Hello, I use TimeLab and the HP5370B and a Prologix GPIB interface. After making several 10 Hr runs with the same oscillator I noticed something When laying the successive runs on top of each other there are little blips and bumps that line up perfectly on top of each other. For example each run has a small blip at 10 seconds in, and a rise from 50 seconds to 150 seconds This was happening when I was using the NI PCM-CIA interface as well. If time is the X axis and variation of frequency is the y axis , how can something repeatedly happen at 2 points in time. I am sampling at 1 S per sec and 10 Hours duration in these particular traces. Can I have some sort of cabling issue? Or is there something in ADEV algorithm that forces this to happen.? Thank you Paul A. Cianciolo W1VLF http://www.rescueelectronics.com/ Our business computer network is powered exclusively by solar and wind power. Converting Photons to Electrons for over 20 years

> Hello, > > I use TimeLab and the HP5370B and a Prologix GPIB interface. > After making several 10 Hr runs with the same oscillator I noticed something > > When laying the successive runs on top of each other there are little blips > and bumps that line up perfectly on top of each other. > For example each run has a small blip at 10 seconds in, and a rise from 50 > seconds to 150 seconds > > This was happening when I was using the NI PCM-CIA interface as well. > > If time is the X axis and variation of frequency is the y axis , how can > something repeatedly happen at 2 points in time. The x-axis should be thought of as an indication of period, not absolute time. The whole idea behind the ADEV plot is to tell you how accurate the clock can be expected to be when observed at recurring intervals of T seconds, where T is any given tau value on the X-axis. This can be confusing because when you watch the ADEV trace appear over time, it seems to advance at a rate reminiscent of the time label on the X-axis. In reality this is because the graph can only be updated for a given tau interval once enough samples are available at that timescale. Say you' re checking your watch for accuracy on a day-to-day basis (tau=86400 seconds). You couldn't make an accurate judgment if you only checked it after a single day. You wouldn't feel confident in your t=86400s accuracy estimate until you had checked it every day for a week, for instance. Even then, you might observe that your watch gains an average of 2 seconds per day the first week, 3 the next week, and 8 the week after that. For this reason, you'd need to run your ADEV test for several days if you want to see what the graph looks like at 86400 seconds... and the error is likely to be large when that part of the graph first appears. In your case, if you look at the phase and/or frequency difference plots you may be able to discern some kind of regular variation or structure that recurs every 10 seconds. An ADEV test that runs long enough will often exhibit small bumps corresponding to HVAC cycle times, day/night temperature changes, and other effects. If you were sampling fast enough, you'd also tend to see bumps at the power-line frequency and its first few harmonics. -- john