It is very important to place the first insulator as close to the tower
as possible (3-4 ft) because the tower connects the guys, forming
a continuous "element" right under your Yagi(s) equal to the distance
from insulator, through the tower, and back to another insulator.
I like to space my insulators 3 - 12 - 12 - 27, or 40, or 58 ft.
12 ft is about 25% shorter than a half wavelength on 28 MHz and
is practically invisible in the HF spectrum.
27 ft is very close to a half wave on 17M and 40 ft is a full wave on 12M
If you want to avoid resonances on ALL bands, including the WARC's
you need to break up your guys every 12 ft or use PHILYSTRAN, at
least close to the tower, followed by steel guys near the ground to
prevent damage from fire, abrasion, or cutting.
de Tom N4KG
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