Signal strength in Cisco 1030 APs

Unanswered Question
Jun 17th, 2007

Hi,

We currently have 2 Cisco 1030 APs set up in a bridge connection (root to non-root). However, the signal strength constantly varies between -53dBm and -80 dBm (SNR also drops during this timeframe). We have checked the area with a frequency scanner and there is no noise that should interfere with the WLAN link. I have tried finding Cisco documents that specify how a radio link between 2 AP should behave (will the signal differ with increase/decrease in load?), but as far as I can see there is no documentation discussing this. We have another bridge pair a couple of meters beside this first pair, here the signal strength remains pretty constant around -53dBm, sometimes it jumps up to -80 dBm for a very short time (not at the same time as the other pair of bridges). The two bridge pairs are running on non-overlapping channels (1 and 6).

The other WLAN bridge installations that we have are also quite stable in signal strength.

Has anyone experienced something similar, or know what could be causing this?

Regards

Staale B.

I have this problem too.
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ericgarnel Mon, 06/18/2007 - 08:05

What is the distance and/or are there objects between the 2 1030 APs? Also, have your run the fequency scanner over a 24hr time period?. For example, A microwave heating up a breakfast burrito @ 8am

Also, the 1030 APs have 802.11a radios. have you considered running the bridge over that? Less interference, but may require external antennae.

You do not mention the distance between the APs

staalebotnen Fri, 06/22/2007 - 03:50

The APs we use are 1300's, not 1030's (my mistake).

The distance is approximately 60 meters, we have installed directional antennas on both APs and they are correctly aimed. We have not run the scanner for more than a couple of hours, but the signal constantly varies between -51dBm and -82dBm, so it can't be a microwave or similar (this was my first thought as well).

There is a radar installation right by, but this does not affect the 2.4GHz frequency, and the neighbour bridges (approximatly 2 meters away) do not experience this signal fluctuation.

We also thought that this could be caused by bad cabling or antennas, so we switches the cables and antennas on the 2 bridge pairs, the fluctuation followed the APs.

We are now shipping out some 1030's and will try running the 802.11a instead.

ericgarnel Fri, 06/22/2007 - 06:00

hmmm... what about foliage?

Also, the 1300 is an outdoor AP, while the 1030 is an indoor AP. Are you going to enclose the AP in a NEMA box? and/or mount the AP inside and run the LMR and/or antenna outside?

Or is this an indoor installation? We have spaces that exceed 60 meters, but also have APs or panels in those areas

bauti1428 Fri, 06/22/2007 - 07:42

What is the signal strength set to both AP's? We have a couple of cisco 1200's in here running on 2.4Ghz BG and I noticed that we were having the same issues with clients. I found out the the AP's were overlapping and it was all set to 50mw. I lowered it to 32mw and seems to be working better than when it was set to 50mw.

staalebotnen Sun, 06/24/2007 - 22:04

These AP's are installed on an offshore drilling platform so there is no foliage between them ;) Actually there is only air between them. The AP's are installed inside, with cabling extending the antennas to the outside.

To begin with all 4 AP's were set to 50mW, but we tried lowering the transmit power on all, we got it down to about 10-20mW on all of them. But we still experienced this fluctuation, the only difference was that now the signal was fluctuating between -60dBm and -90dBm, instead of -51dBm and -81dBm.

In the begingin we also had all the data-rates enabled, but then the link constantly changed data-rates. So we disabled data-rates above 6Mbps (we only need 2Mbps on the link). The link is now stable at 6Mbps, but the signal still fluctuates.

The only trafic crossing this bridge link is IP Telephone data, and the fluctuating link is degrading the quality of the conversations.

ericgarnel Mon, 06/25/2007 - 05:04

Only air - hmmm....

What if your antennas are being affected by wind gusts? What kind of antennas are you using? Do they have a high wind load?

You may need to add another layer of duct tape to hold them down ;-)

Perhaps monitoring the wind velocity during the fluctuations may indicate something (or not)

scottmac Mon, 06/25/2007 - 09:16

What flavor of "Directional Antenna" are you using?

At 60 Meters, if you get too directional (i. e., dish or high-gain yagi) your beamwidth is pretty narrow and you may see these types of fluctuations as the antennas dance in the wind ... it really doesn't take much.

You may want to verify the alignment (both vertical and horizontal) and polarity of your antennas.

Good Luck

Scott

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