On 11/04/2022 10.25, Arie de Muijnck wrote:> On 2022-04-09 10:59, Klaus Kragelund wrote: >> Hi >> >> I am working on a product that connects to an access point via >> ethernet 100 Base TX >> I am having some problems with common mode noise on the ethernet >> cable, and have been trying all sorts of tricks, nothing help as of now >> >> So staring at the signals on the cable, there is a lot of traffic even >> though we just use it for sub kB/s traffic. The reason for the traffic >> is the MLT-3 encoding, so even with nothing to transfer, the line is >> busy as xxxx >> >> So it occurred to me, why not just disable the line, and send a >> preamble with some data, and shut down the line again to remove this >> EMC issue. It seems there is a low power mode, that could be used. >> >> Anyone tried something like this? >> >> We are using DP83822 >> >> :https://www.ti.com/document-viewer/DP83822I/datasheet/GUID-024DD3DE-0EAA-4F18-9EF3-9C0B37F9613C#TITLE-SNLS505SNLS5058467 >> >> -- >> Klaus > > > Hi Klaus, > > I could not find this info in the thread, but: > > You DO use CAT 5 SFTP instead of the noise radiating UTP type? > And with properly terminated connectors (the shield fully > connected, not just through a pigtal wire? > > Products are EMC (CE) qualified using 'the recommended cable'. > Recommending CAT5 SFTP (or better) to the end user allows you to use > SFTP during EMC testing. What the customer actually uses is his > responsibility. > > I noticed this type of problems when my UTP cabled network was radiating > so much noise that it affected my measurements. Replacing everything > with SFTP solved a lot of problems. >Yes, we are using the shielded cable CAT5. Tests done here and in a notified body did not match up, and we have narrowed it down to them not using the correct cable, just as you mention
Halting the ethernet signaling
Started by ●April 9, 2022
Reply by ●April 15, 20222022-04-15
Reply by ●April 15, 20222022-04-15
On 11/04/2022 10.53, John Walliker wrote:> On Monday, 11 April 2022 at 09:25:32 UTC+1, Arie de Muijnck wrote: >> On 2022-04-09 10:59, Klaus Kragelund wrote: >>> Hi >>> >>> I am working on a product that connects to an access point via ethernet >>> 100 Base TX >>> I am having some problems with common mode noise on the ethernet cable, >>> and have been trying all sorts of tricks, nothing help as of now >>> >>> So staring at the signals on the cable, there is a lot of traffic even >>> though we just use it for sub kB/s traffic. The reason for the traffic >>> is the MLT-3 encoding, so even with nothing to transfer, the line is >>> busy as xxxx >>> >>> So it occurred to me, why not just disable the line, and send a preamble >>> with some data, and shut down the line again to remove this EMC issue. >>> It seems there is a low power mode, that could be used. >>> >>> Anyone tried something like this? >>> >>> We are using DP83822 >>> >>> :https://www.ti.com/document-viewer/DP83822I/datasheet/GUID-024DD3DE-0EAA-4F18-9EF3-9C0B37F9613C#TITLE-SNLS505SNLS5058467 >>> >>> -- >>> Klaus >> >> >> Hi Klaus, >> >> I could not find this info in the thread, but: >> >> You DO use CAT 5 SFTP instead of the noise radiating UTP type? >> And with properly terminated connectors (the shield fully >> connected, not just through a pigtal wire? >> >> Products are EMC (CE) qualified using 'the recommended cable'. >> Recommending CAT5 SFTP (or better) to the end user allows you to use >> SFTP during EMC testing. What the customer actually uses is his >> responsibility. >> >> I noticed this type of problems when my UTP cabled network was radiating >> so much noise that it affected my measurements. Replacing everything >> with SFTP solved a lot of problems. >> >> Arie > > But it can introduce some new ones as it introduces the possibility of > ground loops (as does PoE). Some, but not all devices have capacitors > in series with the shield connection. > Last time I was at an EMC test lab all the ethernet cables hanging on > the wall for customers to use were shielded. I was told that most > customers preferred to use shielded cables for testing. I brought my > own unshielded cables as we were able to pass (just) with unshielded. > I did come across some unshielded patch cables that worked fine but > radiated badly at 125MHz. Swapping them for alternatives solved the > problem, so do try substituting patch cables if you are having difficulties. > > JohnIn our system we follow standard procedure, that is to have a transformer to isolate the system from the ethernet line, and then a 1500V rated capacitor to earth
Reply by ●April 15, 20222022-04-15
On 11/04/2022 11.00, Sylvia Else wrote:> On 09-Apr-22 6:59 pm, Klaus Kragelund wrote: >> Hi >> >> I am working on a product that connects to an access point via >> ethernet 100 Base TX >> I am having some problems with common mode noise on the ethernet >> cable, and have been trying all sorts of tricks, nothing help as of now >> >> So staring at the signals on the cable, there is a lot of traffic even >> though we just use it for sub kB/s traffic. The reason for the traffic >> is the MLT-3 encoding, so even with nothing to transfer, the line is >> busy as xxxx >> >> So it occurred to me, why not just disable the line, and send a >> preamble with some data, and shut down the line again to remove this >> EMC issue. It seems there is a low power mode, that could be used. >> >> Anyone tried something like this? >> >> We are using DP83822 >> >> :https://www.ti.com/document-viewer/DP83822I/datasheet/GUID-024DD3DE-0EAA-4F18-9EF3-9C0B37F9613C#TITLE-SNLS505SNLS5058467 >> >> >> >> >> -- >> Klaus > > Obvious questions to ask are: > > 1) Does the noise go away if the board is not powered? >Yes, did test that :-)> 2) Does the noise go away if the other end of the cable is disconnected, > or is connected to a different router? >Yes, also> 3) Does the noise go away if you use a different short cable plugged > into a nearby router? >Sadly no, by I do see a small difference in the resonance peak frequency when using longer ethernet cable. If I use a longer mains cable, I can move the mains resonance at 30MHz radiated tests easily
Reply by ●June 16, 20222022-06-16
Klaus Kragelund wrote:> Hi > > I am working on a product that connects to an access point via ethernet > 100 Base TX > I am having some problems with common mode noise on the ethernet cable, > and have been trying all sorts of tricks, nothing help as of now > > So staring at the signals on the cable, there is a lot of traffic even > though we just use it for sub kB/s traffic. The reason for the traffic > is the MLT-3 encoding, so even with nothing to transfer, the line is > busy as xxxx > > So it occurred to me, why not just disable the line, and send a preamble > with some data, and shut down the line again to remove this EMC issue. > It seems there is a low power mode, that could be used. > > Anyone tried something like this? > > We are using DP83822 > > :https://www.ti.com/document-viewer/DP83822I/datasheet/GUID-024DD3DE-0EAA-4F18-9EF3-9C0B37F9613C#TITLE-SNLS505SNLS5058467 > > > > > -- > KlausGo optical. I haven't tested this, so it's here only as an idea starter: https://www.fs.com/products/96396.html?country=US¤cy=USD&languages=English&paid=google_shopping&gclid=CjwKCAjwqauVBhBGEiwAXOepkQjO0zc0YTKm3zO27fEChydyUJUJfkKkDgDHz_C7MCRvcD9-kRGbZBoCbeoQAvD_BwE You may still get emitted energy in harmonics of 25 MHz because of the interface to the PHY chip. I guess it's MII these days. Or: > we just use it for sub kB/s traffic. Perhaps use RS485/RS422. Even TCP/IP over those can work with some work. -- Les Cargill
