Mike, you said
>Another way of
>thinking about this would be to consider the case where you would
>replace a 20" long inductor (used in a center loading configuration)
>with a very short closewound? inductor (say 5" long) having the same
>inductance value and Q and an equivalent amount of additional tubing
>to make up for the shorter inductor length (in this case 15" of tubing).
Well Mike, Any 20" long coil that we used would have already been closewound
and would have been for 160 or 75 if it had bigger wire. So to change it to a
5" long coil with the same inductance, we would have to either multi-layer,
increase the diameter, use much smaller wire, add a core or a combination of
these.
In our measurements, we used long and short coils and the current taper was
was almost identical if the topmast capacitance was held the same. If the
"make up" was above the coil, there was slightly less taper down of current,
due to the larger capacitance above. It would also resonate lower in freq.
It appears to us that the current decrease in the coil has most to do with
the section of the quarterwave element that it effectively replaces. The
actual decrease in our tests was always a little more than the decrease
calculated for the "replaced" section, no matter what coil was used. I hope
that answers your questions. Barry
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