Re: [time-nuts] Expected 10 MHz offset from a GPSDO?
Hi At the most basic level, ADEV is a standard deviation. When people read an instrument they usually want a "max error" sort of number. ADEV operates on delta between readings so a simple "three sigma" mental math conversion is not all you need. It *is* the right measure. It can take a bit of work to convert it to useful units . Bob > On Aug 20, 2016, at 7:38 AM, Charles Steinmetz wrote: > > Bryan wrote: > >> With a GPSDO as a general rule is there much variation of the 0.005 to 0.02 >> ppb range. Would there me much if only 2 satellites were visible but the >> unit was no in holdover vs say 6 satellites. I assume there is probably a >> lot of variables such as quality of GPSDO and OCXO, multi path interference, >> antenna location, etc, but worse case what would a user expect assuming the >> unit isn't in holdover. > > There are lots of ADEV plots of GPSDOs on the web, if you search for them. > Tom has the attached plot posted on his web site -- it includes one decent > (but not stellar) GPSDO, the HP Z3801. That is about what you can expect > without heroic tuning efforts (on a GPSDO that supports user fiddling, such > as the Trimble Thunderbolt). > > Since many counters gate for one second (or gate faster, then average), the > ADEV at tau=1 second is a reasonable estimate of the real-world performance > of a good counter driven by a GPSDO. Note that, since the ADEV at 1 second > depends largely on the OCXO, the heroic tuning efforts mentioned above won't > change the ADEV at tau=1 second hardly at all. That is attributable strictly > to the OCXO (unless the GPSDO is very poorly designed). Building a GPSDO > using the best OCXO available can improve things. For example, look at the > "BVA" plot -- at 1 second, its ADEV is nearly a full decade better than the > Z3801, better even than the hydrogen masers. (While I referred to the 3801 > above as "decent but not stellar," that is based on its performance at tau > from 100-100k seconds. Its OCXO -- and, thus, its ADEV -- is better than > most others at 1 second.) > > 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.
Re: [time-nuts] Expected 10 MHz offset from a GPSDO?
Hi If your time base is doing < 5 ppb per year, that is an unusual 10811. I suspect it does not spend a lot of time powered off. Bob Sent from my iPad > On Aug 19, 2016, at 10:10 PM, Hal Murray wrote: > > > kb...@n1k.org said: >> Ok let's toss some numbers into the mix. >> The counter time base one day after calibration is in the 0.5 to 1.5 ppb >> range. > > I have two 5334Bs wih opt 010. It's been many years since either was near a > calibration lab. > > One is 30 ppb fast, the other is 75 ppb fast. (I might have the sign > backwards.) > > One swings roughly 0.15 ppb over 10F. > > -- > These are my opinions. I hate spam. > > > > ___ > 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] Expected 10 MHz offset from a GPSDO?
Bryan wrote: With a GPSDO as a general rule is there much variation of the 0.005 to 0.02 ppb range. Would there me much if only 2 satellites were visible but the unit was no in holdover vs say 6 satellites. I assume there is probably a lot of variables such as quality of GPSDO and OCXO, multi path interference, antenna location, etc, but worse case what would a user expect assuming the unit isn't in holdover. There are lots of ADEV plots of GPSDOs on the web, if you search for them. Tom has the attached plot posted on his web site -- it includes one decent (but not stellar) GPSDO, the HP Z3801. That is about what you can expect without heroic tuning efforts (on a GPSDO that supports user fiddling, such as the Trimble Thunderbolt). Since many counters gate for one second (or gate faster, then average), the ADEV at tau=1 second is a reasonable estimate of the real-world performance of a good counter driven by a GPSDO. Note that, since the ADEV at 1 second depends largely on the OCXO, the heroic tuning efforts mentioned above won't change the ADEV at tau=1 second hardly at all. That is attributable strictly to the OCXO (unless the GPSDO is very poorly designed). Building a GPSDO using the best OCXO available can improve things. For example, look at the "BVA" plot -- at 1 second, its ADEV is nearly a full decade better than the Z3801, better even than the hydrogen masers. (While I referred to the 3801 above as "decent but not stellar," that is based on its performance at tau from 100-100k seconds. Its OCXO -- and, thus, its ADEV -- is better than most others at 1 second.) 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.
Re: [time-nuts] Expected 10 MHz offset from a GPSDO?
Hi I do not know of any commercial GPSDO's that do not have a holdover feature. There are a lot of variables. With a large package OCXO and a couple days operation, the numbers I gave should be good 90 to 99% of the time.(99 seconds out of 100). If the unit has such a poor antenna location that (unlike the original post) it never completes survey, then all bets are off... The basic assumption is "locked to > 4 sats at all times. That generally translates to 6 or more most of the time. Bob Sent from my iPad > On Aug 20, 2016, at 5:43 AM, Bryan _ wrote: > > Bob: > With a GPSDO as a general rule is there much variation of the 0.005 to 0.02 > ppb range. Would there me much if only 2 satellites were visible but the unit > was no in holdover vs say 6 satellites. I assume there is probably a lot of > variables such as quality of GPSDO and OCXO, multi path interference, antenna > location, etc, but worse case what would a user expect assuming the unit > isn't in holdover. > > -=Bryan=- > >> From: kb...@n1k.org >> Date: Fri, 19 Aug 2016 20:03:59 -0400 >> To: time-nuts@febo.com >> Subject: Re: [time-nuts] Expected 10 MHz offset from a GPSDO? >> >> Hi >> >> Ok let's toss some numbers into the mix. >> >> The counter time base one day after calibration is in the 0.5 to 1.5 ppb >> range. >> >> The LPRO ten years after it left the factory is in the 0.5 to 1.5 ppb range. >> >> The GPSDO when running properly should be in the 0.005 to 0.02 ppb range at >> one second. >> >> One ppb at 10 MHz is 0.01 Hz. It also is a the resolution limit on a 5335 at >> 1 second. >> >> Bob >> >> >> >>> On Aug 19, 2016, at 5:29 PM, Mark Sims wrote: >>> >>> Try driving your counter frequency reference input with the LPRO or >>> comparing the LPRO with the GPSDO. The LPRO is (most likely) much more >>> accurate the counters' internal timebase. >>> ___ >>> 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. ___ 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] Expected 10 MHz offset from a GPSDO?
Bob: With a GPSDO as a general rule is there much variation of the 0.005 to 0.02 ppb range. Would there me much if only 2 satellites were visible but the unit was no in holdover vs say 6 satellites. I assume there is probably a lot of variables such as quality of GPSDO and OCXO, multi path interference, antenna location, etc, but worse case what would a user expect assuming the unit isn't in holdover. -=Bryan=- > From: kb...@n1k.org > Date: Fri, 19 Aug 2016 20:03:59 -0400 > To: time-nuts@febo.com > Subject: Re: [time-nuts] Expected 10 MHz offset from a GPSDO? > > Hi > > Ok let's toss some numbers into the mix. > > The counter time base one day after calibration is in the 0.5 to 1.5 ppb > range. > > The LPRO ten years after it left the factory is in the 0.5 to 1.5 ppb range. > > The GPSDO when running properly should be in the 0.005 to 0.02 ppb range at > one second. > > One ppb at 10 MHz is 0.01 Hz. It also is a the resolution limit on a 5335 at > 1 second. > > Bob > > > > > On Aug 19, 2016, at 5:29 PM, Mark Sims wrote: > > > > Try driving your counter frequency reference input with the LPRO or > > comparing the LPRO with the GPSDO. The LPRO is (most likely) much more > > accurate the counters' internal timebase. > > ___ > > 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] Expected 10 MHz offset from a GPSDO?
kb...@n1k.org said: > Ok let's toss some numbers into the mix. > The counter time base one day after calibration is in the 0.5 to 1.5 ppb > range. I have two 5334Bs wih opt 010. It's been many years since either was near a calibration lab. One is 30 ppb fast, the other is 75 ppb fast. (I might have the sign backwards.) One swings roughly 0.15 ppb over 10F. -- These are my opinions. I hate spam. ___ 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] Expected 10 MHz offset from a GPSDO?
Hi Ok let's toss some numbers into the mix. The counter time base one day after calibration is in the 0.5 to 1.5 ppb range. The LPRO ten years after it left the factory is in the 0.5 to 1.5 ppb range. The GPSDO when running properly should be in the 0.005 to 0.02 ppb range at one second. One ppb at 10 MHz is 0.01 Hz. It also is a the resolution limit on a 5335 at 1 second. Bob > On Aug 19, 2016, at 5:29 PM, Mark Sims wrote: > > Try driving your counter frequency reference input with the LPRO or comparing > the LPRO with the GPSDO. The LPRO is (most likely) much more accurate the > counters' internal timebase. > ___ > 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] Expected 10 MHz offset from a GPSDO?
Try driving your counter frequency reference input with the LPRO or comparing the LPRO with the GPSDO. The LPRO is (most likely) much more accurate the counters' internal timebase. ___ 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] Expected 10 MHz offset from a GPSDO?
On Fri, Aug 19, 2016 at 12:24 PM, Hal Murray wrote: > > lister...@gmail.com said: >> Connecting the 10 MHz output to the Channel A input (on the 5334B) or the >> frequency input (on the 5370B) and setting 50 Ohm termination and AC signals >> but without any other input or external reference results in a frequency >> that is off by about 0.1-0.2 Hz. Is this amount of offset expected or a sign >> something is not right with the GPSDO? > > Your GPSDO is more accurate than your counter. You are measuring the > frequency offset of the crystal in the counter rather than the GPSDO. > > You may have to stand on your head to understand what I'm trying to say. It > will be obvious once you see it. > > > If/when you power cycle the GPSDO (without power cycling the counter) you can > watch it shift when it locks up to GPS. If you disconnect the antenna it > will stay unlocked and you can watch the crystal in the GPSDO drift as it > warms up. > > If you unplug the counter for a while but leave the GPSDO powered on, you can > watch the crystal in the counter warm up. (Turning it off isn't good enough, > it keeps the crystal warm even when the switch says off.) > > If you have a GPIB connection to the 5334B, you can get a few more digits by > asking it to count for 99 seconds. If you get that working and your lab is > not air conditioned, you can see the temperature effects on the 5334B. > > Thanks to everyone for the replies, this definitely helps clear things up. I had my suspicions that I wasn't measuring what I thought I was as the resulting ADEV curve I was getting in Timelab (I forgot to mention I have a Prologix GPIB->USB interface and have been using it for logging/capture) had the '\_/' (down, flat, up) shape that I gather you get from OCXO's. I did also have a suspicion that this could lead down a slippery slope of needing another GPSDO to compare it with and then and then... ;-) (While I see there is a 5071A available on ebay right now, those are somewhat out of my budget by several orders of magnitude...) Thanks, Tim ___ 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] Expected 10 MHz offset from a GPSDO?
lister...@gmail.com said: > Connecting the 10 MHz output to the Channel A input (on the 5334B) or the > frequency input (on the 5370B) and setting 50 Ohm termination and AC signals > but without any other input or external reference results in a frequency > that is off by about 0.1-0.2 Hz. Is this amount of offset expected or a sign > something is not right with the GPSDO? Your GPSDO is more accurate than your counter. You are measuring the frequency offset of the crystal in the counter rather than the GPSDO. You may have to stand on your head to understand what I'm trying to say. It will be obvious once you see it. If/when you power cycle the GPSDO (without power cycling the counter) you can watch it shift when it locks up to GPS. If you disconnect the antenna it will stay unlocked and you can watch the crystal in the GPSDO drift as it warms up. If you unplug the counter for a while but leave the GPSDO powered on, you can watch the crystal in the counter warm up. (Turning it off isn't good enough, it keeps the crystal warm even when the switch says off.) If you have a GPIB connection to the 5334B, you can get a few more digits by asking it to count for 99 seconds. If you get that working and your lab is not air conditioned, you can see the temperature effects on the 5334B. -- These are my opinions. I hate spam. ___ 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] Expected 10 MHz offset from a GPSDO?
On Fri, August 19, 2016 1:20 pm, Tim Lister wrote: > reference results in a frequency that is off by about 0.1-0.2 Hz. Is > this amount of offset expected or a sign something is not right with > the GPSDO? It just indicates that the internal oscillators in your 5334 and 5370 are off by that amount. -- Chris Caudle ___ 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] Expected 10 MHz offset from a GPSDO?
Hi Tim, If I understand your post correctly, you're using a frequency counter to measure the accuracy of your GPSDO. Assuming there's nothing wrong with the GPSDO, what you're actually doing is measuring the frequency accuracy of your counters. Unless you have something that is known to be more accurate than your GPSDO, such as a *calibrated* cesium standard or hydrogen maser, then the GPSDO is the most accurate frequency reference you own. At this point, other than work on improving your antenna, all you can do is compare your GPSDO to other GPSDOs, or a cesium standard or hydrogen maser, in order to quantify the phase error of your GPSDO. Frequency error, except down at the milli-Hertz level or smaller, is no longer an issue. Bob - AE6RV.com GFS GPSDO list: groups.yahoo.com/neo/groups/GFS-GPSDOs/info From: Tim Lister To: time-nuts@febo.com Sent: Friday, August 19, 2016 1:20 PM Subject: [time-nuts] Expected 10 MHz offset from a GPSDO? Hi all, I am starting to dip my toes into time-nuttery after being interested in precise time/position for quite a while (I'm an astronomer IRL). I have acquired a used OCXO and LPRO-101 rubidium, along with a HP5334B (with Option 10) and a HP5370B from ebay and almost done assembling a TADD-2 kit from TAPR. I recently acquired one of the re-packaged Trimble UCCM GPSDO's (it doesn't seem to be one of the bg7tbl ones) from ebay and have it setup with the supplied puck antenna outside (it's not in a great location (close to the house) but I have set the elevation mask to 20 degrees in the GPSDO) and it's been running for 2 days. The results of the SYST:STAT? command indicate it is in position hold and tracking 3-4+ satellites. Connecting the 10 MHz output to the Channel A input (on the 5334B) or the frequency input (on the 5370B) and setting 50 Ohm termination and AC signals but without any other input or external reference results in a frequency that is off by about 0.1-0.2 Hz. Is this amount of offset expected or a sign something is not right with the GPSDO? Thanks, Tim ___ 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] Expected 10 MHz offset from a GPSDO?
Hi all, I am starting to dip my toes into time-nuttery after being interested in precise time/position for quite a while (I'm an astronomer IRL). I have acquired a used OCXO and LPRO-101 rubidium, along with a HP5334B (with Option 10) and a HP5370B from ebay and almost done assembling a TADD-2 kit from TAPR. I recently acquired one of the re-packaged Trimble UCCM GPSDO's (it doesn't seem to be one of the bg7tbl ones) from ebay and have it setup with the supplied puck antenna outside (it's not in a great location (close to the house) but I have set the elevation mask to 20 degrees in the GPSDO) and it's been running for 2 days. The results of the SYST:STAT? command indicate it is in position hold and tracking 3-4+ satellites. Connecting the 10 MHz output to the Channel A input (on the 5334B) or the frequency input (on the 5370B) and setting 50 Ohm termination and AC signals but without any other input or external reference results in a frequency that is off by about 0.1-0.2 Hz. Is this amount of offset expected or a sign something is not right with the GPSDO? Thanks, Tim ___ 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.
