Re: [time-nuts] Updated VLBI tutorial available on gpstime.com
Brooke Clarke asked: > I didn't see in the VLBI slides what was done to "tune" the delay > line, but did see a hint that there's been a firmware upgrade for it. > Can you elaborate? Rick's latest version uses a delay line with more per-bit precision (now 150 psec steps). We also found that Motorola (correction byte) and Maxim/DSI (delay line bits) seemed to use different definitions of "one nsec" and Rick needed to sort out a scale difference (the reason my new slides #29 & 30 are different from what's in our PTTI talk). I think Rick got the cursor clock code from TvB. 73, Tom ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] retry: PRS10 has spurious frequencies
Henk Do any of the spurious signals show on the SA with a search antenna (located in your lab environment)connected instead of the PRS10? DaveB - Original Message - From: "Henk ten Pierick" <[EMAIL PROTECTED]> To: "Discussion of precise time and frequency measurement" Sent: Thursday, April 26, 2007 8:42 AM Subject: Re: [time-nuts] retry: PRS10 has spurious frequencies > Hi Poul-Henning, > > 1. It is not a stupid question but a very valid one. > > 2. I was aware of the EMI possibility and tried ferrites on the > supply and signal wires with no result. > > 3. I will try batteries but have to find enough of them. > > 4. On the spectrum analyzer, I checked the amplitude setting and > 10dB > change gave 10dB change of signal level. Also a mixer level change > had no influence on the spurious. > > Henk > > > On Apr 25, 2007, at 22:07, Poul-Henning Kamp wrote: > >> >> I'm going to ask a seemingly stupid question, but bear with me: >> >> Are you sure those signals are really present on the output ? >> >> The reason why I ask is that you are in a frequency territory where >> EMI is both radiated and conducted so you have to be really careful >> with your setup, grounding in particular, to make sure you do not >> actually measure the PRS10 acting as an antenna. >> >> The best way to ensure this, is to run your PRS10 off batteries, >> Sealed Lead Acid for instance, and the only other connection to >> the PRS10 should be the coax to the spectrum analyzer. >> >> Poul-Henning >> >> -- >> Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 >> [EMAIL PROTECTED] | TCP/IP since RFC 956 >> FreeBSD committer | BSD since 4.3-tahoe >> Never attribute to malice what can adequately be explained by >> incompetence. >> >> ___ >> time-nuts mailing list >> time-nuts@febo.com >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > > ___ > time-nuts mailing list > time-nuts@febo.com > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] retry: PRS10 has spurious frequencies
In message <[EMAIL PROTECTED]>, Henk ten Pi erick writes: >2. I was aware of the EMI possibility and tried ferrites on the >supply and signal wires with no result. If your powersupply is not very high quality, you are almost certain to create a ground-loop through the power-cords of the power-supply and the spectrum analyzer. That's why batteries are such a good thing: they don't offer a path for ground loops. If you have a isolating transformer, you can try that in the signal cable between the oscilloscope and the PRS10, but it's not as good as running off batteries. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [EMAIL PROTECTED] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] retry: PRS10 has spurious frequencies
In a message dated 4/25/2007 12:49:47 Pacific Daylight Time, [EMAIL PROTECTED] writes: spurious. The spurious seem to be harmonics of the 357MHz synthesizer, we see the 1st, 2nd, 3rd and 4th harmonic. (The marker is on the 3rd harmonic). The spurious between 500MHz and 700MHz are not yet explained. Around 357MHz are sidebands at 290kHz distance. Does anyone have schematics? Hi Henk, if you can't fix the unit (seems it has much more spurs than my unit) then maybe a simple high-quality low ESR 100pF to ground after a 4.7 Ohm series resistor on the 10MHz output may reduce the high-frequency stuff a bit... bye, Said ** See what's free at http://www.aol.com. ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] retry: PRS10 has spurious frequencies
Hi Poul-Henning, 1. It is not a stupid question but a very valid one. 2. I was aware of the EMI possibility and tried ferrites on the supply and signal wires with no result. 3. I will try batteries but have to find enough of them. 4. On the spectrum analyzer, I checked the amplitude setting and 10dB change gave 10dB change of signal level. Also a mixer level change had no influence on the spurious. Henk On Apr 25, 2007, at 22:07, Poul-Henning Kamp wrote: > > I'm going to ask a seemingly stupid question, but bear with me: > > Are you sure those signals are really present on the output ? > > The reason why I ask is that you are in a frequency territory where > EMI is both radiated and conducted so you have to be really careful > with your setup, grounding in particular, to make sure you do not > actually measure the PRS10 acting as an antenna. > > The best way to ensure this, is to run your PRS10 off batteries, > Sealed Lead Acid for instance, and the only other connection to > the PRS10 should be the coax to the spectrum analyzer. > > Poul-Henning > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > [EMAIL PROTECTED] | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by > incompetence. > > ___ > time-nuts mailing list > time-nuts@febo.com > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Updated VLBI tutorial available on gpstime.com
Hi Tom: I didn't see in the VLBI slides what was done to "tune" the delay line, but did see a hint that there's been a firmware upgrade for it. Can you elaborate? I like the Cursor Clock on your web page. Have Fun, Brooke Clarke http://www.PRC68.com http://www.pacificsites.com/~brooke/PRC68COM.shtml http://www.precisionclock.com Tom Clark, K3IO wrote: > Next week the VLBI community is having another TOW (Technical Operations > Workshop) at the Haystack Observatory NW of Boston. The audience for the > TOW is mainly the technicians at each site who drive the telescopes and > keep the hardware running. VLBI is crucially dependent on timing and > every station is equipped with at least one Hydrogen Maser. As usual, I > have been tapped as the timing "teacher". > > My PowerPoint class notes "Timing for VLBI" are now posted available on > http://gpstime.com/. > > These notes include some fairly recent data on how well the new > real-time "de-sawtooth" hardware in Rick's CNS Clock II works as > compared with the software correction we have been using for many years > (the two agree to 300 psec RMS now that we learned how to "tune" the > programmable delay line). > > 73, Tom > > ___ > time-nuts mailing list > time-nuts@febo.com > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] retry: PRS10 has spurious frequencies
I'm going to ask a seemingly stupid question, but bear with me: Are you sure those signals are really present on the output ? The reason why I ask is that you are in a frequency territory where EMI is both radiated and conducted so you have to be really careful with your setup, grounding in particular, to make sure you do not actually measure the PRS10 acting as an antenna. The best way to ensure this, is to run your PRS10 off batteries, Sealed Lead Acid for instance, and the only other connection to the PRS10 should be the coax to the spectrum analyzer. Poul-Henning -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [EMAIL PROTECTED] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] retry: PRS10 has spurious frequencies
Hi, Thank you all for the frequency plots of the PRS10. It is very interesting to see these and find the differences. In the mean time I have restarted my PRS10 and have seen that some spurious signals are large at start up and reduce after that. I have attached a screen shot of the hp8590 spectrum analyzer showing the spurious. The spurious seem to be harmonics of the 357MHz synthesizer, we see the 1st, 2nd, 3rd and 4th harmonic. (The marker is on the 3rd harmonic). The spurious between 500MHz and 700MHz are not yet explained. Around 357MHz are sidebands at 290kHz distance. Does anyone have schematics? Henk ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
[time-nuts] Updated VLBI tutorial available on gpstime.com
Next week the VLBI community is having another TOW (Technical Operations Workshop) at the Haystack Observatory NW of Boston. The audience for the TOW is mainly the technicians at each site who drive the telescopes and keep the hardware running. VLBI is crucially dependent on timing and every station is equipped with at least one Hydrogen Maser. As usual, I have been tapped as the timing "teacher". My PowerPoint class notes "Timing for VLBI" are now posted available on http://gpstime.com/. These notes include some fairly recent data on how well the new real-time "de-sawtooth" hardware in Rick's CNS Clock II works as compared with the software correction we have been using for many years (the two agree to 300 psec RMS now that we learned how to "tune" the programmable delay line). 73, Tom ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] GPS Disciplined Oscillators
Mike, If you have three different oscillators that are locked to GPS, then any difference seen when you read your clock once a day will be caused by the short term noise. When you take the noise difference counts as a percentage of counts in a day, the result is a smaller number than if the oscillators were not locked to GPS. Some people on this list are worried down to the phase noise level because they are correlating events that have been timed by clocks whose only link is GPS or a portable secondary time standard. Primary standards tend not to be portable, but quantum physics could change that. Locking means that there is only a phase difference between GPS and the oscillator, not a frequency difference. For 10 MHz, that's 100 nanoseconds or (much) better while locked. Said another way, if GPS lock is maintained for some length of time, the maximum difference at the end of that length of time is 100 nanoseconds, plus the drift of GPS, if any. Ageing is compensated by a control servo while the frequencies are locked. The full name for "lock" is "phase lock" which means that any phase error is restored to nominal by the control servo. The servo is constrained by a long time constant filter so that it won't dither around zero error, trying to follow every noise spike and always being too late. Losing lock means that the control servo has saturated, and can no longer move in the direction required to maintain lock. At that point, there is no controlled relationship between GPS and the oscillator. The performance of the oscillator is then the performance with no GPS available. You can measure ageing by measuring the output of the controller. If the loss of lock was due to some hiccup, then lock could be restored but the clock counter will be wrong by the number of counts added or dropped while lock was lost. Hope that helps. Bill Hawkins -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Mike Feher Sent: Wednesday, April 25, 2007 11:46 AM To: 'Discussion of precise time and frequency measurement' Subject: [time-nuts] GPS Disciplined Oscillators I have to show my ignorance here, because this has been bothering me for a while, and, I wonder if there is a relatively simple answer. This question has to do with frequency accuracy and stability only. Also, let's talk of long term like 24 hours or more, so let's ignore phase noise and just concern ourselves with long term accuracy/stability. If I have three separate oscillators, let's say a Rubidium, an OCXO and a TCXO all with EFC's capable of closing the loop to lock to GPS, what kind of absolute frequency difference should I see amongst the three at any given time, random times, or, over the entire test period. Let's also make it simple and say all three are at 10 MHz nominal, unlocked to GPS. When locked, and properly designed with a narrow loop filter, I would expect the long term accuracy to be very close amongst all 3 oscillators. Certainly better than a few parts in 10^-11. First, am I wrong in this assumption? In either case, crystals, and even Rubidium cells do age, while at different rates, so, it is possible, that if lock with GPS is lost for some reason, because the oscillator may have drifted/aged out of loop range, it cannot be disciplined again. I, for the time being, also assume that the EFC on all 3 oscillators has a range wide enough to keep the oscillator locked even as it ages. Are the narrow loop bandwidths and wide EFC ranges contradictory? So, to reiterate the question, if I was clear enough, what kind of frequency excursions should I anticipate to see amongst my three disciplined oscillators in lets say 24 hours, or in a month. Assume GPS disciplining was working all of that time (can I even assume that with aging?). BTW, how is my assumption regarding the oscillators aging? If the oscillator basic frequency determining element drifts out of lock range, during lock, will it stay in lock? - Thanks in advance for any enlightenment - Mike Mike B. Feher, N4FS 89 Arnold Blvd. Howell, NJ, 07731 732-886-5960 ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Wavecrest noise measurement hardware
In a message dated 4/25/2007 11:45:41 Pacific Daylight Time, [EMAIL PROTECTED] writes: >As an aside, how do the Wavecrest machines work? Do they just run the >signal into a low-jitter ADC with a high-quality clock and derive all the >timing information digitally, or is the box full of low-noise tunable >synthesizers, mixers, filters, and the usual stuff? Hi John, Wavecrest's DTS-2070 and DTS-2075 manuals have a pretty decent discription including block diagrams of just how they do it, and why their approach is so "revolutionary" and so much better than anyone else's. First off, they do true time-intervall (A to B) measurements with an interpolator with 800fs or less resolution. So no phase noise measurement using the NIST mixer setup, or the TSC ADC-based cross-correlation approach (which are bandwidth limited by design) There are no mixers or filters, just fast ECL comparators with some delay lines (actual coax cables wound into loops etc), and the usual coarse capture (100MHz) and fine capture (ADC working on charge pump). There are no bandwidth limits except the speed of the ECL gates/comparators and that's several GHz. With this time intervall data, they do FFT's for phase noise, jitter analysis, histograms, and all sorts of other fancy stuff, including analog "oscilloscope" mode. bye, Said ** See what's free at http://www.aol.com. ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] retry: PRS10 has spurious frequencies
In a message dated 4/25/2007 11:55:53 Pacific Daylight Time, [EMAIL PROTECTED] writes: >And on the opposite front, the TSC-5120 isn't very happy with a square >wave input, particularly if harmonics fall within its input range. The >symptom is lots of spurs showing up in the phase noise plots. Adding a >low pass filter with an appropriate cutoff helps a lot. Very true! Have seen these spurs on the 5210A as well. A sharp 13MHz or so cut-off filter will help that. bye, Said ** See what's free at http://www.aol.com. ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Wavecrest noise measurement hardware
From: "John Miles" <[EMAIL PROTECTED]> Subject: [time-nuts] Wavecrest noise measurement hardware Date: Wed, 25 Apr 2007 11:43:30 -0700 Message-ID: <[EMAIL PROTECTED]> > As an aside, how do the Wavecrest machines work? Do they just run the > signal into a low-jitter ADC with a high-quality clock and derive all the > timing information digitally, or is the box full of low-noise tunable > synthesizers, mixers, filters, and the usual stuff? It is a fairly traditional design in which they have a coarse clock (100 MHz for the DTS-207X and 200 MHz for the SIA-3000), generate an error signal which charge a capacitor and then A/D convert the accumulated voltage into digital. They have a patent from the DTS-207X days which should give you more than enought feeling of how it works. ;) Cheers, Magnus ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] retry: PRS10 has spurious frequencies
[EMAIL PROTECTED] wrote: > Also, try making the sine wave of the PRS10 into a nice, fast edge rate > square-wave with a Fairchild NC7SZ04 driver inverter for example. The > Wavecrest > units don't work as well with sine waves as with square waves. On the SZ04, > put > a 10nF cap in series to the input, and a 1 MEG resistor from it's input pin > to it's output pin. Feed the chip from a very low noise 5V power source. > Insert a 40-50 Ohm resistor into the output path going to the coax. Put an > attenuator/AC-coupler into the coax so the Wavecrest doesen't get overloaded > by > the 2.5Vpp DC signal. Result: low noise comparator/buffer :) And on the opposite front, the TSC-5120 isn't very happy with a square wave input, particularly if harmonics fall within its input range. The symptom is lots of spurs showing up in the phase noise plots. Adding a low pass filter with an appropriate cutoff helps a lot. John ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] GPS Disciplined Oscillators
Hi Mike: Nice to see you here. This is my take on it, but there are others on this list that are much more knowledgeable. The key to the performance of a GPSDO has to do with the Allan plots for the oscillator, GPS receiver and it's antenna and . . . . Also the Time Interval counter used in the GPSDO that compares the oscillator and the GPS 1 PPS is important. The key idea is that when you overlay the GPS receiver's plot with the oscillator plot there will be only one point where they intersect. That's what the loop time constant should be for the PLL. That way for time intervals that are shorter you get the good performance of the xtal oscillator and for longer time intervals you get the long term stability of GPS. Inside the GPSDO it somehow compares the oscillator output with the 1 PPS from GPS. It's very important how that's done. Suppose that it's done by dividing the oscillator's output down to 1 PPS and then measuring the time interval between the two pulses. The one shot resolution of that TI counter is a point on the Allan plot at 1 second (because we're using 1 pulse/second). You can draw a line through this point slopping down at 45 degrees to indicate what stability you will get if you average for longer times or if you make measurements at a faster pace. If that line is below the GPS - Oscillator intersection point then all is well. But it the TI line is above the intersection point then the TI counter is limiting the performance of the GPSDO. Of all the GPSDOs kits out there It's my understanding that the Brooks Shera is the best. But it was designed back when the 8 channel Motorola GPS receivers were the standard. But now with the M12+T (or other newer 12 channel) receivers that have much better performance it's limited by the TI counter. It's difficult to answer your questions in a general way. One of the problems has to do with the sensitivity and range of the EFC input to the oscillator. On one hand you want to use a D/A converter that has very small steps in order to allow tuning the oscillator with steps of E-12 or smaller. And if you know the direction of drift and set the manual adjustment so the EFC is very near one end of it's range you then have almost the full range available until the next manual adjustment is needed. When you combine both of these it turns out that you can't buy a DAC with that many bits. So you can see that it's hard to generalize about what the stability will be at 24 hours for different designs of GPSDO. A well designed GPSDO would have long term performance that was about the same as the GPS receiver. Tom has a number of plots on his web page, but this one compares a number of GPS receivers. http://www.leapsecond.com/pages/3gps/gps-adev-mdev.gif The Datum2000 is a GPSDO, not just a receiver. It would be interesting to see what happens to these receivers if the test was extended. I expect that they all would bottom out and go horizontal in after a few days. But at different stability values. Seeing that would answer your question in a better way. I have some T&F info at: http://www.pacificsites.com/~brooke/timefreq.shtml Have Fun, Brooke Clarke, N6GCE http://www.PRC68.com http://www.pacificsites.com/~brooke/PRC68COM.shtml http://www.precisionclock.com Mike Feher wrote: > I have to show my ignorance here, because this has been bothering me for a > while, and, I wonder if there is a relatively simple answer. This question > has to do with frequency accuracy and stability only. Also, let's talk of > long term like 24 hours or more, so let's ignore phase noise and just > concern ourselves with long term accuracy/stability. If I have three > separate oscillators, let's say a Rubidium, an OCXO and a TCXO all with > EFC's capable of closing the loop to lock to GPS, what kind of absolute > frequency difference should I see amongst the three at any given time, > random times, or, over the entire test period. Let's also make it simple and > say all three are at 10 MHz nominal, unlocked to GPS. When locked, and > properly designed with a narrow loop filter, I would expect the long term > accuracy to be very close amongst all 3 oscillators. Certainly better than a > few parts in 10^-11. First, am I wrong in this assumption? In either case, > crystals, and even Rubidium cells do age, while at different rates, so, it > is possible, that if lock with GPS is lost for some reason, because the > oscillator may have drifted/aged out of loop range, it cannot be disciplined > again. I, for the time being, also assume that the EFC on all 3 oscillators > has a range wide enough to keep the oscillator locked even as it ages. Are > the narrow loop bandwidths and wide EFC ranges contradictory? So, to > reiterate the question, if I was clear enough, what kind of frequency > excursions should I anticipate to see amongst my three disciplined > oscillators in lets say 24 hours, or in a month. Assume GPS disciplining was >
[time-nuts] Wavecrest noise measurement hardware
As an aside, how do the Wavecrest machines work? Do they just run the signal into a low-jitter ADC with a high-quality clock and derive all the timing information digitally, or is the box full of low-noise tunable synthesizers, mixers, filters, and the usual stuff? -- john, KE5FX > > Hi Henk, > > try running your PRS10 from a Pb battery, with nothing else > connected (no > RS232 etc). > > The plot I sent you was from a PRS running from a switching power > supply, > with RS-232 connected to some other stuff. > > Also, try making the sine wave of the PRS10 into a nice, fast edge rate > square-wave with a Fairchild NC7SZ04 driver inverter for example. > The Wavecrest > units don't work as well with sine waves as with square waves. On > the SZ04, put > a 10nF cap in series to the input, and a 1 MEG resistor from > it's input pin > to it's output pin. Feed the chip from a very low noise 5V power source. > Insert a 40-50 Ohm resistor into the output path going to the > coax. Put an > attenuator/AC-coupler into the coax so the Wavecrest doesen't get > overloaded by > the 2.5Vpp DC signal. Result: low noise comparator/buffer :) > ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] retry: PRS10 has spurious frequencies
In a message dated 4/24/2007 15:14:11 Pacific Daylight Time, [EMAIL PROTECTED] writes: >> It is unclear to me if the spurious is normal or not. The spurious of >> my PRS10 is 60dB down the 10MHz so it is strange that you see no >> spurious. >> Hi Henk, try running your PRS10 from a Pb battery, with nothing else connected (no RS232 etc). The plot I sent you was from a PRS running from a switching power supply, with RS-232 connected to some other stuff. Also, try making the sine wave of the PRS10 into a nice, fast edge rate square-wave with a Fairchild NC7SZ04 driver inverter for example. The Wavecrest units don't work as well with sine waves as with square waves. On the SZ04, put a 10nF cap in series to the input, and a 1 MEG resistor from it's input pin to it's output pin. Feed the chip from a very low noise 5V power source. Insert a 40-50 Ohm resistor into the output path going to the coax. Put an attenuator/AC-coupler into the coax so the Wavecrest doesen't get overloaded by the 2.5Vpp DC signal. Result: low noise comparator/buffer :) bye, Said ** See what's free at http://www.aol.com. ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] GPS Disciplined Oscillators
In a message dated 4/25/2007 09:50:38 Pacific Daylight Time, [EMAIL PROTECTED] writes: >So, to >reiterate the question, if I was clear enough, what kind of frequency >excursions should I anticipate to see amongst my three disciplined >oscillators in lets say 24 hours, or in a month. Assume GPS disciplining was >working all of that time (can I even assume that with aging?). BTW, how is >my assumption regarding the oscillators aging? Hello Mike, from my experience, good oscillators will age parts in 1E-08 per day or less. Bad ones can age much faster, some parts in 1E-06 in the first days even. That's a pretty significant variation in EFC voltage required to compensate that. We have seen units that age significantly in the first 2 - 3 days, then slow down, and after 6 months or so almost have no aging. We have seen units where the aging actually accelerates over time. Aging is a very slow changing process after the crystal has run some days (second derivative is small), so GPS locking will usually easily compensate this error. There are oscillators that have popcorn noise (frequency jumps) that can be really annoying, and this effect is similar to rapid aging (from one second to another): almost sudden the phase/frequency of the OCXO changes radically from one second to another. This is usually caused by either dust particles leaving, or landing on the crystal, the crystal "cracking" in it's holders, or radioactive particles hitting the crystal. Also, thermal effects will usually require much larger shifts in EFC voltage than aging, unless you are using a double-oven high quality OCXO. Thermal effects on the required EFC voltage usually swamp aging effects and are harder to deal with because they are more or less random, and not a nice (almost) straight line on the EFC voltage. bye, Said ** See what's free at http://www.aol.com. ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] GPS Disciplined Oscillators
Mike, I just so happened to be reading through my TS2100 manual and came across a bit of info that might be applicable to your question: The info below is for the various oscillator options you can get, and while the number can vary based on the exact oscillator used (and its age), it should give you a good ballpark idea of the differences. VCXO: 48 milliseconds/day long term "flywheeling" OCXO: 5 milliseconds/day long term "flywheeling" Rubidium: 6.5 microseconds/month long term "flywheeling" Jason ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
[time-nuts] GPS Disciplined Oscillators
I have to show my ignorance here, because this has been bothering me for a while, and, I wonder if there is a relatively simple answer. This question has to do with frequency accuracy and stability only. Also, let's talk of long term like 24 hours or more, so let's ignore phase noise and just concern ourselves with long term accuracy/stability. If I have three separate oscillators, let's say a Rubidium, an OCXO and a TCXO all with EFC's capable of closing the loop to lock to GPS, what kind of absolute frequency difference should I see amongst the three at any given time, random times, or, over the entire test period. Let's also make it simple and say all three are at 10 MHz nominal, unlocked to GPS. When locked, and properly designed with a narrow loop filter, I would expect the long term accuracy to be very close amongst all 3 oscillators. Certainly better than a few parts in 10^-11. First, am I wrong in this assumption? In either case, crystals, and even Rubidium cells do age, while at different rates, so, it is possible, that if lock with GPS is lost for some reason, because the oscillator may have drifted/aged out of loop range, it cannot be disciplined again. I, for the time being, also assume that the EFC on all 3 oscillators has a range wide enough to keep the oscillator locked even as it ages. Are the narrow loop bandwidths and wide EFC ranges contradictory? So, to reiterate the question, if I was clear enough, what kind of frequency excursions should I anticipate to see amongst my three disciplined oscillators in lets say 24 hours, or in a month. Assume GPS disciplining was working all of that time (can I even assume that with aging?). BTW, how is my assumption regarding the oscillators aging? If the oscillator basic frequency determining element drifts out of lock range, during lock, will it stay in lock? - Thanks in advance for any enlightenment - Mike Mike B. Feher, N4FS 89 Arnold Blvd. Howell, NJ, 07731 732-886-5960 ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
[time-nuts] FMT
For details of the next run see: http://pages.suddenlink.net/k5cm/ Connie K5CM ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] SMB-F to SMA-F Cable
If no one stepped up yet, let me see what connectors I have. I know I got LMR-100 but not sure if I have the connectors, but this will be the excuse I need to run to the supply house and stock up... Jamie --- Jason Rabel <[EMAIL PROTECTED]> wrote: > I figured I would make the request to you guys > before I hit fleabay (they > have some but I don't need a dozen - just one). > > Does anyone have a short SMB-F to SMA-F cable I > could buy? This is to > connect to a Trimble ACE-III receiver. I have some > extra receivers too if > someone would rather do a swap. > > Jason > > > ___ > time-nuts mailing list > time-nuts@febo.com > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > Fedora Core 4 Linux __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
[time-nuts] HP59309A HP-IB Digital Clock Operating and Service Manual
Hello Community, thank you all for your hints concerning the HP59309A Clock and your kind assistance with making available the Operating and Service Manual. My HP 59309A had a real problem: One of the input protection diodes of the EXT FREQ STD input was shot. Suspect the previous owner confused the EXT FREQ STD input with the line input... ;-) Regards Martin mailto:[EMAIL PROTECTED] ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
