I would like to make a circuit that allows to detect activity on a RJ45 cable (on which Ethernet would be used). When the cable is only connected to a single computer, link test pusles are emitted. These signals are about 1 us long and between 0,5 mV and 3 V. Otherwise, data is Manchester-encoded, with a frequency of 100 MHz. I do not know the amplitude. I would like to detect, with a diode, activity on the RJ45 cable. As the signal is not continuous, a simple LED would not work. I also would like not to damage the signal. Do you have an idea on how it would be possible to do it?
Evaluated by measuring CM current on cable
RF current probe place on ... cable
You do not need a spectrum analyzer but an appropriate filter/amplifier+integrator. Cannot provide you with schematics but think the method may be useful for you.