closely, but I know it happens when the
self-resonant frequency of the inductor is twice the operating frequency or
closer.
This is typical of several commercial coil designs when the antenna area
above the coil is small.
The important point is we should never use narrow bandwidth to assume low
loss. We can also make coils "too big" in small antennas.
73 Tom
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