Exactly, although of course a coil at the very top sees no current so
doesn't do any good there unless there is some capacitive loading above it.
Dave AB7E
On 7/20/2015 2:44 PM, Jim Brown wrote:
On Mon,7/20/2015 1:56 PM, David Gilbert wrote:
It all depends on the rest of the antenna, and yes, a very short
antenna with a crummy coil in the wrong place is going to suck. But
some of the best antennas on the market right now use coil loading
very effectively.
There was an excellent piece in QEX a year or two ago devoted to the
design of short loaded antennas. It was published in two parts -- one
dealt with measurement, the other with studying the effect of the
position of the loading coil.
The executive summary -- the part of the antenna carrying the greatest
current does the most radiating, and for most short antennas, that's
the part of the antenna closest to the feedpoint. The current
distribution depends on the electrical length, including that coil. A
loading coil near the feedpoint seriously degrades the radiation
efficiency of the antenna, because the current maxima is in the coil,
but the coil doesn't radiate! SO -- loading should be as far as
possible from the feedpoint! All of this was borne out by the
measurments.
73, Jim K9YC
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