[600MRG] Extra Turns - Open or Shorted or Removed

[Brian Pease]

I think your reasoning is sound.  The only problem I see with open turns 
is a possible high voltage at the open end.

On 3/31/2016 10:22 PM, Frank Lotito wrote:
> Any thoughts on what should be done with the unused turns of LF and MF loading coils?  For example, the RSGB book "LF Today, Guide to Success on 136 and 500 KHz" by G3XDV and M0BMU, 2nd edition, Figures 3-13 and 3-21.  In figure 3-13 the loading coils' unused turns are shorted. In figure 3-21 the unused turns of the 6 mH loading coil are not shorted.  We also see similar examples by the bushel full in the older literature for antenna tuners of many different configurations, PI and PI-L matching circuits, etc.
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> In my own station I have noticed that antenna resonant frequency changes if I remove the short at loading coil's unused turns (but feed the coil at the tap point where the short was attached.)  I can recover resonance by variometer readjustment and / or choosing another loading coil tap point.
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> Of course, with iron core 60 Hz AC transformers, or even a 60 Hz variac, the unused turns of a tapped winding are not shorted.  I know the reason for that.  But what about air-core coils used at LF and MF?  I would think there is some residual mutual inductance between the coil portion with the shorted turns to the active part of the loading coil.   That circulating current through the shorted turns, in my mind, acts as a loss, which means lower Q.  Obviously, we are reluctant to compromise the future utility of a higher than necessary inductance by physically removing the unused turns of an existing loading coil.
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> Your thoughts will be appreciated.
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> 73 Frank Lotito  K3DZ / WH2XHA
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