Topband: 160 meter 1/4 vertical
mikewate at gmail.com
Mon Jul 3 18:30:47 EDT 2017
Respectfully, there's a lot of misinformation here.
"Clearly, size matters." If you are saying that the taller a vertical then
the better the signal, then that is simply *not the case*. It is a very
well established fact that a 160m vertical taller than λ/4 has little --IF
ANY-- DX advantage. (Rather, the opposite is true.)
The free-space pattern of any antenna depends _on its dimensions_. They are
not all "crescent shaped".
And improper matching does LITTLE to affect the pattern of an antenna,
unless we are discussing phased arrays. The pattern of a vertical or dipole
by itself will not be affected by a mismatch.
Perhaps the 73 article you mentioned described some type of phased array,
and is correct. However, 73 was noted for some gross technical inaccuracies.
On Mon, Jul 3, 2017 at 5:09 PM, Charles Moizeau <w2sh at msn.com> wrote:
> The free-space pattern of current in a vertical (and also horizontal)
> antenna is crescent shaped with its maximum at the midpoint, and a minimum
> at each end. It shows nothing that could be termed an extraneous lobe.
> Any such lobes would seem to be the result of improper matching, or more
> likely, the fact that in the real world such an antenna is in an
> environment that is certainly not free space.
> The Franklin collinear antenna is usually shown either with in-line
> 1/4-wave inverted coaxial segments, or for wire antennas with quarter-wave
> decoupling stubs hanging down from the adjacent ends of the in-line
> half-wave radiating sections. For the latter, the quarter-wave decoupling
> stubs can be reshaped so that they run parallel to the half-wave radiating
> sections, and this makes for a neater configuration.
> Years ago 73 Magazine had an article describing a 7/8 wavelength vertical
> mobile antenna for VHF (two meters). The bottom section was 1/2 wave and
> presented a high input impedance, and I believe used a LC matching
> arrangement to the 50-Ohm coaxial feedline. The top section was 3/8
> wavelength and decoupled from the bottom section with just a low-value
> capacitor. I seem to recall that the overall dimensions were for a length
> that was 5/6 wavelength, but that is only five percent less than 7/8
> wavelength. The article showed comparative field-strength readings that
> showed superior results for this antenna versus 1/4, 1/2and 5/8 wavelength
> antennas. Clearly, size matters.
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