Charles --

Thanks for setting me straight.  I had heard it was diamagnetism years ag=
o,
but your explanation makes more sense.

Karl

At 03:40 PM 9/25/99 -0700, you wrote:
>First:
>Karl, sorry, but diamagnetism may be present, but the main effect of RF
>tuning with brass slugs is due to the shorted turn effect of the slug.
>As the slug is brought into the coil it couples a shorted turn to the
>coil, thus lowering its effective primary inductance, thereby causing
>the resonance frequency to rise.  The key is to use a very conductive
>material so the Q doesn=92t take too big a hit.  That is the main drawba=
ck
>to the slug, Q has to go down from the coil=92s Q alone, conversely, the
>use of ferrite can be accompanied by an increase in Q (as long as the
>loss of the ferrite is low in comparison to the loss in the coil). So
>decreasing Q can be OK in an oscillator, but generally is at odds with
>tuned filter type applications where a constant BW is desired.  So to
>maintain constant BW, Q has to increase in proportion to the frequency
>(or inductance).


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