Hello, Thanks to all for your replies and suggesting especially Brooke, Bruce and Pete. I am already using the Stanford technique with the 1 kHz output. That's how I get 2 x 10E-12/sec accuracy. Using this technique, the accuracy should be 7.9 uHz at 10 MHz (7.9E-13). But I don't reliably achieve this. I reliably get 20 uHz, sometimes 10 uHz and I do have resolution to parts in 10E-13, but the last digit isn't reliable. Brooke do you do better than me here with this technique? I see you publish results with accuracy better than I can achieve, I was wondering how you do it. I think the answer from Bruce identifies my problem. I need to take more care with my measurement techniques If it was easy, people wouldn't charge $20 - 50k for a box that dies it well. Thanks all again Martyn

Hi Martyn: An important aspect is to properly set the trigger levels for each input. A mistake I made early on was to ass-u-me that the 1 PPS trigger level should be half of 5 Volts, i.e. 2.5 volts, but that's very wrong. The best approach is to install a BNC-T connector at the front panel and use a scope probe to look at the signal. The best place to trigger is at the steepest slope. Have Fun, Brooke Clarke http://www.prc68.com/P/Prod.html Products I make and sell http://www.prc68.com/Alpha.shtml All my web pages listed based on html name http://www.PRC68.com http://www.precisionclock.com http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Web Cam Martyn Smith wrote: > Hello, > > Thanks to all for your replies and suggesting especially Brooke, Bruce and > Pete. > > I am already using the Stanford technique with the 1 kHz output. That's how > I get 2 x 10E-12/sec accuracy. > Using this technique, the accuracy should be 7.9 uHz at 10 MHz (7.9E-13). > But I don't reliably achieve this. I reliably get 20 uHz, sometimes 10 uHz > and I do have resolution to parts in 10E-13, but the last digit isn't > reliable. > > Brooke do you do better than me here with this technique? I see you publish > results with accuracy better than I can achieve, I was wondering how you do > it. > > I think the answer from Bruce identifies my problem. I need to take more > care with my measurement techniques > > If it was easy, people wouldn't charge $20 - 50k for a box that dies it > well. > > Thanks all again > > Martyn > > > > _______________________________________________ > 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. >

> Hello, > > Thanks to all for your replies and suggesting especially Brooke, Bruce and > Pete. > > I am already using the Stanford technique with the 1 kHz output. That's how > I get 2 x 10E-12/sec accuracy. Martyn, Just to make sure -- when you do this with your SR620 (i.e., 1000 externally gated TI readings per second), what sort of wiggling do you see in the last digit of your display? Also, how much did the mean change over a minute or two? Finally, if you display jitter instead of mean, approximately what numbers are you seeing with your setup? > Using this technique, the accuracy should be 7.9 uHz at 10 MHz (7.9E-13). > But I don't reliably achieve this. I reliably get 20 uHz, sometimes 10 uHz > and I do have resolution to parts in 10E-13, but the last digit isn't > reliable. Where did you get the 7.9 number? /tvb