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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