Why do WIFI access points have 2-3 antennae?

[Adrian]

And for the situation I mentioned? Where the external antenna on the router is being replaced to increase - measurably - coverage?

[Scott M]

I think 1.98p for a couple of extension cables which also don't give me USB limitations is tolerable. Oh, and cheaper.

[Rick Hughes]

Some access points have 2 identical antennaes to provide diversity and hopefully better Tx/Rx throughput, others (I have one) have 3 antennaes and the '3rd' uses different frequency. For optimum efficiency antennas have to be matched to wavelength ... so if you have 2 specific frequencies one (usually best) option is a 2 matched antennae.

Although most cheaper access points just have one of more antennae matched to a single frequency.

If you want to remote off an antennae ... you can do this as long as you use correct impedance matched cable, and you either use a physical ground plane, or a wire wound groundplane mimic. If you don't know how important a ground plane is ... here is another page for you:

Even 2 strips of adhesive backed thick aluminium tape in a 'cross' with antennae in middle can be good enough. (often used on fibreglass structures)

[Tim Watts]

Thanks Rick - most informative.

[tony sayer]

Diversity is what is required this isn't a simple point to point link environment.. Plane polarisation also gets badly skewed what starts as Vertical is rarely that when it gets to where its required.

Around mid of the band of interest ..

It can be better than nothing on vehicle roof's for VHF frequencies but nowhere near as good as metal sheet..

>

[Peter Crosland]

Noted. But you are not comparing like with like. The "little stick things" contain a metal antenna albeit a small one and are emphatically not just for show as you suggest. The performance of a properly designed patch antenna concealed within the casing will perform just as well as one of those. Increasing the size of the antenna in the way you describe will usually give performance gains.

[Adrian]

I didn't make any such suggestion.

[dennis]

Put the usb stick inside a piece of plastic drain pipe, cap the top and screw it to the outside wall.

You will probably get more signal "gain" than the losses you get in the down leads for an external aerial.

Some USB sticks can take an external aerial so you could even put one on a few inches of cable and put that in the pipe too.

You could try

and £3 of pipe.