Re: [time-nuts] Rb vs.Crystal OCXO
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Re: [time-nuts] Rb vs.Crystal OCXO
said, if i understand correctly, while in holdover, activated by sync:hold:init, temperature and aging compensation are still active (as it should be). however, to measure drift, i have to somehow disable these compensations, haven't i? yesterday, i wrote down the values of temperature and aging compensation, then set both to 0. in holdover the software does not seem to recalculate the values, at least not during the hour or two i had the oscillator unlocked. on uli's Z38XX the EFC curve was flat, unlike when temperature and aging compensation are active (or not 0) during holdover. one hour or so after sync:hold:rec:init i checked the values again, and they were very close to the values before i reset them to 0. my question is: would this be the correct procedure to have a truely unlocked oscillator: start holdover and then set tempco and aging to 0? thank you, hans Bill, There is an easier method that does not jiggle the board mechanically: The command: sync:hold:init Disables the disciplining. sync:hold:rec:init Re-enables disciplining. The sync:tint? command can be used to check the drift while in holdover.. Bye, Said ___ 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] Rb vs.Crystal OCXO
said, if i understand correctly, while in holdover, activated by sync:hold:init, temperature and aging compensation are still active (as it should be). however, to measure drift, i have to somehow disable these compensations, haven't i? yesterday, i wrote down the values of temperature and aging compensation, then set both to 0. in holdover the software does not seem to recalculate the values, at least not during the hour or two i had the oscillator unlocked. on uli's Z38XX the EFC curve was flat, unlike when temperature and aging compensation are active (or not 0) during holdover. one hour or so after sync:hold:rec:init i checked the values again, and they were very close to the values before i reset them to 0. my question is: would this be the correct procedure to have a truely unlocked oscillator: start holdover and then set tempco and aging to 0? thank you, hans Bill, There is an easier method that does not jiggle the board mechanically: The command: sync:hold:init Disables the disciplining. sync:hold:rec:init Re-enables disciplining. The sync:tint? command can be used to check the drift while in holdover.. Bye, Said ___ 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] Rb vs.Crystal OCXO
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Re: [time-nuts] Rb vs.Crystal OCXO
Hi Hans, in order not to chase the tempco and aging algorithm (it will reset the values by itself every 10 minutes while locked to GPS as you have noted) you may simply turn tempco and aging compensation off manually during your test period. This can be done by the serv:tas x, yy... command. The first parameter is the mode; 0 being both off, 1 being aging compensation only, and 2 being both aging and temperature compensation. So the commands would be: serv:tas? to query the current settings, then issuing the command: serv: tas 0, xx, xx ... where xx, xx.. are the same values that were shown with the query command. To re-enable the aging and tempco compensation when you are done with your measurement, simply send the serv: tas 2, xx, xx ... command using the same settings again as the query command had returned. Hope that helps, Said In a message dated 4/28/2014 05:32:41 Pacific Daylight Time, hans.holz...@gmail.com writes: said, if i understand correctly, while in holdover, activated by sync:hold:init, temperature and aging compensation are still active (as it should be). however, to measure drift, i have to somehow disable these compensations, haven't i? yesterday, i wrote down the values of temperature and aging compensation, then set both to 0. in holdover the software does not seem to recalculate the values, at least not during the hour or two i had the oscillator unlocked. on uli's Z38XX the EFC curve was flat, unlike when temperature and aging compensation are active (or not 0) during holdover. one hour or so after sync:hold:rec:init i checked the values again, and they were very close to the values before i reset them to 0. my question is: would this be the correct procedure to have a truely unlocked oscillator: start holdover and then set tempco and aging to 0? thank you, hans Bill, There is an easier method that does not jiggle the board mechanically: The command: sync:hold:init Disables the disciplining. sync:hold:rec:init Re-enables disciplining. The sync:tint? command can be used to check the drift while in holdover.. Bye, Said ___ 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] Rb vs.Crystal OCXO
Yeah, we have to have some undocumented commands.. The 600 is 10 minute sample intervals. The 288 is number of samples saved, so it samples 48 hours of data.. Bye, Said Sent From iPhone On Apr 28, 2014, at 12:02, Hans Holzach hans.holz...@gmail.com wrote: said, very nice, a secret command that is not mentioned in the manual! i'll play with it a bit next weekend. seems quite useful, at least to me. hmm, i wonder what other commands there are on that misterious list... :-) thank you, hans Hi Hans, in order not to chase the tempco and aging algorithm (it will reset the values by itself every 10 minutes while locked to GPS as you have noted) you may simply turn tempco and aging compensation off manually during your test period. This can be done by the serv:tas x, yy... command. The first parameter is the mode; 0 being both off, 1 being aging compensation only, and 2 being both aging and temperature compensation. So the commands would be: serv:tas? to query the current settings, then issuing the command: serv: tas 0, xx, xx ... where xx, xx.. are the same values that were shown with the query command. To re-enable the aging and tempco compensation when you are done with your measurement, simply send the serv: tas 2, xx, xx ... command using the same settings again as the query command had returned. Hope that helps, Said In a message dated 4/28/2014 05:32:41 Pacific Daylight Time, hans.holzach at gmail.com writes: said, if i understand correctly, while in holdover, activated by sync:hold:init, temperature and aging compensation are still active (as it should be). however, to measure drift, i have to somehow disable these compensations, haven't i? yesterday, i wrote down the values of temperature and aging compensation, then set both to 0. in holdover the software does not seem to recalculate the values, at least not during the hour or two i had the oscillator unlocked. on uli's Z38XX the EFC curve was flat, unlike when temperature and aging compensation are active (or not 0) during holdover. one hour or so after sync:hold:rec:init i checked the values again, and they were very close to the values before i reset them to 0. my question is: would this be the correct procedure to have a truely unlocked oscillator: start holdover and then set tempco and aging to 0? thank you, hans ___ 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] Rb vs.Crystal OCXO
Bert wrote: The thunderbolt is one of the best timing devices but not for frequency, if you want high resolution. Over time it is ok but high resolution short gate times and you see the frequency changes. They use the OCXO to correct for timing error I concur with Tom's comments -- I think you have the diagnosis wrong. Using the OCXO to correct the timing error is a feature of the TBolt architecture, and it provides a powerful benefit -- no need for sawtooth correction. By optimizing the oscillator disciplining parameters and protecting the OCXO from fast temperature changes (see my previous posts on metal boxes), you can improve the frequency AND timing performance of a TBolt to the point that it doesn't have to apologize to any other GPSDO. Lady Heather is an invaluable aid here, and compatibility with LH is a huge advantage in favor of any GPSDO. Indeed, Make sure it is compatible with LH should probably be Rule #2 for time nuts acquiring GPSDOs. (Make sure it uses a 10811-class OCXO being Rule #1.) Again, I don't want to discourage anyone from building DIY GPSDOs. But it seems to me the first thing any aspiring time nut needs is a benchmark -- a known reliable standard for frequency and timing. Without one, it will be impossible to quantify (or possibly, even to qualify) how well an experimental DIY circuit works. So it makes extremely good sense to first acquire a GPSDO with which the time nuts community has had extensive experience, and which is compatible with a very powerful diagnostic tool (LH). Then start experimenting. If you do better (or, at least, well enough to satisfy yourself), you can always sell the commercial GPSDO and recover your investment. Best regards, Charles ___ 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] Rb vs.Crystal OCXO
On 04/27/2014 04:15 AM, Tom Van Baak wrote: The thunderbolt is one of the best timing devices but not for frequency, if you want high resolution. Over time it is ok but high resolution short gate times and you see the frequency changes. They use the OCXO to correct for timing error and if you have a Tracor 527E you can see it. Also how else do you think they control the 1 pps. Bert Kehren Hi Bert, Put your TBolt (or any other GPSDO) in holdover (freeze the DAC) and then take a close look again. Tell me what you see. The difference (if any) is due to steering. What's common (if any) is due to the OCXO itself. Have a look at http://leapsecond.com/pages/gpsdo/ to see the results for 4 common GPSDO. Focus on the left edge of the plots only. Note also that tuning parameters can make a big difference in the results (I used only defaults for those plots). The Pendulum GPS-88 and GPS-89 have a button on the front you push when you want to force it into hold-over to do your measurement, for this very reason. PPS steering and OCXO steering is the same thing once you forced the PPS into the right range. Some *really* depend on the synchronicity between 10 MHz and PPS, and you should not obscure it if possible. Cheers, Magnus ___ 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] Rb vs.Crystal OCXO
The Pendulum GPS-88 and GPS-89 have a button on the front you push when you want to force it into hold-over to do your measurement, for this very reason. PPS steering and OCXO steering is the same thing once you forced the PPS into the right range. Some *really* depend on the synchronicity between 10 MHz and PPS, and you should not obscure it if possible. Cheers, Magnus When doing a sensitive measurement where stability is more important than accuracy I turn off GPS disciplining. The TBolt has commands to go into and out of holdover. But more effective are the 0x8E,0xA3,4 and 0x8E,0xA3,5 commands which simply disable and enable disciplining. /tvb ___ 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] Rb vs.Crystal OCXO
Bert Kehren wrote : The thunderbolt is one of the best timing devices but not for frequency, if you want high resolution. Bert, Would my old HP Z3801A be better for frequency than the Thunderbolt? Could you put some quantitative difference to it? Thanks, ... MartinVE3OAT ___ 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] Rb vs.Crystal OCXO
I unplug the antenna from my fury boards. I hope this is an effective alternative. Sent from mobile On Apr 27, 2014, at 9:02 AM, Tom Van Baak t...@leapsecond.com wrote: The Pendulum GPS-88 and GPS-89 have a button on the front you push when you want to force it into hold-over to do your measurement, for this very reason. PPS steering and OCXO steering is the same thing once you forced the PPS into the right range. Some *really* depend on the synchronicity between 10 MHz and PPS, and you should not obscure it if possible. Cheers, Magnus When doing a sensitive measurement where stability is more important than accuracy I turn off GPS disciplining. The TBolt has commands to go into and out of holdover. But more effective are the 0x8E,0xA3,4 and 0x8E,0xA3,5 commands which simply disable and enable disciplining. /tvb ___ 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] Rb vs.Crystal OCXO
Bill, There is an easier method that does not jiggle the board mechanically: The command: sync:hold:init Disables the disciplining. sync:hold:rec:init Re-enables disciplining. The sync:tint? command can be used to check the drift while in holdover.. Bye, Said Sent From iPhone On Apr 27, 2014, at 10:04, Bill Dailey docdai...@gmail.com wrote: I unplug the antenna from my fury boards. I hope this is an effective alternative. Sent from mobile On Apr 27, 2014, at 9:02 AM, Tom Van Baak t...@leapsecond.com wrote: The Pendulum GPS-88 and GPS-89 have a button on the front you push when you want to force it into hold-over to do your measurement, for this very reason. PPS steering and OCXO steering is the same thing once you forced the PPS into the right range. Some *really* depend on the synchronicity between 10 MHz and PPS, and you should not obscure it if possible. Cheers, Magnus When doing a sensitive measurement where stability is more important than accuracy I turn off GPS disciplining. The TBolt has commands to go into and out of holdover. But more effective are the 0x8E,0xA3,4 and 0x8E,0xA3,5 commands which simply disable and enable disciplining. /tvb ___ 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.
Re: [time-nuts] Rb vs.Crystal OCXO
I unplug the antenna from my fury boards. I hope this is an effective alternative. Bill, That's probably what I did for my tests. Or maybe I just used a SCPI command to do it. I don't remember anymore. Sometimes when I test multiple GPSDO at once it's convenient to just remove the antenna coax from the splitter; leaving everything else in the lab untouched. That method is also nice since you can see in parallel how quickly or slowly each GPSDO reacts to LOS. Then there's the John Miles' method: a hp RF relay to remotely connect/disconnect the antenna line on demand. In the plot I made many years ago (http://leapsecond.com/pages/gpsdo/) you can see the Fury has very similar short-term performance with and without the antenna. So perhaps you have less to worry about on that GPSDO. Again, a lot of it depends on the tuning parameters (user adjustable), and your antenna/reception, and your lab environment, so I wouldn't want to make too many generalizations based on make/model alone. Even identical GPSDO can show significant differences. My plots are for my Fury. It's hard to know how close your Fury performs to mine. See also section 6, Fury vs. Z8301A (http://leapsecond.com/pages/fury/) for another comparison. /tvb - Original Message - From: Bill Dailey docdai...@gmail.com To: Tom Van Baak t...@leapsecond.com; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Sunday, April 27, 2014 10:04 AM Subject: Re: [time-nuts] Rb vs.Crystal OCXO Sent from mobile On Apr 27, 2014, at 9:02 AM, Tom Van Baak t...@leapsecond.com wrote: The Pendulum GPS-88 and GPS-89 have a button on the front you push when you want to force it into hold-over to do your measurement, for this very reason. PPS steering and OCXO steering is the same thing once you forced the PPS into the right range. Some *really* depend on the synchronicity between 10 MHz and PPS, and you should not obscure it if possible. Cheers, Magnus When doing a sensitive measurement where stability is more important than accuracy I turn off GPS disciplining. The TBolt has commands to go into and out of holdover. But more effective are the 0x8E,0xA3,4 and 0x8E,0xA3,5 commands which simply disable and enable disciplining. /tvb ___ 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] Rb vs.Crystal OCXO
Shane, The trade off for most applications is as follows: Rb has much faster stabilization time after power on. Ocxos suffer from retrace, that can take hours to days to get rid off. Retrace could cause a frequency shift of several ppb or more from say 15 minutes after power on compared to 10 hours after power on Retrace on a good Rb is very low, turn on a PRS-10 and after 10 minutes or so it will be stable and drift much less than 1ppb over the next days typically. 10x to 50x less retrace than on a good ocxo Is possible. This is important when you do not have a GPS to remove retrace error from the ocxo. If you run without gps (holdover) the best docxo will start to drift more and more after a day. Rb will stay stable for months or years. Important for base station applications where the amount of drift determines how much time can pass before a repair crew has to be sent. They do not want to send crews over the weekend for example because it could cost double overtime pay. Because the loop BW of a Rb is larger than a GPSDO (say 10Hz vs 0.001Hz) a typical Rb will have higher ADEV noise close in than a really good GPSDO due to the loop steering noise being additive to the ocxo noise. This is why a GPSDO can have significantly lower phase noise below 10Hz. But it depends on the Rb. For example the CSAC which works on the Rb vapor cell principle actually improves noise close in as Rick explained because it has a fairly low cost tcxo and the vapor cell thus is more stable than the tcxo by itself. On a PRS-10 one can see a steering hump below 1 Hz (around 20s or so depending on the selected loop time constant) that probably would not be there without the loop steering.. Most of the time Rbs are used because they require much less calibration, have much less g (tilt) sensitivity and much less initial retrace/warmup error. In the case of the CSAC they also have more than an order of magnitude less power consumption than a good Ocxo (0.12W vs 1.7W on a typical docxo) Bye, Said Sent From iPhone On Apr 25, 2014, at 15:40, Bob Camp li...@rtty.us wrote: Hi At least on the Rb I have seen, the phase noise (in to 1 Hz) is generally better if the Rb loop is narrower rather than wider. That of course assumes that the internal OCXO has pretty good phase noise to start. Maybe I’ve been slumming it …. Bob On Apr 25, 2014, at 6:29 PM, Richard (Rick) Karlquist rich...@karlquist.com wrote: My understanding is that a really good Rb standard use a fairly wide bandwidth loop to control its own internal XO, and therefore improve its close in phase noise to be better than you can get with quartz alone. The Rb standard is able to do this because the S/N ratio of its rubidium vapor frequency reference (RVFR) is fairly high, and in any event considerably better than the S/N out of a CBT. Also, Rb standards have much smaller frequency jumps, if any, than quartz. Phase noise specs conveniently don't include the effects of jumps. Newer laser diode pumped Rb standards may make the comparison even more lopsided. Rick On 4/25/2014 9:12 AM, Shane Kirkbride wrote: Hi Everyone, I'm newer to this forum but I really enjoy reading the discussions. I have a pretty basic question. I'm wondering why one would chose an Rb Oscillator over a traditional OCXO? It does not immediately appear there is a phase noise advantage in the Rb.. Thanks, ~Shane On Fri, Apr 25, 2014 at 10:00 AM, time-nuts-requ...@febo.com wrote: Send time-nuts mailing list submissions to time-nuts@febo.com To subscribe or unsubscribe via the World Wide Web, visit https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts or, via email, send a message with subject or body 'help' to time-nuts-requ...@febo.com You can reach the person managing the list at time-nuts-ow...@febo.com When replying, please edit your Subject line so it is more specific than Re: Contents of time-nuts digest... Today's Topics: 1. Low SNR GPS reception and cheap LNAs (Attila Kinali) 2. Re: Symmetricom chip scale atomic clock (Tom Knox) 3. Re: How to accurately measure an oscillator's temperature. (Didier Juges) 4. Re: Low SNR GPS reception and cheap LNAs (Chris Albertson) -- Message: 1 Date: Fri, 25 Apr 2014 15:28:22 +0200 From: Attila Kinali att...@kinali.ch To: time-nuts@febo.com Subject: [time-nuts] Low SNR GPS reception and cheap LNAs Message-ID: 20140425152822.203775c003a761042e269...@kinali.ch Content-Type: text/plain; charset=US-ASCII Hi, I recently bought a bladeRF[1] to experiment a bit with GPS decoding. I tried to get GNSS-SDR[2] which seems quite good, but has its flaws. One of the things was that i cannot seem to get a fix in my environment. One of the problems seems that my antenna position is far from optimal. Aparently, GNSS-SDR uses only a very
Re: [time-nuts] Rb vs.Crystal OCXO
On 04/26/2014 06:34 PM, Said Jackson wrote: Shane, The trade off for most applications is as follows: Rb has much faster stabilization time after power on. Ocxos suffer from retrace, that can take hours to days to get rid off. Retrace could cause a frequency shift of several ppb or more from say 15 minutes after power on compared to 10 hours after power on Retrace on a good Rb is very low, turn on a PRS-10 and after 10 minutes or so it will be stable and drift much less than 1ppb over the next days typically. 10x to 50x less retrace than on a good ocxo Is possible. This is important when you do not have a GPS to remove retrace error from the ocxo. If you run without gps (holdover) the best docxo will start to drift more and more after a day. Rb will stay stable for months or years. Important for base station applications where the amount of drift determines how much time can pass before a repair crew has to be sent. They do not want to send crews over the weekend for example because it could cost double overtime pay. Because the loop BW of a Rb is larger than a GPSDO (say 10Hz vs 0.001Hz) a typical Rb will have higher ADEV noise close in than a really good GPSDO due to the loop steering noise being additive to the ocxo noise. This is why a GPSDO can have significantly lower phase noise below 10Hz. But it depends on the Rb. For example the CSAC which works on the Rb vapor cell principle actually improves noise close in as Rick explained because it has a fairly low cost tcxo and the vapor cell thus is more stable than the tcxo by itself. On a PRS-10 one can see a steering hump below 1 Hz (around 20s or so depending on the selected loop time constant) that probably would not be there without the loop steering.. Most of the time Rbs are used because they require much less calibration, have much less g (tilt) sensitivity and much less initial retrace/warmup error. In the case of the CSAC they also have more than an order of magnitude less power consumption than a good Ocxo (0.12W vs 1.7W on a typical docxo) The PRS-10 have a nice little trick in it, it stores the previous OCXO steering value, so on power-up it sets the OCXO to this and that gives it about the right frequency and only once the rubidium have heated up it locks to it. That gives a relatively quick stable signal for starters, which is quite quick. Cheers, Magnus ___ 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] Rb vs.Crystal OCXO
Magnus wrote: The PRS-10 have a nice little trick in it, it stores the previous OCXO steering value, so on power-up it sets the OCXO to this The PRS-10 has quite a number of nice tricks, in addition to particularly good engineering and high-quality construction of the basic physics package and support circuitry. The OP (and others) should not expect the same level of performance from $30-$100 ebay Rubidiums (LPRO, FRS, FE-56xx, etc., etc.). Very good to excellent OCXOs are available readily for $5 to $50. IMO, those should be the standard of comparison for any aspiring time nut. I'm not aware of any economy Rubidium that has close-in phase noise or low-to-medium-tau AVAR nearly as good as one of these very good OCXOs. As mentioned by others, some Ru may do better than a TCXO close in and at low tau. But so what? The TCXO should not be a time nut's standard of comparison as far as a lab standard is concerned. One quickly concludes that a good GPSDO, which includes a good OCXO, is the optimal solution for most time nuts. The OCXO has excellent stability with respect to close-in phase noise and low-to-medium-tau AVAR, and is disciplined by the GPS for excellent stability at longer tau. Probably the best turn-key solution is a Trimble Thunderbolt (although prices have risen in the last few years, so they are not the bargain they once were). Other, less expensive Trimble units that are also supported by the Lady Heather monitoring program are available on ebay, and are probably the best bet today for bargain-hunters. While I applaud the recent efforts to build simple DIY GPSDOs using inexpensive microcontrollers, from what I have seen so far most of them do not yet have the programming sophistication, particularly in the PLL loop filter and the houskeeping functions, to rival a good off-the-shelf GPSDO from a quality manufacturer. Final thought for specifying/designing/buying a GPSDO for time nuts purposes: Do not settle for a low-quality crystal oscillator (and especially not a TCXO). You will never achieve best performance at tau about 100 seconds that way. Insist on a 10811-quality OCXO (one of the many nice things about the Thunderbolt is that it has a very good OCXO). Best regards, Charles ___ 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] Rb vs.Crystal OCXO
The thunderbolt is one of the best timing devices but not for frequency, if you want high resolution. Over time it is ok but high resolution short gate times and you see the frequency changes. They use the OCXO to correct for timing error and if you have a Tracor 527E you can see it. Also how else do you think they control the 1 pps. Bert Kehren In a message dated 4/26/2014 1:52:10 P.M. Eastern Daylight Time, csteinm...@yandex.com writes: Magnus wrote: The PRS-10 have a nice little trick in it, it stores the previous OCXO steering value, so on power-up it sets the OCXO to this The PRS-10 has quite a number of nice tricks, in addition to particularly good engineering and high-quality construction of the basic physics package and support circuitry. The OP (and others) should not expect the same level of performance from $30-$100 ebay Rubidiums (LPRO, FRS, FE-56xx, etc., etc.). Very good to excellent OCXOs are available readily for $5 to $50. IMO, those should be the standard of comparison for any aspiring time nut. I'm not aware of any economy Rubidium that has close-in phase noise or low-to-medium-tau AVAR nearly as good as one of these very good OCXOs. As mentioned by others, some Ru may do better than a TCXO close in and at low tau. But so what? The TCXO should not be a time nut's standard of comparison as far as a lab standard is concerned. One quickly concludes that a good GPSDO, which includes a good OCXO, is the optimal solution for most time nuts. The OCXO has excellent stability with respect to close-in phase noise and low-to-medium-tau AVAR, and is disciplined by the GPS for excellent stability at longer tau. Probably the best turn-key solution is a Trimble Thunderbolt (although prices have risen in the last few years, so they are not the bargain they once were). Other, less expensive Trimble units that are also supported by the Lady Heather monitoring program are available on ebay, and are probably the best bet today for bargain-hunters. While I applaud the recent efforts to build simple DIY GPSDOs using inexpensive microcontrollers, from what I have seen so far most of them do not yet have the programming sophistication, particularly in the PLL loop filter and the houskeeping functions, to rival a good off-the-shelf GPSDO from a quality manufacturer. Final thought for specifying/designing/buying a GPSDO for time nuts purposes: Do not settle for a low-quality crystal oscillator (and especially not a TCXO). You will never achieve best performance at tau about 100 seconds that way. Insist on a 10811-quality OCXO (one of the many nice things about the Thunderbolt is that it has a very good OCXO). Best regards, Charles ___ 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] Rb vs.Crystal OCXO
The thunderbolt is one of the best timing devices but not for frequency, if you want high resolution. Over time it is ok but high resolution short gate times and you see the frequency changes. They use the OCXO to correct for timing error and if you have a Tracor 527E you can see it. Also how else do you think they control the 1 pps. Bert Kehren Hi Bert, Put your TBolt (or any other GPSDO) in holdover (freeze the DAC) and then take a close look again. Tell me what you see. The difference (if any) is due to steering. What's common (if any) is due to the OCXO itself. Have a look at http://leapsecond.com/pages/gpsdo/ to see the results for 4 common GPSDO. Focus on the left edge of the plots only. Note also that tuning parameters can make a big difference in the results (I used only defaults for those plots). /tvb ___ 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] Rb vs.Crystal OCXO
Hi Everyone, I'm newer to this forum but I really enjoy reading the discussions. I have a pretty basic question. I'm wondering why one would chose an Rb Oscillator over a traditional OCXO? It does not immediately appear there is a phase noise advantage in the Rb.. Thanks, ~Shane On Fri, Apr 25, 2014 at 10:00 AM, time-nuts-requ...@febo.com wrote: Send time-nuts mailing list submissions to time-nuts@febo.com To subscribe or unsubscribe via the World Wide Web, visit https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts or, via email, send a message with subject or body 'help' to time-nuts-requ...@febo.com You can reach the person managing the list at time-nuts-ow...@febo.com When replying, please edit your Subject line so it is more specific than Re: Contents of time-nuts digest... Today's Topics: 1. Low SNR GPS reception and cheap LNAs (Attila Kinali) 2. Re: Symmetricom chip scale atomic clock (Tom Knox) 3. Re: How to accurately measure an oscillator's temperature. (Didier Juges) 4. Re: Low SNR GPS reception and cheap LNAs (Chris Albertson) -- Message: 1 Date: Fri, 25 Apr 2014 15:28:22 +0200 From: Attila Kinali att...@kinali.ch To: time-nuts@febo.com Subject: [time-nuts] Low SNR GPS reception and cheap LNAs Message-ID: 20140425152822.203775c003a761042e269...@kinali.ch Content-Type: text/plain; charset=US-ASCII Hi, I recently bought a bladeRF[1] to experiment a bit with GPS decoding. I tried to get GNSS-SDR[2] which seems quite good, but has its flaws. One of the things was that i cannot seem to get a fix in my environment. One of the problems seems that my antenna position is far from optimal. Aparently, GNSS-SDR uses only a very rudimentary acquisition technique (at least so i have been told). Now i wonder what techniques for low SNR acquisition are around. Would someone be so kind and give me some key words to google for? I also am looking to add an LNA to my reception chain, which is a mix of a 50R antenna with 75R Coaxcable (sat coax stuff is just a lot cheaper :-). Has anyone a recomendation for a good LNA that can be used in a flying construction (soldering onto two back-to-back glued connectors)? Ie it shouldnt be a QFN or BGA. DFN works but i'd rather have something with pins, like SC-70/SOT-323 or similar/larger. Attila Kinali [1] www.nuand.com/bladeRF [2] www.gnss-sdr.org -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin -- Message: 2 Date: Fri, 25 Apr 2014 08:53:25 -0600 From: Tom Knox act...@hotmail.com To: Time-Nuts time-nuts@febo.com Subject: Re: [time-nuts] Symmetricom chip scale atomic clock Message-ID: col130-w35b7069ee8d042e122a563df...@phx.gbl Content-Type: text/plain; charset=iso-8859-1 For the sake of discussion let me just add that even if medesigns comments were true of Microsemi, the Microsemi responses on this form have been from long time Time-Nuts who have for years contributed their knowledge to the betterment of the community in the proudest traditions of acadimia. Never have I seen them use the form for financial gain. Sure corporate greed is a problem in todays society but knowing some of the individuals at Microsemi it is clearly not a black and white issue. Further where it may be acceptable in some cases to release a product early and perform some of the final development on the backs of the customers to better serve their needs such as in the case of the fantastic TimeLab. In a mission critical product like the CSAC a problem like this will cost Microsemi far more then they would profit from a premature release. These manufacturing defects were clearly something they could not anticipate. I for one will be purchasing many more Microsemi products in the future and viewing their performance on TimeLab with full confidence. Please keep the group update on your progress resolving this issue. It will be interesting to see if a single point of failure is found, a smoking gun so to speak; or whether it will be resolved with a number of minor changes during product evolution. In any case I hope the problem is resolved quickly. Thomas Knox Date: Fri, 25 Apr 2014 08:14:06 +0200 From: att...@kinali.ch To: time-nuts@febo.com Subject: Re: [time-nuts] Symmetricom chip scale atomic clock On Fri, 25 Apr 2014 08:33:06 +0300 MailLists li...@medesign.ro wrote: The recently acquired cash cow isn't working exactly as expected/advertised. We still don't have a clue when/if the fundamental (as in physics laws) design (we can't officially blame the cheap Chinese
Re: [time-nuts] Rb vs.Crystal OCXO
Hi Everyone, I'm newer to this forum but I really enjoy reading the discussions. I have a pretty basic question. I'm wondering why one would chose an Rb Oscillator over a traditional OCXO? It does not immediately appear there is a phase noise advantage in the Rb.. Thanks, ~Shane Welcome to time-nuts. Good question. In some applications the exceptional long-term frequency accuracy and stability you get with Rb is more important than the better phase noise, smaller size, lower power, better short-term stability, longer lifetime, or cheaper price that you get with an OCXO. When you buy a new OCXO, it might be accurate to 4 or 5 or 6 digits, out-of-the-box. You have to mechanically (screw) or electronically (EFC) calibrate it to get closer. If you want, say, 9 digits of accuracy, then you may have to re-calibrate it every day or at least once a week. When you buy a new Rb, it might be accurate to 9 or 10 or 11 digits, out-of-the-box. If you want, say, 9 digits of accuracy, then you may have to calibrate it every couple of years. /tvb ___ 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] Rb vs.Crystal OCXO
Welcome to time-nuts. I have to agree with Tom for an out of the box experience. However as so many time-nuts experiment with GPS control of these oscillators you really can get great stability with both today and I believe even better in the future. I like the low power of the xtal oscillator. Thats handy when running on emergency battery here in New England. My RB will run 2 days before the batteries shut down. But a OCXO would most likely increase that another day or more. Plus run the GPS lock system. However since the rest of the house has no power somewhat of a useless point. Far bigger concerns at least in the winter. It really boils down to what you need to do with the solution. Regards Paul WB8TSL On Fri, Apr 25, 2014 at 4:30 PM, Tom Van Baak t...@leapsecond.com wrote: Hi Everyone, I'm newer to this forum but I really enjoy reading the discussions. I have a pretty basic question. I'm wondering why one would chose an Rb Oscillator over a traditional OCXO? It does not immediately appear there is a phase noise advantage in the Rb.. Thanks, ~Shane Welcome to time-nuts. Good question. In some applications the exceptional long-term frequency accuracy and stability you get with Rb is more important than the better phase noise, smaller size, lower power, better short-term stability, longer lifetime, or cheaper price that you get with an OCXO. When you buy a new OCXO, it might be accurate to 4 or 5 or 6 digits, out-of-the-box. You have to mechanically (screw) or electronically (EFC) calibrate it to get closer. If you want, say, 9 digits of accuracy, then you may have to re-calibrate it every day or at least once a week. When you buy a new Rb, it might be accurate to 9 or 10 or 11 digits, out-of-the-box. If you want, say, 9 digits of accuracy, then you may have to calibrate it every couple of years. /tvb ___ 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] Rb vs.Crystal OCXO
My understanding is that a really good Rb standard use a fairly wide bandwidth loop to control its own internal XO, and therefore improve its close in phase noise to be better than you can get with quartz alone. The Rb standard is able to do this because the S/N ratio of its rubidium vapor frequency reference (RVFR) is fairly high, and in any event considerably better than the S/N out of a CBT. Also, Rb standards have much smaller frequency jumps, if any, than quartz. Phase noise specs conveniently don't include the effects of jumps. Newer laser diode pumped Rb standards may make the comparison even more lopsided. Rick On 4/25/2014 9:12 AM, Shane Kirkbride wrote: Hi Everyone, I'm newer to this forum but I really enjoy reading the discussions. I have a pretty basic question. I'm wondering why one would chose an Rb Oscillator over a traditional OCXO? It does not immediately appear there is a phase noise advantage in the Rb.. Thanks, ~Shane On Fri, Apr 25, 2014 at 10:00 AM, time-nuts-requ...@febo.com wrote: Send time-nuts mailing list submissions to time-nuts@febo.com To subscribe or unsubscribe via the World Wide Web, visit https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts or, via email, send a message with subject or body 'help' to time-nuts-requ...@febo.com You can reach the person managing the list at time-nuts-ow...@febo.com When replying, please edit your Subject line so it is more specific than Re: Contents of time-nuts digest... Today's Topics: 1. Low SNR GPS reception and cheap LNAs (Attila Kinali) 2. Re: Symmetricom chip scale atomic clock (Tom Knox) 3. Re: How to accurately measure an oscillator's temperature. (Didier Juges) 4. Re: Low SNR GPS reception and cheap LNAs (Chris Albertson) -- Message: 1 Date: Fri, 25 Apr 2014 15:28:22 +0200 From: Attila Kinali att...@kinali.ch To: time-nuts@febo.com Subject: [time-nuts] Low SNR GPS reception and cheap LNAs Message-ID: 20140425152822.203775c003a761042e269...@kinali.ch Content-Type: text/plain; charset=US-ASCII Hi, I recently bought a bladeRF[1] to experiment a bit with GPS decoding. I tried to get GNSS-SDR[2] which seems quite good, but has its flaws. One of the things was that i cannot seem to get a fix in my environment. One of the problems seems that my antenna position is far from optimal. Aparently, GNSS-SDR uses only a very rudimentary acquisition technique (at least so i have been told). Now i wonder what techniques for low SNR acquisition are around. Would someone be so kind and give me some key words to google for? I also am looking to add an LNA to my reception chain, which is a mix of a 50R antenna with 75R Coaxcable (sat coax stuff is just a lot cheaper :-). Has anyone a recomendation for a good LNA that can be used in a flying construction (soldering onto two back-to-back glued connectors)? Ie it shouldnt be a QFN or BGA. DFN works but i'd rather have something with pins, like SC-70/SOT-323 or similar/larger. Attila Kinali [1] www.nuand.com/bladeRF [2] www.gnss-sdr.org -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin -- Message: 2 Date: Fri, 25 Apr 2014 08:53:25 -0600 From: Tom Knox act...@hotmail.com To: Time-Nuts time-nuts@febo.com Subject: Re: [time-nuts] Symmetricom chip scale atomic clock Message-ID: col130-w35b7069ee8d042e122a563df...@phx.gbl Content-Type: text/plain; charset=iso-8859-1 For the sake of discussion let me just add that even if medesigns comments were true of Microsemi, the Microsemi responses on this form have been from long time Time-Nuts who have for years contributed their knowledge to the betterment of the community in the proudest traditions of acadimia. Never have I seen them use the form for financial gain. Sure corporate greed is a problem in todays society but knowing some of the individuals at Microsemi it is clearly not a black and white issue. Further where it may be acceptable in some cases to release a product early and perform some of the final development on the backs of the customers to better serve their needs such as in the case of the fantastic TimeLab. In a mission critical product like the CSAC a problem like this will cost Microsemi far more then they would profit from a premature release. These manufacturing defects were clearly something they could not anticipate. I for one will be purchasing many more Microsemi products in the future and viewing their performance on TimeLab with full confidence. Please keep the group update on your progress resolving this issue. It will be interesting to see if a single point of failure is found, a smoking gun so
Re: [time-nuts] Rb vs.Crystal OCXO
Hi At least on the Rb I have seen, the phase noise (in to 1 Hz) is generally better if the Rb loop is narrower rather than wider. That of course assumes that the internal OCXO has pretty good phase noise to start. Maybe I’ve been slumming it …. Bob On Apr 25, 2014, at 6:29 PM, Richard (Rick) Karlquist rich...@karlquist.com wrote: My understanding is that a really good Rb standard use a fairly wide bandwidth loop to control its own internal XO, and therefore improve its close in phase noise to be better than you can get with quartz alone. The Rb standard is able to do this because the S/N ratio of its rubidium vapor frequency reference (RVFR) is fairly high, and in any event considerably better than the S/N out of a CBT. Also, Rb standards have much smaller frequency jumps, if any, than quartz. Phase noise specs conveniently don't include the effects of jumps. Newer laser diode pumped Rb standards may make the comparison even more lopsided. Rick On 4/25/2014 9:12 AM, Shane Kirkbride wrote: Hi Everyone, I'm newer to this forum but I really enjoy reading the discussions. I have a pretty basic question. I'm wondering why one would chose an Rb Oscillator over a traditional OCXO? It does not immediately appear there is a phase noise advantage in the Rb.. Thanks, ~Shane On Fri, Apr 25, 2014 at 10:00 AM, time-nuts-requ...@febo.com wrote: Send time-nuts mailing list submissions to time-nuts@febo.com To subscribe or unsubscribe via the World Wide Web, visit https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts or, via email, send a message with subject or body 'help' to time-nuts-requ...@febo.com You can reach the person managing the list at time-nuts-ow...@febo.com When replying, please edit your Subject line so it is more specific than Re: Contents of time-nuts digest... Today's Topics: 1. Low SNR GPS reception and cheap LNAs (Attila Kinali) 2. Re: Symmetricom chip scale atomic clock (Tom Knox) 3. Re: How to accurately measure an oscillator's temperature. (Didier Juges) 4. Re: Low SNR GPS reception and cheap LNAs (Chris Albertson) -- Message: 1 Date: Fri, 25 Apr 2014 15:28:22 +0200 From: Attila Kinali att...@kinali.ch To: time-nuts@febo.com Subject: [time-nuts] Low SNR GPS reception and cheap LNAs Message-ID: 20140425152822.203775c003a761042e269...@kinali.ch Content-Type: text/plain; charset=US-ASCII Hi, I recently bought a bladeRF[1] to experiment a bit with GPS decoding. I tried to get GNSS-SDR[2] which seems quite good, but has its flaws. One of the things was that i cannot seem to get a fix in my environment. One of the problems seems that my antenna position is far from optimal. Aparently, GNSS-SDR uses only a very rudimentary acquisition technique (at least so i have been told). Now i wonder what techniques for low SNR acquisition are around. Would someone be so kind and give me some key words to google for? I also am looking to add an LNA to my reception chain, which is a mix of a 50R antenna with 75R Coaxcable (sat coax stuff is just a lot cheaper :-). Has anyone a recomendation for a good LNA that can be used in a flying construction (soldering onto two back-to-back glued connectors)? Ie it shouldnt be a QFN or BGA. DFN works but i'd rather have something with pins, like SC-70/SOT-323 or similar/larger. Attila Kinali [1] www.nuand.com/bladeRF [2] www.gnss-sdr.org -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin -- Message: 2 Date: Fri, 25 Apr 2014 08:53:25 -0600 From: Tom Knox act...@hotmail.com To: Time-Nuts time-nuts@febo.com Subject: Re: [time-nuts] Symmetricom chip scale atomic clock Message-ID: col130-w35b7069ee8d042e122a563df...@phx.gbl Content-Type: text/plain; charset=iso-8859-1 For the sake of discussion let me just add that even if medesigns comments were true of Microsemi, the Microsemi responses on this form have been from long time Time-Nuts who have for years contributed their knowledge to the betterment of the community in the proudest traditions of acadimia. Never have I seen them use the form for financial gain. Sure corporate greed is a problem in todays society but knowing some of the individuals at Microsemi it is clearly not a black and white issue. Further where it may be acceptable in some cases to release a product early and perform some of the final development on the backs of the customers to better serve their needs such as in the case of the fantastic TimeLab. In a mission critical product like the CSAC a problem like this will
Re: [time-nuts] Rb vs.Crystal OCXO
On 04/25/2014 10:30 PM, Tom Van Baak wrote: Hi Everyone, I'm newer to this forum but I really enjoy reading the discussions. I have a pretty basic question. I'm wondering why one would chose an Rb Oscillator over a traditional OCXO? It does not immediately appear there is a phase noise advantage in the Rb.. Thanks, ~Shane Welcome to time-nuts. Good question. In some applications the exceptional long-term frequency accuracy and stability you get with Rb is more important than the better phase noise, smaller size, lower power, better short-term stability, longer lifetime, or cheaper price that you get with an OCXO. When you buy a new OCXO, it might be accurate to 4 or 5 or 6 digits, out-of-the-box. You have to mechanically (screw) or electronically (EFC) calibrate it to get closer. If you want, say, 9 digits of accuracy, then you may have to re-calibrate it every day or at least once a week. When you buy a new Rb, it might be accurate to 9 or 10 or 11 digits, out-of-the-box. If you want, say, 9 digits of accuracy, then you may have to calibrate it every couple of years. Size, weight and cost may also be issues. In todays age of modernization, a well-sized OCXO or rubidium isn't an option, and well, smaller OCXOs exist while rubidiums starts to become really scarse below a certain volume, and when the volume come downs further, the CSAC is the only atomic reference and then you only see OCXO and TCXOs. Cost-wise some high-performance OCXOs gives the rubidiums a match performance-wise (even if they need a bit more trimming) but not price-wise or even volume-wise. Them some telecom rubidiums just isn't very good at phase-noise, but have fair stability for the size and cost. In the end, there is no one choice which always fits, it *really* depends on what you need it for, and the requirements, then it plays itself out as you look through the options. Cheers, Magnus ___ 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.
