[time-nuts] Rubidium oscillator controlled clock
Dear list members - a couple of weeks ago I found the time-nuts mailing list and had a wonderful time reading through old posts as well as having a look at the web pages of some of its participants. This triggered a long desire of mine to have some kind of a homebrew atomic clock - not necessarily based on a cesium primary standard, but maybe something built around a cheaper rubidium oscillator. Since I was lucky to find an EFRATOM LPRO-101 for a quite reasonable price, I decided to build my own frequency standard and clock around this. I am sure this does not (yet? :-) ) qualify me as a time nut, but maybe you will like my contraption which is described at http://www.vaxman.de/projects/rb_clock/ Best regards - sincerely, Bernd. :-) ___ 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] Rubidium oscillator controlled clock
Hello Ulrich - thank you very much for kind reply - this is a great suggestion. Would you recommend simple 74xx74 flipflops driven by the original 10 MHz signal delivered by the rubidium oscillator for resynching? Thank you very much and have a great day - sincerely, Bernd. :-) ___ 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] Rubidium oscillator controlled clock
Hello Magnus, hello Ulrich - thank you very much for your replies and your suggestions! I will dig deeper into that issue (I begin to get fascinated about precise timing - what a change for someone who once built amplifiers for measuring signals with periods down to 1/100 Hz :-) ). It will take some time (some weeks, since I am preparing for a conference etc.) until I will find time again to improve my oscillator, but I will let you know when I have decided on a circuit design and ask you for advice before actually building it. All the best - have a great day - Bernd. :-) >Message: 3 >Date: Mon, 12 Jul 2010 14:18:35 +0200 >From: Magnus Danielson >Subject: Re: [time-nuts] Rubidium oscillator controlled clock >To: time-nuts@febo.com >Message-ID: <4c3b081b.3090...@rubidium.dyndns.org> >Content-Type: text/plain; charset=ISO-8859-1; format=flowed > >Bernd, > >On 07/12/2010 02:05 PM, ulm...@vaxman.de wrote: >> Hello Ulrich - >> thank you very much for kind reply - this is a great suggestion. Would you >> recommend simple 74xx74 flipflops driven by the original 10 MHz signal >> delivered by the rubidium oscillator for resynching? > >That should do the trick. Even if I doubt the gain would be significant, >you can use both the DFFs in there in series. It is the common way to >reduce the effect of unsynchronized signal into DFFs as there may be >meta-stability, so using two DFFs in series helps reducing the added >noise if the first DFF goes meta-stable. The '74 should be protected to >some degree if I recall things correctly, but it's there and free... so >why not? > >Cheers, >Magnus > >-- > >Message: 4 >Date: Mon, 12 Jul 2010 14:47:29 +0200 >From: "Ulrich Bangert" >Subject: Re: [time-nuts] Rubidium oscillator controlled clock >To: "'Discussion of precise time and frequency measurement'" > >Message-ID: <87aa1e4d813c493a9f325307ac987...@athlon> >Content-Type: text/plain; charset="us-ascii" > >Bernd, > >> Would you recommend simple 74xx74 flipflops >> driven by the original 10 MHz signal delivered by the >> rubidium oscillator for resynching? > >In principle, yes. However not directly clocked by the rubidium itself but >from a clean ttl signal that has been made out of the LPRO's sine. There has >been a long discussion here about the "howto" of this. As a good starting >point I suggest this: > >http://www.ko4bb.com/~bruce/CLKSHPR.html > >While the ADCMP600 are available well in Germany (for example from FARNELL) >the MSOP enclosure is very tricky to solder and for a bit less in frequency >performance a LT1016 will do it for you too. > >Best regards >Ulrich Bangert > ___ 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] Homebrew Rubidium oscillator, jitter and other tales :-)
Hello all - first of all, I would like to thank you for the many replies I got regarding my first posting a couple of weeks ago where I described my homebrew Rubidium oscillator based on an LPRO-101. During the last couple of days I found enough spare time to dig deeper into some issues. In addition to that I was lucky enough to find a Tracor 527E (literally from a scrap heap) for 50 EUR which looked horrible and was non- functional with a large red sticker "REJECT". After two evenings of digging through its circuitry it is now in perfect working condition again (actually there were only two faults: a defective transistor in the mixer of the first error multiplier which essentially rendered the machine useless, and a cold solder joint in the single shot which caused erratic operation after fixing the first bug). Since some of you mentioned that my (way too?) simple digital divider chain would produce output signals with non-neglectible phase jitter, I had a deeper look into this issue using the Tracor 527E and an old HCD 1519 precision oscillator which I assume to have better phase stability than my initial dividing circuitry. First of all, you were perfectly right - there was substantial jitter which I got rid of by inserting a 74LS175 between the respective divider stages and the output drivers of my divider circuit. The common clock line of the 74LS175 is driven by the TTL converted output of the LPRO-101. (I am aware of the problem that with enough temperatur shift it might happen that my divider chain might "slip" a whole clock period, but at the moment this simple solution seems to work really nice.) What came quite as a surprise to me was that my stupid idea of having a LED which blinks once per second would cause me so much headaches. Using the Tracor 527E and the HCD 1519 which was running for more than a day, I was able to adjust the quartz oscillator to the Rubidium clock with an error of < 1 in 10**10. After switching the Tracor to a resolution of 10**11 it became apparent that there still was a substantial phase shift every second then the *...* LED blinked. This problem was eventually solved by driving the LED with a discrete transistor instead of a free 74AC14 gate and decoupling this driver with an RC-combination. All in all, I think my Rubidium oscillator is now way better than its first incarnation, so thank you all very much for your help and hints. Best regards - Bernd. :-) ___ 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] Frequency difference between LPRO-101 and HP 105B
Dear list members - being a proud owner of a LRPO-101 as well as a HP 105B and a TRACOR 527E Frequency Difference meter, I decided to compare these two oscillators with each other after some days of running them. The attached plot (if this won't work, you can find it here online: http://fafner.dyndns.org/~ulmann/30_nov_2010_tracor_small.jpg) shows the output of the TRACOR 527E (frequency difference, sensitivity set to 10**11 - this corresponds to a multiplication factor of 10**4 regarding the frequency difference) plotted with an old thermal plotter - this is just a qualitative plot but the amplitude difference between the minimum and maximum peaks corresponds to about +/- 1 parts in 10^-11. I would like to hear your opinion about this - does this look reasonable to you? The inputs to the TRACOR were the 10 MHz output of the LPRO and the 1 MHz output of the HP 105B - both oscillators were running for a little bit more than three days without interruption. All the best - Bernd. :-) <>___ 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.
