On Mon, 7 Aug 2006 10:09:32 +0100, Ian White GM3SEK wrote:
>Without a closed loop, no current can flow from one part of the circuit
>to another, so there can be no exchange of stored energy between
>electric and magnetic fields, and therefore no possibility of resonance,
>no coupling with the coil of a GDO, and no "dip".
Right. But I think we can agree that a half wave dipole looks like a series
resonant circuit ALL BY ITSELF -- that is, the exchange of energy
accomplished by the antenna closes the loop. The same is true of an antenna
like a typical quarter-wave ground plane antenna (i.e., a mobile whip). So
if you couple into that antenna, you'll see a dip.
Likewise, consider an active circuit driving a series resonant load. The
active element in that circuit (i.e., the tube or transistor) looks like a
short circuit WHEN IT IS POWERED UP, and completes the circuit, so you'll
see a dip if you couple into it.
Like every other measurement problem in the world, you must know what you
are measuring and how the measuring tool behaves.
73,
Jim Brown K9YC
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