1/4 wave ground plane antenna

The 1/4 wave ground plane antenna

The 1/4 wave ground plane antenna

The 1/4Λ ground plane antenna is rather interesting because it has a driven element (vertical) and a minimum two quarter wave radials. This antenna radiates in an omnidirectional pattern, ¼λ vertical antennas nearly always have losses that exceed a vertical dipole that is standing free and clear of the ground. However, unless the antenna is mounted a substantial distance from the real ground ( IE, more than ½λ) the ground still has an effect on the radiation characteristics of the antenna system.14waveradiation

There has been much dispute into the effect of radials, if more is better, or what the ideal number is! for what I have used I have only ever needed 4! To build a 1/4λ vertical all you need is some cable. Remember that your feed point and Radials have to be the same height above the ground.

A connector for working with 1/4waves

Fig 1: A connector for working with 1/4waves

When building a 1/4λ I use a plastic box with three bolts and wing nuts looking at the primitive image in Fig 1. The bottom represents a female socket with the three M8 nuts above, two to the side one to the top, I use split washers to allow the bolts not to slip then place another washer and nut the other side of the container, Next connect the center of the socket (HOT hense red) to the top Bolt, solder in place or use electricians connectors if you wish. now connect the body of the socket to the other two bolts in a similar fashion. Tighten but not enough to crack the container. then I use lots of Hot Glue to seal the bolts. Seal the box up with so it suffers from no ingress, however, just to be sure drill a couple of small holes in the base to allow any excess humidity to drain of. You could also build a choke Balun into the box should you wish, I prefer not to however! On your driven Element (the vertical, you can connect the wire by Spade connector, or any other way you choose, but the wing nut is there to make it easier. Likewise the radials are attached similarly.

I tend to use wire fence supports as they are cheap and insulated. I then have pre-marked at the same height. If you have children about or animals for that matter, putting a screened area around your antenna’s is a must.

 

Expansions on this subject will include a driven element and a reflector ie: 1/4λ Ground plane 3 element Beam

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