Earth loops in IT equipment !!!

[sivan_and]

I was wondering Is there anything like this in IT equipment ? I had this problem of power supply loops & motor boating when i was young diy..in the early eighties..but always found the solutions myself..BUT in my home network setup..I was disgusted with so many power adapters each feeding various devices, I want to know whether if i can connect the wireless router (Airlink 101) & Siemens broadband DSL modem on a common power supply of 1.5 Amps both using 12 Volts.(Airlink draws around 250~300ma & DSL modem 300ma MAX)
The ethernet port of Modem connects to internet port of the router. Is it safe to to run both on a common supply..will there be any loops in the "LAN" cable ???

[star882]

Ethernet is AC coupled so no problems.

[sivan_and]

Originally Posted by star882

Ethernet is AC coupled so no problems.

how ? pls explain ..(ur dealing with high speed digital signals)

[kevinkr]

I haven't been able to determine whether or not ethernet is required to be AC coupled, but it is 2, 3, and 5 voltage level differential bipolar signaling (AC) depending on the speed.. Given it is differential it would likely be AC coupled but isn't necessarily so, however IIRC pulse transformers are pretty commonly used in ethernet applications..

Ethernet - Wikipedia, the free encyclopedia

Ethernet over twisted pair - Wikipedia, the free encyclopedia

Ethernet physical layer - Wikipedia, the free encyclopedia

Seem likely to me that it would be AC coupled precisely to avoid issues with ground loops.

[sivan_and]

Originally Posted by kevinkr

I haven't been able to determine whether or not ethernet is required to be AC coupled, but it is 2, 3, and 5 voltage level differential bipolar signaling (AC) depending on the speed.. Given it is differential it would likely be AC coupled but isn't necessarily so, however IIRC pulse transformers are pretty commonly used in ethernet applications..

Ethernet - Wikipedia, the free encyclopedia

Ethernet over twisted pair - Wikipedia, the free encyclopedia

Ethernet physical layer - Wikipedia, the free encyclopedia

Seem likely to me that it would be AC coupled precisely to avoid issues with ground loops.

best way will be open the case and find out...the coupling/capacitor or transformer or Opto (least likely reason being slowness)

[star882]

Every Ethernet port I have seen is transformer coupled.

[sivan_and]

Originally Posted by star882

Every Ethernet port I have seen is transformer coupled.

In the DSL side its a/c coupled (telephone line) to a balanced transformer..but ethernet side is not sure..goes straight to a IC chip & could see chip caps around.

[leadbelly]

Except for: Power over Ethernet - Wikipedia, the free encyclopedia which cannot be isolated

[sivan_and]

Originally Posted by leadbelly

Except for: Power over Ethernet - Wikipedia, the free encyclopedia which cannot be isolated

What isolation..ethernet signal or power (shock ?)

[leadbelly]

Originally Posted by sivan_and

What isolation..ethernet signal or power (shock ?)

Not sure if that is a question, but no, if DC is flowing between 2 devices, they simply cannot be galvanically isolated, even if there is is one of those pulse tranformers on the signal circuitry.