HI > On Feb 21, 2020, at 5:26 PM, Taka Kamiya via time-nuts > <time-nuts@lists.febo.com> wrote: > > I'm sorry, I messed up. I jumped on more advance topic than I intended. I'm > sure there were answers in the replies but they must have gone way over my > head because some of original questions still remain. I bulletized (is that > a word?) the original question with my NEW understanding. Would someone > please respond for me, point-to-point?
> > 1) A frequency counter that measures DUT basically puts out a reading every > second during the measurement. When TimeLab is well into 1000s or so, it is > still reading every second; it does not change the gate time to say, 1000s. > I understand now, Adev is about phase, not the frequency. But assuming DUT > is sine wave, if there is enough phase change, frequency do change. I think > of phase change as frequency change that is less than full cycle. So how > does counters that outputs every 1 second end up in tau of 1000s? It will > entirely miss phase change that spans more than 1 cycle. It does not come up with a 1000 s tau ADEV by doing that. The gate time would need to be open for 1000 seconds. > > 2) I recall reading on TICC manual, in time interval mode, anything that's > reasonably good is good enough, because it has time stamp and the count > reading. Clock is used to chunk the data. Is this still true? Through this > discussion, I ended up with conclusion that there is no inherent advantage > over TI measurement when compared to frequency measurement. Am I > understanding this correctly? If you are measuring the difference between two one 1 pps signals, and they are < 0.1 seconds apart, and the TICC has a resolution of 0.1 ns …. Then the reference clock for the TICC only needs to be good to 0.1 ns / 0.1 s = 1x10^-9 > > 3) I understand even the BEST counter is only good for Adev nE-12 > measurement. Then, with my collection of counters, HP53132A (which averages > tons of short period measurement), 5335A (not enough resolution), HP5370A > (interval reading is no better than frequency), TICC by TAPR, Do I even > have a chance of doing any meaningful work? (say work with GPSDO and Rb > which some of it does reach E-13) Yes, I know now, it is NOT possible to do > 1 sec Adev but say over 100 seconds? Right now, I don't have any standard > that has adev that good at 1 sec anyway. A counter that will do 1x10^-12 at 1 second would need errors below 1 ps. I do not know of any such counter. As you go to other tau’s (like 1,000 seconds) a counter that will keep a gate open for 1000 seconds might do the trick. > > 4) Would one person who has infinite patience and experience guide me > through getting one reading done correctly with what I already have? That > may include email and phone call. (I speak English and Japanese) I don't > want to lower S/N of this mailing list by doing this here. We have been doing that off list …. > > 5) One time, it was mentioned many of Adev graphs posted are basically a > graph of instruments noise graph. How do I tell when a given reading/graph > is exceeding the limit of a setup? I did do base line where same signal goes > to counter's reference input and signal input. I always have that on my > chart so traces does not go below. Is that enough? Look at the counter’s stated accuracy information and do the math. If it’s a 100 ps counter, then that is 100 x 10^-12 at 1 second. If there are no other errors, and the reference is perfect, you will hit 10X better each time the gate increases by 10X. Bob > I appreciate everyone's input. I am learning a lot but just not digesting > well enough. I'd like to do DMTD after I understand the basics. > --------------------------------------- > (Mr.) Taka Kamiya > KB4EMF / ex JF2DKG > > > On Thursday, February 20, 2020, 1:41:06 PM EST, Taka Kamiya via time-nuts > <time-nuts@lists.febo.com> wrote: > > I have a question concerning frequency standard and their Allen deviation. > (to measure Allen Dev in frequency mode using TimeLab) > > It is commonly said that for shorter tau measurement, I'd need OCXO because > it's short tau jitter is superior to just about anything else. Also, it is > said that for longer tau measurement, I'd need something like Rb or Cs which > has superior stability over longer term. > Here's the question part. A frequency counter that measures DUT basically > puts out a reading every second during the measurement. When TimeLab is well > into 1000s or so, it is still reading every second; it does not change the > gate time to say, 1000s. > That being the case, why this consensus of what time source to use for what > tau? > I recall reading on TICC, in time interval mode, anything that's reasonably > good is good enough. I'm aware TI mode and Freq mode is entirely different, > but it is the same in fact that measurement is made for very short time span > AT A TIME. > I'm still trying to wrap my small head around this. > > --------------------------------------- > (Mr.) Taka Kamiya > KB4EMF / ex JF2DKG > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
