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New Member

Diversity with One Antenna

The Diversity option has the ability to pick the better antenna for a particular client or signal and then discard the other, multi-pathed signals. If I have one antenna installed, does enabling diversity still provide the discard function for the instance of multiple signals from a multi-pathed client? Just curious what happens...

Thanks!!

5 REPLIES
Cisco Employee

Re: Diversity with One Antenna

No you can not have antenna diversity with only one antenna.

It will compare the signal strength on the 2 antenna ports and take the strongest as you have no antenna plugged into the second port then it will always be the weakest signal and as such discarded

New Member

Re: Diversity with One Antenna

And how is that different than with two antenna's? I'm not trying to be rude, but that's the same results I would get with two antenna's disabled. Any packets other than the first one to get to the single antenna would be dropped and that's what I want. Granted, with two antenna's the process would be more efficient since there's a good chance the other antenna has a better view for some clients.

Thanks!!

"It will compare the signal strength on the 2 antenna ports and take the strongest as you have no antenna plugged into the second port then it will always be the weakest signal and as such discarded"

Cisco Employee

Re: Diversity with One Antenna

Your not being rude question away until you understand I dont mind.

Antenna diversity or to be more correct in RF terms spacial diversity is used to combat the effects of mutil path loss.

Multi path loss is caused when a wave radiates out from a transmitter but some of the wave is reflected of an object, this reflected wave now also reaches the receiver.

As radio waves travel at very close to the speed of light ( doest matter at what speed as long as its a constant) and the 2 paths are of different lengths

Path one is direct

Path two is via the object we reflect of

This means that the waves will arrive at 2 different times.

Now think of 2 sine waves and of set one by 90degrees (the amount of time that it takes for that wave to travel half a wave length) If you look at these 2 sine waves you will see at some points in time the 2 waves areat their peak but in oposite and other times they are at their minimum. At the time they are at their peak but oposite the average vaule of these 2 waves is close to 0 they cancel each other out and at the other times they add together to make the average value bigger. If we hit 180 degress out of phase they will completly cancel each other at all points

Back to our radio waves, they have taken different times to get to the reciever so they are out of phase, this will mean that these waves may either add together or cancel each other out if you move the receiver over by a few inches then the results of adding and subtracting will be very different.

The 2 anttenna play of this fact that if one antenna is receiving 2 signals that are 180deg phase shifted then a few inches away the 2nd antenna will not be seeing these same 2 signals at 180 deg phase shift.

I hope from this you will see that you need 2 anntena for diversity.

If you have only 1 but configure diversity then it is of no harm as the port with no antenna should always be the lowest signal strength and blocked but this is not antenna diversity and you have no immunity to multi path loss.

New Member

Re: Diversity with One Antenna

That was a good response...and I think I understand much better. Thanks for your help!!

Re: Diversity with One Antenna

Agreeing with Derwin,

Antenna diversity, also known as space diversity, is any one of several wireless diversity schemes that uses two or more antennas to improve the quality and reliability of a wireless link.

Source :

http://en.wikipedia.org/wiki/Antenna_diversity

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