Re: [time-nuts] A simple sampling DMTD
Hi You are not going to get useful phase noise data out of a normal DMTD …. The DMTD is targeted at ADEV and similar long term / high accuracy measurements. If a DMTD “makes it” to a 10 Hz beat note that is about as far as most people take it. Bob > On Sep 16, 2019, at 10:41 AM, tim...@timeok.it wrote: > > > Hi Jan, > > this is precisely the instrument that is lacking at a hobbyist price. > > It would be excellent to have the possibility of measuring phase noise. > > Can you anticipate the features of the Sampling DMTD? > > Can it be used with Timelab? > > We are waiting for your new ones. > > Luciano > > > Da "time-nuts" time-nuts-boun...@lists.febo.com > A "Discussion of precise time and frequency measurement" > time-nuts@lists.febo.com > Cc > Data Sat, 14 Sep 2019 14:25:48 +0200 > Oggetto Re: [time-nuts] A simple sampling DMTD > Update: I have finished routing the board (placement diagram at > http://www.lartmaker.nl/time-nuts/DMTD%20rev1.00%20assembly.pdf ) and > ordered a few prototype PCBs. > > After the earlier discussions on the list I've grown sufficiently concerned > about the impact of 1/f converter noise that I have added headers to the > board to allow me to replace the D-flipflop sampler with an FPGA-based I/Q > downconverter. While the main PCBs are in production I'll draw a simple > daughterboard with dual ice40 UltraPlus FPGAs, If the FPGA solution turns > out to be necessary (or a noticeable improvement), I'll redraw the main PCB. > > To be continued, > > JDB. > > On Sun, Sep 1, 2019 at 2:09 AM Jan-Derk Bakker wrote: > >> Dear all, >> >> I've been working on a design for a (relatively) simple, standalone >> sampling DMTD. Very rough preliminary schematics can be found at >> http://www.lartmaker.nl/time-nuts/DMTD_rev0.99.pdf . >> >> Design goals are: >> - ps-level accuracy >> - comparison of frequencies between at least 10 and 50MHz, preferably >> between 1 and 100MHz >> - comparison of (selected) different frequencies (in my case: 10MHz vs >> 50MHz) >> - standalone operation, field-portable >> - option for raw data sampling / (post)processing on a PC >> - option for generating a tuning voltage to lock the measured oscillator >> to the reference, so the DMTD can act as a PLL in phase noise test setups >> >> Context: you may remember that a year or two ago I posted to time-nuts >> about a GPSDO-design geared for mobile applications, which I was working on >> for an SDR-platform my students are working with. This SDR-platform has now >> grown to include a 100-channel phased array receiver. To validate the >> reference clock distribution in this array (amongst other things) I would >> like to have a DMTD. As the commercial offerings are outside the budget of >> our lab, I was planning to roll my own. >> >> The core of the system is a transformer-coupled LTC2140-14 dual 14-bit >> ADC, sampling at an offset frequency of nominally 10MHz+10Hz generated by a >> VCTCXO (with an option for an OCXO). The ADC was chosen for its large input >> bandwidth and small aperture jitter. Simulations of a simple software ZCD >> consisting of a digital filter and least-squares fitting showed that >> 100ksps would be more than enough to get the desired accuracy. As the ADC >> design is unable to achieve sample rates lower than 1MSPS, D-flipflops are >> used to decimate the samples. These DFFs are also used to multiplex the >> 2x14-bit samples to an 8-bit data bus going into one of the GPIO-ports of >> an XMega. The XMega runs the ZCD, and generates a tuning voltage for the >> offset oscillator. Communication to a logging PC is done with a >> galvanically isolated FT2232H, which has both an ASCII COM-port for the ZCD >> data and a control interface and an asynchronous FIFO to transfer raw >> samples. System power comes from the isolated USB bus or a barrel jack; BOM >> cost in qty10+ is around 100US$. >> >> (The DMTD has a few more power rails than I would have liked. Originally I >> had planned to use the LTC2295 and have a 3v3-only system, but after >> re-reading the NIST paper on SDR-as-a-DMTD I concluded that the single >> clocking path of the 2140 would likely have better aperture jitter >> correlation between the channels. As a 1.8V/10MHz XMega would only be >> borderline able to handle the computations, I ended up with this design. >> LVC logic is used to go from 3.3V->1.8V, LV1T translators for the opposite >> direction.) >> >> Design decisions and/or non-goals: >> - I considered putting a small FPGA (specifically a Lattice ice40 >> UltraPlus) between the ADC and the processor. This was rejected because the >> performance of the decimator appeared to be sufficient, and I wasn't >> certain that I could get DDR mode + a CORDIC working in this FPGA. >> - Especially when I found the necessity to move part of the system to 1.8V >> I considered moving to an ARM. I stuck with the XMega as performance was >> sufficient, and I am very famil
Re: [time-nuts] Beginner's Atomic Clock
All of the available Rb standards that I've seen have a 10 MHz output, Some have a 1 PPS output as well. The nice thing about a Rb is that its short term stability (seconds to minutes and perhaps even longer) is much better than that of a GPS timing receiver. The bad news is that Rb standards exhibit long term frequency drift in the neighborhood of a few parts in 10^11 per month. A pretty fair compromise is to use an Rb standard that is disciplined by GPS PPS pulses with a loop time constant on the order of a day or so. The SRS model PRS-10 seems to be well-regarded and can be had for $1500 factory new. Many are on sale by ebay and similar sources- however these are often left over from telecom service and are actually a modified model that has had the PPS locking facility removed so that the original buyer could save a few bucks. My PRS-10 is one of these. The Rb standards seem to prefer being powered up continuously, and if one is turned back on after any significant storage without power, it can cake several days to really settle down to its steady state behavior. Also, because of the long-term frequency drift, one must periodically retune the unit back on frequency by referring it to GPS. Both units I own (a PRS-10 and an L-PRO) have an analog tuner port, wherein application of 0 to 5V DC tunes the frequency of the Rb through the range of +/- a few parts in 10^9. This has been straightforward but a bit tedious; if I want to get it within a few parts in 10^12, even a good 10-turn pot is barely adequate to the task, and I'm sometimes turning the shaft through an angle so small that I'm not sure I even moved it until I've observed the phase drift against GPS for an hour or more. So, that's my version of Rb 101. See what others have to say as well, as I'm also fairly new at the game. Dana (K8YUM) On Mon, Sep 16, 2019 at 4:02 PM pisymbol . wrote: > First off, thanks to everyone who replied. > > On Mon, Sep 16, 2019 at 11:00 AM Bob kb8tq wrote: > > > What are you really trying to do here? > > > > Take over the world - one epoch at a time. > > If it’s a “from scratch” atomic standard, then you just aren’t going to get > > there. Sorry about that ... > > > > Ok. > > > > If it’s a wall clock sync’d to an external radio service then indeed you > > might get there. > > > > Well, I want something maybe in between. Currently I think I have that: I > have a RPi disciplined to the Adafruit Ultimate GPS HAT via chrony (PPS > etc.). This works well. > > > > In-between those two lie tings like buying eBay telecom Rubidium’s, > > attaching them to a power supply and you have a working standard. > > > > So I think this is what I'm talking about. I want something a little bit > more esoteric than a GPS 1PPS. Can you explain a bit about these > prepackaged Rubidium standards? Upside/downside etc. Do I have to > maintain/check these black boxes? > > > > Lots of very different directions this could go and and they all could be > > called an atomic clock …. Not at all knock on doing something, just > > confusion > > about what exactly you want to do. > > > > Again, take over the world. Sorry for not being upfront about that. That > would have made things A LOT clearer. > > So I guess: How can I get a simple Rubidium standard that outputs a > reference frequency as a discipline to say ntpd or chrony. > > Btw, I'm a noob. Please be gentle. > > -aps > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Beginner's Atomic Clock
First off, thanks to everyone who replied. On Mon, Sep 16, 2019 at 11:00 AM Bob kb8tq wrote: > What are you really trying to do here? > Take over the world - one epoch at a time. If it’s a “from scratch” atomic standard, then you just aren’t going to get > there. Sorry about that ... > Ok. > If it’s a wall clock sync’d to an external radio service then indeed you > might get there. > Well, I want something maybe in between. Currently I think I have that: I have a RPi disciplined to the Adafruit Ultimate GPS HAT via chrony (PPS etc.). This works well. > In-between those two lie tings like buying eBay telecom Rubidium’s, > attaching them to a power supply and you have a working standard. > So I think this is what I'm talking about. I want something a little bit more esoteric than a GPS 1PPS. Can you explain a bit about these prepackaged Rubidium standards? Upside/downside etc. Do I have to maintain/check these black boxes? > Lots of very different directions this could go and and they all could be > called an atomic clock …. Not at all knock on doing something, just > confusion > about what exactly you want to do. > Again, take over the world. Sorry for not being upfront about that. That would have made things A LOT clearer. So I guess: How can I get a simple Rubidium standard that outputs a reference frequency as a discipline to say ntpd or chrony. Btw, I'm a noob. Please be gentle. -aps ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] A simple sampling DMTD
Hi Jan, this is precisely the instrument that is lacking at a hobbyist price. It would be excellent to have the possibility of measuring phase noise. Can you anticipate the features of the Sampling DMTD? Can it be used with Timelab? We are waiting for your new ones. Luciano Da "time-nuts" time-nuts-boun...@lists.febo.com A "Discussion of precise time and frequency measurement" time-nuts@lists.febo.com Cc Data Sat, 14 Sep 2019 14:25:48 +0200 Oggetto Re: [time-nuts] A simple sampling DMTD Update: I have finished routing the board (placement diagram at http://www.lartmaker.nl/time-nuts/DMTD%20rev1.00%20assembly.pdf ) and ordered a few prototype PCBs. After the earlier discussions on the list I've grown sufficiently concerned about the impact of 1/f converter noise that I have added headers to the board to allow me to replace the D-flipflop sampler with an FPGA-based I/Q downconverter. While the main PCBs are in production I'll draw a simple daughterboard with dual ice40 UltraPlus FPGAs, If the FPGA solution turns out to be necessary (or a noticeable improvement), I'll redraw the main PCB. To be continued, JDB. On Sun, Sep 1, 2019 at 2:09 AM Jan-Derk Bakker wrote: > Dear all, > > I've been working on a design for a (relatively) simple, standalone > sampling DMTD. Very rough preliminary schematics can be found at > http://www.lartmaker.nl/time-nuts/DMTD_rev0.99.pdf . > > Design goals are: > - ps-level accuracy > - comparison of frequencies between at least 10 and 50MHz, preferably > between 1 and 100MHz > - comparison of (selected) different frequencies (in my case: 10MHz vs > 50MHz) > - standalone operation, field-portable > - option for raw data sampling / (post)processing on a PC > - option for generating a tuning voltage to lock the measured oscillator > to the reference, so the DMTD can act as a PLL in phase noise test setups > > Context: you may remember that a year or two ago I posted to time-nuts > about a GPSDO-design geared for mobile applications, which I was working on > for an SDR-platform my students are working with. This SDR-platform has now > grown to include a 100-channel phased array receiver. To validate the > reference clock distribution in this array (amongst other things) I would > like to have a DMTD. As the commercial offerings are outside the budget of > our lab, I was planning to roll my own. > > The core of the system is a transformer-coupled LTC2140-14 dual 14-bit > ADC, sampling at an offset frequency of nominally 10MHz+10Hz generated by a > VCTCXO (with an option for an OCXO). The ADC was chosen for its large input > bandwidth and small aperture jitter. Simulations of a simple software ZCD > consisting of a digital filter and least-squares fitting showed that > 100ksps would be more than enough to get the desired accuracy. As the ADC > design is unable to achieve sample rates lower than 1MSPS, D-flipflops are > used to decimate the samples. These DFFs are also used to multiplex the > 2x14-bit samples to an 8-bit data bus going into one of the GPIO-ports of > an XMega. The XMega runs the ZCD, and generates a tuning voltage for the > offset oscillator. Communication to a logging PC is done with a > galvanically isolated FT2232H, which has both an ASCII COM-port for the ZCD > data and a control interface and an asynchronous FIFO to transfer raw > samples. System power comes from the isolated USB bus or a barrel jack; BOM > cost in qty10+ is around 100US$. > > (The DMTD has a few more power rails than I would have liked. Originally I > had planned to use the LTC2295 and have a 3v3-only system, but after > re-reading the NIST paper on SDR-as-a-DMTD I concluded that the single > clocking path of the 2140 would likely have better aperture jitter > correlation between the channels. As a 1.8V/10MHz XMega would only be > borderline able to handle the computations, I ended up with this design. > LVC logic is used to go from 3.3V->1.8V, LV1T translators for the opposite > direction.) > > Design decisions and/or non-goals: > - I considered putting a small FPGA (specifically a Lattice ice40 > UltraPlus) between the ADC and the processor. This was rejected because the > performance of the decimator appeared to be sufficient, and I wasn't > certain that I could get DDR mode + a CORDIC working in this FPGA. > - Especially when I found the necessity to move part of the system to 1.8V > I considered moving to an ARM. I stuck with the XMega as performance was > sufficient, and I am very familiar with both the CPU and the peripherals > (particularly time-stamping counters and the Event system) that would ease > the ZCD implementation and issues like synchronization between processor > and sampling system. > - I looked into integrat
Re: [time-nuts] 10811-Parts... (Using the thermal regulator circuitry)
I understand several of the modern MEMS OCXO's use microcontroller PID control for the temperature, avoiding the need for any large capacitors for compensation. The microcontroller does a lot more than the heating job, judging by the PhD thesis I see coming out of China. They seem to feed-forward the delta temperature into microtemperature oscillator compensation too so it's less like a traditional OCXO and more like an OCXO with some TCXO enhancements. Tim N3QE On Sat, Sep 14, 2019 at 5:01 PM Ulf Kylenfall via time-nuts < time-nuts@lists.febo.com> wrote: > > Yes, I have more or less cloned the temperature regulation circuitryand > used it for various heat control circuitry using > other/similarsemiconductors that can handle elevated temperatures. > The basic principle is nothing exotic. It can be found inmany applications > all over the internet. > > What is important is that the feed-backto the thermistor bridge (R+C) is > selected for a proper timeconstant so that the regulation does not > thermally oscillate. > > The thermal delay between the mechanics/heat dissipatingcomponents and the > isolation resistance between the thermistorand chassis is also important. > > > All the best > Ulf KylenfallSM6GXV > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Beginner's Atomic Clock
Hi What are you really trying to do here? If it’s a “from scratch” atomic standard, then you just aren’t going to get there. Sorry about that ... If it’s a wall clock sync’d to an external radio service then indeed you might get there. In-between those two lie tings like buying eBay telecom Rubidium’s, attaching them to a power supply and you have a working standard. Lots of very different directions this could go and and they all could be called an atomic clock …. Not at all knock on doing something, just confusion about what exactly you want to do. Bob > On Sep 16, 2019, at 5:16 AM, pisymbol . wrote: > > Can anyone suggest a "starter" atomic clock project? By beginner's > something that is fairly easy to put together and isn't cost prohibited > (maybe a few hundred but not thousand). > > Thanks! > > -aps (Alex) > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] 10811-Parts... (Using the thermal regulator circuitry)
On 9/15/2019 1:32 PM, Club Internet wrote: Rick, Thanks for this information. Actually the technology of C18 is not specified in the manual. Why should it necessarily be « foil » type and metallized? Is « foil » type same as « film » type? Of course the « mass » needs to be there (=> 3D printing services) Best Gilles. See: https://www.sbelectronics.com/products/application-notes/why-specify-filmfoil-capacitors/ Expanding on this: (1) the 10811 oven integrator has a large resistor in series with the capacitor, so there might not be enough available current to vaporize shorts. (2) shorting-and-clearing puts a glitch into the integrator which creates a thermal disturbance (3) the 10811 design engineers, and their boss (who hired me into HP) were extremely methodical and I can assure you that no decision was made by accident. Keep that in mind when reverse engineering the 10811. Foil types basically have 1/2 the capacitance of the same size in metallized. End of lesson :-) Rick N6RK ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Beginner's Atomic Clock
From: pisymbol . Can anyone suggest a "starter" atomic clock project? By beginner's something that is fairly easy to put together and isn't cost prohibited (maybe a few hundred but not thousand). Thanks! -aps (Alex) = Alex, Perhaps you could clarify what exactly you mean by "Atomic Clock"? - a box which has signal outputs of time and frequency? - a box with an hours/minutes/seconds display which fits on the wall? - something you can buy? - something you can assemble? - how accurate? - stand-alone, or using a GPS reference? This is my simple wall clock, accurate to a few tens of microseconds: https://www.satsignal.eu/raspberry-pi/DigitalClock.html Cost to me: ~GBP 50. Cheers, David -- SatSignal Software - Quality software for you Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk Twitter: @gm8arv ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Beginner's Atomic Clock
On 9/16/19 4:16 AM, pisymbol . wrote: Can anyone suggest a "starter" atomic clock project? By beginner's something that is fairly easy to put together and isn't cost prohibited (maybe a few hundred but not thousand). Do you mean "build the physics package", or are you just talking about something like getting a commercial rubidium reference (surplus) and packaging it? Thanks! -aps (Alex) ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
[time-nuts] Beginner's Atomic Clock
Can anyone suggest a "starter" atomic clock project? By beginner's something that is fairly easy to put together and isn't cost prohibited (maybe a few hundred but not thousand). Thanks! -aps (Alex) ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
