Hi Everyone, So I’ve been doing some more testing today. I’ve been walking around in the same area I took the screen grab from with the Wi-Fi turned off on my Surface monitoring the 2.4GHz spectrum and everything looks normal. Then when I turn the Wi-Fi on I see the same thing as my Surface goes through its probe cycle. So Jake, you nailed it! the surprising thing for me is the fact that I have seen this behaviour run continuously for over 10 minutes. No wonder the battery life sucks ☺
Thanks to everyone for their input. I’ll continue to play around and investigate further, but this has been a great education for someone at the early stages of his wireless career. Sean From: The EDUCAUSE Wireless Issues Constituent Group Listserv [mailto:[email protected]] On Behalf Of Jake Snyder Sent: March-08-17 10:37 PM To: [email protected] Subject: Re: [WIRELESS-LAN] 2.4 GHz Interference Power and distance matter greatly in RF. Could be differences in client TX power, distance from the wispy, the client card, or even the filters in the card. Even the same make/model of card can variants in output. Partially why we can't have calibrated cards in wifi. 2.4GHz will look slightly different than 5GHz due to the the non-ofdm nature of the preamble. That signature slope away from channel is a good bet that it's the wifi from your laptop. Also, the strength is absurdly high. If the wispy wasn't on top of the source there's no way it would be at -20 without you glowing or your hair itching. Combine that with the fact that it follows him around and I'm reasonably convinced. Not saying there isn't something else, but taking a capture without the super high ACI and you'll get a better picture. Sent from my iPhone On Mar 8, 2017, at 9:53 PM, CHARLES ALBERT ENFIELD III <[email protected]<mailto:[email protected]>> wrote: Thanks Jake. I was aware of the shape of the side band, but I thought I remembered it starting 30 dB below the peak. I guess it’s more like 20. Jason’s trace seems to corroborate that. Sean’s trace seems to be 10 to 15 dB. The sideband emissions on the Revolution Wi-Fi image looks more like Sean’s than Jason’s. I think this is relevant because the nature of the OFDM sideband emissions is determined by the subcarrier width and channel width. Sean and Jason both have the same parameters for both, but in Jason’s trace the side lobe disappears into the low noise floor within about 35MHz while Sean’s doesn’t disappear into the much higher noise floor until about 55Mhz. Sean’s 20MHz channel looks much more like the 80MHz channel image on Rev Wifi. FWIW, I’m increasingly convinced your hunch is right. Perhaps I’m taking these traces from inexpensive equipment a little too literally. I know they are approximations at best, but I’m trying to figure out what’s going on. I’m hopeful that thinking this through will improve my understanding. Something in Sean’s trace still doesn’t add up for me. From: Jake Snyder<mailto:[email protected]> Sent: Wednesday, March 8, 2017 9:16 PM To: Chuck Enfield<mailto:[email protected]> Cc: [email protected]<mailto:[email protected]> Subject: Re: [WIRELESS-LAN] 2.4 GHz Interference Might check this out: http://revolutionwifi.blogspot.com/2014/08/80211ac-adjacent-channel-interference.html?m=1 There's and image there you should find similar. Sent from my iPhone On Mar 8, 2017, at 4:58 PM, Chuck Enfield <[email protected]<mailto:[email protected]>> wrote: Cool images. I’ve never tried this. I would have this afternoon, but our operations guys have the spectrum analyzer in another building. I’m a little surprised to see as nice a plot as you got in the second trace. Between near field effects and the potential to push the Rx amplifiers into a non-linear region I would have expected something more messy. Do you know what the max signal strength was in the two traces? Also, do you know how to account for the increased duty cycle in the second one? I’m wondering if this is due to different iperf behavior or if it’s weirdness caused by proximity. I’ve been doing Wi-Fi for 15 years and still find myself guessing on a regular basis. From: The EDUCAUSE Wireless Issues Constituent Group Listserv [mailto:[email protected]] On Behalf Of Jason Cook Sent: Wednesday, March 08, 2017 6:08 PM To: [email protected]<mailto:[email protected]> Subject: Re: [WIRELESS-LAN] 2.4 GHz Interference Still learning my way through signatures but I have been caught out before with the anaylzer being too close to a wifi source Below shows this on channel 132, using iperf for a data burst in the first image the anaylzer is 1m away from a Mac Air, In the second it’s a few centimetres away from it. You can really see the impact on neighbouring channels at that distance (I think there’s even a bit in the 36-40 area) I now keep the anaylzer away from wifi devices as much as possible ☺ <image003.jpg> <image005.jpg> -- Jason Cook Technology Services The University of Adelaide, AUSTRALIA 5005 Ph : +61 8 8313 4800 From: The EDUCAUSE Wireless Issues Constituent Group Listserv [mailto:[email protected]] On Behalf Of Gray, Sean Sent: Thursday, 9 March 2017 7:26 AM To: [email protected]<mailto:[email protected]> Subject: Re: [WIRELESS-LAN] 2.4 GHz Interference Nope, the spectrum analyzer is going directly into a Surface Pro 2. From: The EDUCAUSE Wireless Issues Constituent Group Listserv [mailto:[email protected]] On Behalf Of Jake Snyder Sent: March-08-17 1:30 PM To: [email protected]<mailto:[email protected]> Subject: Re: [WIRELESS-LAN] 2.4 GHz Interference Are you using a USB 3.0 hub? On Mar 8, 2017, at 1:23 PM, Jason Heffner <[email protected]<mailto:[email protected]>> wrote: I’ve seen something similar when running some of the older Cisco controllers. If you ruled out everything else and are starting to look for devices causing interference I'd check out some of your wireless mic systems. We had some 800Mhz that we had to salvage that were causing harmonic distortion on 2.4GHZ similar to this on the lower channels. On Mar 8, 2017, at 2:32 PM, Gray, Sean <[email protected]<mailto:[email protected]>> wrote: Hi Everyone, I’ve been doing a little spectrum analysis around campus and I keep seeing the same interference signature in different buildings. I was wondering if anyone had seen anything like this before. It is typically visible for well over 10 minutes at a time and then it completely disappears. Thanks Sean Sean Gray | B.Sc (Hons) Voice, Collaboration & Wireless Network Analyst ITS, University of Lethbridge ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/discuss. <Unknown Interference Source.PNG> ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/discuss. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/discuss. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/discuss. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/discuss. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/discuss. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/discuss. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/discuss.
