VHF 1/2wave vertical antenna for the 6-meterband (50 Mhz)
RE-A50V12
VHF vertical 1/2 wave antenna
By Guy, de ON6MU

Schematic fig1

1/2 wave antenna principle

A much better type of antenna then a simple quatre wave and that has more gain is the 1/2 wavelength vertical. We know that the impedance of the 1/2 dipole is 70 Ohms when we attach the coax in the middle, but what if we were to attach our coax directly to the end? The impedance at this point is high, very high, so we must make a matching device to match the antennas impedance to the 50 Ohm coax. What would happen if we did not use this matching device? Well...you would know that this would result in a very very high SWR.
The bandwidth of these antennas are good, they can easily span the entire 50Mc band and more with a low SWR. But, in this design, the bandwidth is limited to approx. 600kc (without re-tuning C1 or C2). This allows you to tweak the antenna to your desired band and avoid interference and reduce intermodulation.
The antenna and ground are connected across the tuned circuit while a 50-ohm coaxial cable is connected to taps on the inductor. The tuned circuit presents a high impedance to the antenna and the tapped inductor steps this impedance down to 50 ohms. Adjusting the tuning capacitor tunes out slight reactance variation if the antenna is not an exact electrical half-wavelength.

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. Also, the diameters of the tubing described here is not too critical.

Links of interest:

The antenna

Highlighted

 

Specifications ON6MU Vertical Antenna RE-A50V12

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

 

5/8 vertical groundplane antenna for 50MHz
RE-A50V58

Homebrew groundplane vertical antenna

This is how Greg, SP5LGN constructed my 5/8 lambda 6-meter GP antenna:
Construction of 5/8 vertical GP antenna, de SP5LGN Construction of 5/8 vertical GP antenna, de SP5LGN
Click to enlarge
Many thanks
Greg!

You can fine-tune the SWR to peak in the bandsection you are planning to use the 5/8 groundplane antenna by:  

Today's specials:

.ON6MU Homebrew projects
.Radioamateur related projects

.ON6MU Ham mods
.Modifications of transceivers

PA3BEN sent me a lot of pics on how to convert an old CB antenna using my schematic (shown here above) for 50Mc! I've put here 2 resized pics (do to lack of webspace, sorry):


Thanks Ben!

Please take a look at my 50mc wide-spaced yagi antenna

 



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