>
>>>ALWAYS SHORT OUT UNUSED TURNS OF A
>>>TANK COIL, whether a roller or switched circuit.
>
>>? Amen. And the short should contain minimal R.
>
>I've had problems with a transmatch by doing that.
? As have I.
>When most of the inductor
>is in use, and there's only a few shorted turns, the currents in them can
>cause problems - even at 150 watts. Similarly, I've had problems with not
>shorting, because of resonance of the unused portion of coil with stray C to
>the operating frequency. If you short, then as Rich says, it should be a
>minimal resistance short, but be prepared to unshort if using most of the
>coil.
? Good advice, however, the switch and actuating mechanism adds
complexity. A simpler workaround is to put 1 to 2 uH in series with the
shorting circuit to automatically limit current through the shorted turns
to a reasonable value. // The 1 to 2 uH current-limiting inductor
should be made of at least as heavy a conductor as the roller coil.
- later, Peter.
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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