Re: [time-nuts] ADEV with very short Tau
Thanks to you three for the answers. I don't have the skills to make a frequency mixer yet, but if I think a good tutorial, I can try ! My goal is to estimate the stability of a rubidium at 0.1s,1s and 10s. I have a GPSDO, some picDiv and one Pulse Generator. I believe the OCXO in the GPSDO (a HP 58530A) is better in stability than the Rubidium for shorts taus even if it has not a clear view of the sky (it doesn't see 6 satellites all the time) so I locked the 53131A counter to the GPSDO. I made some tests with TI measurements, see attached picture. In order to going to 0.1s, I generate 10 Hz on the pulse generator locked on the GPSDO (channel 1 of the counter) and feed the channel 2 with rubidium's 10 MHz. I get ADEV(0.1s) = 1.1 E-8 ADEV(1s) = 1.1 E-9 ADEV(10s) = 1.1 E-10 It's not wonderful, but I will be happy if I can measure 1E-9 at 0.1s. In fact, I think I measure the noise floor of the Pulse Generator. So I need to improve the setup. I manage to measure TI every 0.1s but when I want to measure frequency with Gate Time at 0.1s (with poor resolution I agree, but I will have access to a Frequency Difference Multiplier soon) it seems there is gaps in the records : for example,TI record gives with 10 Hz on channel 1: 1430740210.00.0007515140 1430740210.10.0007515140 1430740210.50.0007515140 1430740210.60.0007515125 1430740210.70.0007515150 1430740210.80.0007515140 1430740210.90.0007515135 Frequency record with Gate Time 1 s gives: 1430741572.77 1000.000 1430741573.96 1000.001 1430741575.15 1000.001 1430741576.34 1000.000 1430741577.53 1000.001 1430741578.72 1000.001 1430741579.92 1000.001 1430741581.11 1000.000 Frequency record with Gate Time 0.1 s gives : 1430741673.61000.00 1430741673.89 1000.00 1430741674.18 1000.00 1430741674.47 1000.00 1430741674.77 1000.00 1430741675.06 1000.00 1430741675.35 1000.00 First colomn is timestamp of the computer, I disabled auto trigger on the counter. What are the gaps in the frequency records, are they Dead Time ? They look to be constant, about 0,2s even when the Gate Time is 10s. Are they a problem for ADEV calculation? Thanks Claude - Mail original - De: Charles Steinmetz csteinm...@yandex.com À: Discussion of precise time and frequency measurement time-nuts@febo.com Envoyé: Mercredi 29 Avril 2015 22:04:14 Objet: Re: [time-nuts] ADEV with very short Tau Claude wrote: I know how to measure ADEV with frequency method (using a 53131A counter) or time difference method (using 1 PPS of a GPSDO for example) but I would like to measure ADEV in the sub-second domain (from 0.1s to 1s for example). Do I need a Time Interval Analyzer, if so, an HP 5371A is ok for that ? Or there are simpliest method ? You may do better with a Phase Noise measurement, depending on what instruments you have available. Generally, we think of oscillator stability over times = 1 second in the time domain, as xDEV, and stability over times = 1 second (or so) (offsets = 1 Hz) in the frequency domain, as Phase Noise. Partly, this is because of the different kinds of phenomena we are concerned about on the two different scales, and partly because different measurement techniques are better suited to each of the two time scales. These limits are not absolute, particularly if you digitize signals at a high sample rate with high resolution and do the analysis in the digital domain. Fancy xDEV/PN analyzers, such as the Microsemi 5125A, can measure xDEV down to tau = 1 mS and PN below a 1mHz offset. (But sit down before you ask the price.) I usually measure xDEV down to 0.1 second, and PN at offsets = 1 Hz. Of course, to measure xDEV at 0.1 second, you need to take at least ten TI or frequency measurements per second with no dead time between measurements, and with good accuracy -- so you need an instrument with very high resolution at short gate times and fairly fast data throughput. For that, I use a Wavecrest DTS2075. Best regards, Charles ___ 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. ___ 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.
[time-nuts] ADEV with very short Tau
Hello I know how to measure ADEV with frequency method (using a 53131A counter) or time difference method (using 1 PPS of a GPSDO for example) but I would like to measure ADEV in the sub-second domain (from 0.1s to 1s for example). Do I need a Time Interval Analyzer, if so, an HP 5371A is ok for that ? Or there are simpliest method ? Thanks for your advices. Claude ___ 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.
Re: [time-nuts] ADEV with very short Tau
Hi The cheap / simple approach for ADEV is a single or dual mixer setup. Mix the signal(s) down to an audio frequency and measure those. Mix down frequencies like 10 KHz will let you measure some pretty short Tau’s. If you want a purchased single box solution, then something like a TimePod will be needed. There are a multitude of options other than those …. Bob On Apr 29, 2015, at 5:29 AM, claude...@aliceadsl.fr wrote: Hello I know how to measure ADEV with frequency method (using a 53131A counter) or time difference method (using 1 PPS of a GPSDO for example) but I would like to measure ADEV in the sub-second domain (from 0.1s to 1s for example). Do I need a Time Interval Analyzer, if so, an HP 5371A is ok for that ? Or there are simpliest method ? Thanks for your advices. Claude ___ 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. ___ 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.
Re: [time-nuts] ADEV with very short Tau
Claude what is the simplest method to measure sub second ADEV? The answer depends on many unstated things. Among them is your definition of simple, the Frequency of the DUT, the noise floor, your budget and your available time.. After budget and frequency, the next most important thing is the noise floor or resolution that you want. Many of sub second ADEV plots you see end up showing the limitations of the tester and not the DUT. One answer If you want meaningful ADEV numbers at 0.1 sec, it is best to sample at = 20 samples per second. I find sampling at line freq or its multiple has several advantages to allow good repeatable results for 0.1 sec ADEV. For North American that means a sample rate of 60 or 120Hz. If you want to test Time-nut type oscillators with ADEV's below 1e-11 then you will need something with sub Pico second resolution. Also measuring a frequency of 5 or 10 MHz, instead of measuring say a 20 pps divided down signal has many advantages. After defining the frequency and resolution you want, it comes down to what you mean by simple.. If you need to do it just once, find a Time-nuts that already has the right capability and is willing to measure it for you. If simples does not include budget get a TimePod. If simple includes low cost and you need a low noise floor, then you're going to have to consider some custom built thing. Who is doing the building, depends on how you value your time. ws ** Hello I know how to measure ADEV with frequency method (using a 53131A counter) or time difference method (using 1 PPS of a GPSDO for example) but I would like to measure ADEV in the sub-second domain (from 0.1s to 1s for example). Do I need a Time Interval Analyzer, if so, an HP 5371A is ok for that ? Or there are simpliest method ? Thanks for your advices. Claude ___ 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.
Re: [time-nuts] ADEV with very short Tau
Claude wrote: I know how to measure ADEV with frequency method (using a 53131A counter) or time difference method (using 1 PPS of a GPSDO for example) but I would like to measure ADEV in the sub-second domain (from 0.1s to 1s for example). Do I need a Time Interval Analyzer, if so, an HP 5371A is ok for that ? Or there are simpliest method ? You may do better with a Phase Noise measurement, depending on what instruments you have available. Generally, we think of oscillator stability over times = 1 second in the time domain, as xDEV, and stability over times = 1 second (or so) (offsets = 1 Hz) in the frequency domain, as Phase Noise. Partly, this is because of the different kinds of phenomena we are concerned about on the two different scales, and partly because different measurement techniques are better suited to each of the two time scales. These limits are not absolute, particularly if you digitize signals at a high sample rate with high resolution and do the analysis in the digital domain. Fancy xDEV/PN analyzers, such as the Microsemi 5125A, can measure xDEV down to tau = 1 mS and PN below a 1mHz offset. (But sit down before you ask the price.) I usually measure xDEV down to 0.1 second, and PN at offsets = 1 Hz. Of course, to measure xDEV at 0.1 second, you need to take at least ten TI or frequency measurements per second with no dead time between measurements, and with good accuracy -- so you need an instrument with very high resolution at short gate times and fairly fast data throughput. For that, I use a Wavecrest DTS2075. Best regards, Charles ___ 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.
