Have you checked the design with EZNEC? A little more top hat and you
won't need a coil. I had an 80m top loaded 3" dia vertical 40' tall
which resonated at 3.8MHz. A tweak of that model to 70' showed the 8 x
8 ft spokes at the top would resonate at 1.8MHZ, 33 ohms. A perimeter
wire seems to help a lot for lowering the resonance according to the
modeling, but was not in your antenna model.
Grant KZ1W
On 9/8/2014 5:35 AM, rich kennedy via Topband wrote:
When base-mounting a loading coil (inductor) on a shortened monopole vertical,
is there a preferred method for the physical placement of the coil? Is it
better to orient the coil in the vertical axis, horizontal axis; very close to
the radiator element or a number of feet away; positioned close to ground level
or elevated (such as on a mounting post ~ 3 feet above ground)?
Assume freq = 1.83 mHz; H = 70 feet aluminum; soil = average to good; small
capacitive hat (spokes, 5’ diameter).
thanks, 73, Rich, K3VAT
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