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UHF Antennae – is bigger always better?

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Don't get caught up in the sales pitch when selecting a UHF antenna, know which is best for you.

When it comes to choosing the right antenna for your UHF radio, the old 'bigger is better' motto doesn't always work. The different properties of a range of antennae mean that each is better suited to a particular application; one will work best for high country cruising, while flat desert terrain will call for a different solution.

UHF Antennae – is bigger always better?_Hema_Maps
(Image: The different properties of a range of antennae mean that each is better suited to a particular application.)

One way in which we can measure the properties of an antenna is gain; this indicates how well the antenna converts input into radio waves and transmits them in a given direction (or the other way around when receiving). This figure is given in dBi (decibels-isotropic), which can denote some complex figures, but we'll stick with the basics for now.

The simple version, as it relates to 4WD use is that a tall antenna will likely have a high dBi (9 dBi is considered high in this case), indicating an ability to transmit over a greater distance in a given direction. Imagine the signal spreading out from the antenna like ripples on the surface of a pond, making it great for flat terrain where all it needs to do is glide out over an even landscape.

For hilly terrain, however, this kind of high dBi will be blocked by terrain features or redirected when the vehicle is on an incline. Instead, hilly terrain calls for a low dBi antenna (closer to 3 dBi). These cover less distance but radiate in a more general field. This creates a sphere of transmission, reaching out in every direction, up toward high peaks and down into valleys.

UHF Antenna Hema Maps(Image: The best place to mount your antenna would be in the middle of your roof, but this is not always practical. Mounting on your bullbar is still effective.)

If you're unsure where you'll end up, a mid-range antenna of 6 dBi is a good general-purpose solution. It's also possible to have two antennae, either linked to separate UHF radios, connected to the same system with a switch, or simply changed by hand when necessary.

In theory, the best place to mount your antenna would be in the middle of your roof, where it would have maximum unobstructed range. Since this isn't entirely practical, they're commonly mounted on the bullbar, which is still very effective. It's best to avoid placing them low down or up against panels and other objects that can impede broadcasting range.

5 comments

  • Paul Kelly: April 26, 2021

    One consideration that was not mentioned, is to mount the ariels on the drivers side of the vehicle soas to reduce the interference of any part of the vehicle,\’s body work. If mounted high on the drivers side, there is clear unobstructed transmission both forward of & to the rear of the vehicle. A good position is on the roof rack, vehicle gutter or using a bracket which comes out from under the bonnet close to the front windscreen. This is what I have & there is no obstruction to the drivers view.

  • Wes: April 26, 2021

    Antenna’s you are spot on.

  • George: April 26, 2021

    Very informative thanks I never new what the difference in the dBi rating did

  • Alan : April 26, 2021

    I’ve worked around worksites and in the Mining industry and found this to be correct. On some occasions Grader operators have had problems with communication and I have explained what was occurring. We changed out to the smaller antennae and the difference immediate.

  • Greg Fletcher: April 26, 2021

    a smaller 4db antenna mounted of a roof rack mount point or roof rack will out perform an antenna mounted on the bull bar every time.

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