[600MRG] Estimating Rr for non-confirming verticals

[Ben Gelb]

Hi all -

I decided to try feeding my HF dipole (ladder-line fed) as a vertical
on 630m. I did so, and it works. But I'm wondering a bit about how
best to estimate Rr, given that the ladder line feed is not actually
vertical. The first 20 ft or so are close to vertical, followed by a
roughly 40ft slanted section (45 degrees-ish, though not a straight
line since it is not held taught - so it follows a catenary curve).

Top load is 93.8'.

That is what I mean by "non-conforming".

So the question is how to reason about this antenna in service of Rr estimation.

Since the whole antenna is pretty small relative to a wavelength,
perhaps I can get pretty close by decomposing the antenna into its
vertical and horizontal components? The vertical component (at least
ignoring that the 45 degress section actually has a nonlinear shape)
would basically be the height of the dipole feedpoint.

The horizontal component of the ladderline section I imagine would add
to the effective capacitance of the top loading from the dipole
(though its more like "mid load" since its not at the top). Perhaps I
can estimate the increase in effective *top* loading length by
measuring apparent C of the antenna at the feedpoint - and backsolve
the equivalent *conforming* T-top antenna (w/ save vertical component)
that would yield that capacitance. Then use the Rr result for that
antenna.

Other thoughts?

I could also learn how to use antenna modeling software. But sort of
fun to try to think about how you might get there intuitively.

73,
Ben N1VF