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In Reply to: RE: Yes. I am looking especially for galvanic isolation posted by beppe61 on August 01, 2016 at 03:12:28
fmak hates it when I post pictures!The original intent:
Ethernet can support long runs such that equipment on different ends can be powered from distant branches of the AC power distribution system within a building or across different buildings.This means there can be significant ground offset between Ethernet devices. The Ethernet coupling transformers mitigate these ground offsets and provides galvanic isolation.
The transformers also provide for common mode noise rejection as well as relatively high voltage isolation between the primary and secondary sides of the transformer.
Simplified Schematic Example
The small transformers can be separate devices on the PCB or built into the RJ45 Ethernet jack itself.
If your low-cost USB / Ethernet extender device does not use some sort of transformer (magnetic coupling) or optical coupling you will not achieve the benefit of galvanic isolation. One way to tell w/o breaking into the device is to use a DMM to measure for DC continuity from the input to output end of the device. Transformers are meant to pass AC. You do NOT want DC continuity between each end.
Example Ethernet transformers
Example RJ45 jacks with built-in transformers
Edits: 08/01/16Follow Ups:
Hi ! sorry to disturb you again.
In case the extender ports will not be transformer-coupled, are you aware of RJ-45 adapters (male to female) with transformers inside ?
That would solve the issue.
Thanks a lot again for the very valuable advice.
Have a nice day !
Kind regards,
bg
Edits: 08/02/16
transformer coupling a signal pair isolates but can be at the expense of signal integrity. There are issues of transformer quality as well as ground bounce and lack of symmetry.
IT guys talk about 'isolation' in isolation as though this is a magic fix. Well, it ain't, as those with electronics know-how will know.
Hi !
thanks for the valuable advice.
I think I see your point. Transformers really have and effect on signal.
Giving the good reviews of some lan streamers like the microRendu I guess it is an issue of build quality ?
However ... i will do a simple experiment. I will use this extender without the accompaining psu.
If the usb dac will not work it means that it does not receive electrical power from the pc. So is at least electrically isolated.
I have to see inside and I will post some pictures to get advice.
I do not know if the sender takes power from the pc by the way.
I am quite sure that the receiver has its own psu.
Thanks a lot again.
Kind regards,
bg
Was that your contribution for the day? Helpful as usual, I see.
Edits: 08/02/16
I don't know if they exist. I have never had the need to investigate because Ethernet devices that are truly compliant will already be galvanically isolated w/o the need for inline transformers.
Hi ! thanks a lot indeed.
I will open them and see inside.
I really hope it will be the case.
Kind regards,
bg
Hi !
thanks a lot for the very valuable advice.
Asa i will receive them i will open and see. I am crossing fingers.
Actually they are not exactly cheap on the catalog.
I am very curious to listen.
At present i am using only a cheap isolator with Audum chip.
Kind regards,
bg
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