high rf noise with 1242ag

Unanswered Question

I have a 1242ag w/ ios 12.4(10b)JA. Clients drop connection and get long delays when working on wireless A or B. I have recieved errors on the ap "maxretries" is there an ios update or procedure guide I can follow to help with my problem? I have set both interfaces to best range, hopping a slower data rate would help but at times clients can't even get a DHCP address. Any help would be greatly appreciated.

Thanks

Mark

I have this problem too.
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CFayNTAdmin83 Thu, 01/29/2009 - 09:40

If you only have one AP, then I would make sure that the AP is at full power (20dBm) and that you have either channel 1,6, or 11 set in the AP for the 2.4Ghz radio. For the 802.11A, I usually set the channel to something in the UNI 1 or 2 band (channels 36 to 64). The A radio should probably be at full power too if the AP is by itself. If you notice that the channel and power is off, you can probably set the data rates back to "defaults" so you can get better speed. Also, make sure that your antennas either point directly up at the ceiling or down at the floor (if the ap is mounted on the ceiling). The antenna orientation can also affect client connections....

I have the channel set to 6 I have also tryed 1 and 11 with no improvment. using a spectum analizer i am consistently getting spikes of -30dbm across the entire band with all in house ap turned off and no external ssid visible. I have also done a spectum analysis around the outside of the building an noice leval are much lower with spikes in the -70dbm range.

mark.cronin Thu, 01/29/2009 - 12:00

A few questions

How many APs have you got?

Have you tested with other APs?

Which antenna are you using?

Have you tested with other Antenna?

Are all the wireless client the same?

Are they all using the same wireless drivers?

1) 1 AP

2) Yes same results

3) 5.2Db cisco for G and 6Db cisco for A

4) yes dlink 14db

5) most but not all using atheros ar5006x with driver version 7.4.2.75 and intel 3945abg with latest driver.

6) yes

The -30dbm spikes across the entire band are killing me. Is there any procedures for determining source?? I have a metageak wispy 2.4x with chanalizer 3.2 on the same tablets (motion le1700) having problems.

Thanks for any help you can offer.

Mark

mark.cronin Thu, 01/29/2009 - 12:27

What industry are you in?

Is it a normal office building or warehouse environment?

CFayNTAdmin83 Thu, 01/29/2009 - 12:11

Since you said the noise levels were higher inside, the cause of the interference is most likely inside your building. Do you have production lines or machines in your building? You'd especially want to look for a device that uses a microwave technology. Microwaves are in the 2.4 Ghz range and can cause problems like that. Do you have any 802.11n equipment in the area? If you had a rogue AP with 802.11n enabled on 2.4Ghz it could possibly cause interference across the band. Since you have a scpectrum analyser, I would try to find the highest signal inside your building and search the area there to see if you notice any rogue equipment. Also, check out your neighbors in that area too, they may have a bridge beaming 2.4Ghz at you. It would be even worse if it was an 802.11n bridge, since they'd probably have the 40mhz channel bonding turned on. Did you just notice the interference or has it been there for awhile?

It has been a problem sence before i took over the client. This is a medium sized medical practice I don't believe any of thier medical equipment uses microwaves. They have no radiolagy equipent. there is a hospital across the street but using the spectrum analizer the spikes are not present outside the building between the hospital and medical practice so unless the beem is highly directional and is over my head I doubt they have anything to do with. Another thing i have noticed is it comes and goes at random for random periods of time from a few minutes to half the day. results from carrier busy test at a quiet time while having no issues.

Frequency Carrier Busy %

2412 0

2417 1

2422 0

2427 2

2432 2

2437 1

2442 2

2447 0

2452 1

2457 1

2462 1

mark.cronin Thu, 01/29/2009 - 13:34

As mentioned previously by another poster this could be 802.11n, does your wi-spy support 802.11n - you have said that it affect 802.11b 2.4ghz and 802.11g 5ghz - 802.11n can cover both spectrums. it maybe worth getting a 802.11n wifi cardbus and seeing if an 802.11n BSS is in the area.

Scott Fella Thu, 01/29/2009 - 14:01

The Wi-Spy will pickup 802.11N by showing a larger bell shape than a normal 802.11b/g 20mhz channel. Since you said this is a small medical practice, do you happen to have cordless phones. You can capture the spectrum using wi-spy so can you post it?

there are no cordless phones although there are some bluetooth headsets but these are in the busines office about 50 ft from the doctors using the wireless. there is an old microwave over that blows out the entire spectrum but I have told them they can't use anymore and the problem still occurs when microwave is not in use. this is a 25 doctor practice in two buildings so it is not really small, the second building with same equipment and same config works great. I have already left this client for today so I can post the capture tomorrow. do you know if there is a directional antenna I can use with the wi-spy as this may help the determine were the noise is coming from. Thank everyone for all the input.

scottmac Thu, 01/29/2009 - 17:05

IT could be so many things, not just in teh 802.11 bands, but multiple / harmonics.

Look for things like bluetooth speakers (headsets, cell phones looking for their pairing partner - did you have *YOUR* cell phone bluetooth turned on?), wireless entry alarms, wireless doorbells ...

Then start looking out the windows and / or go to the roof and look to the 360 degree horizon for point-to-point links ... small microwave dishes, yagis, short omnis, etc ... take your spec up their and take a directional sniff. It might be something like a paging tower in the neighborhood.

Then start checking for things like wireless (but not necessarily 802.11) EKGs, BP system, telemetry systems (like remote-wear & dial-up report stuff).

You can Google for radio tower maps to see who's got what in your area. I susally also Google the local map to see if there are any obvious interfereres (like railroad relays, radio towers, industry ...).

Good luck

Scott

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