VHF 5/8wave vertical antennas
VHF 5/8 wave vertical monopole antenna
By Guy, de ON6MU

Schematic fig1

The 5/8-wave antenna

At VHF, both the 1/4-wavelength monopole and the 5/8-wavelength monopole antennas are widely used. The VHF 5/8-wavelength (144 Mhz) vertical monopole has long held the reputation of providing about a 3-dB gain advantage over the 1/4-wavelength vertical monopole. The foundation of that reputation rests upon theoretical calculations that show the longer monopole to have the derived gain increase when both monopoles are set over a perfect ground.
A second factor contributing to the reputation of the longer monopole for higher gain is the current distribution along the element. Next Fig shows the distribution for both the long and short monopoles, with the ground plane elements omitted for clarity. The 1/4-wavelength antenna presents its "half-dipole" current distribution curve, while the 5/8-wavelength antenna provides a "half-EDZ" distribution curve. The peak current at a position well above the top of the short antenna is said to give the longer monopole a lower-angle of radiation and additional gain.
The third reason you may want to use the 5/8 wave vertical is to obtain a lower angle of radiation.
Dissadvantage: needs a matching device at the base to match it to the coax, it cannot be attached directly. This antenna has about 1.2 db gain over the dipole antenna and 1/2 vertical.

Parts list

Note: there are many ways to build your antenna and I'm sure some can come up with better mechanical designs then described here although the design and material used here is cheap and easy to find.
Both types of 144 Mhz 5/8 wave antenna's described here has the same radiationpattern and gain, but type 2 has the advantage of being electrical (and DC) grounded and can disipate more power.

The antenna type 1


Specifications antenna type 1


The antenna type 2

Specifications antenna type 2

Be sure to seal everything up to avoid moisture, corrosion etc...

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