Isn't the small inductor in an "L" network just there to cancel out
stray capacitance within the network? There was a good article in QST
on L networks a while back, and another good one some years ago by
Ulrich Rhode.
73,
Bob WB2VUF
Jim Brown K9YC wrote:
On Mon, 28 Dec 2009 18:50:28 -1000, Ken Brown wrote:
If that was exactly true, there would be only one setting that would
work. The 238 is not exactly an L network. It is actually a T network
with two inductors and one capacitor. One of the inductors is very
small, and in most cases is so insignificant that you can consider the
238 to be just an L network. In situations where the match is already
very close on the lower bands, or on the higher bands, either case using
very little C, you can find a match with either the big inductor at the
input or at the output. This would be Low Z position 1 or High Z position 1.
If this were not the case, Jim's earlier post regarding trying both
possible settings would be incorrect. Only one setting could ever work.
Thanks Ken. You're right, of course. Your post made me return to the manual
and open up the box to look at the second inductor, which is 5 close-spaced
turns of THHN around the (non-conductive) bandswitch shaft. Although I own
six of these tuners, I'd never studied them that closely, except to replace
blown caps and try to restring dial cords. :)
73,
Jim K9YC
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