This is what we see from my 2db transmition site when we are taken down. Notice that both systems (left hand half comes from the cell phone tower about a mile away, right hand half is the new interference) have about the same wave shape. An 802.11 system will only do this to 2 or 3 channels at a time.
This is right at the Ritzville end of the link to Odessa. This was after the interference went away.
The Odessa end is normally the exact opposite of this.
This is a site survey a hundred feet from an AT&T tower in Ritzville, about 30 miles away from my site in Odessa. I had even worse readings IN Odessa for about two hours on Jan. 30th 2001! I was in panic mode (the signal was so strong it dumped us off line!) and didn't remember to get a screen shot of it from the Odessa side.
The interference came and went so it looked like a new link that was being tuned up. I first thought that the source was right in Odessa so we drove all around town looking for it. When we dropped down into the valley things cleared up nicely. We also looked for the signal from a hill on the south side of town but got nothing. We then went back up on the north side of town and there was the interference again!
We popped over to another hill on the north side of town and got an idea of where the interference was originating at. We then drove off into the sunset (so to speak) and took readings from all of the hilltops. Each time fine tuning our direction. About an hour later (might have been less the way I drive ;-) we were dialing the phone number on a building at the base of a really tall tower.
The interference dropped to normal levels before we even got all the way to Ritzville and has not come back so the cause of it remains unknown.... Bad radio, atmospheric skip, or just plain BM (this is the 62% Black Magic part of things). (Remember, Microwave is 50% science and 62% Black Magic.)
I called the number on the building and got passed off to three different people in three different departments. I left a message with the last one. I have to tell ya, at this point I thought for sure that it would be days at least before I could get this situation sorted out and get my customers back online. There were fresh tracks in the snow so it sure looked like there was a new install in place.
Within a couple of hours I had a call from an AT&T guy who took some info from me. He said he'd have someone call me back. I've been an ISP since '97. When the phone company says someone will call you back it's usually a LONG wait so I went back to work (things had cleared up and we were running normally by now).
It was a VERY short time later and the field tech for that site was on the phone! Turns out that the link has been up since about 1997. They had been there working on other equipment. (Here I thought I was going to get to ask them to shut it down till they quit messing with my system!!! hehehe) They dispatched the tech out for the next day to check on the radio. I think they were going to just pull it out and send it in to be checked out. The thought at the time was that it may be acting up and putting out power that it was not supposed to and may be failing (it would sure be nice if we spotted a bad radio before it failed on them!).
At this point we may have to pay them to redesign the link if this happens again. If they were to rotate their antennas 90* and go horizontal then it would open up all of the vertical spectrum in this area and that would sure help me out. Or I might pull down the omni and put in a sectored antenna pointed more toward the ground but I do have a link 7 miles from town that I need to be able to hit. If things keep working OK we'll all likely leave things well enough alone.
And I'd like to say thanks to AT&T's crew. Within hours of getting knocked off line I was talking to the guys that were in a position to help. I surely hope everyone out there learns from this and does things the AT&T way. I was so scared that I was gonna get into a pissin' match with the big boys, but they really seemed to give a darn! I've had an AT&T cell phone for many years due to the coverage in areas other than here. I'm certainly glad that I've been working with them for all these years now.