Hello Jim,
Thank you for this. I don't doubt for a second that my elevated 1/4 wave
radial currents may be unequal. I should throw together an RF current meter
and check them sometime, and add more radials while I'm at it. After the
ticks and chiggers here die, though. :-)
I don't have any Communications Quarterly issues, but K5IU's article sounds
interesting, if anyone has a copy.
73, Mike
www.w0btu.com
**
> Hey Mike
>
> Saw your post to TB reflector:
>
> "I suppose if you made the elevated radials long, then you could adjust
> the current balance with series variable capacitors. You could use a simple
> clamp-on meter like W8JI has on his site to measure the relative current,
> perhaps.I didn't bother with that myself, I was just careful to keep the
> radial lengths the same length and height."
>
> My old friend K5IU had an article "Optimum Elevated Radial Vertical
> Antennas" in Communication Quarterly, Spring 1997, pp 9 - 27. He showed
> why 1/4 wave elevated radials are the worst length as it invariably results
> in radials having unequal currents (at least on the low bands where the
> height is small in terms of lambda). He only concluded the pattern was
> distorted, explicitly stating no opinion on efficiency. Dick is pretty
> careful - he likes actual measurements. The fix was to use non-1/4 wave
> radials with a single lumped reactance between the shield and the junction
> of all the radials to bring to resonance. Using separate reactors for each
> radial makes it too critical to adjust.
>
> Since some of his measurements showed next to no current in some radials,
> I figured right off the efficiency would almost always be higher with equal
> currents, even when using shorter radials of the same number. I never
> needed to use elevated radials, so it was all merely academic for me.
>
> I'll bet anything you have very unequal currents in your elevated radials
> despite their being precisely the same physical length. Dick's article
> shows how he measured the currents with a simple HB device. Don't know if
> it is simpler than W8JI's or not.
>
_________________
Topband Reflector
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