A first approximation of the effectiveness of a choke in a specific
installation can be computed in NEC by adding a resistive load equal to
the resistive choking Z to the model, which includes the feedline as an
element of the antenna, including the physical geometry of the feedline
and it's connection at the station (for example, to an entry panel
bonded to premises ground).
A better approximation would be provided by adding the parallel resonant
equivalent circuit of the choke, computed empirically from the measured
impedance curve. One of my more valuable EE courses was freshman year to
develop equations like this.
And it's important to realize that results need not be computed to the
smallest knat's ass to be useful. One of my favorite stories from EE was
about the engineer and the scientist drinking at one end of a bar, with
a hot chick at the other end. The scientist never got there, but the got
close enough for practical purposes.
73, Jim K9YC
On 1/23/2026 11:18 PM, Brian Beezley wrote:
Measurement of the choke and the feedline at the point of installation
lets you calculates the benefit of adding the choke:
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