AIR-ANT24120

[Rene Melendez Cabrera]

Hi,

I`d like to know if that antenna AIR-ANT24120 works with the LAP 1252 in a Mesh deploy.

Thanks for your advices,

[Stephen Rodriguez]

According to the data sheet for that antenna, it's designed for outdoor usage, as it's 12dBi.

http://www.cisco.com/en/US/partner/products/hw/wireless/ps469/prod_installation_guide09186a0080148acf.html

I suppose that if you were using the 1252 for indoor mesh, you could use this antenna, but I wouldn't.  For indoor, you wouldn't need that much gain.

HTH,
Steve

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[Kayle Miller]

You can cetainly use this antenna for an outdoor mesh deployment, the only warning i would give you is that if your intending this to provide client coverage just keep in mind that you could potentially encounter a scenario where a client device can hear (see) the access point, but the client can't transmit back.  Also beaware that using this antenna on this ap will require lowering the transmit power.

[George Stefanick]

Kayle +5

And why you need to lower the TX power is becuase the AP is spec'd at 12 dBi which will increase the TX power of the AP 4 times.

Simple math ..

Ap TX radio at 100mw + 12 dBi antenna  = ERP 800mw

Clients are normally at 25mW or there around ... So you can see the AP will scream at the client (so to speak).

[Kayle Miller]

Also as George mentions the output power math (unless the FCC has changed the regulation); transmit power is limited to 1w which is 30db (1-watt), unless it's a point to point link which means that it can be 36db (4-Watts) I believe (if memory serves me correctly)

To calculate EIRP (ERP) follow this math formula (Values are db or dbi):  Transmitter Power - Cable Loss + Antenna Gain = EIRP

So if you assume the transmitter is at 100mw which is 20db, and the antenna is 12dbi and on a 3ft cable it's less than .25 loss (I'd hope) so we won't count it that makes the formula look like this

20db - 0db + 12dbi = 32db EIRP or just shy of 2 watts and as George mentioned a typical client is 25mw or 14db and only a 0dbi antenna so their effective EIRP is

14db + 0dbi = 25mw EIRP  drastically lower transmit power.

For quick reference ERP Values

36db = 4 Watts

33 db = 2 Watts

30db = 1 Watt

27db = 500mw

24 db = 250mw

21db = 125mw

20db = 100mw

17db = 50mw

14db = 25mw

11db = 12.5mw

8db = 6.25mw

5db = 3.125mw

2db = 1.0mw

-1db = .5mw

0dbm = -1mw

Hope this all helps you out...

Great comments George

[George Stefanick]

Preach it brother ... Preach it !

[Rene Melendez Cabrera]

Thanks a lot,

We will deploy a Mesh with AP 1520HZ in 5 5Ghz, the distance between AP 1520 will be about 200 mts and the AP 1250 will be about 60 mts to AP 1520 in mesh too.

Do you think this deployment works?

Thanks again,

[George Stefanick]

Rene,

It would be unfair to speculate if this would work not knowing the enviroment, clients and even what application might run over this mesh.

[Kayle Miller]

Rene,

     We could say in theory it should work, but there are so many variables that can impact the function and performance it's very hard to speculate on it with being able to see all the pieces.