Max antenna size/output

[JakesPK]

Hi Guys

How do I calculate the maximum antenna size or output ?

Thanks in advance

 

[Gromitt]

There is allot of calculations that go in to the answer to your question, but the most simple rule to adhere to is this (please anyone correct me if I am wrong):

For every 3dB rating on your antenna you double the output of your wireless card. So if you have a 100mW card and a 16dBi antenna you should have an output of roughly 533.33mW.

 

[daffy]

output power of card + antenna gain - cable and connect loss = EIRP

eg:
17dBm card + 24dBi grid - 4dB attenuation in cable and connectors = 37dB

Maximum legal EIRP in 2.4Ghz is (or was? not sure on new regulations) 100mW (20dB).

Here's a page with a dB to mW table.
http://www.jawug.za.net/dBmChart

 

[JakesPK]

Great stuff! Thanks for your replies so far!

So for example:

I have an AP with a max output of 15dBm and an 15dbi antenna.

So to calculate the total output in mW would be: 15 + 15 - approx 3db = 27dB


So in order ot make sure I'm withing the legal limit I would have to

1. Use a 5dBi antenna
or
2. Decrease my power output on the AP to 5dBm

 

[hisite]

guys can you honestly tell me you set you power down?if yes then i am really suprised,not being ugly but that is never done.

 

[daffy]

In Mikrotik RouterOS, you set the regulatory domain (country), and the antenna gain.
That way, the software knows what the max power output is, and it knows the antenna gain. So it adjusts the power output, to play nice with others.

 

[JakesPK]

Well we do want to operate withing the legal limits.. So yes, I have adjusted my output on the AP to 5db only.