Why do WIFI access points have 2-3 antennae?

And if you wanted to add a remote antenna on a lead (for better antenna placement), can you just add one and does it matter which of the 2 or 3 sockets you connect it to?
Could you even add 2 or 3 external antennae to the same unit?
Never understood this...
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Well its much like anything else, not only are you going to change the service area, but you are also changing the reception from your device, which is often the important bit, as mobile devices have a limited power, while the base could be quite high in power. It is very complex as the size of the conductor, the length of the cable and the placement all affect the polar diagram of the array as a whole, due to the phase relationships perceived at the receiver. Some cancel out some add. I think in the main they tend to do a suck it and see approach, just tempput aerials around and see what the coverage is like. If its fine, screw them down!
Its even more complex of course as there are a lot of different frequences now and you have to cope with interference as well. Brian
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http://en.wikipedia.org/wiki/MIMO
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On 01/06/14 12:20, Richard Tobin wrote:

Wow. OK - that is complicated... Thank you.
So should all the antennas point in the same axis?
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On 01/06/14 13:48, Tim Watts wrote:

nope. Its that magic word 'diversity'...
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Tim Watts wrote:

With some with a single radio but multiple aerials it's just for diversity, the AP is constantly trying both aerials to see which gives best results and will then use that one for a while (to talk to a specific device)
For others they can use multiple radios each with its own aerial, it increases bandwidth, and the really clever ones use beamforming to 'aim' the signal where it's wanted.

If you fit external aerials, I don't think they like it if you fit them a /long/ way apart, there's an assumption all the aerials cover roughly the same area rather than different areas.
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On Sun, 01 Jun 2014 11:45:00 +0100, Tim Watts wrote:

Nope.

Yep.

So long as the router does, that's all that matters...
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On Sunday, June 1, 2014 11:45:00 AM UTC+1, Tim Watts wrote:

Of course, on some units the antennae may just be pieces of plastic added on at low cost to make the thing look more 'technological', like set-top TV aerials.
Owain
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On 01/06/2014 17:28, snipped-for-privacy@gowanhill.com wrote:

Care to name a router with a dummy antenna such as you suggest?
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On 01/06/14 18:00, Peter Crosland wrote:

My last HP laptop really had 2 antennae - I had to fit the WIFI module because they messed up the order and supplied the module loose. There were 2 aerial wires.
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Ah diversity reception, I don't think most of these systems are that sophisticated, as I say, its often the old we all know what SHOULD work but in fact we need to put this here, and that over there to make it actually work.. grin. Brian
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I guess whether its snake oil or black box technology is according to your take on the science and how applicable it is in the real built environment.
This is why you hear of people on mobiles who can only get a signal standing on one leg on the edge of the bath. Brian
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Do they still do that then? I used a coat hanger for a tv aerial. Bent it into two squares, cut it in half, connected the coax to the gap on one, then stapled it to a 9 inch bit of wood. Joined the two ends of the other square, and stapled that to the other end. Wallah, a set top aerial that was directional. Brian
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On Sun, 01 Jun 2014 09:28:55 -0700, spuorgelgoog wrote:

I think routers have gone the other way these days - even where external antennae would actually improve reception, internal look "smoother" and thereby better.
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On 01/06/2014 20:50, Adrian wrote:

Have you some empirical evidence to substantiate your claim that external antennas are better? Just because they don't protrude does not mean they will significantly improve performance particularly at higher frequencies. Patch antennas concealed within the surface work very well.
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Nope.

Both types are still readily available.
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On Sun, 01 Jun 2014 21:12:21 +0100, Peter Crosland wrote:

Plenty to substantiate that they can, absolutely.
You'll note that I made no claim about the little stick things that come as standard, but unscrewing those and putting a decent one on most certainly can and does. As merely the most recent direct example, how about the neighbour who swapped one of the stick things on his router for a £15-delivered-from-Amazon TPLink antenna the other day, and can now reliably get a connection from his garden office.
Or the business I used to work with, where we used a couple of similar antennae to "bounce" a link between two offices in a serviced building down the walls of an external alleyway, reliable enough for an office of six or seven people to work with the servers that they couldn't otherwise see.
Pity that isn't an option on routers with internal antennae.
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On 01/06/2014 21:27, Adrian wrote:

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.
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Mobile phones don't have external aerials any more.
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Tim Watts wrote:

I can't remember the last laptop that /didn't/ have two antennas. They may always have had two - I can't actually recall meeting anything else. And my first wifi laptops had to use a PCMCIA card!
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