Antennas Issue

[josem_155]

Hi,

If I have a two rp-tnc connector 2.4 GHz anntena already installed and I decided to change it for one new RP-TNC connector dBi antenna (both omnidirectional), am I loosing some kind of coverage? or it is good idea chaged it? My doubt is due to I dont know what i have to do with the  free connector that I will have after install the new one.

[Roman Rodichev]

great question, now that you have only one antenna connected you will need to disable diversity.

interface dot0

antenna receive left (assuming your antenna is connected to the left side)

antenna transmit left

Note, that with a single antenna (no diversity), you are now prone to multipath issues

[josem_155]

Roman,

thank you for you response. Look I just installed the new antenna and the readiation pattern get down. I have not changed the configuration on the AP like you said yet, but  you think that it can be improved with that change? because Im afraid that this solution have not been the best.

thank in advanced.

[George Stefanick · Accepted solution]

Think of an antenna like a light source. Suppose you have a flood light outside of your house and you swap it with a flash light ... Its light will cover differently, right ...

So to better understand your question. What antenna did you do from and to ... Model, type, directional, and gain are all important..

[josem_155]

Im chaging one AIR-ANT24020V-R= to  AIR-ANT2452V-R. The problem is what the first one has two connectors while the other not. the gain is 2 and 5 Dbi respectively. The AP is a 1242AG model.

Thanks

[Roman Rodichev · Accepted solution]

Just do those commands I mentioned, and you'll be ok.

By default, when AP radio transmits signal it will send every other frame over a different antenna side, left right left right...

By default, when AP radio receives signal it will receive the signal on both antennas, compare the frames and choose the best one with least errors

This is called antenna diversity and it improves communication in multipath environments where there are a lot of reflective surfaces

If you connect non-diversity antenna only to one connector, half of your transmitted frames will be sent with low propagation characteristic (because there is no antenna). Receiving will still be ok, because AP will like the signal received on the one side that has an antenna.

By setting those commands I mentioned, you will be transmitting and receiving signal only through the one side where antenna is attached, and that's what you want.

[josem_155]

thank so much... now I understand it .Last question... It change affect the coverage I mean I will have less coverage because only I use one AP radio?

[Roman Rodichev]

No, coverage will actually be better because your antenna has higher gain.

On the other hand, as George is saying below, your signal quality might be worse (sometimes) if you have reflective (metal) surfaces. A good analogy is when you drive in a car and stop at a stop sign, your car radio might start sounding bad, but if you drive forward a foot it suddenly sounds better. By having two antennas you receive signal from two different points.

[George Stefanick]

Roman, great example!

But another bigger concern in my mind is TX levels at the AP

. Say the ap is powered @ 100 mW with a 5 dBi gain antenna. Todays clients are live around 40-50mW area ...

[George Stefanick]

So you know there is a more than double gain in your antennas.

For every 3 dB you gain or loss double the power...

Example --

Your AP is at 100mW with a 2 dBi antenna = 180mW

Your AP is at 100mW with a 5 dBi antenna = 370mW

These are estimates ... just an fyi

[George Stefanick]

Also if you are in a high multipath envrioment with a lot of reflections you should stick with diversity ... (2 antennas) .

[josem_155]

So.. To have diversity I need to buy another AIR-ANT2452V-R  antenna? is my AP capable to use both 5 dBi antenna?

[George Stefanick]

correct and yes. You will want to make sure the antennas are spaced appropriately 2 feet or so a part