Antennas for APs

Unanswered Question
Jul 29th, 2008

I've been using different antennas for my Cisco APs 1242.

I use non-Cisco antennas shaped like smoke detectors in drop down tiles.

Now I only use the right side, but is it possible to use 2 of the same kind for diversity?

or can I use some rubber duck antennas for diversity?

I have this problem too.
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scottmac Tue, 07/29/2008 - 13:25

Non-Cisco antennas are ok electrically, changing from Cisco antennas may put the whole system in legal jeopardy in some regions.

In the USA, if you are using antennas that are substantially identically to the antennas that Cisco used when they submitted the overall system for FCC type approval, you're OK.

If you re-engineer the system (like adding amplifiers, power dividers, etc) then, technically, you should have the system re-certified to meet federally approved specs.

One or two antennas are OK, they should both be functionally identically (like two 2.2dBi ducks, or sectors, or yagis, or dishes ... but not one of one kind and one of another).

Yes, you can use rubber ducks for diversity, as above, they should be substantially the same type and spec for optimal functionality.

Good Luck


mano.hernandez Wed, 08/06/2008 - 07:10

Well, this is for the U.S., I was just wondering what would be better overall.

Say if I had an 8db antenna from Hyperlink Technologies would be fine.

I am trying to fix some issues where clients drop, but then reconnect.

scottmac Wed, 08/06/2008 - 16:32

I'd love to be able to tell you that you can do that and everything would be OK. However, it's frequently just not that simple.

You see, adding passive gain (more dB at the antenna) means they have to get that gain from somewhere ... that "somewhere" is the shape of the signal.

When you get more gain from (what appears to be) an omni-directional (360 degrees lateral) antenna, the only place to redirect that exta energy from is the top and bottom of the radiated (former) sphere.

That means for some angle vertically, there is a shadow. Higher gain antennas tend to be sky shooters ... i.e., the pattern is not completely lateral (like a lighthouse).

You need to look at (understand, compare ...) the pattern and how it will fit your environment. That should be coupled and verified with a follow-up site survey to ensure the coverage is what you expected.

It is possible that your issue is noise/interference ... beefing up the gain on the antenna has as much chance of breaking ot more as it does fixing it.

Or it could be as simple as just moving the antenna a few inches (or a few feet, or a few meters).

There's no way to blind guess this; you need to at least light up Netstumbler ( it's free) and then verify your signal strengths and noise characteristics in your work areas.

Good Luck



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