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I am working on LAN Bypass circuit for 1000 Mb/s Ethernet ports. I need to use relays to turn the bypass mode or no link mode on during power failure.

My doubt is whether the relays should be used between RJ45 & Magnetics i.e Line side or between Magnetics & Ethernet PHY i.e. PHY side.

Also, if someone can help with some information on HW implementation of LAN Bypass will be helpful!!

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  • \$\begingroup\$ relays will be un-controlled impedance, in a stored/reflected-energy critical application. \$\endgroup\$ – analogsystemsrf Mar 30 at 17:19
  • \$\begingroup\$ You're going to have to find an 8-pole, double-throw relay that has carefully controlled impedance in both positions. You can get solid-state versions, but I doubt that any mechanical versions exist. \$\endgroup\$ – Dave Tweed Mar 30 at 18:11
  • \$\begingroup\$ Is there a reason you need to use relays instead of solid-state analog switches or similar? They are made with very high pass-bandwidths and (often) matching impedances... \$\endgroup\$ – Araho Apr 2 at 22:51
  • \$\begingroup\$ Crosspoint switches need to be powered to work. A bypass function goal is to avoid ethernet link "cut" when the equipment is off. \$\endgroup\$ – zeqL Apr 2 at 23:41
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You'll need to implement your relays before magnetics else your signal will be go through two transformers and that can trigger issues. Unfortunately I haven't found the document I read few years back on this topic.

We used IM26GR relays from TE. They support up to 2500V/3000V surge and have a 0.03dB insertion loss at 100MHz. It was few years back, so you should check other suppliers for equivalent products also (Panasonic GN series, Omron G6K series or newer).

I only draw the schematic and redacted some hardware documentation but I left when the layout began. I didn't get any feedback regarding the bypass function, so I assumed it worked. Also it was not the first time the company has done an Ethernet bypass function.

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