Didier Juges wrote: > The Thunderbolt's output impedance on the PPS output is much less than 50 > ohms, more like 5 ohms. > > If you terminate the other end of the cable with a good 50 ohms termination, > you will be OK, even though it would be better to put a ~47 ohms series > resistor right at the TB output before driving the cable. This will reduce > the available amplitude, but will reduce ringing even more. > > Check this page: > > http://www.ko4bb.com/Test_Equipment/CoaxCableMatching.html > > I used the PPS output of the Thunderbolt as a fast rise time pulse generator > for cable matching/reflections experiments. > > It will show you what to expect when you use that output to drive a long > cable. > > Didier KO4BB > > A 5V PECL to CMOS level translator capable of driving a 50 ohm load is shown:
http://www.eds-fl.com/~bruce/5V_PECLtoCMOS_50_OhmDriver.html <http://www.eds-fl.com/%7Ebruce/5V_PECLtoCMOS_50_OhmDriver.html> Input transistors can be 2N3907 although they will be a little slow since the transistor capacitances will be larger than usual because of the low collector base voltages, however the input stage propagation delay will only be a few nanosec. For a faster input stage use high ft low capacitance transistors (eg BFT92/93). The values of the output series resistors can be changed to 240 ohms to provide a better match to a 50 ohm load if the load and consequently lower reflections termination has significant shunt capacitance. Bruce _______________________________________________ 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.