On Sun, 10 Apr 2022 20:07:20 +1000, Sylvia Else <sylvia@email.invalid>
wrote:

>On 10-Apr-22 7:13 am, jlarkin@highlandsniptechnology.com wrote:
>> On Sat, 9 Apr 2022 21:54:53 +0200, Klaus Vestergaard Kragelund
>> <klauskvik@hotmail.com> wrote:
>>
>>> On 09/04/2022 16.14, jlarkin@highlandsniptechnology.com wrote:
>>>> On Sat, 09 Apr 2022 10:59:07 +0200, Klaus Kragelund
>>>> <klauskvik@hotmail.com> 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
>>>>
>>>> You might go optical, with SFP modules.
>>>>
>>>>
>>>>
>>> The product is just weeks away from final design, so we cannot change to
>>> optical (also, the other end does not accept optical, since it is a
>>> standard switch)
>>
>> Cat5 to SFP converters are cheap. Maybe you could add those on both
>> ends.
>>
>> Biggish switches often have SFP slots too.
>>
>>
>>
>
>If the noise is originating from poor board layout, then going optical
>isn't going to help.
>
>Sylvia

True, but the complaint was "common mode noise on the ethernet cable",
which fiber could fix.

SFPs are astounding technology for the price. 10 gbit modules are
under $20 from Amazon. I'd want maybe $2000 to make one.

We are using a Micrel laser driver chip that was apparently designed
to go inside an SFP module. We're paying about $10 for it. And that's
just one part of what in an SFP.

https://tinyurl.com/2wwty2km

plus there's the board, and lots of metal bits.

--

I yam what I yam - Popeye

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

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.

John

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?

2) Does the noise go away if the other end of the cable is disconnected,
or is connected to a different router?

3) Does the noise go away if you use a different short cable plugged
into a nearby router?

Sylvia.

On 2022-04-11 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.
>
> John

Ground loops can be a real problem, but PoE should NOT cause it because
it MUST be floating on the PD (powered device) end. Lots of PSE side
equipment has the + side grounded and switch in the - side!
See IEEE std 802.3 section 33.4.1: PD, Isolation, 1500V rms test.

A famous error here in the Netherlands was made by a yacht builder. The
functional test for the PoE powered WiFi base stations in each cabin was
only made after all (very expensive) wood ceilings were put in place.
The WiFi stations were not isolated and connected to the ship's metal
structure. All ceilings had to be re-opened and partly replaced.

Arie

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

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.
>
> John

In 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

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

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

Go optical. I haven't tested this, so it's here only as an idea starter:

https://www.fs.com/products/96396.html?country=US&currency=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