Yes, you are right of course. My bad. This should have been written as: "The Thunderbolt has less than 5 Ohms output impedance, so if you get a reflection coming from the cable stubs or non-end-terminated cable back into the Thunderbolt, then you get ringing on the cable because the impedance is mismatched!" On a properly series terminated device, any reflections on the open-ended cable coming back to the source will end in the sources' 50 Ohms terminator, and be removed. One more advantage I didn't mention for series termination versus the Thunderbolt used with end-termination.
In a message dated 5/15/2012 15:03:12 Pacific Daylight Time, hmur...@megapathdsl.net writes: saidj...@aol.com said: > Also, the Thunderbolt has less than 5 Ohms output impedance, so you get a > reflection going back from the 50 Ohms end-termination anyway because the > impedance is mismatched! I think that's a different problem. If the far end termination matches the cable there won't be any reflection. If the far end isn't terminated correctly, there will be reflections from the far end. There may also be reflections from joints in cables or a Tee and input load if you are daisy chaining multiple instruments. When those reflections get back to the typical low impedance driver, they will get reflected back again. It's not uncommon to use both source/series and end/parallel terminations. The series terminator drops the signal level by 2 but minimizes reflections if you are working in a less than ideal setup. It also provides a current limit on the driver in case something gets shorted. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.