[600MRG] Estimating Rr for non-confirming verticals

[K9FD]

Reading comprehension dude
He said hes feeding the open line as a vertical and the wires at the top 
are acting as top loading,
Nothing to do with open line,

> I'm no fan of ladder line, because there are all kinds of extra 
> variables it introduces into the picture.
> ( most people who have antenna problems are using ladder line)
> The actual feed point ( at the antenna dipole )  is sure to be very 
> capacitive and the Rr is probably less than 1 ohm on 630 meters.
>
> Now you have a massive mismatch at the feed point, so the length of 
> the transmission line makes a difference as to what impedance is 
> presented at the shack end.
>
> The efficiency of such a system is just about nil.
>
> However , they did have the " lightbulb dx challenge" where the 
> participants used lightbulbs as their antennas -and they made 
> contacts! Anything is possible...
>
> On Friday, July 17, 2020, 5:37:38 PM EDT, Ben Gelb <ben at gelbnet.com> 
> wrote:
>
>
> 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
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