Very fast time-stamping like a stable 5GHz counter? The resolution of a 200ps (one shot) interpolator can be replaced by a 5GHz time-stamping counter.
On Thu, Apr 26, 2018 at 12:28 AM, Bob kb8tq <[email protected]> wrote: > Hi > > Unfortunately there is no “quick and dirty” way to come up with an accurate > “number of digits” for a > math intensive counter. There are a *lot* of examples of various counter > architectures that have specific > weak points in what they do. One sort of signal works one way, another signal > works very differently. > > All that said, the data you show suggests you are in the 10 digits per second > range. > > Bob > >> On Apr 25, 2018, at 3:01 PM, Oleg Skydan <[email protected]> wrote: >> >> Dear Ladies and Gentlemen, >> >> Let me tell a little story so you will be able to better understand what my >> question and what I am doing. >> >> I needed to check frequency in several GHz range from time to time. I do not >> need high absolute precision (anyway this is a reference oscillator problem, >> not a counter), but I need fast high resolution instrument (at least 10 >> digits in one second). I have only a very old slow unit so, I constructed a >> frequency counter (yes, yet another frequency counter project :-). I is a >> bit unusual - I decided not to use interpolators and maximally simplify >> hardware and provide the necessary resolution by very fast timestamping and >> heavy math processing. In the current configuration I should get 11+ digits >> in one second, for input frequencies more then 5MHz. >> >> But this is theoretical number and it does not count for some factors. Now I >> have an ugly build prototype with insanely simple hardware running the >> counter core. And I need to check how well it performs. >> >> I have already done some checks and even found and fixed some FW bugs :). >> Now it works pretty well and I enjoyed looking how one OCXO drifts against >> the other one in the mHz range. I would like to check how many significant >> digits I am getting in reality. >> >> The test setup now comprises of two 5MHz OCXO (those are very old units and >> far from the perfect oscillators - the 1sec and 10sec stability is claimed >> to be 1e-10, but they are the best I have now). I measure the frequency of >> the first OCXO using the second one as counter reference. The frequency >> counter processes data in real time and sends the continuous one second >> frequency stamps to the PC. Here are experiment results - plots from the >> Timelab. The frequency difference (the oscillators are being on for more >> than 36hours now, but still drift against each other) and ADEV plots. There >> are three measurements and six traces - two for each measurement. One for >> the simple reciprocal frequency counting (with R letter in the title) and >> one with the math processing (LR in the title). As far as I understand I am >> getting 10+ significant digits of frequency in one second and it is >> questionable if I see counter noise or oscillators one. >> >> I also calculated the usual standard deviation for the measurements results >> (and tried to remove the drift before the calculations), I got STD in the >> 3e-4..4e-4Hz (or 6e-11..8e-11) range in many experiments. >> >> Now the questions: >> 1. Are there any testing methods that will allow to determine if I see >> oscillators noise or counter does not perform in accordance with the theory >> (11+ digits)? I know this can be done with better OCXO, but currently I >> cannot get better ones. >> 2. Is my interpretation of the ADEV value at tau=1sec (that I have 10+ >> significant digits) right? >> >> As far as I understand the situation I need better OCXO's to check if HW/SW >> really can do 11+ significant digits frequency measurement in one second. >> >> Your comments are greatly appreciated! >> >> P.S. If I feed the counter reference to its input I got 13 absolutely stable >> and correct digits and can get more, but this test method is not very useful >> for the used counter architecture. >> >> Thanks! >> Oleg >> 73 de UR3IQO >> <1124.png><1127.png>_______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
