I just unsheathed an Ethernet cable and probed it with a scope. What I see is an almost perfect 60Hz sine wave signal. Why is this? I can't find anything that would explain to me why this is the case.

What I expect to see at least is a modulated signal, but in this case all I see is a clean sine wave. I am continuously running a ping command on the computers connected to both ends of the Ethernet cable.

  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer. – Ron Maupin Aug 10 '17 at 22:56

A: your scope (or probe, or whatever you have between the probe and the wire) isn't fast enough.

B: you are not running a differential probe.

Ethernet signals are differential - the 60 (or elsewhere 50) Hz picked up from electrical supply wiring is picked up by both wires equally and rejected at the receiver, which only looks at the difference in the signals. If you don't do the same, you can't see the signals (it's a scale problem - they are there, but hard to see.) Also, if you can see the 60 Hz wave, you can't see the 100-250MHz-class signals at the same time on nearly all scopes, as the time domain is vastly different - so even if your scope is fast enough, your display window isn't.

If your scope and probes are fast enough, try sampling both wires in one pair and subtracting (the crude approach to a differential signal.)

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