Cisco Yagi AIR1949 polarization change

remi-reszka · ‎03-14-2010

Hi there,

Few times I heard you can change the polarization of the Cisco Yagi antennas from vertical to horizontal by turning the cubical part of the antenna by 90 degrees. What do I gain from doing that and how would it improve my signal lever and SNR levels on point to point over 2km distance and with use of 2 bridges BR1310G? At the moment I get pretty low values, -65dB and around 17-23dB SNR.

Thanks in advance.

Scott Fella · ‎03-17-2010

The main reason you would change the antenna polarization is to provide more channel separation. This is good when you have multiple bridges (4 or more) or interference in the channel your bridges are on. For example... if you have 4 2.4ghz bridges, 3 using channels 1 ,6 and 11, you might be able to set the fourth to channel 1 and setting the polarization opposite of the antenna being already used for channel one on the other bridge. You would also try to separate the two bridges on the same channel as far possible as you can. These two methods help to aid in channel separation.

-Scott
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remi-reszka · ‎03-17-2010

Hi Scott and thanks again for your help. I have only 2 bridges in point2point configuration so guess here no need for antennas polarization change, actually I was going to do that today but I'll leave it then. We checked the connectors, realligned the antennas and now get around -61dB signal strength and SNR jumps like a crazy from 20dB to 12dB, what could be causing that? We installed the bridges and antennas very close to huge telecoms antennas, do you think that could be causing the low SNR values?

On the other hand, we have around 200 PCs connecting a server on the other side. I deployed WPA-TKIP encryption so we did some tests. WIth around 20 stations connected we have a very good and stable link. Those 20 PCs generate about 200Kbps traffic. Now, when we connect around 200 PCs that generate around 2.5Mbps the link saturates very quickly and responses to the server over the link come to 300-500ms and worse, as opose with the 20 PCs, the responses are about 2-3ms.

Another observation, when we disable the encryption and connect all the 200 PCs, the link seems to be stable and responses from the server are mainteined at around 30ms, it jums occasionaly to 60-70ms but accasionally.

Do you think low values of SNR could be causing this? What can we do in this situation? We cannot leave the client without any security on the wireless link.

Please respond today if you can, I am at the client's site already so I could use your expertise.

Thanks in advance,

Remi