Interference w/ a capital "I"

Last Friday night all of our 2.4Ghz SM’s on 2 AP’s dropped like a rock. We have not been able to locate the interference as of yet - need an analyzer. Here is a shot of the built-in analyzer with everything on the tower powered down. What should a decent site look like? Next time I will do a survey before we deploy - this time we just installed and it worked, until now that is.


Yep, the 2.4 is used up! I look for -70 when running a spectrum test.

Maybe you can run the new 5.4

Yikes! Whatever it is it’s very close.

With some diplomacy, you should be able to get them to co-ordinate freq’s with you.

When did you first launch your 2.4?

The whole story. We’ve had Breezeaccess on the tower for years. Then people start complaining of low bw speeds. So, in an attempt to satisfy them we move from a FHSS system to a faster DSSS canopy system. We were able to have them running at the same time on the same tower by crunching the 3 sector Alvarion to 2460-2480Mhz, and only using 2 sectors of the 6 sector Canopy cluster at 2415. After 2 weeks of in service and switching over 25 or so subs, changing the RJ-58 to cat-5 at every subscribers house, suddenly the 25 subs drop sync and never come back. (Friday August 31st, at 7:40PM, just before the long weekend). Thinking hardware, our tower guy comes and replaces the 2 AU’s - nothing. Doing a spectrum scan shows, well, you know. Yesterday was spent calling everyone else who was doing any wireless in the town to see if they added any equipment, made any changes, ect. Today we took an SM out as a spectrum analyser to try to find the source. We found it to be coming from a food (canned corn) processing plant. I think it’s more mechanical RF ie from lighting or motors or something. It’s a fenced in gated plant with security guards and the whole bit. Should be fun asking the security guard to let us in because your plant is emitting RF strong enough to knock down our entire customer base. 1/3 of the customers have come back on-line after changing to 2435Mhz - although upload eff. is around 18%.

So, to answer the question, first 2.4 in 2003. First Canopy 2006 (on another tower). First Canopy on this site - 2 weeks ago.

Ok, you might try turning your other 2.4 off and see if it’s self interferance.

We run 3 of the 2.4 120 degree cyclones… We have put in a 4th cyclone but it was very difficult, the sm units have to be put on the strongest cyclone. or it will cause customers to drop like flies.

From that analysis it looks like the upper portion of the band is fairly quiet compared to the lower portion. What freqs is your equipment on?

The BreezeAccess is running on 2460, 2470, and 2480. The scan that I posted was taken with everything turned off on the tower. Also we ran for 2 weeks fine with it on. We have tested the Canopy on 2415 and 2435 and they don’t interfere with each other or the Alvarion. The plan was to migrate to the Canopy one freq. (2 sectors) at a time. First 2415 then 2435 which would cover 240 degrees and 90% of our customers. Then shut down the BAII and turn on the last 2 sectors (2455) and go like mad to cut people over, actually we would notify the customers first, but you get the idea. The 2 “humps” is a definite signature of the plant. It looks exactly the same standing on the ground with an SM pointed at it. We actually used a reflector dish to cut down the beamwidth and make a more directional antenna for pinpointing the source. I hope they let us in there to find out what is causing it - even if it can’t be fixed I’m curious as hell. It may be a little tricky to find. The closer we got the more intense the signal was, and it didn’t really matter where the antenna was pointing. Standing right up close to the fence there was just signal everywhere. With the reflector on and as close as we got, the humps were as low as -36. It looks to me like 2 distinct bands centered at 2412 and 2447. Wireless video camera perhaps?

Supposing they do let us in there to look around what would be the best way to find it? SM analyzer? True spectrum analyzer? We were thinking about getting a Fluke Analyzair, anyone used one or can recommend another one?

If talking fails probably you could rent spectrum analyzer and report them to the government.

In the meantime you could use the hidden menu and use the high frequencies for your transition.

Highly likely it’s wireless cameras. Just ran into that recently. They come out of the box at full power and may or may not have Tx power adjustments.

Turned out to be 2 wireless video transmitters. The trucking company that hauls away the corn husks was using one on either side of the truck to watch the truck being filled from the cab. One was on channel A (2412Mhz) and the other on channel C (2450Mhz). They had direct LOS to the watertower. We GPS’d it to be 1180 ft from the tower. FCC docs say 112mW. They were using 3dB omni’s.

Getting a little sidetracked but…
Are these calculations correct?

TX Ant=3dB
RX Ant=8dB
Power delivered = 20.5+3-91+8 = -59.5

Shouldn’t I be seeing it at -59.5 rather than -45 as shown on the analyzer?

What would be the best way to measure the RF output of this device. We are starting to think it’s output is greater that 112mW reported here.

The SM spectrum analyzer shows -35 at 5 feet, but that may be as high as an SM will read so I don’t know if it’s a true reading.