Which aerial might be better?

[Scubbie]

A nice easy question for those who know, but which external aerial might be better for a 3G MiFi?

1. 2dBi
2. 5dbi
3. 12dB
4. 18dbi

I've copied the case of the letters as they appear in the specs. I'm not sure if the case is as significant as it is with data transmission.

[seawright]

It depends on the application and to some extent on the cost. The gain relates to the directional properties of the aerial. A perfect aerial also known as isotropic radiator (which probably doesn't exist) has a gain of 0dB and radiates (or receives) with equal strength in all directions. It wouldn't be that useful as who wants an antenna that transmits to every point of the compass including up and down. For a point to point link over large distances (remembering that such links are essentially line of sight) a very high gain antenna would probably be best as it requires the lowest RF power and provides good rejection for any off axis interfering signal. The disadvantages of such an antenna is its cost and the fact that it requires a rigid mount. If an omni-directional or mobile antenna is required then a low gain aerial is more likely to meet your requirement. When selecting the correct aerial for any particular application other factors as well as the gain should be taken into account. Any good quality aerial will include vertical and horizontal radiation pattern diagrams within the specification.

Edit:
A dB (decibel) is a relative measurement typically used to compare the difference between input and output power. When referring to aerials it is probably better to use dBi as this explicitly states that an isotropic radiator is used as one of the reference points thereby making it an absolute measurement.

[Scubbie]

Thank you seawright.

Cost wise they range from ~£5 to £15. The 12dB and 5dbi are both around £5, with the 18dB @£10 and 2dbi £15.

The reviews are a little inconclusive with varying comments.

[seawright]

The two at £5 sound cheap and cheerful. Quality may not be that great but provided the mounting is in an accessible location replacing them after a couple of years should be cost effective. As for 12dB or 5dBi it depends on the purpose. If all round coverage is required choose 5dBi but if the requirement is to communicate with one particular mast then the 12dB is probably better though it will need to be roughly aligned to get the best possible signal. I'm guessing on the coverage based on the gain. Radiation pattern diagrams could help you make a more informed choice. For instance you could find that instead of having one main lobe the 12dB aerial may have two nearly equal lobes 180 degrees apart which may not matter unless you are specifically trying to reject a signal coming from the opposite direction to the intended signal. In that situation the extra cost of the 18dB aerial may be justified.

[Scubbie]

It is to fit in an Huawei E5332 (3G Modem).

Hopefully it will be a little more reliable than the the Dongle I have been using and more flexible too.

The whole idea will be that I won't always know where the mast is.

[seawright]

It is to fit in an Huawei E5332 (3G Modem).The whole idea will be that I won't always know where the mast is.

In which case the 5dBi aerial would be better.

[Scubbie]

Thanks seawright.