Re: NEC-LIST:Effects of boom-to-element connections on YAGI

Subject: NEC-LIST:Effects of boom-to-element connections on YAGI

I havn't done enough work to be certain that the following is fully
accurate, but at least it gives an estimate..

Model theantenna from one end to the plate in the usual way.
Model the plate with actual length and an " equivalent radius", about 3
segments long
Finish from the plate to the other end of the antenna in the usual way.
According to the 1994 ACES Convention, the equivalent radius is:

R=(SQR(area/PI) + Perimeter/2*PI)/2

To check the accuracy, determine the resonant frequency of the element and
plate, no other elements present,
at the height to be used in test, with best estimate of soil conditions
(best if above 0.2 wavelengths). Fastest way seems to be successive trials.
Measure the actual antenna element using a grid dip meter, moinitored by a
frequency counter for accuracy. A special coil with a long straight section
( D or coat-hangar shape) is helful, or a few pf from one side of the coil
to the antenna end. Close coupling is needed so the dipper is "pulled" to
the antenna resonant frequency.

See Lawson's discussion in his Yagi Antenna Design (from ARRL) for a method
of estimating.

Hopefully, the question will start a thread on the effects of clamps, size
changes, etc.
bob w4mb

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