Re: [time-nuts] time-nuts equipment verification from scratch (was: WTB: GPSDO)
Hi > On Mar 21, 2017, at 1:07 AM, Chris Albertson > wrote: > > I built one of these using a PWM DAC also. The design was posted to this > list so I can't take credit for the idea. But we used two PWM output > pins. The PWM provides more voltage range than is needed by the OXO's > EFC. To the output was scaled by a voltage divider. This also scaled down > thew step size. The second PWN output was scale down even more, like > maybe 100X more. The two PWM outputs were added. One does course > adjustment the other fine. The software first sets the course PWM and > then the fine one takes over. > > But the PWM output was just run through an RC filter with a very long time > constants low pass filter with corner freq. < 1 Hz. The goal was to build > a VERY low cost GPSDO and adding a good external DAC would add to the cost. > > Someone here recently suggested that one could do as well by simply > adjusting a good oversized crystal with a screw driver as they could using > a simple GPSDO. Well, before building the GPSDO I tried keeping my OXO in > sync with my Tunderbolt using just a screw driver and a dual trace analog > tektronix scope. It is REALLY hard to do with a screw driver. You need a finer adjust pot on the EFC. It’s no different than the process you describe above with the PWM’s. With a PPS that is good to 10 ns, you can get to 0.1 ppb in 1000 seconds with margin. You will have a pretty good idea of what is going on in 100 seconds. If you are going to rig it up, a 20 turn wire wound pot with a dial on it is the high end approach. Set up the pot with a ~1x10^-8 full scale range. You then have roughly 5x10^-10 per turn. The cool part is that you can log the readings and work out what’s going on with the OCXO. Bob > Some tines > I'd think I had it right then I'd look at the scope after 30 minutes and > fine one sine wave had gained 1/4 cycle on the other. Lots of reason for > this, perhaps one of my voltage regulators are temperature sensitive, > "stiction" in the screw I was turning. Who knows. But my simple GPSDO > would notice the 1/4 cycle error and fix it automatically > > It real life for practical purposes I use the Rb clock, was lucky to get > one at the old $35 price. > > On Mon, Mar 20, 2017 at 4:43 PM, Mark Sims wrote: > >> The "DAC" was PWM based, but used a separate voltage regulator for the >> "reference". I never tried it using the USB power as the reference. >> >> The OCXO (+board) uses less than 500 mA warming up (which it does rather >> quickly). It's in a small hermetic package about twice the size of a >> standard DIP-14 oscillator package. There was a Ebay seller several years >> ago offering them at $15 each or 10 for $100. >> >> The Chinese "Arduino" board (it's not really and Arduino, just a MEGA 328 >> and a proto area) has a micro-USB connector for power input but does not >> implement USB data. I used the processor serial port with a level shifter >> dongle. The firmware was a cheap and dirty hack and I didn't implement >> much in the way of control or monitoring... never got around to improving >> it. The project was basically "Hey, I forgot I had those parts... Hmmm, >> one could build a simple GPSDO... why not? >> >> - >> >>> Did you use the Arduino's PWM output plus a LPF for the DAC, or a >> separate >> DAC? If PWM, did you have problems with noise or sensitivity to the >> USB-provided supply voltage? >> ___ >> 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. >> > > > > -- > > Chris Albertson > Redondo Beach, California > ___ > 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] time-nuts equipment verification from scratch (was: WTB: GPSDO)
I built one of these using a PWM DAC also. The design was posted to this list so I can't take credit for the idea. But we used two PWM output pins. The PWM provides more voltage range than is needed by the OXO's EFC. To the output was scaled by a voltage divider. This also scaled down thew step size. The second PWN output was scale down even more, like maybe 100X more. The two PWM outputs were added. One does course adjustment the other fine. The software first sets the course PWM and then the fine one takes over. But the PWM output was just run through an RC filter with a very long time constants low pass filter with corner freq. < 1 Hz. The goal was to build a VERY low cost GPSDO and adding a good external DAC would add to the cost. Someone here recently suggested that one could do as well by simply adjusting a good oversized crystal with a screw driver as they could using a simple GPSDO. Well, before building the GPSDO I tried keeping my OXO in sync with my Tunderbolt using just a screw driver and a dual trace analog tektronix scope. It is REALLY hard to do with a screw driver. Some tines I'd think I had it right then I'd look at the scope after 30 minutes and fine one sine wave had gained 1/4 cycle on the other. Lots of reason for this, perhaps one of my voltage regulators are temperature sensitive, "stiction" in the screw I was turning. Who knows. But my simple GPSDO would notice the 1/4 cycle error and fix it automatically It real life for practical purposes I use the Rb clock, was lucky to get one at the old $35 price. On Mon, Mar 20, 2017 at 4:43 PM, Mark Sims wrote: > The "DAC" was PWM based, but used a separate voltage regulator for the > "reference". I never tried it using the USB power as the reference. > > The OCXO (+board) uses less than 500 mA warming up (which it does rather > quickly). It's in a small hermetic package about twice the size of a > standard DIP-14 oscillator package. There was a Ebay seller several years > ago offering them at $15 each or 10 for $100. > > The Chinese "Arduino" board (it's not really and Arduino, just a MEGA 328 > and a proto area) has a micro-USB connector for power input but does not > implement USB data. I used the processor serial port with a level shifter > dongle. The firmware was a cheap and dirty hack and I didn't implement > much in the way of control or monitoring... never got around to improving > it. The project was basically "Hey, I forgot I had those parts... Hmmm, > one could build a simple GPSDO... why not? > > - > > > Did you use the Arduino's PWM output plus a LPF for the DAC, or a > separate > DAC? If PWM, did you have problems with noise or sensitivity to the > USB-provided supply voltage? > ___ > 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. > -- Chris Albertson Redondo Beach, California ___ 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] time-nuts equipment verification from scratch (was: WTB: GPSDO)
The "DAC" was PWM based, but used a separate voltage regulator for the "reference". I never tried it using the USB power as the reference. The OCXO (+board) uses less than 500 mA warming up (which it does rather quickly). It's in a small hermetic package about twice the size of a standard DIP-14 oscillator package. There was a Ebay seller several years ago offering them at $15 each or 10 for $100. The Chinese "Arduino" board (it's not really and Arduino, just a MEGA 328 and a proto area) has a micro-USB connector for power input but does not implement USB data. I used the processor serial port with a level shifter dongle. The firmware was a cheap and dirty hack and I didn't implement much in the way of control or monitoring... never got around to improving it. The project was basically "Hey, I forgot I had those parts... Hmmm, one could build a simple GPSDO... why not? - > Did you use the Arduino's PWM output plus a LPF for the DAC, or a separate DAC? If PWM, did you have problems with noise or sensitivity to the USB-provided supply voltage? ___ 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] time-nuts equipment verification from scratch (was: WTB: GPSDO)
Moin, On Mon, 20 Mar 2017 17:11:36 -0400 "William H. Fite" wrote: > You are talking about product design, development and optimization, not the > production of a one-off for home use. Since performance standards are > already well established, it is only necessary for the developer to test > the bench built instrument against published standards and determine if > performance is good enough to suit him. Given a sound understanding of the > role of various components in the system, it will be a great deal faster > and easier for the builder to tinker with the one-off then to go through an > extensive process of model development and verification. > > I have spent a good deal of my career doing performance modeling, > verification, and validation in collaboration with other scientists and > also engineers. You describe the process correctly but I think it is > generous overkill for the topic under discussion here. Or have I missed > something in the discussion? Is the desired end result a device for > manufacture and sale? If so, then your approach is right on target. The question kind of started of from how to verify a GPSDO works correctly. My answer to that was to use a known-good GPSDO and an vapor cell Rb standard. Both can be had for quite cheap (<200$ each) or borrowed from a fellow time-nut. With this and a suitable counter (e.g. PICTIC or TICC) one can verify the homebew GPSDO quickly and quantify the result. Chris Albertson injected, that he wanted to do the verification with stuff he could build on his own, not relying on another GPSDO or "expensive" Rb standard. I then showed that, while possible to do so, it takes a lot of effort and time to verify instruments without using known-good references. Yes, you are right that for Joe Average, this is way overkill. For most it will be enough to check whether the GPSDO is within 10-20ns of another GPS (without DO) receiver, and whether the EFC correlates well with the temperature of the OCXO housing. Both checks can be done relatively quickly, given access to a counter, a precise thermometer, and a DMM. But then, this is time-nuts. We love to get the best out of a specific system... even if it takes more effort than just simply buying better equipment :-) 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] time-nuts equipment verification from scratch (was: WTB: GPSDO)
On Mon, Mar 20, 2017 at 4:14 PM, Mark Sims wrote: > $3 for an Arduino chip on a PCB with proto area from China (should have > bought a lot more when they were available),$10 for a small ovenized 5V > TTL output OCXO (also should have bought a lot more), and $5 for misc > parts (OK, beer money not included in the BOM). Batteries not needed, > powered off USB. Hi Mark, Did you use the Arduino's PWM output plus a LPF for the DAC, or a separate DAC? If PWM, did you have problems with noise or sensitivity to the USB-provided supply voltage? Also I have found that not all computer USB ports can supply enough warm-up current for a 5V OCXO. Or did you use a hefty USB charger and miss out on the ability to get logging info back over the USB port? -- --Jim Harman ___ 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] time-nuts equipment verification from scratch (was: WTB: GPSDO)
Attilla, You are talking about product design, development and optimization, not the production of a one-off for home use. Since performance standards are already well established, it is only necessary for the developer to test the bench built instrument against published standards and determine if performance is good enough to suit him. Given a sound understanding of the role of various components in the system, it will be a great deal faster and easier for the builder to tinker with the one-off then to go through an extensive process of model development and verification. I have spent a good deal of my career doing performance modeling, verification, and validation in collaboration with other scientists and also engineers. You describe the process correctly but I think it is generous overkill for the topic under discussion here. Or have I missed something in the discussion? Is the desired end result a device for manufacture and sale? If so, then your approach is right on target. Bill On Monday, March 20, 2017, Attila Kinali > wrote: > On Thu, 16 Mar 2017 00:06:49 -0700 > Chris Albertson wrote: > > > I actually did use your method. I have a Rb and Thunderbolt, a pair > > of freq. counters and so on.But still I wanted to see if I could > > build from scratch and verify proper operation and keep the budget > > under say $50 for everything from antenna to power cord. I think > > it can be done but one can only verify longer term stability. > > Hmm.. doing verification of self-built (or aquired) equipment from > scratch is a different game altogether. If you want to build things > yourself, you first have to form a model of what disturbs your system, > measure these parameters and verify the model against your measurements. > Then you start building systems that exhibit different distortions, > model these, measure and verify them. After you have built enough > systems with different environmental characteristics, you verify > them against eachother to make sure that your models faithully > model reality and contain all parameters up to the error bound of the > model. > > After a couple of decades of building and verification, you can be > reasonably sure your GPSDO works correctly ;-) > > > > (Yes you were correct a GOOD oversized XO is not sensitive to the > > environment. But notice the above budget.) > > 50$ for a complete GPSDO, batteries included, is quite a low price limit. > A decent OCXO already costs 20-30$ on ebay. 100-200$ is a more realistic > limit for a homebrew GPSDO with time-nuts like performance. > A non-ovenized XO will not come close to time-nuts standards ;-) > > > Attila Kinali > -- > It is upon moral qualities that a society is ultimately founded. All > the prosperity and technological sophistication in the world is of no > use without that foundation. > -- Miss Matheson, The Diamond Age, Neil Stephenson > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/m > ailman/listinfo/time-nuts > and follow the instructions there. > -- William H Fite, PhD Independent Consultant Statistical Analysis & Research Methods ___ 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] time-nuts equipment verification from scratch (was: WTB: GPSDO)
I did it for $25... $7 for the GPS+antenna module, $3 for an Arduino chip on a PCB with proto area from China (should have bought a lot more when they were available),$10 for a small ovenized 5V TTL output OCXO (also should have bought a lot more), and $5 for misc parts (OK, beer money not included in the BOM). Batteries not needed, powered off USB. It worked better than I expected... not Tbolt quality, but not too shabby for a thee-day weekend hack. $50 (and a lot of work) is certainly doable for a decent home-brew GPSDO. --- > 50$ for a complete GPSDO, batteries included, is quite a low price limit. ___ 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] time-nuts equipment verification from scratch (was: WTB: GPSDO)
I would say that the price for a home-built time-nuts quality GPSDO is going to be significantly greater than $200. Yes, if you are making them for sale, eventually the unit cost will get down there. But to build one single good GPSDO, you're going to throw away a lot of prototypes on the way to the one that works well enough to stand up to the scrutiny of this group. The costs of those prototypes add up, and then there's your time engineering, building and testing. It adds up to a lot. Bob From: Attila Kinali To: Discussion of precise time and frequency measurement Sent: Monday, March 20, 2017 2:01 PM Subject: [time-nuts] time-nuts equipment verification from scratch (was: WTB: GPSDO) On Thu, 16 Mar 2017 00:06:49 -0700 Chris Albertson wrote: > I actually did use your method. I have a Rb and Thunderbolt, a pair > of freq. counters and so on. But still I wanted to see if I could > build from scratch and verify proper operation and keep the budget > under say $50 for everything from antenna to power cord. I think > it can be done but one can only verify longer term stability. Hmm.. doing verification of self-built (or aquired) equipment from scratch is a different game altogether. If you want to build things yourself, you first have to form a model of what disturbs your system, measure these parameters and verify the model against your measurements. Then you start building systems that exhibit different distortions, model these, measure and verify them. After you have built enough systems with different environmental characteristics, you verify them against eachother to make sure that your models faithully model reality and contain all parameters up to the error bound of the model. After a couple of decades of building and verification, you can be reasonably sure your GPSDO works correctly ;-) > (Yes you were correct a GOOD oversized XO is not sensitive to the > environment. But notice the above budget.) 50$ for a complete GPSDO, batteries included, is quite a low price limit. A decent OCXO already costs 20-30$ on ebay. 100-200$ is a more realistic limit for a homebrew GPSDO with time-nuts like performance. A non-ovenized XO will not come close to time-nuts standards ;-) Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ 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] time-nuts equipment verification from scratch (was: WTB: GPSDO)
On Thu, 16 Mar 2017 00:06:49 -0700 Chris Albertson wrote: > I actually did use your method. I have a Rb and Thunderbolt, a pair > of freq. counters and so on.But still I wanted to see if I could > build from scratch and verify proper operation and keep the budget > under say $50 for everything from antenna to power cord. I think > it can be done but one can only verify longer term stability. Hmm.. doing verification of self-built (or aquired) equipment from scratch is a different game altogether. If you want to build things yourself, you first have to form a model of what disturbs your system, measure these parameters and verify the model against your measurements. Then you start building systems that exhibit different distortions, model these, measure and verify them. After you have built enough systems with different environmental characteristics, you verify them against eachother to make sure that your models faithully model reality and contain all parameters up to the error bound of the model. After a couple of decades of building and verification, you can be reasonably sure your GPSDO works correctly ;-) > (Yes you were correct a GOOD oversized XO is not sensitive to the > environment. But notice the above budget.) 50$ for a complete GPSDO, batteries included, is quite a low price limit. A decent OCXO already costs 20-30$ on ebay. 100-200$ is a more realistic limit for a homebrew GPSDO with time-nuts like performance. A non-ovenized XO will not come close to time-nuts standards ;-) Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ 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.