I have just read some recent correspondence on this net concerning the pros
and cons of placing the antenna loading coil in the shack or at the base of
the vertical aerial wire.
The loading coil is not just a matching device, it is also a primary source
of vector potential and it is the vector potential, rather than its
offspring, the magnetic and electric fields, which is the fundamental
source of electromagnetic radiation. It is therefore advantageous to place
the coil upright at the base of the antenna. Furthermore, as a large
component of the vector potential is locally concentrated in this region,
it may be possible to gain a few dBs by placing an aluminium or copper
plate, somewhat larger than the diameter of the solenoid, a few centimetres
under the solenoid, insulated from the earth but it may be connected
directly to the TX ground terminal. (It reflects the vector potental
instead of allowing it to be absorbed in the terrain, but DON'T stand on
the plate to adjust the solenoid whilst running at full power !!!).
I appreciate that some readers may not be au fait with vector potential
and perhaps its fundamental role deserves to be lightly aired in the
amateur radio journals.
73, Roger, G2AJV.
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