Mifi

RONS TECHNICAL TIPS NO. MIMO WIFI MIFI WIBBLE 

MIFI'S AND ANTENNAS EXPLAINED FOR MOBILE DATA

There are two types of Mifi device - those with sockets for an external antenna, and those without. Those without are in the majority, and they rely on a built in antenna. The built in antenna is identical to those used in normal phones, so a mifi with an internal antenna should perform the same as a normal phone, for data, on the same network. This is good enough for most users. The networks claim that they have over 90% coverage, but we all know that out in the country there is always a chance that you won't get a signal. Sometimes you will be in a "fringe" area, where the signal is weak, and sometimes you can improve things by moving the device around - putting it near a window, or higher up. I have often managed to get a signal on a mifi device by velcroing it to the rooflight!

Radio waves travel in straight lines, so it is common knowledge that you get much better reception if your antenna is high up and unobstructed. That's why TV antennas are mounted up on the chimney, and commercial radio masts are located on high masts on top of hills.

So for those people who want the maximum performance from a mifi device, adding an external antenna can make a big difference. In fact it is a very big difference, because an external antenna is much bigger and more efficient. Generally speaking an external antenna will give you at least 10 times more signal than an internal one. However it will not guarantee you a signal everywhere. Some places just don't have any coverage - full stop. But many places have a weak signal - too weak for an internal antenna, but no problem for a big external antenna.

But it's not cheap, and no compromises can be made - approx £40 to £80 for the antenna, plus fitting. Coax cable has to be run into the van from the antenna, and properly weatherproofed. Coax cable also loses a proportion of the signal per metre, so it's length should be minimised. Because the antenna sockets on mifi units are so small, they can be very fiddly, so it is best to locate the unit in a place where it will not be moved very much.

You will also come across something called MIMO, which stands for Multiple Input Multiple Output (open loop spatial multiplexing). This is a system where two antennas are used for simultaneous transmit and receive, resulting in better performance. That's why most mifis have two antenna sockets, and most external antennas have two coax leads - one for each socket. There isn't much alternative nowadays - it's nearly all MIMO - that's why most external antennas are plastic domes - there are 2 antennas inside.

What to go for is entirely up to you - it's basically the same as the old portable tellys. You would get a decent picture if you were lucky, sometimes a grainy one, and quite often none at all. If you then plugged in an external antenna up on the roof or on a pole outside, then the picture suddenly went perfect.

What I like about my external antenna is that it is always on - no setting up. The van has wifi all the time, which feeds a laptop, two phones, two tablets and a GPS. If we are in the middle of nowhere, and there is no signal, we just accept it, because we know that we have an excellent antenna, so we don't have to bother messing about about trying to reposition devices for better reception. 

Mifi devices with antenna sockets are a little more expensive, and those that have their own display are preferable, because you can can see at a glance if you have a signal. Quite often just moving the van from one pitch to another can make a difference - radio waves can act in very strange ways, because they tend to reflect off rocks and buildings, so moving the van just a few feet can make a difference.

Suitable mifi units with antenna sockets include the following - 

HUAWEI: E5372, E5377, E5786, E8278, E392, E398, 5577, B315, E5186
VODAFONE: R210 R212 R215 R216 K5150
ZTE: MF821 MF823 MF93E

This is not a complete list. Personally I use Huawei, and have found them to offer good value for money.