----- Original Message -----
From: "Mike Harris" <mike.harris@horizon.co.fk>
> I'm wondering how the "effective diameter" of element to boom mounting
> plates is calculated.
>
> In the ARRL Antenna Book the mounting plate for the 20 metre Yagi elements
> is 0.375 inch thick, 6 inches wide by 8 inches long. This is quoted to be
> electrically equivalent to an effective diameter of 3.7063 inches for the
> heavy duty element and 3.4194 inches for the medium duty element. So
> element diameter is also a factor.
>
> The calculations in the spread sheet "Element Strength and Equivalent
> Length" Leeson 1991, released by the ARRL seems to come up with a
> different number i.e. for the heavy duty element 2.08 inches, if I'm
> reading things correctly.
There is considerable material (with references) on this subject in
Dave Leeson's book "Physical Design of Yagi Antennas". Chapter 8
deals with element taper equivalent cylinderical diameter calculations
and Chapter 9 gives information on mounting clamp and other
non-circular cross section equivalent diameters. I think the element taper
equivalent cylindrical diameter calculations used in EZNEC for instance
our based on Leeson's work.
73 de Mike, W4EF..............................
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