Bwana Bob wrote:
> Isn't the small inductor in an "L" network just there to cancel out
> stray capacitance within the network?
That is correct. It IS there, so it is a Tee network, not a simple L
network. If that inductor was not there, some loads could not be
matched, because of the stray capacitance. Because the inductor is in
there, the loads which otherwise could not have been matched, can be
matched two ways. One way is using the Low Z 1 switch position, and the
other way is using the High Z 1 switch position.
> 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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