> But is it really an improvement that you get out of it? The answer is > NO! He, why not? The answer is: Because you have to PAY the increase in > precision with the increase in observation time. For every increase of > 10 in precision you need to increase the observation time by 10!
Ulrich, Thanks for the long contribution. One minor correction: you imply that increase in observation time is a bad or undesirable thing. This is usually true. But not really in the case of a GPSDO. Due to GPS receiver 1PPS noise you must average over many minutes anyway so this greatly relaxes the requirements on the TIC. What you say later about the sigma-tau lines is all correct. I just wanted to point out, for example, that a picosecond accurate TIC is a complete waste for a GPSDO when the 1PPS jitter is on the order of several nanoseconds. > Would the Shera design make use of a Agilent 51151 > as a phase comparator its noise floor would start at > 5E-10 @ 1s which is a REAL improvement by a factor > of almost 100!!! For any given precision the Shera TIC > will need 100 X the time that the 51131 needs. Don't mislead yourself. At 1 s you are limited by GPS 1PPS noise. Having a better TIC doesn't fix this. If your GPS noise is 2e-9 at 1 s you don't really need a TIC that is good to 5e-10 at 1 s. So the gain isn't as useful as you might think. I should remind readers that the Shera design came from an era of S/A and Oncore VP receivers where the modern numbers you throw around do not apply. /tvb _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts