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I have been having some problems with my Ethernet lately and would like to test the cable. I was thinking I could borrow a signal generator and oscilloscope from work and get them hooked up to the cable and send a 25 MHz sine wave down the line and measure the attenuation at the other end. Does this make sense? How should I go about connecting the coax from the signal generator and scope to an RJ-45?

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    \$\begingroup\$ Just throw the cable away and use a new one. Cheaper, easier and less time consuming. \$\endgroup\$ – PlasmaHH Aug 21 '18 at 13:14
  • \$\begingroup\$ A balun is used to convert from differential signals to single-ended signals. But there is a lot more testing to Ethernet cable than attenuation: crosstalk, return loss, propagation delay, etc. \$\endgroup\$ – davidmneedham Aug 21 '18 at 15:20
  • \$\begingroup\$ Unless you have loose connections, your problem is unlikely to be attenuation though you could have a problem with the wrong impedance, or especially with the conductors being used by the wiring scheme as twisted pairs not being the pairs of wires that are actually twisted together in the cable. These things can be detected, but you may need better equipment than you have access to, and you'll probably need a known-good cable to establish a reference of what you should be looking for. \$\endgroup\$ – Chris Stratton Aug 21 '18 at 17:11
  • \$\begingroup\$ @PlasmaHH, not an option: the cable is running through the walls of the house. \$\endgroup\$ – psusi Aug 27 '18 at 18:03
  • \$\begingroup\$ Assuming you already ruled out switch and Ethernet card, the only thing wrong must be the cable, so what does measuring more than continuity/resistance gain you? Btw a lot of switches have the ability to measure impedance discontinuities \$\endgroup\$ – PlasmaHH Aug 27 '18 at 19:02

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