The UHF has revolutionized 4WD Touring and Outback travel. The convenience of inter-vehicle communications while travelling in convoy, for breakdown, emergency or simple chit chat can really improve the overall trip experience. GME has an extensive range of Australian designed and manufactured UHF radios and accessories for all applications, particularly 4x4s, with convenient vehicle mounted smart electronic models and a range of durable antenna.
Currently all UHF radios sold in Australia are limited to 5w power output. The correct antenna selection is vital to radio performance.
Important factors when choosing an antenna are the mounting position and the dBi gain or ‘radiating pattern’ best suited to the application – to the terrain in which the antenna is to be used.
UHF antenna perform at their best when mounted as high as possible. This is because the signal is largely radiated in ‘line of sight’. If you can see the antenna, you will have good signal.
In theory, on a perfectly flat surface, the curvature of the earth will start to attenuate the signal at around 40kms. Obviously terrain will interfere with this ‘line of sight’, so unless you are transmitting between 2 hill tops, even 100kms apart, the selection of the correct antenna is going to have a dramatic effect of reception and transmission.
dBi GAIN or RADIATING PATTERN
As the design of the antenna is changed to increase the gain, the omnidirectional pattern is flattened in a vertical plane and is extended in the horizontal. This makes for a longer, more directional signal which performs best on flat terrain, but poorly in hills and gullies. Typical use is on large flat farming properties.
High dBi gain is considered above 7dBi.
The lower the dBi gain, the more rounded the signal pattern, less directional, less likely to be obstructed by obstacles, so less than say 4dBi is fantastic in mountainous areas, but limited in reach on the flat.
Hence the compromise of approximately 6.5dBi is commonly selected for 4WD Touring.
See Figure 1 and 2.
Mounting
Antenna are best mounted to a large uniform metal surface. This metal surface is referred to as a ‘ground plane’. The best position to install an antenna is in the centre of the roof, but this is rarely possible and installation on a Bull Bar, SWC or Roof Rack is the practical compromise.
In this case a ‘ground independent’ antenna should be used to give the antenna its all round radiating pattern, without the metal surface base.
If a ‘non ground independent’ antenna is chosen, and not mounted in the centre of the ground plane, ie is mistakenly mounted on a Bull Bar, SWC or on one side of a Roof Rack, there is significant compromise in performance in the direction to the side of mounting.
Note: It is recommended that fiberglass antenna are used on diesel 4×4 vehicles, due to their increased durability in high vibration applications compared with stainless steel.
