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Re: [Question] CTI OSC5A2B02 OXCO module high precision frequency reference project
Jerry, Thanks as always. That's very helpful, though ti adds a 3rd option to test.. This seems like a good application for 1-2 Farad caps on all the DC lines adjacent to the device being powered. That should yield sub 1 Hz RC time constants. As Ken Thompson said, "When it doubt, use brute force." One of the things that scares me is EMI. A "make before break" relay to switch between mains supply and a battery for measurements. At the moment I'm swamped by the consequences of a buying binge arriving. Have Fun! Reg On Friday, August 11, 2023 at 11:59:02 AM CDT, Jerry <jerry@...> wrote: This person named Adrian Rus, pretty sharp engineer and entrepreneur, (co-authored some papers with Ulrich) said (and we tested it) that you should have a minimum of 15,000uf on an individual oscillator for references. Also, and I tested this for him, we switched to lt3045 regulators as they were proven to be exceptionally low-noise and cleaned-up even dirty power supplies. We used these modules and others like them: https://www.ebay.com/itm/274137165726?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=pX50eYVtSOq&sssrc=2047675&ssuid=UQSWHCvkTY2&widget_ver=artemis&media=COPY For testing, I used a 60dB amp that tapped off the residual noise and A/C from the DC voltage and then fed that into my low frequency spectrum analyzer and the noise reduction was amazing. Andrew Holme, who authored our phase noise test set, used a capacitance multiplier circuit with large caps on it. I tested it and then fed it into the lt3045s and it was pretty clean. You can stack the lt3045s for more current and also in series to reduce noise. Big problem turned out to be shielding when testing very low PN oscillators in the -180 dBc range so for testing I switched to Dewalt 20V power tool batteries followed by the lt3045 regulators. When using batteries and 15kuf caps though, I first used the LM317 regulators and didn¡¯t see much difference but running off of mains, the lt3045s made all the difference. Every noise spike we found later was related to external energy. If I was building a bench, I think I would have a rack of the lt3045s with a switch that fed them from batteries or from mains. Sent from Mail for Windows |
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Re: [Question] CTI OSC5A2B02 OXCO module high precision frequency reference project
¿ªÔÆÌåÓýThis person named Adrian Rus, pretty sharp engineer and entrepreneur, (co-authored some papers with Ulrich) said (and we tested it) that you should have a minimum of 15,000uf on an individual oscillator for references.? Also, and I tested this for him, we switched to lt3045 regulators as they were proven to be exceptionally low-noise and cleaned-up even dirty power supplies.? We used these modules and others like them: ?
? For testing, I used a 60dB amp that tapped off the residual noise and A/C from the DC voltage and then fed that into my low frequency spectrum analyzer and the noise reduction was amazing. ? Andrew Holme, who authored our phase noise test set, used a capacitance multiplier circuit with large caps on it.? I tested it and then fed it into the lt3045s and it was pretty clean.? You can stack the lt3045s for more current and also in series to reduce noise. ? Big problem turned out to be shielding when testing very low PN oscillators in the -180 dBc range so for testing I switched to Dewalt 20V power tool batteries followed by the lt3045 regulators.? When using batteries and 15kuf caps though, I first used the LM317 regulators and didn¡¯t see much difference but running off of mains, the lt3045s made all the difference.? Every noise spike we found later was related to external energy. ? If I was building a bench, I think I would have a rack of the lt3045s with a switch that fed them from batteries or from mains. ? ? ? ? Sent from for Windows ? From: Reginald Beardsley via groups.io
Sent: Thursday, August 10, 2023 11:15 AM To: [email protected] Subject: Re: [qex] [Question] CTI OSC5A2B02 OXCO module high precision frequency reference project ? I am just starting on this project. So far all I have done is test 4 of the trimmer next to OXCO PCBs and measured the voltage required to set 10 bare OXCOs to 10 MHz. ? |
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Re: [Question] CTI OSC5A2B02 OXCO module high precision frequency reference project
I am just starting on this project. So far all I have done is test 4 of the trimmer next to OXCO PCBs and measured the voltage required to set 10 bare OXCOs to 10 MHz. Tests on the first two PCB units set them set to 10 MHz and showed 0.1 ppb over a couple of days comparing the OXCOs to a GPSDO and the OXCO in my HP 5386A and timing how long it took for the OXCOs to vary by a cycle or half cycle relative to GPSDO on a 4 channel DSO. That is all the testing I have done. It was very informal and was solely for the sake of determining whether I wanted to buy more. I ordered 3 more PCBs and 10 bare OXCOs. Of the 3 PCBs one had a cap broken off which I've not dealt with yet and the other two would not tune to 10 MHz. That alerted me to the drift of the voltage required to set the OXCO to 10 MHz. So when the 10 bare OXCOs arrived I adjusted them to as close to 10 MHz as I could with a lab supply and noted the voltage and frequency as reported by the 5386A using the GPSDO as the reference. I am still waiting for the 2nd batch of 10 bare OXCOs to arrive. I have only done qa very preliminary error budget assessment focused solely on the PS to the LM399 and OXCO. The most basic steps for such an endeavor are not complete. I've only gotten far enough to know that the PS will have to be *very* much more stable and accurate than anything I currently have in functional form. I have lots of nice T&M kit, but nothing in the 0.001 ppb range, so I'll have to build that. While retrieving an ancient CB radio PSU to repurpose for this effort I found a Sola Constant Voltage ferroresonant transformer which will accept 90-130 Vac and output 118 Vac. The net result is I now have 2 different PS designs for feeding the LM399 and AD8429 to test: Sola and single LM317 Dual LM317 I'm busier than the proverbial one armed paper hanger with hives. I'm building a rack and bench to hold all the T&M gear which has never all been in operation at the same time, managing 16,000 sq ft of commercial space comprised of 4 discrete buildings and attempting to dispose of a staggering volume of stuff my Dad left ranging from WW II surplus electronics parts to an NOS Montgomery Ward cement mixer still on the pallet. Add to that multiple pieces of T&M kit, cables and adapters, etc arriving which need to be checked within the return period. The PS for this project is the absolute limit of what I have time for. Have Fun! Reg |
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Re: [Question] CTI OSC5A2B02 OXCO module high precision frequency reference project
¿ªÔÆÌåÓýHave you run a phase noise test on them? ? From: Reginald Beardsley via groups.io
Sent: Wednesday, August 9, 2023 4:04 PM To: [email protected] Subject: Re: [qex] [Question] CTI OSC5A2B02 OXCO module high precision frequency reference project ? As a consequence of a completely unrelated conversation I got the idea of comparing the OXCOs to a GPSDO or another OXCO by filtering out the harmonics, mixing with a GPSDO, filtering out everything above a few Hz and timing the interval between zero crossings of the difference frequency which should be in the milliHertz range. By using higher harmonics the measurement period can be reduced from 100 s as desired. ? |
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Re: [Question] CTI OSC5A2B02 OXCO module high precision frequency reference project
As a consequence of a completely unrelated conversation I got the idea of comparing the OXCOs to a GPSDO or another OXCO by filtering out the harmonics, mixing with a GPSDO, filtering out everything above a few Hz and timing the interval between zero crossings of the difference frequency which should be in the milliHertz range. By using higher harmonics the measurement period can be reduced from 100 s as desired. Has anyone tried or heard of someone using such a technique? Given the long history of frequency comparisons I should expect it's been done by many others prior to the advances in the '70s and '80s in semiconductor technology. Have Fun! Reg |
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Re: CTI OSC5A2B02 OXCO module high precision frequency reference project
A few general comments about how I intend to pursue this:
1) To the maximum extent possible I'm going to use comparison rather than measurement 2) I'm going to build the project in the smallest possible increments with lots of performance testing before moving on to the next section starting from the wall plug out. 3) A screened enclosure is absolutely essential and I expect that magnetic shielding will also be required. I know this from previous EMI mitigation efforts for projects with less stringent requirements. 4) DSP and numerical work will be the last step and results of that may force going back and reworking portions of the system. It is highly likely that DSP will clean up the data enough to demonstrate that there are undetected flaws in prvious work. 5) There are a number of items I shall need to design and build for testing which will present their own can of worms to resolve and I anticipate some of those may prove time consuming to get correct. 6) Once it is complete, testing will take years. 7) Failure is highly likely, possibly multiple times. My response to Dan is already so lengthy I've set it aside for review. Have Fun! Reg |
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Re: CTI OSC5A2B02 OXCO module high precision frequency reference project
Daniel Marks
You can look at some papers here: I have my publications accessible from a Google Drive link: I also have the course lectures from my "Math and Physics in Imaging" course on-line that the lecture came from. I have to admit I never found compressive sensing compelling mostly because I never found anyone who really compared their inferred reconstruction to the actual object being measured quantitatively.? Most of the work seemed to be rather contrived, and I concluded that in a situation in which there was a genuine unknown object to be measured, compressive sensing probably would not provide a reliable result.? However it was very popular at the time and I thought I should present it so that students could understand what it is about.? I spent a while trying to find the parameters of fractional-order diffusion processes that were being used to model biological diffusion processes.? These processes have mean-squared diffusion lengths that do not grow linearly with time.? These processes are generalizations of time-invariant, space-invariant random walks.? Unfortunately, you get into some weird stuff trying to calculate moments of this distribution, including having to employ contour integration. ? This results in a process that does not have a well-defined autocorrelation.? Then one has to try to match moments of the distribution to measurements to determine the parameters of the distribution.? I found that the process memory is so long that no reliable estimator could be obtained from the sampled moments.? So even if the process could be modeled by a fractional-order diffusion process, proving that it was by observations was going to be impossible. By the way, the Open Research Institute is going to offer my QRP radio as a kit, you can check it out: 73, Dan KW4TI On Tue, Aug 8, 2023 at 7:15?PM Reginald Beardsley via <pulaskite=[email protected]> wrote:
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Re: CTI OSC5A2B02 OXCO module high precision frequency reference project
i"m gob smacked! In the 10 years since I got into the topic I've never run across anyone other than an couple of oil industry friends who knew anything about it. Foucart & Rauhut is rather heavy going with no one to talk to except the wall. I evaluated the analytic 1D heat equation for something like 50,000 parameter choices, picked a few and summed them to generate y, solved Ax=y using the simplex algorithm in GLPK and compared the results to what I had created. At 2x the period of my trial data I reached 1-2% error. I was inverting flow rates from multiple cracks in porous media. The machine I was using is not running at present so I can't readily find my work and after 10 years it would require a couple of days to figure out what I did where in 4-5 TB of disk space. The main mathematical obstacle I see is starting with very old OXCOs and LM399s where there is very little curvature left. Please send me PDFs of your papers. After reading one paper, I'm pretty sure by Donoho, I bought and read Ziegler's "Lectures on Polytopes" and Grunbaum's "Convex Polytopes". I only read the sections relevant to the paper I'd read as the general topic is very far from my normal activities. Having taken a BA in English lit, I find my involvement with rather exotic mathematics a curious turn of events. I just returned from hunting through the "stuff" aka the "Anvil of Conrad". 8000 sq ft filled at the time of his death 4 feet deep. In the process I turned up a 60 VA Sola Constant Voltage transformer. 95 to 130 Vac in 118 Vac out. I plan to set it up with a large (4-6") Ohmite rheostat as a load and see how it does using a large Variac to swing across the 114-126 V service entrance spec. Stable line voltage will significantly simply the PS for the LM399. There certainly is no magic pixie dust. One of the things that makes seismic processing so expensive is all the rabbit holes you come across dealing with 10-12 TB of data. The other is the amount of machine time it requires. A friend had to rent a warehouse for the group of about 400 people he was managing at the time because they had exceeded the available power. This is going to be a very interesting thread with you participating. Have Fun! Reg On Tuesday, August 8, 2023 at 04:10:26 PM CDT, Daniel Marks <profdc9@...> wrote:
I worked in the field of compressed sensing and I taught a course that included this material. I also wrote several papers on compressed sensing instruments. I am very familiar with the works of Donoho, Candes, and Tao. The various measures of sparsity, including mutual coherence, the restricted isometry property, L0, and L1 measures. I also build instruments. I built spectroscopic instruments and inverse scattering radar measurements (which are better conditioned as they are elliptic rather than parabolic systems as in evanescent surface waves) that utilized compressed sensing for data inversion. I also worked on trying to infer the parameters of distributions of time series with long-memory, long-tailed distribution diffusion processes from measurements of these distributions. And there's one thing I know: no magic fairy dust turns bad data into good data. You can not wave your sparsity magic wand over data and miraculously get usable data from noise. It doesn't matter if you have the government spend $100 billion to improve a radar signature or oil companies spend $10 billion to find an oil well. These are the kinds of visions sold by people who want grant money and promise that they can miraculously tease out some data that is somehow latent and overlooked. This is extraordinarily rare as to be unknown. In the end, you have a physical model for a process. You have possible measurements of that process. You have some inference method, for example, maximum a posteriori. Your estimator can only be good as your model. If your model is well enough behaved, you can get an idea using Fisher information or mininum variance estimation as to the accuracy of the estimator. I have spend a career solving inverse problems and have been quite successful at this. And I don't promise what I do not think can deliver. And I would not promise that any compressed sensing or estimation would reliably provide an answer, unless there was some reason to believe that the problem was guaranteed by the physical situation to actually satisfy that sparsity constraint. In reality, most just assume the sparsity constraint, get an answer, and don't bother to compare to reality, or have any sort of cross-validation of the results. I attach a copy of a lecture for a course that briefly summarizes some basic results in compressed sensing theory as of the time the lecture was written. |
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Re: CTI OSC5A2B02 OXCO module high precision frequency reference project
Daniel Marks
I worked in the field of compressed sensing and I taught a course that included this material.? I also wrote several papers on compressed sensing instruments. I am very familiar with the works of Donoho, Candes, and Tao.? The various measures of sparsity, including mutual coherence, the restricted isometry property, L0, and L1 measures. I also build instruments.? I built spectroscopic instruments and inverse scattering radar measurements (which are better conditioned as they are elliptic rather than parabolic systems as in evanescent surface waves) that utilized compressed sensing for data inversion. I also worked on trying to infer the parameters of distributions of time series with long-memory, long-tailed distribution diffusion processes from measurements of these distributions. And there's one thing I know:? no magic fairy dust turns bad data into good data.? You can not wave your sparsity magic wand over data and miraculously get usable data from noise.? It doesn't matter if you have the government spend $100 billion to improve a radar signature or oil companies spend $10 billion to find an oil well. These are the kinds of visions sold by people who want grant money and promise that they can miraculously tease out some data that is somehow latent and overlooked.? This is extraordinarily rare as to be unknown. In the end, you have a physical model for a process.? You have possible measurements of that process.? You have some inference method, for example, maximum a posteriori.? Your estimator can only be good as your model.? If your model is well enough behaved, you can get an idea using Fisher information or mininum variance estimation as to the accuracy of the estimator. I have spend a career solving inverse problems and have been quite successful at this.? And I don't promise what I do not think can deliver.? And I would not promise that any compressed sensing or estimation would reliably provide an answer, unless there was some reason to believe that the problem was guaranteed by the physical situation to actually satisfy that sparsity constraint.? In reality, most just assume the sparsity constraint, get an answer, and don't bother to compare to reality, or have any sort of cross-validation of the results.? On Tue, Aug 8, 2023 at 3:40?PM Reginald Beardsley via <pulaskite=[email protected]> wrote:
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Re: CTI OSC5A2B02 OXCO module high precision frequency reference project
In general I strongly advise against jumping ahead of me to bring up some point such as the problem being illconditioned unless you have read and understand Foucart & Rauhut and "Random Data" by Bendat and Piersol. I am at the preliminary design stage of the basic DC supply.
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If you would like to skip forward to data analysis, please provide data for analysis. For OXCO a minimum of 3 devices contemporaneously measured spanning 3 months or longer. If you have multi-year records, send me the first half of each time series so we can compare predictions to reality. A few mathematical details of major significance: 1) Any power fluctuations will be correlated across N OXCOs and trivial to remove as a consequence. The same applies to environmental variations. There are more stringent requirements on data collection to counter EMI. Suppressing EMI in processing requires simultaneous measurements to remove via DSP. 2) Prior to Candes & Donoho's work in 2004, such problems could not be solved. That is what "NP-Hard" denotes. I am quite amazed that Donoho's 2004 proof remained unknown to me for 9 years. Prior to 2013-2016, a significant concern any time I was handed a programming assignment was "Is it NP-Hard?". I've encountered such requests more than once. In the seismic field the most common example is line intersections as those are of critical importance. Naively finding all the points where two or more of N line segments intersect requires comparing N! combinations. In practice you must *never* attempt such a problem, so identifying such things is critical to completing the work in a timely manner. Fortunately, in many instances one can avoid using an NP-Hard algorithm by exploiting various properties of the problem. Candes found the method and Donoho provided the proof for a broad class of problems in which the solution space was "sparse". To the best of my knowledge it is the *only* published solution to an NP-Hard problem in non-polynomial time. That is a huge breakthrough which ranks with Norbert Weiner's 1940 report titled "The Extrapolation, Interpolation and Smoothing of Stationary Time Series" . And given the mathematical symmetries with regular polytopes and convex hulls in N dimensional space and many other areas of mathematics, I think that it will come to be recognized as eclipsing Weiner which is no mean feat. As I suspect most reading this don't know what NP-Hard means, I shall give a brief precis. If a problem has the form of a sum of M functions from a collection of N functions, the L0 solution prior to September 2004 required evaluating all N factoral combinations. For N = 10, that''s 3.6 million sums that must then be subtracted from the data to be fit and the absolute error summed. For N = 20 it's 2e18 permutations and N = 30 it's >2e32. My calculator is unable to evaluate 100! and an attempt to compute 50,000! would probably require more computer memory than the sum off all the memory of any form which has ever been produced just to hold all the digits of the resulting integer. For now let's stick to properly feeding an LM399 and an AD8429 so that everything above 0 Hz is -120 dB or lower. With LM317s if possible and something better if not. Have Fun! Reg On Monday, August 7, 2023 at 09:16:06 PM CDT, Daniel Marks <profdc9@...> wrote:
You might need to consider some kind of chopper-type amplifier for stabilizing the voltage at those very low input offsets and microvolt-ranges over long time scales. Otherwise drift is going to be problematic over minutes-to-hours time scale as even small input offsets vary. Even a LM399 has to have its own aging effects, given it's constructed from diffusion, ion implantation, and other deposition processes that experience relaxation over time. These are likely to be significant over a year. Also, trying to fit the various exponential-type aging processes, which could vary over orders of magnitude of time, to a sum of exponentials is going to be a poorly conditioned problem. This is the kind of thing that NIST standards were created for. I suppose it's worth a try, but I think it would need to be compared to something like a rubidium clock. |
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Re: CTI OSC5A2B02 OXCO module high precision frequency reference project
I've abandoned originating posts on other lists. It's too hard to keep track of the discussion as evidenced by 2 on EEVblog and the most substantive on the HPAK repair list. On Tuesday, August 8, 2023 at 10:19:40 AM CDT, Harke Smits via groups.io <yrrah@...> wrote: There are already two threads on Eevblog. Another one here? Best regards, Harke |
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Re: CTI OSC5A2B02 OXCO module high precision frequency reference project
I've bought 20 bare modules from this seller: https://www.ebay.com/itm/266143027936 Still waiting on the 2nd batch of 10. This is the pattern of the PCB version I bought: https://www.ebay.com/itm/195752609455 ebay refuses to tell me whom I bought them from. I've had a 50% out of tuning range because of OXCO aging out of the divider range. Simple fix, change 2 SMD resistors. There are many things I don't like about the general design, particularly the trimmer next to the OXCO. But it's still quite remarkable for the price which has actually come down as there are now 3 different PCBs using the CTI OXCOs on ebay. Have Fun! Reg On Tuesday, August 8, 2023 at 07:48:09 AM CDT, N2MS <mstangelo@...> wrote: Reg, I would like to try out some of these OCXO's. Can you recommend an EBay seller? Mike N2MS > On 08/07/2023 9:42 PM EDT Reginald Beardsley via groups.io <pulaskite@...> wrote: > >? > I've?discussed?these?in?threads?on?several?lists?and?concluded?that?it?would?be?best?to?stick?to?a?single?thread?here. > > These?are?available?for?$3?each?on?ebay.??They?are?salvaged?from?old?cell?tower?GPSDOs.??The?new?specs?are?very?good?and?they?are?well?aged?so?long?term?stability?should?be?excellent?and?an?order?of?magnitude?or?more?better?than?a?new?OXCO.??10?year?aging?rate?is?specified?at?0.4?ppb/yr. > > The?tuning?rate?is?1?ppb/mV?or?0.001?ppb/uV.??On?the??datasheet?the?short?term?stability?is?stated?as?0.02?ppb/s.??That?happens?to?correspond?to?the?20?uVrms?spec?of?an?LM399?which?are?also?available?as?salvage?parts?and?which?I?plan?to?use?for?the?Vref.??That?gives?me?some?modest?hope?that?if?I?clean?up?the?noise?and?other?factors?I?may?be?able?to?achieve?0.01?ppb. > > There?are?a?couple?of?Chinese?PCBs?that?have?one?of?these?on?them.??I?have?two?of?the?version?with?the?trimmer?next?to?the?OXCO?module?that?are?0.1?ppb?after?adjustment?using?a?GPSDO?and?DSO.??Two?others?have?drifted?out?of?range?of?the?tuning?voltage?divider?and?can't?be?set?to?10?MHz?without?changing?the?fixed?resistors?in?the?divider. > > After?some?study,?I've?concluded?that?the?main?limitation?on?the?stability?of?these?is?power?supply?noise?and?temperature?stability.??I'd?like?to?get?to?0.01?ppb/yr?just?to?see?if?I?can.??The?10x?rule?of?thumb?dictates?that?I?need?noise?and?voltage?drift?in?the?single?uV?range?which?will?not?be?easy?or?quick. > <snip> |
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Re: CTI OSC5A2B02 OXCO module high precision frequency reference project
Reg,
I would like to try out some of these OCXO's. Can you recommend an EBay seller? Mike N2MS On 08/07/2023 9:42 PM EDT Reginald Beardsley via groups.io <pulaskite@...> wrote:<snip> |
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Re: CTI OSC5A2B02 OXCO module high precision frequency reference project
Daniel Marks
You might need to consider some kind of chopper-type amplifier for stabilizing the voltage at those very low input offsets and microvolt-ranges over long time scales.? Otherwise drift is going to be problematic over minutes-to-hours time scale as even small input offsets vary.? Even a LM399 has to have its own aging effects, given it's constructed from diffusion, ion implantation, and other deposition processes that experience relaxation over time.? These are likely to be significant over a year. ? Also, trying to fit the various exponential-type aging processes, which could vary over orders of magnitude of time, to a sum of exponentials is going to be a poorly conditioned problem.? This is the kind of thing that NIST standards were created for.? I suppose it's worth a try, but I think it would need to be compared to something like a rubidium clock. On Mon, Aug 7, 2023 at 8:42?PM Reginald Beardsley via <pulaskite=[email protected]> wrote: I've?discussed?these?in?threads?on?several?lists?and?concluded?that?it?would?be?best?to?stick?to?a?single?thread?here. |
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CTI OSC5A2B02 OXCO module high precision frequency reference project
I've?discussed?these?in?threads?on?several?lists?and?concluded?that?it?would?be?best?to?stick?to?a?single?thread?here.
These?are?available?for?$3?each?on?ebay.??They?are?salvaged?from?old?cell?tower?GPSDOs.??The?new?specs?are?very?good?and?they?are?well?aged?so?long?term?stability?should?be?excellent?and?an?order?of?magnitude?or?more?better?than?a?new?OXCO.??10?year?aging?rate?is?specified?at?0.4?ppb/yr. The?tuning?rate?is?1?ppb/mV?or?0.001?ppb/uV.??On?the??datasheet?the?short?term?stability?is?stated?as?0.02?ppb/s.??That?happens?to?correspond?to?the?20?uVrms?spec?of?an?LM399?which?are?also?available?as?salvage?parts?and?which?I?plan?to?use?for?the?Vref.??That?gives?me?some?modest?hope?that?if?I?clean?up?the?noise?and?other?factors?I?may?be?able?to?achieve?0.01?ppb. There?are?a?couple?of?Chinese?PCBs?that?have?one?of?these?on?them.??I?have?two?of?the?version?with?the?trimmer?next?to?the?OXCO?module?that?are?0.1?ppb?after?adjustment?using?a?GPSDO?and?DSO.??Two?others?have?drifted?out?of?range?of?the?tuning?voltage?divider?and?can't?be?set?to?10?MHz?without?changing?the?fixed?resistors?in?the?divider. After?some?study,?I've?concluded?that?the?main?limitation?on?the?stability?of?these?is?power?supply?noise?and?temperature?stability.??I'd?like?to?get?to?0.01?ppb/yr?just?to?see?if?I?can.??The?10x?rule?of?thumb?dictates?that?I?need?noise?and?voltage?drift?in?the?single?uV?range?which?will?not?be?easy?or?quick. Preliminary?error?budget?analysis?reveals?that?mains?line?voltage?varies?+/-?5%?between?114?and?126?V.??After?reviewing?the?datasheet?for??the?LM317?it?appears?that?a?mains?supply?which?uses?two?LM317s?in?series?with?an?AD?584JH?to?set?the?10?V?to?feed?the?LM399?will?prevent?mains?fluctuations?from?affecting?the?LM399?output. There?are?also?temperature,?device?noise?and?EMI?to?contend?with?which?I?shall?get?to?in?due?course.??To?save?time?and?effort?I?am?going?to?attempt?to?use?Chinese?LM317?and?AD584?PCBs?which?I?have?on?hand?to?supply?the?LM399?and?an?AD8429?ultra?low?noise?instrumentation?amp?to?buffer?the?LM399?from?the?OXCO?Vctl?line.?The?20?uVrms?noise?of?the?LM399?will?need?to?be?filtered?out?and?I'll?have?to?find?a?truce?among?the?various?tempcos. In?general?I?intend?to?follow?Ken?Thompson's?aphorism,?"When?in?doubt,?use?brute?force."?and?rely?on?lots?of?filtering?from?the?wall?to?the?OXCO?and?several?levels?of?thermal?isolation?and?regulation. As?I?am?certain?that?any?knowledgeable?reader?will?grasp?that?0.01?ppb/yr?for?an?OXCO?is?wildly?ambitious,?I?should?like?to?explain?why?I?think?it?might?be?possible. The??viscothermoelastoplastic?continuum?mechanics?of?crystals?and?voltage?references?produces?an?aging?profile?which?asymptotically?approaches?a?constant?value.??There?can?be?several?different?aging?rates?which?combine,?but?after?enough?time?one?will?come?to?dominate?the?others.??In?general?the?form?of?the?functions?is?very?similar?to?the?1D?heat?equation?with?its?infinite?sum?of?exponentials. Some?years?ago?I?spent?quite?a?bit?of?time?studying?sparse,?underdetermined?solutions?of?arbitrary?sums?of?such?functions.??In?my?numerical?experiments?I?found?that?I?could?predict?future?behavior?to?within?1-2%?for?a?period?in?the?future?equal?to?the?duration?of?the?prior?observations.That?result?is?due?to?the?work?by?Emannuel?Candes?and?David?Donoho?in?the?2004?-2008?period.??In?particular,?Donoho?proved?in?2004?that?if?and?only?if?a?sparse?L1?solution?to?an?underdetermined?system?of?linear?equations?existed?it?was?the?L0?optimal?solution?which?is?NP-Hard. I?was?already?solving?massively?underdetermined?systems?with?50,000?unknowns?and?100?or?fewer?equations?following?the?discussion?of?bais?pursuit?in?the?3rd?edition?of?Mallat's?"A?Wavelet?Tour?of?Signal?Processing"?when?it?sank?it?I?had?always?been?taught?that?was?not?possible?because?there?were?an?infinite?number?of?solutions.??As?a?result?I?spent?the?next?3?years?reading?3000?pages?of?the?most?difficult?math?I've?ever?seen.??A?single?proof?in?one?of?Donoho's?papers?ran?14?pages. Ever?since?I?have?been?searching?for?data?with?which?to?demonstrate?the?power?of?sparse?L1?decompositions?for?the?solution?of?inverse?problems.??A?bunch?of?cheap,?high?spec?voltage?references?and?OXCOs?led?me?to?speculate?on?whether?I?could?combine?solutions?for?the?aging?rate?of?individual?OXCOs?to?eliminate?the?systematic?errors?caused?by?aging?by?continuously?adjusting?the?control?voltages?using?an?L1??solution?for?the?proper?control?voltages?to?hold?each?OXCO?to?within?0.01?ppb/yr.??The?nominal?set?point?for?10?MHz?output?is?2?V?so?I?need?something?on?the?order?of?2-5?ppm/yr?voltage?stability?which?is?extremely?difficult?to?achieve?*if*?it?can?be?done?at?all.??A?figure?I?was?recently?sent?showing?the?100?day?variation?of?3?high?quality?OXCOs?is?dominated?by?correlated?noise.??For?each?OXCO?the?magnitude?of?the?excursions?and?the?slopes?of?the?curves?is?different. Having?spent?my?career?in?reflection?seismology,?I?am?quite?accustomed?to?suppressing?both?correlated?and?uncorrelated?noise?in?multi-channel?time?series?by?a?wide?range?of?methods?chosen?to?fit?the?nuances?of?the?noise?in?question.??Recovering?good?signals?which?are?well?below?the?noise?is?daily?fare?in?seismic?exploration.??There?is?not?much?energy?that?makes?it?6?miles?into?the?earth?and?back.??But?that's?all?that?one?has?to?work?with.??At?$100+?million?per?well,?a?lot?of?time?and?money?gets?spent?trying?to?make?marginal?improvements?in?the?success?rate?be?means?of?better?seismic?imaging. This?is?a?low?financial?cost,?hobby?project.??Failure?is?a?perfectly?acceptable?outcome,?but?only?after?I?have?made?a?best?effort?attempt..?You?don't?know?until?you?try.??I?think?I'll?learn?enough?to?enjoy?the?attempt?however?it?turns?out. My?next?post?will?be?on?the?topic?of?the?results?I??achieve?with?the?LM317s.??I?have?Variacs,?so?I?can?measure?the?effect?of??mains?voltage?variations?quite?easily.??It?will?become?a?lot?more?difficult?when?I?start?looking?at?uV?level?noise.??I?expect?amplifying?uV?signals?so?I?can?see?them?on?a?1?mV/div?DSO?will?be?"interesting".??Fortunately?I?won't?need?that?until?I?start?work?with?the?LM399. Have?Fun! Reg |
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Chinese MT3608 based 2 A DC-DC boost converter
FYI This is a repost from qrptech. I'm reposting this here so I can consolidate threads I start in one place. I've had people on one list bring up something I mentioned on another list and it's become confusing and difficult to avoid repeating myself. So threads I start will appear here. Threads other people start will remain where they started.
I saw these? for under $1 on temu.com and bought 10. I want to see if they can be used to maintain the input voltage for a portable QRP rig as the battery drains. With ~10 V @ 2.8 A input it produces 13.8 V @ 1.8 A output under load.? It can just get to 2 A @ 13.8 V at which point I hit the 3.2 A? limit of the lab supply current. However, under load the switching noise is quite bad.? The screenshots are from my Instek MSO which has the MDO spectrum analyzer function enabled.? As you can see there is both broadband noise and lots of strong harmonics of the switching frequency of 1.2 MHz. 160 is with the power off and 161 with it on.? I'm going to need a lot of filtering to make it usable as power for a radio receiver.? The DSO was connected directly to the Vout of the MT3608 via a 10x probe. I was using a wirewound rheostat for the load, so that likely has some influence. I'll run some experiments to see how well I can reduced the EMI output.? It gets fairly warm, so a heatsink is also probably a good idea. Have Fun! Reg |
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