Hi Tom, >Can you refresh me on the topic? I didn't see any >PRS10 humps here: >http://www.leapsecond.com/museum/prs10/ We had a discussion about this, and some other folks did see it also. Sometime around June last year or so, I need to dig up my measurements. >Just to get a clear idea of your lab set up; how is your counter >configured exactly; int or ext ref? trigger levels? 1X or 10X >attenuation, etc. I am using the PRS10 as the external reference to the 53132A. Maybe not a good idea? I will try another reference as well. Also, one more datapoint: I changed the phase relationship away from 80ns, and the problem seems to have gone away... I need to check into this further. Maybe it's related to the absolute phase difference between the two channels? >If you can see the readings on the 53132 display, do they also >happen when your PC (RS232 or GPIB?) is not electrically >connected to the counter? Desktop or floating laptop? RS-232, floating laptop, I get the same readings on the LED and RS232. >Is the Fury floating (wall wart) or are you using a grounded >power supply? How is the PRS10 powered? etc. The Fury wall-wart is also floating, but the PRS10 is grounded. But I think the periodicity of exactly 15s would indicate some sort of digital issue rather than analog ground loop etc, wouldn't it? >Also do the 10 MHz RF outputs show this phase jump or is it >only in the 1PPS outputs? Need to check that. thanks again for your feedback, bye, Said /tvb ************************************** See what's free at http://www.aol.com.