Hi: Bob's comment about adjusting an oscillator from time to time aligns well with my limited experience in the time nuts hobby. Once I realized that in practice my better OCXO's were typically more than stable enough for my intended uses things became much simpler. I also realized that I could utilize my collection of time interval counters to compare my chosen reference to other references (including a GPSDO) while also comparing the chosen reference to the "Device Under Test." I realize this isn't likely an approach that a commercial lab would use but for my hobby use it seems to work ok for me. I've more or less shelved my plans to discipline one of my high end OCXO's via a home brew GPSDO scheme. Mark Spencer > On Mar 14, 2017, at 5:24 PM, Bob Camp <kb8tq@n1k.org> wrote: > > Hi > > >> On Mar 14, 2017, at 6:33 PM, Tim Lister <listertim@gmail.com> wrote: >> >> On Fri, Mar 10, 2017 at 2:35 PM, Chris Albertson >> <albertson.chris@gmail.com> wrote: >>> A GPSDO is not hard to make. All you need is some way to compare the >>> phase of two signals, an XOR gate can do that. Then a small $2 >>> process moves the control voltage on the crystal. I tried one to >>> build the simplest GPSDO that could still work. Got the parts count >>> down to about four or five and the cost well under $10 plus the OXO >>> which was about $20. The simplest dumb one I could make keeps about >>> e-10. Not great but enough for many uses. I compared to my >>> Thunderbolt and I could see the phase advance and retreat. Just a >>> little most sophistication and I likely could do much better but my >>> goal was to prove to myself that a GPSDO could be build VERY simply >>> with cheap parts >> >> Hi Chris, that's good news that a GPSDO is that easy to make (at least >> a basic one) as that is exactly my medium term plan ! > > Actually it’s much easier. Just put a DVM on the XOR once a week and > adjust your oscillator with a screwdriver. It saves *lots* of time and money. > > Bob > > >> The issue of >> course is having something to test the newly built GPSDO against... I >> got one of the rehoused Trimble UCCM-based GPSDOs off ebay a while ago >> but haven't been super happy with it. It's quite a bit less sensitive >> than more modern GPS receivers and it often struggles to get even 1 >> satellite with the indoor patch antenna. At one point both red alarm >> LEDs came on and stayed on despite power cycles - I eventually fixed >> that by taking it apart and finding and hitting a reset button on the >> board. Currently although I can talk to the unit over serial and it >> seems to respond, Lady Heather is not seeing any output from it. >> >> Combined these things don't give me a great deal of confidence that >> this unit will act as a stable master reference. I was wondering if a >> second GPSDO like Russ linked to would work better (I have a ublox >> LEA-6T GPS already which I plan to use as the basis of the homebuilt >> GPSDO and it consistently sees many more satellites than the UCCM >> with a similar indoor antenna) or put the money to getting an outdoor >> antenna mounted (don't feel happy drilling holes in the house myself) >> by someone. Do 2 GPSDOs tell you much more or just that each is >> different and you need a third to adjudicate ? (I can see a slippery >> slope looming from here...) >> >> Cheers, >> Tim >> _______________________________________________ >> 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. >

Hi A good OCXO run continuously should get down to < 0.1 ppb / week. Doing a tweak every Saturday is likely enough to keep it in that range. The *big* advantage is that you have the ADEV of the OCXO without any scruffy stuff from the control loop getting in the way. If your objective is to run something like a frequency counter, you probably are better off with the trimmed OCXO. Bob > On Mar 20, 2017, at 5:26 PM, Mark Spencer <mark@alignedsolutions.com> wrote: > > Hi: > > Bob's comment about adjusting an oscillator from time to time aligns well with my limited experience in the time nuts hobby. Once I realized that in practice my better OCXO's were typically more than stable enough for my intended uses things became much simpler. I also realized that I could utilize my collection of time interval counters to compare my chosen reference to other references (including a GPSDO) while also comparing the chosen reference to the "Device Under Test." I realize this isn't likely an approach that a commercial lab would use but for my hobby use it seems to work ok for me. > > I've more or less shelved my plans to discipline one of my high end OCXO's via a home brew GPSDO scheme. > > Mark Spencer > > >> On Mar 14, 2017, at 5:24 PM, Bob Camp <kb8tq@n1k.org> wrote: >> >> Hi >> >> >>> On Mar 14, 2017, at 6:33 PM, Tim Lister <listertim@gmail.com> wrote: >>> >>> On Fri, Mar 10, 2017 at 2:35 PM, Chris Albertson >>> <albertson.chris@gmail.com> wrote: >>>> A GPSDO is not hard to make. All you need is some way to compare the >>>> phase of two signals, an XOR gate can do that. Then a small $2 >>>> process moves the control voltage on the crystal. I tried one to >>>> build the simplest GPSDO that could still work. Got the parts count >>>> down to about four or five and the cost well under $10 plus the OXO >>>> which was about $20. The simplest dumb one I could make keeps about >>>> e-10. Not great but enough for many uses. I compared to my >>>> Thunderbolt and I could see the phase advance and retreat. Just a >>>> little most sophistication and I likely could do much better but my >>>> goal was to prove to myself that a GPSDO could be build VERY simply >>>> with cheap parts >>> >>> Hi Chris, that's good news that a GPSDO is that easy to make (at least >>> a basic one) as that is exactly my medium term plan ! >> >> Actually it’s much easier. Just put a DVM on the XOR once a week and >> adjust your oscillator with a screwdriver. It saves *lots* of time and money. >> >> Bob >> >> >>> The issue of >>> course is having something to test the newly built GPSDO against... I >>> got one of the rehoused Trimble UCCM-based GPSDOs off ebay a while ago >>> but haven't been super happy with it. It's quite a bit less sensitive >>> than more modern GPS receivers and it often struggles to get even 1 >>> satellite with the indoor patch antenna. At one point both red alarm >>> LEDs came on and stayed on despite power cycles - I eventually fixed >>> that by taking it apart and finding and hitting a reset button on the >>> board. Currently although I can talk to the unit over serial and it >>> seems to respond, Lady Heather is not seeing any output from it. >>> >>> Combined these things don't give me a great deal of confidence that >>> this unit will act as a stable master reference. I was wondering if a >>> second GPSDO like Russ linked to would work better (I have a ublox >>> LEA-6T GPS already which I plan to use as the basis of the homebuilt >>> GPSDO and it consistently sees many more satellites than the UCCM >>> with a similar indoor antenna) or put the money to getting an outdoor >>> antenna mounted (don't feel happy drilling holes in the house myself) >>> by someone. Do 2 GPSDOs tell you much more or just that each is >>> different and you need a third to adjudicate ? (I can see a slippery >>> slope looming from here...) >>> >>> Cheers, >>> Tim >>> _______________________________________________ >>> 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.

On 3/20/17 2:26 PM, Mark Spencer wrote: > Hi: > > Bob's comment about adjusting an oscillator from time to time aligns well with my limited experience in the time nuts hobby. Once I realized that in practice my better OCXO's were typically more than stable enough for my intended uses things became much simpler. I also realized that I could utilize my collection of time interval counters to compare my chosen reference to other references (including a GPSDO) while also comparing the chosen reference to the "Device Under Test." I realize this isn't likely an approach that a commercial lab would use but for my hobby use it seems to work ok for me. > > I've more or less shelved my plans to discipline one of my high end OCXO's via a home brew GPSDO scheme. > You already have a home brew GPSDO.. YOU are the control loop and the screwdriver is the actuator.<grin>

		Attila Kinali

Moin, On Mon, 20 Mar 2017 17:11:36 -0400 "William H. Fite" <omniryx@gmail.com> 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