[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] Getting Better All the Time: JILA Strontium Atomic Clock Sets New Records
On Mon, 27 Apr 2015 14:49:37 -0400 d0ct0r t...@patoka.org wrote: In another advance at the far frontiers of timekeeping by National Institute of Standards and Technology (NIST) researchers, the latest modification of a record-setting strontium atomic clock has achieved precision and stability levels that now mean the clock would neither gain nor lose one second in some 15 billion years*—roughly the age of the universe. http://www.nist.gov/pml/div689/20150421_strontium_clock.cfm You can find the referenced paper at: http://dx.doi.org/10.1038/ncomms7896 respectively: http://www.nature.com/ncomms/2015/150421/ncomms7896/full/ncomms7896.html Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ 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] Question about UT1 and the IERS Reference Meridian
Okay, I've tried to research this for a few days, and seem to be running into conflicting data. Some articles say that UT1 is based on the IERS Reference Meridian (IRM). Other articles say that UT1 is based on mean solar time at the Prime Meridian (Greenwich). It can't be both! Which one is it? In other words, which meridian would I need to stand on to indicate Solar Noon as 12:00:00.000 (UT1) on a day of the year where the equation of time is 0 seconds offset? From what I can reckon, a 200-400 millisecond difference exists between the two longitudes, which are separated by about ~102 meters at Greenwich. So, if UT1 (and hence UTC) is based on the IRM and not the Prime Meridian, then at some point did clocks have to be adjusted ~200 milliseconds away from the Prime Meridian when the IRM was defined? Or was it sloppy and they treated the two as one and the same? Anyone know? ___ 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] More recent information on BG7TBL GPSDO?
Bob, Understood regarding NTP; I just thought if it had to be monitored anyway it could pull double duty. I guess that is not so important. It appears they are selling well enough to keep up with or otherwise deplete their supply of surplus OCXOs, so there is probably little motivation to fix problems. Maybe some additional information will surface in the future. The design looks simple enough perhaps if the hardware is documented properly an alternative firmware might be developed - that is a long shot I know. John On Tue, Apr 28, 2015 at 4:47 PM, Bob Camp kb...@n1k.org wrote: Hi The accuracy required by NTP can be met with a $20 GPS board. It’s much easier to simply do a stand alone device than to try to tie everything together. Fewer ground loops / fewer things to go wrong / easier to keep running. The frequency offset in the device appears to be a design choice made by the people running the project. There is no way to find out if they have changed their design other than buying more devices. That *assumes* that the later devices have later firmware versions …. Bob On Apr 28, 2015, at 2:57 PM, John Laur johnl...@gmail.com wrote: Hello all. Long time listener; first time caller. I picked up one of the BG7TBL GPSDO units from Ebay, and I am still waiting for it to arrive. I understand it has its flaws, but my needs are fairly simple, and I think it will serve. My intent is to use it as a reference which is better than the 0.1ppm TCXO in my HF radio, an ANAN-100D (HPSDR architecture); I would like a PPS reference so that I can experiment with timestamped IQ samples; and I would like to build an NTP server using a BeagleBone Black. I think this will serve to do these things even if it is not the ideal equipment. I have read I believe all of the previous discussion on this list over the past few months including the excellent study by John KE5FX, and I had a few questions to see if there had been any new developments. I understand some may have communicated with the designer as well. Does anyone else have further information on the serial interface? Is the NMEA data directly to/from the U-Blox module or does the internal firmware filter/augment it to allow monitoring or tuning of other internal parameters - for instance can one set cable delay? What is its suitability for running as a GPS/PPS reference for an NTP server? Any other software suggestions for keeping an eye on it? Second, has the small frequency error identified by John been corrected, or is it a problem endemic to the design (I think maybe this was identified as a resolution limit of the DAC providing OCXO control voltage; could it be dithered?) As this is my first moderately accurate device in the shack, is my best approach just to put it on the shelf, leave it on for a long time, and trust it? I can see how its easy to begin the slide when there is only one clock to stare at skeptically. Thanks, John Laur K5IT ___ 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 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.
[time-nuts] Important parameters for a GPS/GNSS antenna
Moin, I recently discovered openEMS[1], which is, very simply put, a fancy antenna simulator. I played a little with it and thought about trying to optimize an GPS patch antenna design for timing use. But I had to discover that I actually do not know what to optimze for. There are many paramters I can think of (RHCP/LHCP, symmetry of gain, feedpoint impedance vs frequency, stability of phase centre,) which all seem to be to some extend important, but which ones do actually matter for the timing reference performance? My google skills failed to locate any relevant documents on this topic. Could someone be so kind and give me some pointers, what to search for, documents or the like? Attila Kinali [1] http://openems.de -- _av500_ phd is easy _av500_ getting dsl is hard ___ 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] UT+ receivers are all spoken for
My internet has been down all day, and now that it's back up, I see a bunch of requests for receivers. They're all spoken for now, and in fact maybe a bit over-subscribed. I'll contact each of you individually who responded offline. Bob ___ 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.
