Bob wrote:

Most PPS signals these days are very low duty cycle. If you AC couple them, you 
can easily be triggering on the wrong edge.

??? All of the triggers I'm familiar with have slope selection (rising edge/falling edge), and in my experience HP counters do not have problems mistaking a falling edge for a rising edge. I suppose there's always a first time, but....

See the attached image, which shows both the DC (green) and AC (red) trigger channels. The value I used for C1 came from the 5370B input amplifier. I shortened the pulse to 10uS just because 10 more uS of 0v baseline didn't really add anything useful. I've shown two trigger levels, 1.25v (half peak) and 0.5v. I would generally use 0.5 to 0.75v with a 2.5v logic pulse, unless experience showed that a different value worked better in the particular instance.

In both the DC and AC cases, the next rising edge that transits the trigger points is the rising edge of the following PPS pulse.

Best regards,


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