Not really, your setup requires all inputs except the very last one to be high-impedance to work, and to have a trigger point of 1.25V as well to work properly (when used with a proper 50 Ohms source). So no difference there. So it doesn't make any difference, since the same exact inputs will work just as well with the open-ended circuit if the trigger point is set to 1.25V on those inputs. Same requirement for both setups. Daisy-chaining is a bad idea because you are getting the propagation delay between the different hubs as mentioned. Using a simple T with open-ended cables would make all inputs switch simultaneously if the cable lengths after the T are the same. Daisy chaining also creates stubs along the way due to the capacitive loading on the cable at the inputs, and the small amount of additional wiring at the stub, and these stubs will cause reflections going wild due to impedance mismatch at the stub, and run amok between stubs and between the ends of the cable.
BTW: when setting the threshold to 2.5V and tapping-off somewhere in the cable, this is called reflected wave switching, as opposed to incident wave switching, which is what happens when you set the threshold to 1.25V. 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! The signal won't stop at 2.5V, it will go all the way up to 5V in static conditions just the same as in my scenario. This can be seen in the plots that Didier had sent earlier. But worst of all: if your 50 Ohms end-termination falls off, or goes away because you turn-off that piece of equipment providing that termination, then almost sudden all of your inputs can see 10 Volts on the line, and could blow up due to overload. Having a 1.25V threshold input seeing a 10V signal is not a good idea.. You get all the drawbacks and more, and no real advantage. At least when connecting to e.g. a Thunderbolt output that has << 50 Ohms series impedance. bye, Said In a message dated 5/15/2012 13:44:42 Pacific Daylight Time, dave.martind...@gmail.com writes: It is worth noting that skipping the end termination is probably a bad idea when daisy-chaining a signal from one output to more than one device input. The input at the end of the cable will see a clean rise from zero to 5 V (or whatever the driver's open-circuit voltage is), but the other inputs along the length of the cable will not. They will see an initial rise from 0 to 2.5 V as the series termination at the driver and the cable impedance act as a voltage divider while the cable is being charged. Later, they will see another step change from 2.5 V to 5 V as the reflection returns from the open-circuit far end of the cable. If the input threshold is automatically set at half the input voltage swing, the input could trigger on the outbound or the reflected pulse, or even somewhere in between. This is in contrast to having a 50 ohm termination at the end of the cable (plus the 50 ohm series termination at the source), where all inputs along the length of the cable see a single edge transition from 0 to 2.5 V. They will each see the edge at a different time due to propagation delay, but all will see a clean edge. Dave _______________________________________________ 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.