Re: [time-nuts] Beginner's Atomic Clock
Hi You probably are not going to find the Nano’s on the used market. The last one I worked with was very much a pre-production unit and that was only a few years back. Indeed if you are simply looking for a lab clock, the miniature Rb’s may not be the best choice. Their stability is generally not as good as that of their bigger cousins. That applies to temperature as well as short term stability. Since you pay a premium for the smaller parts, the “bang for the buck” really isn’t there in a home bench application. If indeed you are trying to build something to go in a drone or put into space, they make a lot of sense. If you are carrying it on your back along with all the batteries to power it, again a very reasonable thing to go with. Lots of fun !!! > On Sep 17, 2019, at 7:18 AM, pisymbol . wrote: > > On Mon, Sep 16, 2019 at 11:00 PM Dana Whitlow wrote: > >> All of the available Rb standards that I've seen have a 10 MHz output, >> Some have a >> 1 PPS output as well. >> original buyer could save a few bucks. My PRS-10 is one of these. >> >> > How does this compare with say a used Accubeat AR133/60 substance? I also > see they have a Nano unit that looks awesome (but I have no idea what the > price is and if they are ever sold used?). > > -aps > ___ > 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.
Re: [time-nuts] Beginner's Atomic Clock
On 9/17/2019 12:33 AM, Dr. David Kirkby wrote: Is there any advantage in using a GPS Rb disciplined oscillator vs a GPS disciplined high quality OCXO like the HP 10811A? I can’t understand why there should be, as a Rb source would use an OCCO in its output stage Therefore in each case * Short term stability depends upon the quality of the OCXO * Long term stability depends upon GPS. Perhaps there’s is period over which the the overall stability can be improved by adding a rubidium oscillator. I would be interested to know if that is the case or not. Dave What I was always told was that Rb has low enough noise coming off the atoms such that it can use a relatively fast loop to lock the OCXO and clean it up. OTOH, the 5071 Cs has to use a very long time constant loop to control the 10811, hence it doesn't clean it up except very close to the carrier. Even the high performance version of the 5071 doesn't compare with Rb. Rick N6RK ___ 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.
Re: [time-nuts] Beginner's Atomic Clock
Dr. Kirby, et al, Remember that a GPS-disciplined Rb has two loops, hence two time constants, to consider: a) the loop which locks the Rb's internal OCXO to the atomic transition, and b) the GPS disciplining loop. I surmise that the internal loop (a) is fast enough to thoroughly suppress drifts of the unit's internal OCXO in the face of local temperature variations etc. But the other loop (b) can be, and should be, pretty slow (time constant of hours or more), so as to prevent the disciplined source being jerked around by GPS "noise". This is why the Rb can advantageous over the OCXO- the Rb is inherently stable enough to permit using a very slow loop for disciplining by GPS. In my own experience to date, the one GPSDO I have with user-adjustable loop bandwidth suffers greatly from ambient temperature variations when I make the disciplining loop TC large enough to effectively remove GPS noise. I can easily see HVAC cycling, for example, when I use a long time constant. I've played with numbers ranging from 5 sec up to 500 sec, and think the best compromise is around 40 sec. This with an old Trimble T'Bolt which was apparently built around 2004 or thereabouts. My other GPSDO is a CNS Clock II, purchased new about a year ago. It does *not* have provisions for user adjustment of the disciplining loop, which is fixed at some rather short time constant (I'm estimating roughly 5 sec). So its OCXO is kept pretty honest in the face of ambient temperature variations; however GPS noise jerks it around very considerably. in the short term. I'm finding this device's greatest utility in looking at phase drift in my Rb sources over a period of several hours at a time, mainly for purposes of frequency setting. My two Rb's are an old (telecom-modded) PRS-10 and an old L-PRO, neither of which has GPS disciplining capability. I continue to agonize over whether or not I should buy new (standard-featured) PRS-10- I've been trying to make this decision for about 2.5 years so far :-) I do not have access to the revered HP 10811A, so can't speak to its value for my interests. I'd dearly love to borrow one, as it would undoubtedly provide a good learning experience for me. Dana On Tue, Sep 17, 2019 at 3:11 AM Dr. David Kirkby < drkir...@kirkbymicrowave.co.uk> wrote: > On Tue, 17 Sep 2019 at 04:00, Dana Whitlow wrote: > > > The nice thing about a Rb is that its short term stability (seconds to > > minutes and perhaps > > even longer) is much better than that of a GPS timing receiver. The bad > > news is that Rb > > standards exhibit long term frequency drift in the neighborhood of a few > > parts in 10^11 > > per month. A pretty fair compromise is to use an Rb standard that is > > disciplined by GPS > > PPS pulses with a loop time constant on the order of a day or so. > > > > Dana (K8YUM) > > > Is there any advantage in using a GPS Rb disciplined oscillator vs a GPS > disciplined high quality OCXO like the HP 10811A? I can’t understand why > there should be, as a Rb source would use an OCCO in its output stage > Therefore in each case > > * Short term stability depends upon the quality of the OCXO > * Long term stability depends upon GPS. > > Perhaps there’s is period over which the the overall stability can be > improved by adding a rubidium oscillator. I would be interested to know if > that is the case or not. > > Dave > > > -- > Dr. David Kirkby, > Kirkby Microwave Ltd, > drkir...@kirkbymicrowave.co.uk > https://www.kirkbymicrowave.co.uk/ > Telephone 01621-680100./ +44 1621 680100 > > Registered in England & Wales. > Company number 08914892. > Registered office: > Stokes Hall Lodge, > Burnham Rd, > Althorne, > Chelmsford, > Essex, > CM3 6DT, > United Kingdom > ___ > 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.
Re: [time-nuts] Beginner's Atomic Clock
On 9/17/19 3:33 AM, Dr. David Kirkby wrote: > On Tue, 17 Sep 2019 at 04:00, Dana Whitlow wrote: > >> The nice thing about a Rb is that its short term stability (seconds to >> minutes and perhaps >> even longer) is much better than that of a GPS timing receiver. The bad >> news is that Rb >> standards exhibit long term frequency drift in the neighborhood of a few >> parts in 10^11 >> per month. A pretty fair compromise is to use an Rb standard that is >> disciplined by GPS >> PPS pulses with a loop time constant on the order of a day or so. >> >> Dana (K8YUM) > > > Is there any advantage in using a GPS Rb disciplined oscillator vs a GPS > disciplined high quality OCXO like the HP 10811A? I can’t understand why > there should be, as a Rb source would use an OCCO in its output stage > Therefore in each case > > * Short term stability depends upon the quality of the OCXO > * Long term stability depends upon GPS. > > Perhaps there’s is period over which the the overall stability can be > improved by adding a rubidium oscillator. I would be interested to know if > that is the case or not. There are a bunch of interesting tradeoffs in choosing a frequency reference. Any Rb (except the HP 5065A which is in a different class as a lab instrument vs. the small telecom units) will be worse at short tau than a good OCXO, and is also likely to have much worse phase noise. A typical telecom Rb will be around 1e-11 at 1 second while a good OCXO can be one or even two orders of magnitude better. At medium tau (say a few thousand seconds) the Rb will likely be in the mid to upper 13s, which is better than any but a very good OCXO. At long tau, the Rb should show at least an order of magnitude less drift than even a very good OCXO. A Cesium at short tau will typically be worse than either an OCXO or an Rb. The Cs only wins (a) at long tau since there is zero drift; and (b) for absolute accuracy. But at anything shorter than around 10K seconds, it's not the best choice. A good GPSDO is really the overall performance winner -- short term stability and phase noise limited only by the quality of the OCXO, and very good long term stability and accuracy due to the GPS lock. It's only in the mid range of a few hundred to to a couple of thousand seconds, where the OCXO drift kicks in before the GPS discipline takes over, that a GPSDO will underperform a telecom Rb. In short, the GPSDO takes much of the fun out of time-nuttery. :-\ John ___ 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.
Re: [time-nuts] Beginner's Atomic Clock
On Mon, Sep 16, 2019 at 11:00 PM Dana Whitlow wrote: > All of the available Rb standards that I've seen have a 10 MHz output, > Some have a > 1 PPS output as well. > original buyer could save a few bucks. My PRS-10 is one of these. > > How does this compare with say a used Accubeat AR133/60 substance? I also see they have a Nano unit that looks awesome (but I have no idea what the price is and if they are ever sold used?). -aps ___ 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.
Re: [time-nuts] Beginner's Atomic Clock
On Tue, 17 Sep 2019 at 04:00, Dana Whitlow wrote: > The nice thing about a Rb is that its short term stability (seconds to > minutes and perhaps > even longer) is much better than that of a GPS timing receiver. The bad > news is that Rb > standards exhibit long term frequency drift in the neighborhood of a few > parts in 10^11 > per month. A pretty fair compromise is to use an Rb standard that is > disciplined by GPS > PPS pulses with a loop time constant on the order of a day or so. > > Dana (K8YUM) Is there any advantage in using a GPS Rb disciplined oscillator vs a GPS disciplined high quality OCXO like the HP 10811A? I can’t understand why there should be, as a Rb source would use an OCCO in its output stage Therefore in each case * Short term stability depends upon the quality of the OCXO * Long term stability depends upon GPS. Perhaps there’s is period over which the the overall stability can be improved by adding a rubidium oscillator. I would be interested to know if that is the case or not. Dave > -- Dr. David Kirkby, Kirkby Microwave Ltd, drkir...@kirkbymicrowave.co.uk https://www.kirkbymicrowave.co.uk/ Telephone 01621-680100./ +44 1621 680100 Registered in England & Wales. Company number 08914892. Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United Kingdom ___ 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.
Re: [time-nuts] Beginner's Atomic Clock
First off, thanks to everyone who replied. On Mon, Sep 16, 2019 at 11:00 AM Bob kb8tq wrote: > What are you really trying to do here? > Take over the world - one epoch at a time. If it’s a “from scratch” atomic standard, then you just aren’t going to get > there. Sorry about that ... > Ok. > If it’s a wall clock sync’d to an external radio service then indeed you > might get there. > Well, I want something maybe in between. Currently I think I have that: I have a RPi disciplined to the Adafruit Ultimate GPS HAT via chrony (PPS etc.). This works well. > In-between those two lie tings like buying eBay telecom Rubidium’s, > attaching them to a power supply and you have a working standard. > So I think this is what I'm talking about. I want something a little bit more esoteric than a GPS 1PPS. Can you explain a bit about these prepackaged Rubidium standards? Upside/downside etc. Do I have to maintain/check these black boxes? > Lots of very different directions this could go and and they all could be > called an atomic clock …. Not at all knock on doing something, just > confusion > about what exactly you want to do. > Again, take over the world. Sorry for not being upfront about that. That would have made things A LOT clearer. So I guess: How can I get a simple Rubidium standard that outputs a reference frequency as a discipline to say ntpd or chrony. Btw, I'm a noob. Please be gentle. -aps ___ 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.
Re: [time-nuts] Beginner's Atomic Clock
Hi What are you really trying to do here? If it’s a “from scratch” atomic standard, then you just aren’t going to get there. Sorry about that ... If it’s a wall clock sync’d to an external radio service then indeed you might get there. In-between those two lie tings like buying eBay telecom Rubidium’s, attaching them to a power supply and you have a working standard. Lots of very different directions this could go and and they all could be called an atomic clock …. Not at all knock on doing something, just confusion about what exactly you want to do. Bob > On Sep 16, 2019, at 5:16 AM, pisymbol . wrote: > > Can anyone suggest a "starter" atomic clock project? By beginner's > something that is fairly easy to put together and isn't cost prohibited > (maybe a few hundred but not thousand). > > Thanks! > > -aps (Alex) > ___ > 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.
Re: [time-nuts] Beginner's Atomic Clock
From: pisymbol . Can anyone suggest a "starter" atomic clock project? By beginner's something that is fairly easy to put together and isn't cost prohibited (maybe a few hundred but not thousand). Thanks! -aps (Alex) = Alex, Perhaps you could clarify what exactly you mean by "Atomic Clock"? - a box which has signal outputs of time and frequency? - a box with an hours/minutes/seconds display which fits on the wall? - something you can buy? - something you can assemble? - how accurate? - stand-alone, or using a GPS reference? This is my simple wall clock, accurate to a few tens of microseconds: https://www.satsignal.eu/raspberry-pi/DigitalClock.html Cost to me: ~GBP 50. Cheers, David -- SatSignal Software - Quality software for you Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk Twitter: @gm8arv ___ 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.
Re: [time-nuts] Beginner's Atomic Clock
On 9/16/19 4:16 AM, pisymbol . wrote: Can anyone suggest a "starter" atomic clock project? By beginner's something that is fairly easy to put together and isn't cost prohibited (maybe a few hundred but not thousand). Do you mean "build the physics package", or are you just talking about something like getting a commercial rubidium reference (surplus) and packaging it? Thanks! -aps (Alex) ___ 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.
