Dr Bruce Griffiths wrote: > Didier Juges wrote: > >> Dr Bruce Griffiths wrote: >> >> >>> In principle this measurement could be made with a time interval counter: >>> PPS -> START >>> delayed 10KHz -> STOP >>> >>> Vary the delay and watch the jitter jump when the leading edge of the >>> PPS signal occurs during the 10KHz burst which was phase coherent with >>> the previous PPS pulse. >>> The only problem is finding a suitable variable delay device with >>> sufficiently low (<=1ns??) jitter. >>> >>> >>> >>> >> The delay device can be triggered by the 1 PPS, then will drive the ARM >> input of the counter, so as long as the delay device's jitter is less >> than the 10 kHz period, if we adjust the delay to 0.99985 second >> (between the last 2 periods of 10 kHz before the 1 PPS), then the TI >> counter will START on the last 10 kHz pulse before the pps, and STOP on >> the 1 PPS. >> Tek has some time delay generators in the TM-500 and 7000 plug-in >> series. I knew one day I would need one of those, I now know why :-) >> >> Didier >> >> >> _______________________________________________ >> time-nuts mailing list >> [email protected] >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> >> >> > Since the HP5370 arm input is high impedance(1 Megohm) and its input > range lies betwen -2V and +2V its desirable to drive it from a back > terminated source with an amplitude of 2V or less to avoid overdriving > (the comparators are better behaved if the input signal remains within > the specified range) the input and ensure that the pulse at the ARM is > relatively clean and reflection free. A suitable buffer can be built > using 3 74AC04 inverters as depicted below: The 74AC04 inverters load > currents are well within the specified limits even if the buffer output > is shorted to ground. Thus the driver should have a long service life. > ARM driver > > > Bruce > ________________ The trigger levels on the 5370 are strange. The normal inputs have trigger levels that can be adjusted between -1.5 and +0.6 V or something like that. I am not sure where that is coming from. For the ARM input, if someone is going to drive it with long coax cables, the best would be a 50 ohm termination right at the instrument's input. The schematic did not make it, but I believe I understand what you mean: 3 gates with common input, each output has a 150 ohm series resistor and the outputs (far end of the resistors) are tied together, to provide a good 50 ohm drive to the cable. A series capacitor would probably be recommended to center the signal around ground (assuming it's 50% duty cycle).
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