Killing Bluetooth Pollution - Page 1
Forum section: electronics / general

author: Stonent
author_rank: Super Contributor
timestamp: May 02, 2015, 06:11:26 pm
content: Where I work we have an area that has some testing devices that are Bluetooth capable. They are self contained and are designed to connect to a PC via USB or Bluetooth in order to to provide an interface via a diagnostic port.We used to use them over the Bluetooth connection but found that the devices were infinitely more reliable when simply hard wired to the PC via USB and using a long cable that's designed for the differential signaling interface used in testing.The problem is, there's no way to turn the Bluetooth broadcasting off, and the vendor pretty much says that as well. So the one or two areas nearby that have to use the Bluetooth connection sometimes take an hour or so of fiddling to pair a replacement device if it gets damaged because of the 20 or so other devices that are always running in pairing mode and Windows 7 or 8 will show 20 Unknown devices and maybe one or two will identify themselves every scan. Funny thing, and this may not have been considered when designing, but the devices go into pairing mode whenever powered up, whether it is tapping into the power rail on the device being tested like it would normally do in BT mode, or USB. So if you're truly using it in BT mode, it only gets powered up when connected and pollution is low. But when tethered over USB, it is always on and broadcasting.This also has a negative effect on the Wifi signal in that area even with brand new top of the line Cisco access points. (Yes the APs are 5GHz capable but because of interference issues that we encountered with some older equipment we have 5GHz turned off for now)So given that we cannot make any hardware modifications to these testing devices to disable bluetooth does anyone have any ideas for impeding the BT signal? The testing devices are about as big as your entire hand and are affixed to the power pole near each computer station.Anything done has to at least look presentable in the event the suits swing by for a visit, or bring an entourage of potential customers, yet also be doable without a bunch of expense.I was thinking something along the lines of an inexpensive plastic box lined with some material like metal screen, foil, thin sheet metal etc.Basically some kind of 2.4GHz Faraday cage.We aren't yet equipped to monitor the Signal to Noise ratio of the Wifi in the area but that hopefully will be coming soon with some new monitoring software that we'll be getting. Really I can only just see what nearby PCs are doing. And the devices that NEED to run over BT, sometimes have issues with slow connection times or timeouts which I think are related to the BT pollution.Any other ideas or suggestions?

author: aveekbh
author_rank: Regular Contributor
timestamp: May 03, 2015, 05:49:12 am
content: Quote from: Stonent on May 02, 2015, 06:11:26 pmI have built something like this - used a cardboard box lined with copper tape and connected to mains earth. I added a layer of RF absorbent foam to further absorb the radiated energy. I think normal antistatic (black dissipative) foam would also be good enough.QuoteIf you can, get a spectrum analyser and check what the offending devices are doing. BT uses packets as short as 300 us with frequency hopping, so the spectrum analyser needs to be able to sweep fast enough - Agilent E4407B can handle it.Hope this helps!

author: electr_peter
author_rank: Unknown
timestamp: May 03, 2015, 06:30:47 am
content: Quote from: Stonent on May 02, 2015, 06:11:26 pmI would have said to buy box of chocolates, eat them and use foil wrappers as shieldBut that may be in conflict with suits requirement.Find appropriate size and form box and cover it with aluminium or copper foil. There is no reason to go to extreme measures (real EMC chambers) just to kill BT.

author: Jeroen3
author_rank: Super Contributor
timestamp: May 03, 2015, 12:51:42 pm
content: You should get some anti-wifi wallpaper.http://arstechnica.com/information-technology/2012/05/10/anti-wifi-wallpaper-lets-cellular-and-radio-through/

author: Stonent
author_rank: Super Contributor
timestamp: May 03, 2015, 02:54:12 pm
content: Quote from: Jeroen3 on May 03, 2015, 12:51:42 pmWell it's in a large building with masonry walls and concrete floors, and the affected area it self is several hundred square feet total. Everything affected is within that several hundred square foot area and not fully enclosed so it wouldn't help a whole lot.

author: Stonent
author_rank: Super Contributor
timestamp: May 03, 2015, 03:10:52 pm
content: Quote from: aveekbh on May 03, 2015, 05:49:12 amActually we do have 2 or 3 3GHz Spectrum Analyzers. I think one is HP and the others are Agilent. However they are in a restricted access electronics lab and my ability to acquire one would be extremely unlikely.I had forgotten we have a Fluke network analyzer that does wifi stuff. I guess I could do some readings with that for rssi and dbm loss.Hopefully they'll get the monitoring software deployed for the Cisco APs and I can get some heat readings.