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Fixed Wireless Technology

Ain't No Cure for Summertime RF Interference

ISPs discuss the potential terrestrial and solar causes of interference in long distance point to point wireless links.

[October 5, 2004]

On the ISP-Wireless list in September, KP asked:

"Did anybody get unexplained 5.8GHz interference yesterday in the early morning hours or today in the predawn hours. I saw whole band noise level increase of 10-15 dB which lasted 2-2.5 hours and affected my links in all directions at two of my sites. Just curious if others saw anything. We had this same issue last year about this time."

Many had similar suggestions.

[PJ opined] "Solar flare activity? Magnetic atmospheric interference? These have been known to cause RF issues for many years on a very wide range of frequencies."

[GM agreed] "We saw a similar phenomenon yesterday morning in 900 MHz. Noise at all APs across our entire service area went up by almost 20dB. 5.8 was seeing some pretty spectacular fades as well, but that wasn't a noise increase like you describe.

We have been seeing more than usual fading in 5.8 for about two weeks now. The long haul links are experiencing about 45 dB of fade some mornings, 5:30 - 9:00 am generally. In our area this is normally an early summer problem."

[BD added] "Yes, we saw it on two links last night. Only short drops then nothing all ok. I hate responding to stuff like that."

KP responded:

"Well, I was figuring it had to be atmospheric conditions of some sort. And it has been up and down for about the last couple weeks. GM, whereabouts are you? We're in the thumb of Michigan. I know you're across the border there somewhere. I was beginning to think you'd swung one of those monster dishes in my direction :)"

[GM replied] "We connect to fiber a few miles north of Toronto. . . . Propagation has been more than a little weird recently."

[JR added] "Propagation issues, with certain weather conditions, we have seen here in North Central Ohio for years. This usually happens two times a year, spring and fall when the air is extremely still, and weather conditions seem are extremely nice for all outdoor activity, right at the time you think your network would be running the smoothest. Air temps are running +/- 20 degrees from the water temps and a usual noticeable fog layer forms near the body of water and thickens to the point to fade out normally very good links. We have seen 25+ dB of fade and have heard of greater. People forming links over or near regions that these conditions can form need to be aware of them and either plan higher than normal fade margins or know they may have some outages during these conditions. Or on the lighter side you could buy a really big fan and blow the air around a bit to get rid of it.... :-)"

[GM agreed] "You said it. I get a kick from hearing about 30 miles with 2' dishes. You would try that up here only once. :)"

KP thanked everyone for their responses:

"All this feedback is enlightening. This also reinforces my theory that 2' panels won't cut it for 20 mile links either (which is what I'm running). Twice a year for two and a half years I've seen this. It's time to fix it."

—End