Re: [time-nuts] GPS III
Hi Don, Hardly. As long as you do GPS L1 C/A code only, chanses you get any useful improvement isn't all that great. SBAS may help you some thought. Cheers, Magnus On 11/13/2017 05:35 AM, Don wrote: I read where the first GPS III satellite had finally been approved for flight. The report said they will provide three times better location accuracy than current GPS. Will "better" onboard clocks help contribute to this improvement? How are they "better"? Can we expect enhanced timing accuracy from the timing receivers we use in our homemade GPSDO's?. -Don N5CID ___ 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] Wenzel VHF PLO Oscillators Off Frequency
On Sun, Nov 12, 2017 at 6:38 PM, John Miles wrote: > > Most of the 100 and 200 MHz bricks I've seen work with either 5 or 10 MHz > . I don't know if I've seen any 80 MHz units that do. All of the ones > I've bought on eBay have been from the customer-proprietary 500- series > with unusual input frequencies. > > I swept the input from 1 to 100 MHz. They lock at 38.4 MHz in. Yes they are 4-5 kHz off when free running. Locked they are right on frequency. They don't spec the phase noise when locked. I hope it is decent. The phase noise when unlocked is pretty good. I can only measure the phase noise indirectly by driving my Perseus clock with this and comparing phase noise measurements when using the internal clock. I may wind up using the internal clock when measuring phase noise and this when measuring Allan Deviation. Thanks for the suggestions. Mark ___ 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] GPS III
I read where the first GPS III satellite had finally been approved for flight. The report said they will provide three times better location accuracy than current GPS. Will "better" onboard clocks help contribute to this improvement? How are they "better"? Can we expect enhanced timing accuracy from the timing receivers we use in our homemade GPSDO's?. -Don N5CID ___ 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] Wenzel VHF PLO Oscillators Off Frequency
> Yes, exactly those. With no input, would they be expected to be 4 kHz off? > The spec for the standard part wants the input to be within 1e-7. I would > not expect them to be so far off free running. That does seem like a lot. I'd expect a few hundred Hz of error at the most. > I saw 13 MHz on the 500-14273 and stayed away from those. > > Do you know of any part numbers that use 10 MHz in? Wenzel would not tell > me the exact specs of the 500 series parts available on ebay and only sent > me the specs for the standard 501-14057 that takes 10 MHz. Most of the 100 and 200 MHz bricks I've seen work with either 5 or 10 MHz . I don't know if I've seen any 80 MHz units that do. All of the ones I've bought on eBay have been from the customer-proprietary 500- series with unusual input frequencies. > Do you know what the pll lock output does when the input frequency is off? > These toggle high for any frequencies I have put in. Not offhand. If there's a PFD inside it should be easy to zero in on the right frequency, but if there's only a phase detector you may need to set up a sweep and watch the tuning-voltage output on a scope. I don't remember it taking very long to find the correct input frequencies for the ones I bought, though. -- john, KE5FX Miles Design LLC ___ 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] Wenzel VHF PLO Oscillators Off Frequency
Hi If it is a OCVCXO and it pulls > 50 ppm at 80 MHz, it’s got terrible phase noise close in. That’s true with or without the PLL engaged. Bob > On Nov 12, 2017, at 7:46 PM, Mark Goldberg wrote: > > Yes, exactly those. With no input, would they be expected to be 4 kHz off? > The spec for the standard part wants the input to be within 1e-7. I would > not expect them to be so far off free running. > > I saw 13 MHz on the 500-14273 and stayed away from those. > > Do you know of any part numbers that use 10 MHz in? Wenzel would not tell > me the exact specs of the 500 series parts available on ebay and only sent > me the specs for the standard 501-14057 that takes 10 MHz. > > I have a couple 8642As and can generate any frequency I want with decent > phase noise, locked to my 10 MHz reference. I could try these frequencies > above. > > Do you know what the pll lock output does when the input frequency is off? > These toggle high for any frequencies I have put in. > > Any other ideas are appreciated. > > Thanks, > > Mark > > > On Sun, Nov 12, 2017 at 5:19 PM, John Miles wrote: > >> Sounds like he's talking about the small 'bricks' that Wenzel sells with >> internal PLL-disciplined OCXOs. Some of these expect oddball input >> frequencies. Just looking at the 80 MHz parts on the shelf around here, >> 500-14273 wants a 13 MHz input, 500-25010 uses 24.576 MHz, and 500-25009 >> uses 19.2 MHz. So that's probably the issue, if two of them seem to be >> failing the same way. >> >> -- john, KE5FX >> Miles Design LLC >> >> >>> -Original Message- >>> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob >>> Camp >>> Sent: Sunday, November 12, 2017 2:03 PM >>> To: Discussion of precise time and frequency measurement >>> Subject: Re: [time-nuts] Wenzel VHF PLO Oscillators Off Frequency >>> >>> Hi >>> >>> I guess my point was more that there is not a VCO / PLL combo in an OCXO. >>> >>> If dropping the supply gets you on frequency, then you have moved things >> a >>> lot >>> with that voltage change. 50 PPM is a lot of delta T on any normal OCXO >>> crystal. >>> That strongly suggests there is something wrong in the control circuit. >>> >>> Bob >>> On Nov 12, 2017, at 2:52 PM, Mark Goldberg >>> wrote: The standard oscillator, 501-14057 ( www.wenzel.com/wp-content/parts/501-14057.pdf) will lock to an >>> external 10 MHz reference and this one is marked "80 MHz" and "15V on the label. >>> Maybe someone swapped the labels. I did try lowering the supply voltage. It >> got to 80 MHz at about 11V and still did not lock to the reference. This oscillator is specified at 1e-6/year aging. That is way less than it >> is off now. >> >> ___ >> 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] Wenzel VHF PLO Oscillators Off Frequency
Yes, exactly those. With no input, would they be expected to be 4 kHz off? The spec for the standard part wants the input to be within 1e-7. I would not expect them to be so far off free running. I saw 13 MHz on the 500-14273 and stayed away from those. Do you know of any part numbers that use 10 MHz in? Wenzel would not tell me the exact specs of the 500 series parts available on ebay and only sent me the specs for the standard 501-14057 that takes 10 MHz. I have a couple 8642As and can generate any frequency I want with decent phase noise, locked to my 10 MHz reference. I could try these frequencies above. Do you know what the pll lock output does when the input frequency is off? These toggle high for any frequencies I have put in. Any other ideas are appreciated. Thanks, Mark On Sun, Nov 12, 2017 at 5:19 PM, John Miles wrote: > Sounds like he's talking about the small 'bricks' that Wenzel sells with > internal PLL-disciplined OCXOs. Some of these expect oddball input > frequencies. Just looking at the 80 MHz parts on the shelf around here, > 500-14273 wants a 13 MHz input, 500-25010 uses 24.576 MHz, and 500-25009 > uses 19.2 MHz. So that's probably the issue, if two of them seem to be > failing the same way. > > -- john, KE5FX > Miles Design LLC > > > > -Original Message- > > From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob > > Camp > > Sent: Sunday, November 12, 2017 2:03 PM > > To: Discussion of precise time and frequency measurement > > Subject: Re: [time-nuts] Wenzel VHF PLO Oscillators Off Frequency > > > > Hi > > > > I guess my point was more that there is not a VCO / PLL combo in an OCXO. > > > > If dropping the supply gets you on frequency, then you have moved things > a > > lot > > with that voltage change. 50 PPM is a lot of delta T on any normal OCXO > > crystal. > > That strongly suggests there is something wrong in the control circuit. > > > > Bob > > > > > On Nov 12, 2017, at 2:52 PM, Mark Goldberg > > wrote: > > > > > > The standard oscillator, 501-14057 ( > > > www.wenzel.com/wp-content/parts/501-14057.pdf) will lock to an > > external 10 > > > MHz reference and this one is marked "80 MHz" and "15V on the label. > > Maybe > > > someone swapped the labels. I did try lowering the supply voltage. It > got > > > to 80 MHz at about 11V and still did not lock to the reference. This > > > oscillator is specified at 1e-6/year aging. That is way less than it > is off > > > now. > > > > > ___ > 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] Newbie to Time Nuts; Seeking wisdom, re Hydrogen MASER applications
apollo...@gmail.com said: > prior to my senior project most geodetic surveyors used a Wooden boxed, > marine chronometer, to get sub second UT1 time, or back then, GMT How did you get the data out of the wooden box? -- 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] Wenzel VHF PLO Oscillators Off Frequency
Sounds like he's talking about the small 'bricks' that Wenzel sells with internal PLL-disciplined OCXOs. Some of these expect oddball input frequencies. Just looking at the 80 MHz parts on the shelf around here, 500-14273 wants a 13 MHz input, 500-25010 uses 24.576 MHz, and 500-25009 uses 19.2 MHz. So that's probably the issue, if two of them seem to be failing the same way. -- john, KE5FX Miles Design LLC > -Original Message- > From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob > Camp > Sent: Sunday, November 12, 2017 2:03 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] Wenzel VHF PLO Oscillators Off Frequency > > Hi > > I guess my point was more that there is not a VCO / PLL combo in an OCXO. > > If dropping the supply gets you on frequency, then you have moved things a > lot > with that voltage change. 50 PPM is a lot of delta T on any normal OCXO > crystal. > That strongly suggests there is something wrong in the control circuit. > > Bob > > > On Nov 12, 2017, at 2:52 PM, Mark Goldberg > wrote: > > > > The standard oscillator, 501-14057 ( > > www.wenzel.com/wp-content/parts/501-14057.pdf) will lock to an > external 10 > > MHz reference and this one is marked "80 MHz" and "15V on the label. > Maybe > > someone swapped the labels. I did try lowering the supply voltage. It got > > to 80 MHz at about 11V and still did not lock to the reference. This > > oscillator is specified at 1e-6/year aging. That is way less than it is off > > now. > > ___ 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] Newbie to Time Nuts; Seeking wisdom, re Hydrogen MASER applications
Hello fellow Time nuts, I am a newbie here, just joined, first post. But back in college dabbled in "precise time" recording in the field, for Geodetic Surveying field measurements, Star Shots. transiting the meridian. Very crude by today standards, but effective for field measurements that had to be time stamped to sub second accuracy, I got to about 3-4ms UTC absolute, and prior to my senior project most geodetic surveyors used a Wooden boxed, marine chronometer, to get sub second UT1 time, or back then, GMT. I have a project involving use of a Hydrogen Maser as a frequency reference, a STEM activity coming up next year that may be of interest, and for which I need some technical assistance. Involves precisely measuring received frequency of a lunar orbiting satellite, in the 70 cm band. over a period of an hour or so, and from widespread locations (multiple MASERS) around the Earth. But that project will be revealed in my next post. Mean time, for your enjoyment, I copy here a summary of what/how the Arecibo Radio Telescope capabilities were, when I visited there for a moonbounce activity I set up, called "Echoes of Apollo", in 2012. Google and search Youtube videos, KP4AO for commentary. I was interested after returning home from Echoes Of Apollo, to learn more about frequency standards they had and used at the Arecibo Observatory. So I wrote and got an interesting reply from one of their awesomely knowledgeable staff. Here is his reply on Arecibo Time: "Any radio observatory worth its salt has time information at hand to the sub-microsecond level of accuracy. Having experienced only the AO, I can speak of how we do it, but can't speak for other observatories. Basically we start with a highly stable reference oscillator, an active hydrogen maser whose frequency we generally maintain within about 1 part in 10^14. It has an internal synthesizer which provides a 10-MHz output. Note that this level of frequency accuracy is needed primarily for our planetary radar and pulsar timing work, so not all observatories would be as well equipped. The 10-MHz signal is distributed about the place for locking LOs and other synthesizers, but it also "regulates" our master station clock. This clock produces time-of-day (distributed in one of the IRIG formats) and a 1 pulse per second digital output (1PPS). These are also distributed about the observatory. We compare our station clock against UTC via a "common view GPS" measurement scheme, in which we locally record time differences between our master clock and GPS signals received by a special receiver. This receiver, among other things, pays attention solely to GPS signals which come from satellites known to be simultaneously receivable both here and at NIST in Boulder at the time of each comparison measurement. Then we send our locally-recorded difference data to NIST via internet, and they apply relevant corrections and can tell us our time error with respect to UTC. We receive this information as a monthly report, whose major component is a graph of our daily average difference from UTC. We try to keep this difference within ~200 ns. It does drift around, however, because the maser itself does drift around a wee bit and even very tiny frequency errors integrate up to substantial time errors if left alone. >From time to time we make small (a few parts in 10^14) adjustments to our maser's frequency if the time error is getting too large, in order to start our clock drifting back towards correct alignment with UTC. The end result is that an observer has immediate real time access to time within a few hundred ns of correct. Further, he can do much better if he is willing to wait for the monthly report and apply the corrections- then he can get down to ~10 ns error." More, re MASER questions, later... Best, 73, Pat Barthelow AA6EG apol lo...@gmail.com *"The most exciting phrase to hear in Science, the one that heraldsnew discoveries, is not "Eureka, I have found it!"but:* "That's funny..." Isaac Asimov ___ 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] Phase noise measurement experiment by Andrew Holme
> But be aware, that measurements close to the limit of thermal noise > will make your measurement go sour. There the noise of your splitter > will cause an anti-correlation effect and the measured noise will > suddenly drop way below thermal noise. Craig Nelson and Archita Hati > from NIST, Enrico Rubiola from FEMTO, Magnus from time-nuts and several > others have been discussing this for a couple of years now at PTTI, > IFCS and EFTF. > (e.g. https://www.nist.gov/publications/cross-spectral-collapse-anti- > correlated-thermal-noise-power-splitters ) Cross-spectral collapse due to thermal noise is basically Mother Nature complaining that we're trying to do something that's physically ill-advised, by trying to measure the noise in a system at levels near the thermal floor of the termination resistance that's necessary to define such a system in the first place. Unfortunately the issue can affect measurements at levels several dB higher than the thermal floor, making it a genuine occupational hazard. On the bright side, splitter topologies that use a single resistive load with no differential-mode termination have little or no vulnerability to this phenomenon. Of course the common-mode termination imposes its own noise floor, but that's life in this particular universe. That being said, it's still a bit of an awkward situation for designers of future test sets. We can't use Wilkinson splitters anymore -- or at least we shouldn't, given what's been learned over the past couple of years. As a result, some customers' best devices may suddenly start looking noisier than they did when measured on earlier instruments, or (worse) when measured on competing ones. Those customers may not respond agreeably when advised to dunk the termination in liquid helium... > > Since the cross correlation could reduce noise a lot, I am wondering what > > the differences between 14 bits and 16 bits ADC are. None to speak of. The original TSC 5120A used 14-bit parts while the later test sets have used 16-bit parts, and the performance limits are essentially identical. Once you go below a certain point, generally well below -170 dBc/Hz, you tend to run into a correlation floor that arises from one or more different causes unrelated to the quantization precision itself. These effects seem to arise in and near the S/H stage and aren't improved by going beyond 14-bit precision. -- john, KE5FX Miles Design LLC ___ 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] Wenzel VHF PLO Oscillators Off Frequency
Hi I guess my point was more that there is not a VCO / PLL combo in an OCXO. If dropping the supply gets you on frequency, then you have moved things a lot with that voltage change. 50 PPM is a lot of delta T on any normal OCXO crystal. That strongly suggests there is something wrong in the control circuit. Bob > On Nov 12, 2017, at 2:52 PM, Mark Goldberg wrote: > > The standard oscillator, 501-14057 ( > www.wenzel.com/wp-content/parts/501-14057.pdf) will lock to an external 10 > MHz reference and this one is marked "80 MHz" and "15V on the label. Maybe > someone swapped the labels. I did try lowering the supply voltage. It got > to 80 MHz at about 11V and still did not lock to the reference. This > oscillator is specified at 1e-6/year aging. That is way less than it is off > now. > > Mark > > On Sun, Nov 12, 2017 at 12:34 PM, Bob Camp wrote: > >> Hi >> >> It’s pretty certain that there is no PLL inside an 80 MHz low phase noise >> OCXO. >> If it is 4 KHz off frequency at 80 MHz, that gets you into the 50 ppm >> range. Either >> it is running on a really odd crystal spur or it’s not at the right >> temperature. Drifting >> around by 100’s of Hz ( = ppm’s at 80 MHz) is also a good indication that >> the oven >> is not doing it’s job correctly. >> >> If multiple units do the same thing, either they all got busted being >> puled from gear >> (unfortunately that’s common) or you are running it at the wrong supply >> voltage. >> >> Bob >> >> >> >>> On Nov 12, 2017, at 1:19 PM, Mark Goldberg >> wrote: >>> >>> The seller has replaced it with one that does the exact same thing, which >>> is weird to have two fail in the same way. They are getting hot and the >>> frequency varies with the input voltage, so I tended to guess not the >>> heater as I don't think it could pull that far over temp, and it always >> is >>> high. If it has an unlocked PLL on the output, with no control, would it >> go >>> to the max frequency? Since the seller seems to be reasonable, I was >> trying >>> to figure out best not to waste both of our's time, and me get a good >> unit >>> and them getting a sale. >>> >>> Mark >>> >>> >>> On Sun, Nov 12, 2017 at 9:22 AM, Bob Camp wrote: >>> Hi As a guess - the oven circuit has stopped working. Next step would be to tear it open and trace out the schematic. After that make reasonable guesses for any parts that are poorly labeled. Much of what shows up on eBay has been through the ringer in China. A high percentage the OCXO's I get on eBay show up with issues as a result. There is no way to be sure this or that part was ok before it came out of the gear it was in. It’s always a gamble. Bob > On Nov 12, 2017, at 10:41 AM, Mark Goldberg wrote: > > I have obtained a couple 80 MHz Wenzel Oscillators P/N 500-16423A. They are > proprietary but similar to the VHF PLO and 501-14057 Oscillators. I >> want to > use this to replace the internal oscillator in my Perseus SDR, for >> better > accuracy and maybe better phase noise. Both of these are way off in > frequency, about 4-5 kHz high from the ideal 80 MHz, and drift around > hundreds of Hz. I believe they are broken in some way. The PLL lock signal > toggles when I put an input into the 10 MHz reference, but the output > frequency is not affected. > > Wenzel has answered some of my questions, but can't get specific as >> these > are proprietary to a customer. > > Any experts on these oscillators out there? > > Thanks, > > Mark > ___ > 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. >> > ___ > 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] Wenzel VHF PLO Oscillators Off Frequency
The standard oscillator, 501-14057 ( www.wenzel.com/wp-content/parts/501-14057.pdf) will lock to an external 10 MHz reference and this one is marked "80 MHz" and "15V on the label. Maybe someone swapped the labels. I did try lowering the supply voltage. It got to 80 MHz at about 11V and still did not lock to the reference. This oscillator is specified at 1e-6/year aging. That is way less than it is off now. Mark On Sun, Nov 12, 2017 at 12:34 PM, Bob Camp wrote: > Hi > > It’s pretty certain that there is no PLL inside an 80 MHz low phase noise > OCXO. > If it is 4 KHz off frequency at 80 MHz, that gets you into the 50 ppm > range. Either > it is running on a really odd crystal spur or it’s not at the right > temperature. Drifting > around by 100’s of Hz ( = ppm’s at 80 MHz) is also a good indication that > the oven > is not doing it’s job correctly. > > If multiple units do the same thing, either they all got busted being > puled from gear > (unfortunately that’s common) or you are running it at the wrong supply > voltage. > > Bob > > > > > On Nov 12, 2017, at 1:19 PM, Mark Goldberg > wrote: > > > > The seller has replaced it with one that does the exact same thing, which > > is weird to have two fail in the same way. They are getting hot and the > > frequency varies with the input voltage, so I tended to guess not the > > heater as I don't think it could pull that far over temp, and it always > is > > high. If it has an unlocked PLL on the output, with no control, would it > go > > to the max frequency? Since the seller seems to be reasonable, I was > trying > > to figure out best not to waste both of our's time, and me get a good > unit > > and them getting a sale. > > > > Mark > > > > > > On Sun, Nov 12, 2017 at 9:22 AM, Bob Camp wrote: > > > >> Hi > >> > >> As a guess - the oven circuit has stopped working. Next step > >> would be to tear it open and trace out the schematic. After that > >> make reasonable guesses for any parts that are poorly labeled. > >> > >> Much of what shows up on eBay has been through the ringer in > >> China. A high percentage the OCXO's I get on eBay show up with > >> issues as a result. There is no way to be sure this or that part was > >> ok before it came out of the gear it was in. It’s always a gamble. > >> > >> Bob > >> > >>> On Nov 12, 2017, at 10:41 AM, Mark Goldberg > >> wrote: > >>> > >>> I have obtained a couple 80 MHz Wenzel Oscillators P/N 500-16423A. They > >> are > >>> proprietary but similar to the VHF PLO and 501-14057 Oscillators. I > want > >> to > >>> use this to replace the internal oscillator in my Perseus SDR, for > better > >>> accuracy and maybe better phase noise. Both of these are way off in > >>> frequency, about 4-5 kHz high from the ideal 80 MHz, and drift around > >>> hundreds of Hz. I believe they are broken in some way. The PLL lock > >> signal > >>> toggles when I put an input into the 10 MHz reference, but the output > >>> frequency is not affected. > >>> > >>> Wenzel has answered some of my questions, but can't get specific as > these > >>> are proprietary to a customer. > >>> > >>> Any experts on these oscillators out there? > >>> > >>> Thanks, > >>> > >>> Mark > >>> ___ > >>> 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. > ___ 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] Wenzel VHF PLO Oscillators Off Frequency
Hi It’s pretty certain that there is no PLL inside an 80 MHz low phase noise OCXO. If it is 4 KHz off frequency at 80 MHz, that gets you into the 50 ppm range. Either it is running on a really odd crystal spur or it’s not at the right temperature. Drifting around by 100’s of Hz ( = ppm’s at 80 MHz) is also a good indication that the oven is not doing it’s job correctly. If multiple units do the same thing, either they all got busted being puled from gear (unfortunately that’s common) or you are running it at the wrong supply voltage. Bob > On Nov 12, 2017, at 1:19 PM, Mark Goldberg wrote: > > The seller has replaced it with one that does the exact same thing, which > is weird to have two fail in the same way. They are getting hot and the > frequency varies with the input voltage, so I tended to guess not the > heater as I don't think it could pull that far over temp, and it always is > high. If it has an unlocked PLL on the output, with no control, would it go > to the max frequency? Since the seller seems to be reasonable, I was trying > to figure out best not to waste both of our's time, and me get a good unit > and them getting a sale. > > Mark > > > On Sun, Nov 12, 2017 at 9:22 AM, Bob Camp wrote: > >> Hi >> >> As a guess - the oven circuit has stopped working. Next step >> would be to tear it open and trace out the schematic. After that >> make reasonable guesses for any parts that are poorly labeled. >> >> Much of what shows up on eBay has been through the ringer in >> China. A high percentage the OCXO's I get on eBay show up with >> issues as a result. There is no way to be sure this or that part was >> ok before it came out of the gear it was in. It’s always a gamble. >> >> Bob >> >>> On Nov 12, 2017, at 10:41 AM, Mark Goldberg >> wrote: >>> >>> I have obtained a couple 80 MHz Wenzel Oscillators P/N 500-16423A. They >> are >>> proprietary but similar to the VHF PLO and 501-14057 Oscillators. I want >> to >>> use this to replace the internal oscillator in my Perseus SDR, for better >>> accuracy and maybe better phase noise. Both of these are way off in >>> frequency, about 4-5 kHz high from the ideal 80 MHz, and drift around >>> hundreds of Hz. I believe they are broken in some way. The PLL lock >> signal >>> toggles when I put an input into the 10 MHz reference, but the output >>> frequency is not affected. >>> >>> Wenzel has answered some of my questions, but can't get specific as these >>> are proprietary to a customer. >>> >>> Any experts on these oscillators out there? >>> >>> Thanks, >>> >>> Mark >>> ___ >>> 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] Designing an embedded precision GPS time
The 6-7us of latency in this discussion does not involve the network path. In this regard network latency is fairly well addressed with hardware timestamping, although trying to get readings across the clock domains looses dozens of nanos of precision. In this discussion, the 6-7us of latency originates from servicing the serial device interrupt in order to timestamp the TOS pulse. This is entirely in the kernel, and there is no user space context switch involved. If you have a way to dramatically reduce the 6-7us interrupt latency with the Linux kernel, say to a 100 nanos, please do share. > On Nov 12, 2017, at 07:23, Attila Kinali wrote: > > The kernel has already quite a few low-latency network paths. > You just need to enable them and then cut out the biggest timing uncertainty: > the user-space to kernel context switch. ___ 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] Wenzel VHF PLO Oscillators Off Frequency
The seller has replaced it with one that does the exact same thing, which is weird to have two fail in the same way. They are getting hot and the frequency varies with the input voltage, so I tended to guess not the heater as I don't think it could pull that far over temp, and it always is high. If it has an unlocked PLL on the output, with no control, would it go to the max frequency? Since the seller seems to be reasonable, I was trying to figure out best not to waste both of our's time, and me get a good unit and them getting a sale. Mark On Sun, Nov 12, 2017 at 9:22 AM, Bob Camp wrote: > Hi > > As a guess - the oven circuit has stopped working. Next step > would be to tear it open and trace out the schematic. After that > make reasonable guesses for any parts that are poorly labeled. > > Much of what shows up on eBay has been through the ringer in > China. A high percentage the OCXO's I get on eBay show up with > issues as a result. There is no way to be sure this or that part was > ok before it came out of the gear it was in. It’s always a gamble. > > Bob > > > On Nov 12, 2017, at 10:41 AM, Mark Goldberg > wrote: > > > > I have obtained a couple 80 MHz Wenzel Oscillators P/N 500-16423A. They > are > > proprietary but similar to the VHF PLO and 501-14057 Oscillators. I want > to > > use this to replace the internal oscillator in my Perseus SDR, for better > > accuracy and maybe better phase noise. Both of these are way off in > > frequency, about 4-5 kHz high from the ideal 80 MHz, and drift around > > hundreds of Hz. I believe they are broken in some way. The PLL lock > signal > > toggles when I put an input into the 10 MHz reference, but the output > > frequency is not affected. > > > > Wenzel has answered some of my questions, but can't get specific as these > > are proprietary to a customer. > > > > Any experts on these oscillators out there? > > > > Thanks, > > > > Mark > > ___ > > 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] AD9544 clock chip
This beast may have some interesting uses: http://www.analog.com/en/products/clock-and-timing/clock-generation-distribution/clock-synchronization/ad9544.html -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | 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 To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Favorite counters (current production)?
That reminds me, should anyone have a schematic for an SR 830 walking amplifier, can you please get in touch with me. I have one that keeps eating voltage regulators. > On Nov 12, 2017, at 12:12, Dr. David Kirkby (Kirkby Microwave Ltd) > wrote: > >> On 10 November 2017 at 16:37, Bob Camp wrote: >> >> Hi >> >> There is no perfect answer. I’d go with the 53230 simply because it >> *might* be supported >> the longest. >> >> Bob >> > > > If I had to take a bet, I would say the SR620 will be supported longer. > Stanford Research seem to be selling the same products they have for > decades. I started my Ph.D. in about 1994, and bought what was a very new > product - the SR830 lock in amplifier. > > http://www.thinksrs.com/products/SR810830.htm > > 23 years later, it is still a current product. > > Stanford Research also sell a couple of LCR meters > > http://www.thinksrs.com/products/SR715720.htm > > The SR720 looks remarkably like the long obsolete HP E4925A LCR meter. > > There's no doubt in my mind that Stanford Research sell their products much > longer than HP/Agilent/Keysight. Of course, that does mean Stanford > Research are using older technology. > > I would add, when I have contacted Keysight about obsolete products they > have always been helpful. When I contacted Stanford Research to ask what > was the latest firmware for an SR620, I was ignored. They also ignored some > other email I sent them. So their support does not seem as good as > Keysight, but I assume, with persistence, one could get support on a > current product. > > Dave > ___ > 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] Favorite counters (current production)?
On 10 November 2017 at 16:37, Bob Camp wrote: > Hi > > There is no perfect answer. I’d go with the 53230 simply because it > *might* be supported > the longest. > > Bob > If I had to take a bet, I would say the SR620 will be supported longer. Stanford Research seem to be selling the same products they have for decades. I started my Ph.D. in about 1994, and bought what was a very new product - the SR830 lock in amplifier. http://www.thinksrs.com/products/SR810830.htm 23 years later, it is still a current product. Stanford Research also sell a couple of LCR meters http://www.thinksrs.com/products/SR715720.htm The SR720 looks remarkably like the long obsolete HP E4925A LCR meter. There's no doubt in my mind that Stanford Research sell their products much longer than HP/Agilent/Keysight. Of course, that does mean Stanford Research are using older technology. I would add, when I have contacted Keysight about obsolete products they have always been helpful. When I contacted Stanford Research to ask what was the latest firmware for an SR620, I was ignored. They also ignored some other email I sent them. So their support does not seem as good as Keysight, but I assume, with persistence, one could get support on a current product. Dave ___ 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] Oscillators and Ovens
Hi I would say there are *very* few companies out there that will sell you high grade precision OCXO crystals in single piece quantities. I think you would get one much quicker and cheaper by pulling it out of an eBay OCXO. You can do good far removed phase noise with a lot of crystals. Once you look close in, the performance of the resonator matters. ADEV is the same issue, longer Tau’s are very resonator dependent. Bob > On Nov 12, 2017, at 10:14 AM, Attila Kinali wrote: > > Hi Jim, > > On Wed, 1 Nov 2017 11:39:32 -0700 > jimlux wrote: > >> So, it would be nice to have a *cheap* lowish power packaged part that >> has the Q of an OCXO, but without the power consumption of the oven >> (typically measured in watts). >> >> yeah, I'd be operating it *way* far from the optimum turnover temp, so >> the tempco might be huge (in oscillator terms), but I don't really care >> - in fact, that might give me a way to measure the temperature of the >> system. > > Have you tried to build your own oscillator? There are a few companies > that still sell single crystals. If you could piggy pack on some bigger > customers production, you should be able to get the crystals relatively > cheap. All you then have to do is to design an approriate, low noise > oscillator. If you can relax your frequency specs, ie if you don't care > if you are off by a few ppm, then you could scavenge the rejected crystals > from said big customer. > > Attila Kinali > > -- > You know, the very powerful and the very stupid have one thing in common. > They don't alters their views to fit the facts, they alter the facts to > fit the views, which can be uncomfortable if you happen to be one of the > facts that needs altering. -- The Doctor > ___ > 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] Wenzel VHF PLO Oscillators Off Frequency
Hi As a guess - the oven circuit has stopped working. Next step would be to tear it open and trace out the schematic. After that make reasonable guesses for any parts that are poorly labeled. Much of what shows up on eBay has been through the ringer in China. A high percentage the OCXO's I get on eBay show up with issues as a result. There is no way to be sure this or that part was ok before it came out of the gear it was in. It’s always a gamble. Bob > On Nov 12, 2017, at 10:41 AM, Mark Goldberg wrote: > > I have obtained a couple 80 MHz Wenzel Oscillators P/N 500-16423A. They are > proprietary but similar to the VHF PLO and 501-14057 Oscillators. I want to > use this to replace the internal oscillator in my Perseus SDR, for better > accuracy and maybe better phase noise. Both of these are way off in > frequency, about 4-5 kHz high from the ideal 80 MHz, and drift around > hundreds of Hz. I believe they are broken in some way. The PLL lock signal > toggles when I put an input into the 10 MHz reference, but the output > frequency is not affected. > > Wenzel has answered some of my questions, but can't get specific as these > are proprietary to a customer. > > Any experts on these oscillators out there? > > Thanks, > > Mark > ___ > 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] Phase noise measurement experiment by Andrew Holme
On Sun, 12 Nov 2017 16:34:35 +0100 Magnus Danielson wrote: > > That said, it is probably worth trying what actually happens when > > using a 16bit ADC instead of 14bit. If there are any students here > > looking for a bachelor or master thesis project doing noise measurement, > > feel free to contact me :-) > > Just do it. I'm sure I can contribute some to that if it would happen. I would like to. But I don't have the time to do it myself. I already have way too many projects running in parallel as it is. Attila Kinali -- You know, the very powerful and the very stupid have one thing in common. They don't alters their views to fit the facts, they alter the facts to fit the views, which can be uncomfortable if you happen to be one of the facts that needs altering. -- The Doctor ___ 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] Favorite counters (current production)?
On Sat, 11 Nov 2017 04:44:53 -0800 "Tom Van Baak" wrote: > That said, I want to point out that the latest GPSDO / counter from Stanford > Research continues their tradition of relatively open design. If you have an > hour, go through the very detailed user manual, which includes theory of > operation and BOM and schematics, just like the old days: > > http://www.thinksrs.com/downloads/PDFs/Manuals/FS740m.pdf > http://www.thinksrs.com/downloads/PDFs/Catalog/FS740c.pdf Oh.. very nice. I wasn't aware of this beauty! I only had a quick look at the schematics, but a few things stick out: 1) They use "half" Nutt interpolators for time stamping instead of A-B measurements as is usual with the Nutt interpolator. I was wondering why nobody did that, as it is kind of the obvious thing to do, today. 2) They use simple, time-to-amplitude converter for the interpolation. The only interesting bit there, is the, in my opinion, weird way of starting the charge using an opamp, that at the same time compensates for the diode forward voltage. 3) This is the first time I have ever seen someone even mentioning the possibility of metastability in counters or the Nutt interpolator. And they solve it in a quite interesting way too. 4) Even though they call it TCXO in the manual, the normal oscillator in the FS740 is an ovenized AT cut crystal. As it is built manually on the main PCB itself, it's nothing fancy, but apparently does the job quite well. 5) Every other clock source in the instrument is derived from the 20MHz that this central oscillator produces. Even the 12MHz of the frontpanel controller. 6) The OCXO and Rb options only phase lock the central oscillator with a small PLL at 300Hz BW. That explains that the phase noise performance is constant over all 3 options. Though I would have expected a higher close in phase noise for the rubidium, as it does in the ADEV plot. 7) The Rb only performs slightly better between taus of 100 to 10k than the OCXO. I probably have to spend some time reading the schematics, which by the way are superb. So much love to details, even small ones. You can almost feel what kind of trade-offs the engineers made and for what reason. Attila Kinali -- You know, the very powerful and the very stupid have one thing in common. They don't alters their views to fit the facts, they alter the facts to fit the views, which can be uncomfortable if you happen to be one of the facts that needs altering. -- The Doctor ___ 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] ublox NEO-M8T improved by insulated chamber?
On Wed, 8 Nov 2017 14:24:08 -0600 "Chris Caudle" wrote: > On Wed, November 8, 2017 12:55 pm, Gary E. Miller wrote: > > I knew about the errata, I left out that detail to see when someone > > actually read my citation. > > OK, I don't want to quibble about versions, and whether the "latest > version" is 200H or 200H including errata, but I think we both agree that > the currently operating performance would be described by the rollup > document, i.e. the offset information for GPS time to UTC time should be > within 20ns 1 sigma, as opposed to the older 90 ns 1 sigma description. The GPS standard only specifies a _target_ value, what they want to achieve. The actual value has been consistenly better than what is described in the standard for decades. Why standard not updated, you ask? Because in a standard you want to be conservative. People rely on that value and if anything happens and for some reason that value gets much worse than usual, you still want tto be within specs. > > Do you now see how measured GPS time/location can be very precise, but > > UTC from a GPS less so? Have you read the entire 3.3.4? > > Yes, and I do not really understand the "1 sigma" description. Is the > error really random? I'm not sure how the term 1 sigma applies to error > distributions other than a Gaussian distribution, so what "20 ns at 1 > sigma" really means moment to moment for the time value I get from a GPS > receiver is not completely clear to me. At a simplistic level I would > interpret that 66% of the PPS ticks are within 20ns of the "true" UTC > tick, 33+% could be farther away than 20ns from "true" second tick. This is what it means. The distribution is not completely gaussian. There are some periodic (12h, 24h, and various others) contents that look more sinusoidal than random, but if you look at the raw distribution, without extracting any of the periodic components, it looks quite gaussian. > The general interest in GPS based time transfer covers a wide range of > uses, so whether you actually care about absolute offset from UTC or not > needs to be made more explicit in discussions about vaguely defined > "performance." If you are really doing time transfer using GPS and you care about performance. Then you are using at least common-in-view mode with some heavy post-processing. This brings you close to a 5ns one-sigma uncertainty. If you calibrate your GPS receivers frequently, you can get down to 200ps. (over a few 100km baseline). If you need better than that, you go to Timetech ( http://www.timetech.de/ ) and ask them to loan you one of the TWSTFT systems. Attila Kinali -- You know, the very powerful and the very stupid have one thing in common. They don't alters their views to fit the facts, they alter the facts to fit the views, which can be uncomfortable if you happen to be one of the facts that needs altering. -- The Doctor ___ 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] Wenzel VHF PLO Oscillators Off Frequency
I have obtained a couple 80 MHz Wenzel Oscillators P/N 500-16423A. They are proprietary but similar to the VHF PLO and 501-14057 Oscillators. I want to use this to replace the internal oscillator in my Perseus SDR, for better accuracy and maybe better phase noise. Both of these are way off in frequency, about 4-5 kHz high from the ideal 80 MHz, and drift around hundreds of Hz. I believe they are broken in some way. The PLL lock signal toggles when I put an input into the 10 MHz reference, but the output frequency is not affected. Wenzel has answered some of my questions, but can't get specific as these are proprietary to a customer. Any experts on these oscillators out there? Thanks, Mark ___ 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] ublox NEO-M8T improved by insulated chamber?
On Tue, 7 Nov 2017 22:07:43 + Leo Bodnar wrote: > Coincidentally, I have been testing relative phase difference of two GPS > clocks > http://www.leobodnar.com/shop/index.php?main_page=product_info&cPath=107&products_id=301 > since Friday. > They are completely independent, including separate antennas and positioned a > few yards away from each other so ionospheric disturbances would affect both > units equally. Devices use Ublox chipset. > > Average phase difference did not change in four days since Friday but there > is phase wander within around 10ns. > Here is a video of 4 hours worth of data. One horizontal division is 20ns: > > http://leobodnar.com/balloons/NTP/twoGPSclocks.mp4 Do you have this measurement with proper time-differences? Ie like using a simple and cheap counter? That would be quite a bit more interesting than a video of an osciloscope screen. Attila kinali -- You know, the very powerful and the very stupid have one thing in common. They don't alters their views to fit the facts, they alter the facts to fit the views, which can be uncomfortable if you happen to be one of the facts that needs altering. -- The Doctor ___ 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] Holdover, RTC for Pi as NTP GPS source
Hoi Leo, On Thu, 2 Nov 2017 21:45:56 + Leo Bodnar wrote: > I suspect delta-sigma body of knowledge can be applied almost wholesale to > this seemingly silly oscillator concept. > Did I just repeat something trivial that has been discussed to death here > before? Trivial? Yes. Well known? No. I know too many engineers who treat delta-sigma modulators as kind of black magic and don't even want to touch them. Yes, the math behind it is a bit intricate. There are things that we cannot even calculate (only simulate), but a second order D-S modulator will get you quite far and is easy to do. If anyone wants reading material on that topic, let me know. Attila Kinali -- You know, the very powerful and the very stupid have one thing in common. They don't alters their views to fit the facts, they alter the facts to fit the views, which can be uncomfortable if you happen to be one of the facts that needs altering. -- The Doctor ___ 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] Phase noise measurement experiment by Andrew Holme
On 11/12/2017 03:57 PM, Attila Kinali wrote: On Fri, 27 Oct 2017 09:35:08 +0800 "Li Ang" <379...@qq.com> wrote: I just found Andrew recently post a phase noise measruement page on www.aholme.co.uk/PhaseNoise/Main.htm . Indeed a nice post, as usual for Andrew. He uses 4-channel 14bit ADC to do the sampling work. -170dBc noise floor seems not bad for me. Which is close to the theoretical limit. Quite respectable. Averaging may help some but... But be aware, that measurements close to the limit of thermal noise will make your measurement go sour. There the noise of your splitter will cause an anti-correlation effect and the measured noise will suddenly drop way below thermal noise. Craig Nelson and Archita Hati from NIST, Enrico Rubiola from FEMTO, Magnus from time-nuts and several others have been discussing this for a couple of years now at PTTI, IFCS and EFTF. (e.g. https://www.nist.gov/publications/cross-spectral-collapse-anti-correlated-thermal-noise-power-splitters ) This is a hard problem. Turns out that beyond the anti-correlation noise from the splitter, isolation breaks in many interesting ways, creating cross-talk which can or can not cause disruptions. My approach to this is to steer the effects of the cross-talk away from the measurement. This is however a hard balance to maintain in practice, but hopefully will inspire new approaches. Since the cross correlation could reduce noise a lot, I am wondering what the differences between 14 bits and 16 bits ADC are. Beside the price? :-) There are two things that limit the measurement here. One is the noise of the ADC itself and the other is the apperture jitter. The former is almost the same for both 14 and 16bit high speed ADCs. Unless you go well below 30Msps, you will not gain much in noise performance from going to 16bit. The aperture jitter is more or less unrelated to sampling rate and bit width but faster ADCs usually have lower aperture jitter, as the designers take more care (because it becomes more important for "normal" applications). This means, that if you are limited by aperture jitter (which is the case for close in measurements below 1-100Hz probably), then the additional bits of a 16bit ADC will not help you at all. Well, that is not completely true. As you average cross-correlations you sense a thad more of the actual noise, so there is a small gain there. Having too few bits will acts as a discriminator for how low levels become visible, even if covered in noise. We've seen people make this mistake before. Just because it's hidden in noise does not prohibit it from being detected in a correlation process, and cross-correlation is one such process. I saw one such spectrum this summer that had exactly this fault, there is a limit to how deep a cheap SDR goes, and the mistake was quickly pointed out by someone with the bitter experience. Noise tend to smooth over quantization steps, and hum, and I think you recall my poor excuse of a poster-presentation on that topic, but to make benefit it takes lots of samples. So, anyway, there is some benefits in that extra bits. To make good use of them one need to be a bit careful in processing. That said, it is probably worth trying what actually happens when using a 16bit ADC instead of 14bit. If there are any students here looking for a bachelor or master thesis project doing noise measurement, feel free to contact me :-) Just do it. I'm sure I can contribute some to that if it would happen. Cheers, Magnus ___ 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] Designing an embedded precision GPS time
On Wed, 1 Nov 2017 10:15:43 -0700 Denny Page wrote: > > 6-10µs is the interrupt latency of linux on ARM SoC. I guess, to get > > below that you'd have to tweak the kernel a bit. Which should not > > be that difficult. Definitly simpler than writing your own IP and NTP > > stack from scratch. > > Just tweak the Linux kernel a bit? No. You would have to a rewrite > substantial chunks of it. A tremendous effort. Low latency and accurate > timing is not what Linux is designed for. This has been discussed > extensively for years. Not really. The kernel has already quite a few low-latency network paths. You just need to enable them and then cut out the biggest timing uncertainty: the user-space to kernel context switch. If you write a small stub driver that takes from user space the required data to build a NTP packet, you can cut out quite a bit of the latency. You could even get a decent estimate on when the packet will be send out in case of conguestion, if you check the buffer fill marks. My guess, for someone who knows his way around the kernel network stack, that would be 1-4 weeks of effort. > > Spread spectrum can usually be switched off, though requires at least a > > custom DTB or even patching of the kernel. There are a few boards, though > > that do not allow spread spectrum to be switched off. > > Unfortunately is usually has to be done in the bios. The control space that > would allow spread spectrum to be turned off is usually disabled prior to > kernel load. For compliance, most bios implementations have removed spread > spectrum as an option so you have to build a custom one. I can’t begin to > tell you what kind of a chill comes over the conversation with a vendor > (even a maker oriented one) when you tell them you want to create a custom > bios to disable spread spectrum. Ah.. sorry for the confusion. I was specifically talking about embedded systems. On a PC all bets are off, while on a embedded system you have quite a high level of control of what's going on. At most you have to tweak the DT file a bit, or set some initialization values a bit differently. Attila Kinali -- You know, the very powerful and the very stupid have one thing in common. They don't alters their views to fit the facts, they alter the facts to fit the views, which can be uncomfortable if you happen to be one of the facts that needs altering. -- The Doctor ___ 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] Oscillators and Ovens
Hi Jim, On Wed, 1 Nov 2017 11:39:32 -0700 jimlux wrote: > So, it would be nice to have a *cheap* lowish power packaged part that > has the Q of an OCXO, but without the power consumption of the oven > (typically measured in watts). > > yeah, I'd be operating it *way* far from the optimum turnover temp, so > the tempco might be huge (in oscillator terms), but I don't really care > - in fact, that might give me a way to measure the temperature of the > system. Have you tried to build your own oscillator? There are a few companies that still sell single crystals. If you could piggy pack on some bigger customers production, you should be able to get the crystals relatively cheap. All you then have to do is to design an approriate, low noise oscillator. If you can relax your frequency specs, ie if you don't care if you are off by a few ppm, then you could scavenge the rejected crystals from said big customer. Attila Kinali -- You know, the very powerful and the very stupid have one thing in common. They don't alters their views to fit the facts, they alter the facts to fit the views, which can be uncomfortable if you happen to be one of the facts that needs altering. -- The Doctor ___ 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] Designing an embedded precision GPS time
On Wed, 1 Nov 2017 13:11:00 -0400 wrote: > I am trying to beat existing products like the Dallas DS3231 and Micro > Crystal RV-8803-C7-32.768kHz-3PPM-TA-QC, which use (I think) a similar > strategy. I’m hoping I can beat them by using more accurate temp tensing, > longer and more exhaustive calibration effort, and anything else possible! > > Can you give a quick explanation (or point to reference material) covering > the fundamental limits to XTAL compensation accuracy, and how to get there? You probably can get better, but is it worth the effort? The problem with temperaure compensation is, that you have to measure the crystal temperature with very high accuracy. Measuring something close by means you have to model the crystals actual temperature using the temperature measurements you made before. The more parameters you add to your system to be identified, the more problems you get accurately identifying them, as they are not completely independent and cannot be directly measured. Directly measuring the crystal temperature has been done and one quite popular approach is MCXO. [1] and [2] are two early papers that describe the approach in quite some detail. There are a few problems with this. One is that you need a special crystal that is designed for dual mode operation and the other is that you need quite a bit of electronics around it to work. Oh.. and if you are living in the US, please be aware that MCXO are covered by ITAR. For general modeling of crystals, I recommend reading John Vigs Oscillator Tutorial. It covers most of what we know about crystal oscillators and gives lot of references. Attila Kinali [1] "A Microcomputer-Compensated Crystal Oscillator Using a Dual-Mode Resonator", by Benjaminson, 1989 [2] "Resonator Self-Temperature-Sensing Using a Dual-Harmonic-Mode Crystal Oscillator", Schodowski, 1989 -- You know, the very powerful and the very stupid have one thing in common. They don't alters their views to fit the facts, they alter the facts to fit the views, which can be uncomfortable if you happen to be one of the facts that needs altering. -- The Doctor ___ 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] Phase noise measurement experiment by Andrew Holme
On Fri, 27 Oct 2017 09:35:08 +0800 "Li Ang" <379...@qq.com> wrote: > I just found Andrew recently post a phase noise measruement page on > www.aholme.co.uk/PhaseNoise/Main.htm . Indeed a nice post, as usual for Andrew. > He uses 4-channel 14bit ADC to do the sampling work. -170dBc noise floor > seems not bad for me. Which is close to the theoretical limit. But be aware, that measurements close to the limit of thermal noise will make your measurement go sour. There the noise of your splitter will cause an anti-correlation effect and the measured noise will suddenly drop way below thermal noise. Craig Nelson and Archita Hati from NIST, Enrico Rubiola from FEMTO, Magnus from time-nuts and several others have been discussing this for a couple of years now at PTTI, IFCS and EFTF. (e.g. https://www.nist.gov/publications/cross-spectral-collapse-anti-correlated-thermal-noise-power-splitters ) > Since the cross correlation could reduce noise a lot, I am wondering what > the differences between 14 bits and 16 bits ADC are. Beside the price? :-) There are two things that limit the measurement here. One is the noise of the ADC itself and the other is the apperture jitter. The former is almost the same for both 14 and 16bit high speed ADCs. Unless you go well below 30Msps, you will not gain much in noise performance from going to 16bit. The aperture jitter is more or less unrelated to sampling rate and bit width but faster ADCs usually have lower aperture jitter, as the designers take more care (because it becomes more important for "normal" applications). This means, that if you are limited by aperture jitter (which is the case for close in measurements below 1-100Hz probably), then the additional bits of a 16bit ADC will not help you at all. That said, it is probably worth trying what actually happens when using a 16bit ADC instead of 14bit. If there are any students here looking for a bachelor or master thesis project doing noise measurement, feel free to contact me :-) Attila Kinali -- You know, the very powerful and the very stupid have one thing in common. They don't alters their views to fit the facts, they alter the facts to fit the views, which can be uncomfortable if you happen to be one of the facts that needs altering. -- The Doctor ___ 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] Papers on noise by Ulrich Rohde
The first one was a real prove what was possible for the first time, the second paper shows the physics based limitations, 73 de Ulrich Sent from my iPhone > On Nov 12, 2017, at 9:36 AM, Attila Kinali wrote: > > Hi, > > I received two papers by Ulrich: > > "Accurate Noise Simulation of Microwave Amplifiers Using CAD", > by Rohde, Pavio, Pucel, 1988 > http://time.kinali.ch/rohde/noise/accurate_noise_simulation_of_microwave_amplifiers_using_cad-1988-rohde_pavio_pucel.pdf > > This is the paper Ulrich mentioned a few days ago, about accurate > and fast noise simulations in semiconductor circuits. > > > "How Low Can They Go?", by Poddar, Rohde, Apte, 2013 > http://time.kinali.ch/rohde/noise/how_low_can_they_go-2013-poddar_rohde_apte.pdf > > This is a review of noise models for oscillators, their strength > and weaknesses and how they relate to designing low noise oscillators. > > > Happy reading > >Attila Kinali > > > -- > You know, the very powerful and the very stupid have one thing in common. > They don't alters their views to fit the facts, they alter the facts to > fit the views, which can be uncomfortable if you happen to be one of the > facts that needs altering. -- The Doctor > ___ > 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] Papers on noise by Ulrich Rohde
Hi, I received two papers by Ulrich: "Accurate Noise Simulation of Microwave Amplifiers Using CAD", by Rohde, Pavio, Pucel, 1988 http://time.kinali.ch/rohde/noise/accurate_noise_simulation_of_microwave_amplifiers_using_cad-1988-rohde_pavio_pucel.pdf This is the paper Ulrich mentioned a few days ago, about accurate and fast noise simulations in semiconductor circuits. "How Low Can They Go?", by Poddar, Rohde, Apte, 2013 http://time.kinali.ch/rohde/noise/how_low_can_they_go-2013-poddar_rohde_apte.pdf This is a review of noise models for oscillators, their strength and weaknesses and how they relate to designing low noise oscillators. Happy reading Attila Kinali -- You know, the very powerful and the very stupid have one thing in common. They don't alters their views to fit the facts, they alter the facts to fit the views, which can be uncomfortable if you happen to be one of the facts that needs altering. -- The Doctor ___ 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.
