We used to see that a lot in the old Lucent AP1000 and similar units. Two radios in the same case (at least they were 6" or so apart....). Many that used them a lot had to switch to radio versions that had no built in antenna (even if the antenna were turned off). And someone, um, dang, can't remember who, even had a custom metal shade built in a way that it would clip onto the outside of the radio and give more rf insulation.
Out here I've found that even using the same BAND for backhaul and distribution doesn't work nearly as well as using different bands for each service. And far too many operators still think that higher power is the answer to all problems. When what we should really be doing is running LOWER power and making up for it with bigger antennas at the client end. When we dropped our amps and went from 4 watt sites to 1 watt (often less) sites we more than doubled out speeds, even at 15 to 18 miles ptmp! This is possible because the new radios have such high receive sensitivity. Wanna know what you're doing to yourself with your OWN noise? One day put one of your APs into client mode. You'll likely be shocked at how many of your own APs you pick up and how far away they are. Especially when using sectors vs. omnis. I have one site that has a 13 dB sector that can see an AP that's putting out a mere 1 watt. The two systems are roughly 30 miles apart! I didn't even know that they had line of site! It's crazy stuff. Interference is very real. We are usually our own worst enemy. We have a competitor that's starting to loose customers to us (luckily most of our competitors do a pretty good job so churn, both ways, is pretty low, good for the industry's reputation...). I just pulled a customer from him. His tower is about 8 miles from them. On a 19dB antenna they picked him up at -60 dB. I calculate that as a 43dB output on his AP!!! That's basically a 1 watt amp with a 12 dB omni. The legal limit is 36 dB or 4 watts. If we figure that every 3 dB is double the wattage this then becomes: 39dB is 8 watts, 42dB is 16 watts, 43dB is somewhere around 20 watts! He's nearly 7 times the legal power limit! There are two major problems with this. First and most important to him is that his service is starting to really suck. He's got ap's all over hell and high water and they are ALL over powered like this. At least the ones that I've detected are. I've left him to self destruct because he's not been too much of a problem to my network (yet). By using very good gear and intelligent designs we're able to (mostly) ignore him. But he's undoubtedly causing massive problems for himself. Speeds on his system were 1.5 down and .5 up. The other problem is that I can, at pretty much any time, shut him down with a complaint to the FCC. Well, they'll not likely shut him down, but they WILL investigate and make him drop back down to the legal levels. And once they do that he'll be forced to replace CPE all over the place because the customer's antennas will no longer be big enough to handle the range he's designed into his system. So his services suck (based on HIS customer's calls to US) and he's just begging to be slapped around by the FCC. Bad for his customers, bad for his business, bad for our industry etc. All because of limited channel choices and high AP density required by terrain. Oh yeah, OUR service when we switch folks? steady 3 down, 15. to 3 up. We even saw 4 x 4 once. I'll have to upgrade my backhaul to do much better than that. Oh yeah, that particular customer's home shoots RIGHT through another farmer's 40' high Rohn two way radio tower that's about 2 or 3 miles away. MY system comes into the old provider's CPE (the customer owned it so we used the same radio) at about a -77. Because this site will now be a tower site for us we'll probably replace the CPE with a 24dB grid before too long, just to help overcome any issues caused by the other house etc. that sits in the RF path. Never ever forget: Wireless is 50% science and 62% black magic! Kurt, I totally believe your findings. We see similar (though not as extreme) examples all day long out here in the real world. laters, marlon ----- Original Message ----- From: "David E. Smith" <d...@mvn.net> To: "WISPA General List" <wireless@wispa.org> Sent: Wednesday, April 29, 2009 7:42 AM Subject: Re: [WISPA] RB333/433 eliminating self-interference test > Kurt Fankhauser wrote: >> Thoughts anyone? > > Out of idle curiosity, did you try testing with two cards on the same > board, but with both cards and pigtails wrapped in foil, or otherwise > "insulated" from one another? With the two cards just being an inch > apart, I imagine you'd still have that nasty crosstalk even with the > insulation, but I don't know of anyone who's actually tested that > specifically. > > David Smith > MVN.net > > > -------------------------------------------------------------------------------- > WISPA Wants You! 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