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.
73,
Charles, W2SH
________________________________
From: Topband <topband-bounces@contesting.com> on behalf of Herbert Schoenbohm
<herbert.schoenbohm@gmail.com>
Sent: Monday, July 3, 2017 4:46 PM
To: Jos Mols; TopBand List
Subject: Re: Topband: 160 meter 1/4 vertical
Forget about the high impedance issues on 40 and also 80. IMHO the best
and easiest solution for you is to make some simple wire decoupling sleeves
or wire cage for the higher bands and they could be current fed like 160
meters and much less complicated to feed without extensive matching. Also
1/.2 wave vertical are notorious for not working well with some obnoxious
lobes. The only full wave verticals that I know to work are of the
Franklyn antenna design and require a decoupling at the 1/2 part with the
other 1/2 wave above it. This is said to produce some low angle gain and
essentially double the radiated signal without the wasteful lobes at much
higher angles.
On Mon, Jul 3, 2017 at 3:53 PM, Jos Mols <jos.mols2@gmail.com> wrote:
> Hi guys, currently working on getting a radial net worked into my garden &
> pavement. Appr 40 radials ranging from 10 to 40+ meters.
> I can raise vertical to appr 37 meters. main interest is 160 meters.
> I would liketo use this vertical for 80, 60 and 40 meters. Considering
> end-fed configuration for 80/40 so making hi impedance match. Wondering if
> anyone has expereince with different options to achieve the same?
> Thanks in advance for your response.
> Jos PA0LSB
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