Intel: Usb3.0 cables interfere with wireless mouse and other 2.4ghz devices. - Page 1
Forum section: electronics / general

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: November 18, 2012, 10:16:54 am
content: http://www.intel.com/content/www/xa/en/io/universal-serial-bus/usb3-frequency-interference-paper.html

author: M. András
author_rank: Super Contributor
timestamp: November 18, 2012, 12:28:01 pm
content: arent all of the usb cables shielded?

author: SeanB
author_rank: Super Contributor
timestamp: November 18, 2012, 01:17:38 pm
content: Up to a point, but shielding becomes ineffective when the wavelength approaches the length of the cable.

author: jahonen
author_rank: Super Contributor
timestamp: November 18, 2012, 02:09:30 pm
content: I think that the shielding effectiveness is primarily due to low shield impedance, at microwave frequencies the shield braid should be very dense to have good shielding properties. This of course means that a good cable will be more expensive.And of course, another weak point are the connectors, as it is often difficult to maintain 360 degree shield continuity, that's why good RF connectors have such a connection for the shield. A pigtail ground connection is a no-no. Even slight sloppiness in shield continuity may cause tens of dB reduction in shield effectiveness.Regards,Janne

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 18, 2012, 03:06:04 pm
content: For some reason, I can't seem to reproduce the problem. I plugged in a USB 3 hard drive (in a plastic case) and put it right up against the antenna on my wireless router, yet the router does not report a higher noise floor. Maybe it only shows up if a particular line is just about the right length.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: November 18, 2012, 03:24:35 pm
content: Quote from: NiHaoMike on November 18, 2012, 03:06:04 pmYour wireless router probably has a 1 W transmitter or thereabouts. This is going to completely drown out any interference from the USB cable. These tests were made with wireless mice using their own dongles, plugged in to the USB port right next to where the HDD was plugged in. I bet you that these dongles are much lower power than your wireless AP, and more importantly, that the mouse (which is using a battery) has a much lower power too. And we also don't know which modulation type these dongles were using, which may affect their susceptibility to interference.

author: tom66
author_rank: Super Contributor
timestamp: November 18, 2012, 03:50:17 pm
content: I thought wifi was limited to 100mW max?

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 18, 2012, 04:02:49 pm
content: Quote from: nitro2k01 on November 18, 2012, 03:24:35 pmTransmit power has no effect on the receiver, which is what measures the background noise.Quote from: tom66 on November 18, 2012, 03:50:17 pmClient cards generally max out at 100mW to save power, although it turns out that counterintuitively, in many situations, a higher peak transmit power lets you use a higher bitrate and actually saves power in addition to giving a higher throughput for the entire network. Good routers are commonly available at well over 100mW, with my rather ordinary RT-N12 outputting a total of 300mW. I have seen commercial grade routers as high as 3W. The main problem is that high power transistors that work at 2.4GHz are rather expensive.

author: Unknown
author_rank: Unknown
timestamp: November 18, 2012, 05:32:06 pm
content: Another minor issue is that maximum transmit power in the 2.4 GHz ISM band is limited to 30 dBm (1 W) or even 20 dBm (100 mW) in many parts of the world.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: November 18, 2012, 06:20:42 pm
content: Quote from: NiHaoMike on November 18, 2012, 04:02:49 pmHuh? Are you telling me that the mouse's transmit power has no impact on which levels of interference the receiver (dongle) can accept before failing to pick up the signal?

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: November 18, 2012, 07:11:30 pm
content: Quote from: tom66 on November 18, 2012, 03:50:17 pmIn the UK more than half of the 2.4GHz ISM has historically been allocated to military (MoD) and they actually pay the license fees for this part of the spectrum use. I think their approval is one of the reasons max Tx power for ISM users cannot be increased at the moment. I have no idea of what MoD allowed max Tx power is! Kilowatts?Leo

author: SeanB
author_rank: Super Contributor
timestamp: November 18, 2012, 07:22:01 pm
content: At 2.4 GHz you can go up to 1500W, though admittedly most is contained in a cabinet and makes the inside objects rather warm.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 18, 2012, 07:35:03 pm
content: Quote from: nitro2k01 on November 18, 2012, 06:20:42 pmThe transmit power of a transceiver and its receive sensitivity are separate. For single band WiFi, it is a half duplex system meaning that the transmitter does not operate at all during receive.Increasing the transmit power at the other end will improve the (local side) SNR, but would have (ideally) no effect on the background noise level.

author: Unknown
author_rank: Unknown
timestamp: November 18, 2012, 07:36:42 pm
content: Quote from: SeanB on November 18, 2012, 07:22:01 pmFair enough, although the EIRP is fortunately much lower. 1500 W EIRP would quickly get the attention of your local equivalent of the FCC unless you live in a very remote area. Not to mention possible health effects.Quote from: NiHaoMike on November 18, 2012, 07:35:03 pmDon't the receivers employ some form of auto gain control?

author: SeanB
author_rank: Super Contributor
timestamp: November 18, 2012, 07:42:59 pm
content: Increasing Tx power makes the Rx side easier, but with a duplex link you will run onto problems of receiver overload during your transmit time, and with higher losses in the switching, and a need for better shielding and decoupling, especially as you make the units smaller and smaller and try to fit it all into a single chip.

author: T4P
author_rank: Super Contributor
timestamp: November 18, 2012, 07:54:42 pm
content: But ... there are USB WiFi dongles the size of a wireless mouse reciever ... Imagine how poor the signal reception has to be!I wonder how you can stuff all the gobbins of a wifi transceiver into something so small.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: November 18, 2012, 08:11:48 pm
content: Quote from: NiHaoMike on November 18, 2012, 07:35:03 pmOh, I realize I didn't read your original post when writing my second reply. Maybe the answer is that your AP's noise floor detection isn't all that sophisticated.

author: G7PSK
author_rank: Super Contributor
timestamp: November 18, 2012, 08:54:08 pm
content: Quote from: alm on November 18, 2012, 07:36:42 pmI know of amateur radio operators who use the magnetron's from microwave ovens for point to point communications. One uses the local church tower for height.