Thankfully choosing an external antenna for your vehicle usually isn't too complex. You'll notice that all antennas listed here receive from all directions, and follow the same principles as your UHF aerial (if you have one).
Which mobile antenna do I need?
The choice of antenna depends on the area you're travelling through. While a higher gain means a stronger signal, when you increase an antennas gain (ie it's dBi), the angle it can receive from is reduced - this means that high gain antennas are more suited to flatter areas, and moderate gain antennas (such as a 5-6dBi) better suited to hilly areas. The two most popular choices are the 6.2dBi or 6.5dBi antennas for varying terrain, or the 7.5dBi antennas for most highway driving (flat with a few hills).
What sort of range increase can I expect?
As performance is largely determined by the terrain path from the transmitter, the best way to gauge range increase is to look at your network's coverage maps which show expected increase when using a simple external antenna. Often high gain antennas are capable of exceeding the range predicted. You'll see on the below image the solid colour represents normal handheld range, and the diagonal shaded section representing expected increase in range.
Unlike some, we always recommend high quality Australian made antennas - such as the RFI and ZCG Scalar brands. These durable antennas have been specifically designed for the tough Australian environment and have a much more sophisticated internal design, allowing most models to operate on multiple mobile networks.