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MikroTik App
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Joined: Sun Feb 19, 2006 1:02 pm

poor performance on omni / interference?

Sun Feb 26, 2006 2:23 pm


We have just installed our first wireless AP with the OM19 integrated AP and backhaul using 2.4ghz. The omni is 7.4dbi and the backhaul 19dbi flatpanel.
The AP is on a high building and there is very little 2.4ghz traffic in this city (a scan on freq usage reveals very little traffic on all 2.4ghz channels and only 3 or 4 other APs), and the backhaul points down to the building next door (30-40 meters) where there is a 19dbi flatpanel client-unit.

On first try I could connect (from the backhaul uplink) straight to the backhaul in the AP with -21db signal. But I could not connect to the omni at all (got -65dbi signal but not possible to associate).
Doing Snooping with the Omni revealed that it got several 'ghost' APs (from th backhaul in the AP) but these ghosts had wrong MAC address and the SSID was frequently scrambled (some characters wrong).

I then tried to raise the AP 1.75meters and then I could connect (associate) from the backhaul uplink (hooray). I then raised it a further 1.5 meters only to be back to square one and the omni not working and seeing ghosts again.

I lovered the AP 1.5 meters again so I could use the omni, but I do not get very good range with this. Some clients 4-5km away can see it at -80dbi but can not associate.

On top of the building next to the AP are cell-phone sector antennas (GSM900/1800) (maybe 3 meters awayfrom the AP) as well as cell-phone point-to-point links out to other masts and also CDMA gear.
But why does this cause interference (if this is indeed what's happening) when I don't see any freq usage on 2.4ghz?

I'm finding myself using the backhaullink to put clients on....and adding another flatpanel so they work like sector antennas, but this is expensive and not what was intended. (As a test I was even able to put on a client that hooks up to the *back* of the flatpanel that looks in the opposite direction, at -90dbi and 3-4km away not good but works more or less!)

What to do? what can I try? I havent tested the exact range I can get from the omni but wil do so shortly.
Will the big 1.5m 15dbi omni antenna help on this problem?

just joined
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Posts: 7
Joined: Sun Feb 19, 2006 1:02 pm


Sun Feb 26, 2006 5:18 pm

Just measured the noise-floor on this omni, and it is anywhere from -69 to -81 db depending on the frequency in the 2.4ghz range. Is this normal? does this mean that if I choose a frequency where the noisefloor is -81 then I can only connect to it if the signal is above this?

why am I only getting a -85 db signal (and thus not able to connect) when using a 19dbi flat-panel (with atheros card) at 4km range?



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