To All from PA0SE
Several amateurs have found that the current at the bottom end of the
loading coil is higher than at the top (aerial side) of the coil.
In my station the difference is of the order of 10%.
William, PA0WFO, has a large coil of 8 mH and a 23 m long wire as aerial.
He measures 1.5 A at the bottom of the coil en 0.6 A at the top.
My theory is that the "lost current" flows via the capacitance of the coil
to its surrounding (even a metal object in free space has capacitance).
The current at the bottom of the bottom of the coil divides between the
capacitances of coil and aerial.
I suggested to William he measure the capacitance of the coil and of the
aerial. For the coil he found 150 - 200 pF, depending upon the position of
the coil and for the aerial 210 pF.
But these values do not explain the large difference in current at bottom
and top of the coil.
In a transmitting aerial the current increases going from the end of the
radiator towards the coil.
Now to my question: does this increase in current also occur in the
winding of the coil? My feeling is that the current at the beginning and
end of a coil should be the same; apart from the current that flows via its
capacitance to the surrounding.
I also have read that the coil should be considered as an aerial with a
length equal to the length of the coil. But on 2 km
that would be an extremely small aerial, reckoned in wavelength. So
radiation by the coil must be negligible.
There are certainly experts on the reflector who know the answers. I
welcome their views.
73, Dick, PA0SE
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