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Halting the ethernet signaling

Well, I got your point. It is rather a router or switch with LAN access

The cables are defined in the specification of the product, more for EMC reasons. We know that some customers might use crappy cables, but that will then be their own responsibility

You are right in all the other points about the difficulty to control what is actually hooked up on the other end of our connection

Very interesting, but as you wrote about it might mean that some customers will be having problems with compatibility. Anyway, would be interesting to try it out, at least to know the possibilities for coming products

Yes, the layout is not good (another guy on the team did it, and we actually didn't do a proper review). And it should be changed before other hardware solutions are investigated.

And, our design is not unique, a standard design should be able to pass EMC with little problems, so should ours

Ground plane was routed below the magnetics, so possibly shorting the CM coil. Termination resistors in wrong places, etc. I was just looking for a quick fix, SW is free.

I did see a skew between TX_P and TX_N signals, that shouldn't be there, and which cannot be explained with signal trace differences and impedance discontinuities. I was more inclined to blame asymmetric magnetics, but the RX_P and RX_N lines does not have the skew, and when the line auto negotiates crossover, the skew seem to follow the TX_P and TX_N lines, not the channel

Reply to
Klaus Vestergaard Kragelund
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If the noise is originating from poor board layout, then going optical isn't going to help.

Sylvia

Reply to
Sylvia Else

Likely to get product certification (?)

But if the cable ends up making a significant difference to the product's performance (unlikely?), you'll still bear the cost of customer support calls and some possible "bad feelings" (folks like to blame others).

As well as how those "other" things will behave from the perspective of your device. E.g., the MS machines on my network are responsible for almost all of the "idle chatter" -- as they try to perform various discovery and routing activities.

You needn't replace the entire fabric with 10BaseT (which would lower overall performance of the network). Rather, you could selectively define your device as having a slower i/f and let the elastic store in the switch compensate for the "speed difference".

Of course, transport delay is increased but if you're expecting any sort of timeliness guarantees the switch (and "other" traffic that it is managing) already blows those to hell.

The problem wrt doing anything "different"/unexpected/out-of-the-ordinary is that it tends to lead to the introduction of configuration options. Which are just more opportunities for things to get hosed as users poke at options without understanding their consequences (unless your market is very tech savvy). E.g., I've had to "fix" many duplex mismatches over the years for friends/colleagues/clients that didn't understand what the setting did and tinkered with it in ignorance.

That's why we prototype! :>

So, you're not trying to push the bleeding edge in DAS or something...

Well... <frown> The problem then can be perpetuated as folks don't ever realize the root cause and keep making the same mistake.

Until the "fix" isn't effective in some future situation.

I worked for a company that could never get parts made "to spec" from a particular vendor. Rather than find another vendor, they simply changed the rest of the design to reflect that component "as was".

Eventually, ownership of that vendor changed and the new crew started making the parts "to print"...

Ooops! Now the rest of the assembly wasn't compatible because it had been reengineered for the out-of-spec component. Luckily, there was enough institutional knowledge to understand how the problem had come about...

Ummm... are you sure there's nothing wonky in your switch? E.g., its a simple matter to move to another port. Or, another switch. Just to eliminate another variable.

Reply to
Don Y

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.

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

Reply to
jlarkin

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

Reply to
Arie de Muijnck

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

Reply to
John Walliker

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.

Reply to
Sylvia Else

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
Reply to
Klaus Vestergaard Kragelund

Yes, did test that :-)

Yes, also

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 to
Klaus Vestergaard Kragelund

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

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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:

Perhaps use RS485/RS422. Even TCP/IP over those can work with some work.

Reply to
Les Cargill

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