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Hello out there, I would appreciate if you can help me here:

I need to upgrade an existing wireless infrastructure in a production hall and the customer wants, because of budget limitations, to only replace the AP's while keeping the already installed external, patch antennas.

The new access points we plan to install have two RP-SMA connectors for each of its two radios. One radio operates on 2,4 GHz and the other one on 5 GHz.. The already existing antennas have three RP-SMA connectors (three antenna elements?).
The antenna only supports 2.4 GHz so I would connect the 2,4 GHz AP radio to it, which from the performance point of view will be fine since it will be used by low-throughput barcode scanners.

The question is if connecting a "two-anntenna AP radio"  to a "3-elements external antenna" will work? (of course using only two of the three RP-SMA connectors in the antenna)

Won't work at all?
Decreased performance?
Working fine as a "two-element" antenna?
Or...?

Given the case that it would work, the next question is: does it make a difference which two antenna connectors (elements) I choose to use?
I assume the antenna elements are positioned in specific ways for diversity reasons, so would it be better to use a specific pair out of the three antenna connectors? Is there any general rule to find it out (since I dont have the antenna specs) or just try and error?

Here you can see a photo of the current AP (to be replaced) and the existing antenna: https://i.imgur.com/ccOGtJF.jpg

Thanks in advance for you help!

Facundo

I assume you are replacing the AP's because they are MOTOROLA branded ?   Later bought out by Zebra, and then by Extreme Networks.

I can't tell your exact circumstances, there are some missing details.   So please forgive the assumptions below.

(Just as an aside, Extreme Networks may be willing to give you some kind of trade-in discount for the Moto's with one of their new models - no promises, I'm just guessing - ask for Jussi Kiviniemi)  

The older AP's are dual band (2.4 & 5 GHZ), probably 802.11n, but maybe /ac with MIMO, and either a very sophisticated Diversity radio or triple stream MIMO.   The way it's connected here you were only using either the 2.4 or 5GHz band, and not the other.  Strange.   (oversold originally ?)

It sounds like you are giving up a lot - both dual band and MIMO.   Is this the case ?

Let me make clear, THERE IS ALMOST ALMOST NEVER A GOOD PLAN TO DOWNGRADE TO NON-MIMO RADIOS (IF THAT IS WHAT YOU ARE DOING).

Just based on the way you have this antenna connected, you will be giving up a lot in connectivity by connecting it to a single stream radio(s).

The antenna may also not be designed for two radios in different bands.   Check the manufacturers original specifications - not just marketing sheets.

From the size of the antennas, I'm guessing they are high gain.

Too many unknowns to just keep guessing.   Ask the new AP's manufacturer, and give them the SPECIFIC details on your exiting antennas.

Good luck.

Hi Howard, thanks for you answer.

Here some clarifications regarding your comments:

The older APs (as shown on the pic) are indeed only using the 2,4 GHz band, and up to the specs these APs are 2x3 MIMO.

As far as I can tell, I'm not downgrading to non-mimo. I'm downgrading, if you will, from 2x3 MIMO to 2x2 MIMO (as the new AP's are 2x2).

The existing antennas support only 2,4 GHz, I'm aware of that, and it should be fine.

Let me write some more background info for you to get the whole picture:

The customer has a production hall with about 10 AP's, three of which are located between storage racks, using this 2.4 GHz directional antennas to provide connectivity for barcode scanners on forklifts. This directional antennas is what I want to know if I could reuse.
The other AP's will use their factory dipole antennas and be full dual band for serving WLAN to all other kind of devices (I'm not planning to let 5 GHz completely aside).

The specific question is if connecting the access point's two RPSMA connectors to two out of the three RPSMA available connectors on such antenna will work, meaning providing the expected coverage and signal strength.

I know that this is not an optimal solution, but I wanted to have an in-between solution until the customer can afford to buy new, dual-band antennas.

Thanks again for your inputs.

OK.   Thanks for the clarification(s).

The antenna SHOULD work.   I've done similar things by only using 2 of the 3 connectors on an antenna I have.

BUT, for the hell of it I would still try to get the actual specs for the original antennas.   There might be some advantage to using a particular two of the three antennas.

I really doubt it would make a difference, but find out if you can.    I couldn't tell who made your antennas from the pictures, but Cisco, Laird, Tessco, and others all have good documentation on their antennas - and it will be free.

Good luck.