Re: [time-nuts] Any nixie project people out there?
Hi David- Any takers yet? While the last thing I need is another nixie counter (I have 4 or 5 already), I do have a soft spot for nixies, and hate the way so much gear has been chopped up for trendy clocks. That said, what I'd really like to do is make an accurate, self turning hour glass that drives a nixie clock. Or maybe a GPS disciplined hour-glass driving a nixie clock. How the hour-glass could be disciplined, except in turn-over speed, I'm not sure. It's still in the planning stage. My purchasing budget has been greatly reduced due to the economy, so I'm looking for deals where I wouldn't have before. -Dave -- Original message -- From: David Medin [EMAIL PROTECTED] I appreciate the assistance I've gotten here in getting my Tbolts set up and generating that beautiful traceable 10 MHz for my benches at home and work. I've got a giveback IF someone plans to put it to good use. My faithful Ballantine 5700A 9 digit nixie frequency counter isn't counting so well in its upper range as of last week, and as much as I have some affinity for it (I've had it for over 20 years), I have no time to repair it and have a more modern counter with my Tbolt now driving the reference. If anyone out there is looking for a nixie project for a clock or just simply wanting to use the parts, let me know. I'm not really looking for anything for it, but I'd rather just drop it off at a UPS shipping store and have them package and send it at your cost, and that would be your only obligation. It has a 1 MHz (I believe, because the external reference is 1 MHz) ovenized oscillator on a PC board, 9 digits of working nixies soldered to the PCB, a gate to 10 seconds, and a range of 10 Hz to 512 MHz, although the upper octave is not working properly and indicating about twice the applied frequency. It is chock full of ECL and TTL including the nixie driver TTL, most in sockets, so it should be real accessible for those wanting to turn it into something else where just the drivers and divider chain would be of use. The case comes together with Dzus on top and bottom, and has a few dents and also a spot where the NASA inventory tag used to be years ago. It does work, top range aside. I do NOT have a manual. No takers, and the nixie driver chips will go on ebay, but I'd rather give it to someone who can use it in only the whacky way a Time Nut can. Thanks. Dave Medin _ Are you a Techie? Get Your Free Tech Email Address Now! Visit http://www.TechEmail.com ___ 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] Oncore question
In a message dated 24/11/2008 05:43:49 GMT Standard Time, [EMAIL PROTECTED] writes: I simply put large rechargeable Lithium-Vanadium pentoxide coin cell with appropriate charging circuit to GPS carrier board and forgot about this question... Another solution is to put CR123 battery holder to carrier PCB, stuff it with a good quality cell and it will probably last for 15+ years, driving just clock and CMOS RAM during power outages.. And if it's important that the whole system stays working for reasonable length drop outs, lead acid gel batteries on a master 12, 24 or 48 volt (nominal) power supply, again forgetting batteries at board level, are still hard to beat. regards Nigel GM8PZR ___ 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] EZGPIB error
Ian, I will be out of the home today and tomorrow but after that I'll tackle this problem. Best regards Ulrich -Ursprungliche Nachricht- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Im Auftrag von Ian Sheffield Gesendet: Sonntag, 23. November 2008 16:48 An: Discussion of precise time and frequency measurement Betreff: [time-nuts] EZGPIB error Hello chaps, A quick question to the assembled multitude rather than bothering Ulrich directly, as some of you must have seen this problem: What causes the error message Socket Error # 10065 No route to host, when using EZGPIB with my Prologix latest version interface with my laptops? EZGPIB works fine from my desktop PC but gives this error message with both of my laptops running XP (one XP Home, the other is XP Pro). The Prologix itself is working fine, as it controls and reads my HP5334 perfectly using the direct Prologix commands. EZGPIB , as stated, also works fine from the Desktop PC. What is not configured correctly in the laptops? Many thanks in advance, Ian. ___ 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] GPSDO using 100Hz
Bruce Griffiths answered: Its difficult to make much useful comment as you provide few measured results. With an M12+T or equivalent the ADEV of the PPS output (without sawtooth correction) goes below 1E-10 at Tau 200 sec or so. Thus with an optimized GPSDO it wont take an hour or so to achieve 1E-10 stability. However a single shot phase error measurement system resolution of around 1ns or so is usually required. Take a look at the GPSDO ADEV plots at: http://www.leapsecond.com/pages/gpsdo/ Where the ADEV for various GPSDO remains below 1E-11 over the Tau range of [0.1s, 100,000s] The achievable performance also depends a great deal on the quality of the OCXO used in the GPSDO. If the digital phase error measurement techniques you have been comparing your system with have inadequate resolution it will tale longer for the measured ADEV to fall below 1E-10. If the OCXO used has a relatively high ADEV at low values of tau then it may well required averaging over very long time intervals to achieve an ADEV below 1E-10. More detail is required before an analysis of the performance of your system is possible. Bruce * Bruce, Thanks for the feedback, Good information to know, but you seemed to missed my point and question. Yes I am comparing to SIMPLE, and home built type, non optimized, trackers like Brooks Shera's 10 Mhz GPS Frequency Standard. I understand, and even wrote, NIST reports about a 10ns uncertainty with a 10 minute average, which would give a 1e-8 / 600, or 1.5 parts in 1E-11 possible in 600 seconds, 1e-10 in 100 seconds. Its safe to assume NIST is not using Shera's unit, which I believe adds an additional 24 ns or is it 41.7 ns uncertainty to each 1 second reading. Besides asking if anyone is using the 100Hz output, I would like to ask why don't the generally available GPSDO use the 100Hz, which can give about 1 ns of certainly with a simple PLL and analog RC filter, instead of the using the 1 sec which has more like 100 ns of uncorrected uncertainty in it and must use a processor? Also I should comment that on LeapSecond.com http://www.leapsecond.com/pages/gpsdo/ you stated where the ADEV for various GPSDO remains below 1E-11 over the Tau range of [0.1s, 100,000s]. This Tau has NOTHING to do with the tracking time constant that the GPSDO is set to, which is usually recommended to be set for a TC of several hours for optimal results. BTW most of what they have plotted is the results of NOT setting the GPSDO tracking TC slow enough. This is why the Allan Deviation increases in the tracking mode at mid averaging times. The 1 second GPS tracking signal is adding noise, which pretty much makes my point that 1 PPS signal is not so good to use if you want good fast results. Warren ___ 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] GPS Valid Fix Detector
Peter, in general NMEA decoding involves 1) Message type detection 2) End of message detection 4) Checksum test 5) Looking for what is to be found between comma N and comma N+1, having in mind that there may also be NOTHING. Best regards Ulrich Bangert -Ursprungliche Nachricht- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Im Auftrag von Yuri Ostry Gesendet: Montag, 24. November 2008 04:21 An: Peter Putnam; Discussion of precise time and frequency measurement Betreff: Re: [time-nuts] GPS Valid Fix Detector Hello, Monday, November 24, 2008, 1:08:45, Peter Putnam wrote: P Greetings, P For those interested in a very simple means of determining if the P NMEA data stream from a GPS receiver contains valid fix data, I offer P design details for a Valid Fix detector that runs in a Microchip P 12F629, an 8-pin DIP device. P No other components are required if the GPS receiver provides CMOS P output levels: P http://www.ni6e.com/time/GPS_Valid_Fix.html P Regards, P Peter Looks like your firmware will need some correction, as there is a lot of NMEA variations... Below is examples of GPRMC sentences from several different GPS receivers. You'll need to pick character after second comma, not by particular offset, to be compatible. uBlox LEA4A (firmware 4): $GPRMC,214541.00,A,5558.55936,N,03709.54595,E,1.116,104.33,120 107,,,A*6A Trimble Pathfinder Pro XR $GPRMC,050945.00,A,3504.227794,N,13545.810149,E,000.0,57.1,140 302,6.5,W,A*12 Garmin GPS III Plus $GPRMC,031655,A,3404.456,N,13531.788,E,000.0,360.0,110101,006.8,W*6D Garmin GPSMAP 76S $GPRMC,040014,A,4242.0410,N,14134.2795,E,1.4,51.0,010802,8.0,W,A*35 Blue Logger GPS (Something from Japan) $GPRMC,021803.751,A,3501.5666,N,13546.9457,E,0.00,212.31,110604,,*07 uBlox SBR-LS (firmware 3.01) $GPRMC,051250.00,A,5558.55523,N,03709.54211,E,1.177,229.34,080 705,,,A*6E GlobalSat BT-338 (SiRF) $GPRMC,100643.000,A,5522.9036,N,03710.1282,E,0.16,119.11,200507,,*0D -- Best regards, Yuri mailto:[EMAIL PROTECTED] ___ 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] GPSDO using 100Hz
Warren, James Miller, G3RUH, also uses the 100 Hz signal. So it's neither specifically new nor the philosopher's stone that you may perhaps believe to have found. The PPS and the 100 Hz signal come from the SAME oscillator. The jitter in the PPS comes from the fact that the receiver logic decides WHICH slope of the oscillator signal comes next close to the TRUE point of time where the PPS should be generated. The key error in your idea is the assumption that every 100 positive slopes of your 100 Hz is identical with the start of a new second, which is wrong when you look at it at a second to second base. What is true is that the MEAN frequency of the 100 Hz is locked to the GPS and that is why your fast pll works as well as James Miller's. Best regards Ulrich Bangert -Ursprungliche Nachricht- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Im Auftrag von WarrenS Email Gesendet: Montag, 24. November 2008 10:48 An: Discussion of precise time and frequency measurement Betreff: Re: [time-nuts] GPSDO using 100Hz Bruce Griffiths answered: Its difficult to make much useful comment as you provide few measured results. With an M12+T or equivalent the ADEV of the PPS output (without sawtooth correction) goes below 1E-10 at Tau 200 sec or so. Thus with an optimized GPSDO it wont take an hour or so to achieve 1E-10 stability. However a single shot phase error measurement system resolution of around 1ns or so is usually required. Take a look at the GPSDO ADEV plots at: http://www.leapsecond.com/pages/gpsdo/ Where the ADEV for various GPSDO remains below 1E-11 over the Tau range of [0.1s, 100,000s] The achievable performance also depends a great deal on the quality of the OCXO used in the GPSDO. If the digital phase error measurement techniques you have been comparing your system with have inadequate resolution it will tale longer for the measured ADEV to fall below 1E-10. If the OCXO used has a relatively high ADEV at low values of tau then it may well required averaging over very long time intervals to achieve an ADEV below 1E-10. More detail is required before an analysis of the performance of your system is possible. Bruce * Bruce, Thanks for the feedback, Good information to know, but you seemed to missed my point and question. Yes I am comparing to SIMPLE, and home built type, non optimized, trackers like Brooks Shera's 10 Mhz GPS Frequency Standard. I understand, and even wrote, NIST reports about a 10ns uncertainty with a 10 minute average, which would give a 1e-8 / 600, or 1.5 parts in 1E-11 possible in 600 seconds, 1e-10 in 100 seconds. Its safe to assume NIST is not using Shera's unit, which I believe adds an additional 24 ns or is it 41.7 ns uncertainty to each 1 second reading. Besides asking if anyone is using the 100Hz output, I would like to ask why don't the generally available GPSDO use the 100Hz, which can give about 1 ns of certainly with a simple PLL and analog RC filter, instead of the using the 1 sec which has more like 100 ns of uncorrected uncertainty in it and must use a processor? Also I should comment that on LeapSecond.com http://www.leapsecond.com/pages/gpsdo/ you stated where the ADEV for various GPSDO remains below 1E-11 over the Tau range of [0.1s, 100,000s]. This Tau has NOTHING to do with the tracking time constant that the GPSDO is set to, which is usually recommended to be set for a TC of several hours for optimal results. BTW most of what they have plotted is the results of NOT setting the GPSDO tracking TC slow enough. This is why the Allan Deviation increases in the tracking mode at mid averaging times. The 1 second GPS tracking signal is adding noise, which pretty much makes my point that 1 PPS signal is not so good to use if you want good fast results. Warren ___ 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] position determination over short distance
Hi, A graphic tablet (11 square is a common size) should give you about 120 positions/mm for something like a hundred bucks. That's not very different from the mouse solution, but give you absolute position rather than relative. Regards, Jean-Louis Oneto - Original Message - From: Rick Harold [EMAIL PROTECTED] To: time-nuts@febo.com Sent: Monday, November 24, 2008 2:34 AM Subject: [time-nuts] position determination over short distance All, I'm planning doing some experiments in distance measurement. They don't deal with atomic time directly but with extreme short periods of time. I need to determine the position of a instrument with a 1mm accuracy or less. The instrument is not connected to a mechanical device but is separate independent. The surface which the instrument is positioned on is close to the size of a 11x11 square. I thought of using 1 RF transmitters (not sure of freq) on bottom of the device near the surface. The surface would have RF receivers on 3 or 4 edges/corners to receive the signal. If each of the receivers positions are known and they then send a signal to a central circuit (again known positions) how can I differentiate the time of arrival at the central location? Does anybody know of a circuit/chip or system which would determine the time 'difference'. Obviously this is used to triangulate the position of the instrument. Light travels 1 mm in ~3.3 picoseconds so I would suspect the differentiator would have to have that or better resolution. It could also use some proportional method to extrapolate the position since the surface has a fixed size. Any ideas/thoughts? Thanks in advance. Rick Harold ___ 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] GPSDO using 100Hz
Ulrich Bangert Thanks for the great Information. UR) James Miller, G3RUH, also uses the 100 Hz signal Thanks, that is what I was asking for, other people that were using the 100Hz. Now if I could just figure out how to post a response under an existing thread, and not have it start a new one I'd be happy. Concerning your other comments: UR) it's neither specifically new nor ... I did not mean to imply that the 100Hz was new or its use was discovered by me, Mostly I'm wondering why it is so little used, and I'm looking for other people using it. Something that I can do with the 100Hz that you probable have not seen before is the ability to make a GPSDO similar to Brooks Shera's processors based unit using just 3 standard off the self 74HC IC's and a pretty crappy Osc. UR) The key error in your idea is the assumption that every 100 positive slopes of your 100 Hz is identical with the start of a new second, which is wrong when you look at it at a second to second base. Correct that my assumption was that every 100 pulses gives a one second pulse at the same location.You are incorrect that when this is not true, it is a key error in my idea. I did see that the 100Hz pulse that comes out at about the time as the 1Hz sawtooth correction is updated seems to have the same amount of phase error as reported for the 1 Hz, best I could tell. I do know it is sometimes true, I'll check that out better and verify that it is not always true on my unit. Thanks for the information. BUT, NO matter, because the max jitter error of around 100ns is the same in both of the 100Hz and the 1 Hz signal, and the 100Hz error is nonaccumative. That is when I average 100 points each with an uncertainty of 100ns I get at least the Square root of 100 better resolution If they where truly random, which they are not, they have the same basic ramp type phase response as the 1 Hz sawtooth, just much faster so averaging works much better than if they where random. What I have found is that the net effect is for the most part that averaging 100 100Hz signals will give about the same error result as averaging 100 One second pulses. If you want to proof it to yourself use a digital scope with an average function and look at the results. (there are some rare exceptions, I skip over for now) For another example, consider what the results would be if you just used every 100th 1 second pulse. You'd end up with 100ns uncertainty in 100 seconds rather the under 10 ns you get by averaging 100 1 second pulses (most of the time). UR) What is true is that the MEAN frequency of the 100 Hz is locked to the GPS and that is why your fast PLL works as well as James Miller's. What I tried to state is that the 100Hz is fast enough to make a simple analog PPL, something that is not very easy to do with the 1 Hz signals. Thanks for the name, I'll check more on how he is doing his simple GPS tracker. It looks like he is using the 10KHz output of the Jupiter GPS. Unfortunately my oncore does not have a 10KHz output. Thanks, Warren *** James Miller, G3RUH, also uses the 100 Hz signal. So it's neither specifically new nor the philosopher's stone that you may perhaps believe to have found. The PPS and the 100 Hz signal come from the SAME oscillator. The jitter in the PPS comes from the fact that the receiver logic decides WHICH slope of the oscillator signal comes next close to the TRUE point of time where the PPS should be generated. The key error in your idea is the assumption that every 100 positive slopes of your 100 Hz is identical with the start of a new second, which is wrong when you look at it at a second to second base. What is true is that the MEAN frequency of the 100 Hz is locked to the GPS and that is why your fast pll works as well as James Miller's. 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.
Re: [time-nuts] GPSDO using 100Hz
Hii Warren, have a look on this link...http://www.jrmiller.demon.co.uk/projects/ministd/frqstd0.htm and he is using the 10KHz...rpt 10KHz not the 100Hz..compare with your circuit diagram... / I would like to see / or the other solution just make the same circuit and with your testing method chk both unit...with the same OCXO the jupiter eng board is still available in the German Ebay Rgds Ernie. -Original Message- From: WarrenS Email [EMAIL PROTECTED] To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Mon, 24 Nov 2008 12:49 pm Subject: [time-nuts] GPSDO using 100Hz Ulrich Bangert Thanks for the great Information. UR) James Miller, G3RUH, also uses the 100 Hz signal Thanks, that is what I was asking for, other people that were using the 100Hz. Now if I could just figure out how to post a response under an existing thread, and not have it start a new one I'd be happy. Concerning your other comments: UR) it's neither specifically new nor ... I did not mean to imply that the 100Hz was new or its use was discovered by me, Mostly I'm wondering why it is so little used, and I'm looking for other people using it. Something that I can do with the 100Hz that you probable have not seen before is the ability to make a GPSDO similar to Brooks Shera's processors based unit using just 3 standard off the self 74HC IC's and a pretty crappy Osc. UR) The key error in your idea is the assumption that every 100 positive slopes of your 100 Hz is identical with the start of a new second, which is wrong when you look at it at a second to second base. Correct that my assumption was that every 100 pulses gives a one second pulse at the same location.You are incorrect that when this is not true, it is a key error in my idea. I did see that the 100Hz pulse that comes out at about the time as the 1Hz sawtooth correction is updated seems to have the same amount of phase error as reported for the 1 Hz, best I could tell. I do know it is sometimes true, I'll check that out better and verify that it is not always true on my unit. Thanks for the information. BUT, NO matter, because the max jitter error of around 100ns is the same in both of the 100Hz and the 1 Hz signal, and the 100Hz error is nonaccumative. That is when I average 100 points each with an uncertainty of 100ns I get at least the Square root of 100 better resolution If they where truly random, which they are not, they have the same basic ramp type phase response as the 1 Hz sawtooth, just much faster so averaging works much better than if they where random. What I have found is that the net effect is for the most part that averaging 100 100Hz signals will give about the same error result as averaging 100 One second pulses. If you want to proof it to yourself use a digital scope with an average function and look at the results. (there are some rare exceptions, I skip over for now) For another example, consider what the results would be if you just used every 100th 1 second pulse. You'd end up with 100ns uncertainty in 100 seconds rather the under 10 ns you get by averaging 100 1 second pulses (most of the time). UR) What is true is that the MEAN frequency of the 100 Hz is locked to the GPS and that is why your fast PLL works as well as James Miller's. What I tried to state is that the 100Hz is fast enough to make a simple analog PPL, something that is not very easy to do with the 1 Hz signals. Thanks for the name, I'll check more on how he is doing his simple GPS tracker. It looks like he is using the 10KHz output of the Jupiter GPS. Unfortunately my oncore does not have a 10KHz output. Thanks, Warren *** James Miller, G3RUH, also uses the 100 Hz signal. So it's neither specifically new nor the philosopher's stone that you may perhaps believe to have found. The PPS and the 100 Hz signal come from the SAME oscillator. The jitter in the PPS comes from the fact that the receiver logic decides WHICH slope of the oscillator signal comes next close to the TRUE point of time where the PPS should be generated. The key error in your idea is the assumption that every 100 positive slopes of your 100 Hz is identical with the start of a new second, which is wrong when you look at it at a second to second base. What is true is that the MEAN frequency of the 100 Hz is locked to the GPS and that is why your fast pll works as well as James Miller's. 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 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] position determination over short distance
Of course you can use any of the standard photogrammetric tecniques and programs. Even you can do it automatically using image correlation to find the paralax and hence the distance. But I have a simpler and cheaper (and also accurate) solution: Put a transmiting coil in the object to be measured, about 1-2 cm diameter, 0.5 cm high (I don´t remember the frequency now, it is quite low but it doesn't matter). Lay a receiving antenna grid of vertical and horizontal wires, spaced about 1 cm, in a surface below the object. Scan the antennas noting the amplitudes an phases on the 4 or 6 horizontal and vertical wires surrounding the Tx coil in each moment . Calculate the position in real time (you obtain a precision of about 0.1 mm if the antenna surface is calibrated) Sound complicated? buy a digitizing tablet (used ones are really cheap). This is how these things works. Regards, Ignacio Cembreros Lux, James P wrote: There's a fair amount of F/OSS software from JPL available to do this sort of calibration. It's used to calibrate cameras used on Mars rovers, among other things. The target pattern for calibration is a bunch of big circular dots on a background. On 11/23/08 7:56 PM, Bruce Griffiths [EMAIL PROTECTED] wrote: Tom Van Baak wrote: I need to determine the position of a instrument with a 1mm accuracy or less. The instrument is not connected to a mechanical device but is separate independent. The surface which the instrument is positioned on is close to the size of a 11x11 square. 1 mm or better accuracy on a 300x300 mm surface can be obtained with a cheap webcam mounted above the surface and a little bit a creative software. /tvb Dont forget to calibrate the camera distortion and ensure that this doesnt over over time. i.e. lock the focus and ensure the camera position, tilt etc with respect to the reference surface do not vary. Bruce ___ 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] GPSDO using 100Hz
Ernie I do have to agree that the James Miller unit is about as simple as you can get. His BIG advantages is the use of 10KHz to lock on. If the want to use the Jupiter GPS board, Miller's circuit is the way to go for SIMPLE. Bob Q has the same basic circuit configuration running off the 100Hz signal. It is listed in June 08. [time-nuts] Simple GPS 10 MHz frequency standard Bob's circuit has a lot more bills and whistles than Millers to tell when it is locked etc, but the extra bills he added does not effect the performance, for the most part, once it is locked. All else being equal the 100Hz XOR is not going to be as good as the 10KHz, although with about 100 times more care in the analog circuits to control noise, which Bob's seems to have, and with the right RC's they could be pretty similar performance. What I am doing is somewhat different in that I wanted mine to work with my 100 Hz Oncore receiver and I do not use a XOR phase detector because of its very low phase low gain at 100 Hz. Thanks for the response, Warren ** - Original Message - From: [EMAIL PROTECTED] To: time-nuts@febo.com Sent: Monday, November 24, 2008 5:13 AM Subject: Re: [time-nuts] GPSDO using 100Hz Hii Warren, have a look on this link...http://www.jrmiller.demon.co.uk/projects/ministd/frqstd0.htm and he is using the 10KHz...rpt 10KHz not the 100Hz..compare with your circuit diagram... / I would like to see / or the other solution just make the same circuit and with your testing method chk both unit...with the same OCXO the jupiter eng board is still available in the German Ebay Rgds Ernie. -Original Message- From: WarrenS Email [EMAIL PROTECTED] To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Mon, 24 Nov 2008 12:49 pm Subject: [time-nuts] GPSDO using 100Hz Ulrich Bangert Thanks for the great Information. UR) James Miller, G3RUH, also uses the 100 Hz signal Thanks, that is what I was asking for, other people that were using the 100Hz. Now if I could just figure out how to post a response under an existing thread, and not have it start a new one I'd be happy. Concerning your other comments: UR) it's neither specifically new nor ... I did not mean to imply that the 100Hz was new or its use was discovered by me, Mostly I'm wondering why it is so little used, and I'm looking for other people using it. Something that I can do with the 100Hz that you probable have not seen before is the ability to make a GPSDO similar to Brooks Shera's processors based unit using just 3 standard off the self 74HC IC's and a pretty crappy Osc. UR) The key error in your idea is the assumption that every 100 positive slopes of your 100 Hz is identical with the start of a new second, which is wrong when you look at it at a second to second base. Correct that my assumption was that every 100 pulses gives a one second pulse at the same location.You are incorrect that when this is not true, it is a key error in my idea. I did see that the 100Hz pulse that comes out at about the time as the 1Hz sawtooth correction is updated seems to have the same amount of phase error as reported for the 1 Hz, best I could tell. I do know it is sometimes true, I'll check that out better and verify that it is not always true on my unit. Thanks for the information. BUT, NO matter, because the max jitter error of around 100ns is the same in both of the 100Hz and the 1 Hz signal, and the 100Hz error is nonaccumative. That is when I average 100 points each with an uncertainty of 100ns I get at least the Square root of 100 better resolution If they where truly random, which they are not, they have the same basic ramp type phase response as the 1 Hz sawtooth, just much faster so averaging works much better than if they where random. What I have found is that the net effect is for the most part that averaging 100 100Hz signals will give about the same error result as averaging 100 One second pulses. If you want to proof it to yourself use a digital scope with an average function and look at the results. (there are some rare exceptions, I skip over for now) For another example, consider what the results would be if you just used every 100th 1 second pulse. You'd end up with 100ns uncertainty in 100 seconds rather the under 10 ns you get by averaging 100 1 second pulses (most of the time). UR) What is true is that the MEAN frequency of the 100 Hz is locked to the GPS and that is why your fast PLL works as well as James Miller's. What I tried to state is that the 100Hz is fast enough to make a simple analog PPL, something that is not very easy to do with the 1 Hz signals. Thanks for the name, I'll check more on how he is doing his simple GPS tracker. It looks like he is using the 10KHz output of the Jupiter GPS. Unfortunately my oncore does not have a 10KHz
[time-nuts] EZGPIB error
Thank you to all who replied. One vital piece of information I omitted was that this is a USB Prologix - not an Ethernet one, so the suggestions of wrong IP address etc. may not apply. - Which makes me wonder why such an error message should appear. (Both the laptops have WiFi drivers installed, but not the PC hmm?) I will take up the suggestion of using the very latest version of EZGPIB as I am presently using the version before Ulrich's latest download. Ulrich - thank you for your contact. I will download your latest version as soon as possible and report back. I will not be able to test until tomorrow, as tonight I am teaching basic Astronomy to a load of Cubs (Junior Boy Scouts)! Many thanks, Ian. ___ 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] 10 MHz over optical fiber?
Hi all, I have to carry a 10 MHz standard frequency signal inside an EMC screened room via fiber optic cable. Not willing to re-invent the wheel, do something like an optical standard frequency link exist on the market? I think it is possible to use standard 100MB LAN transceivers, and POF. Phase noise requirements are not very stringent, and the distance is in the order of some tens of meters. Marco IK1ODO / AI4YF ___ 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] 10 MHz over optical fiber?
Why fibre optic? You'll only need to convert back to copper when you get it in there (unless the kit that needs the 10Mhz reference has optical 10MHz in), and if you do that you may as well just take it in there using high quality coax (say RG-400U) and a bulkhead connector in the wall of the room. Dave -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Marco IK1ODO -2 Sent: 24 November 2008 15:31 To: Discussion of precise time and frequency measurement Subject: [time-nuts] 10 MHz over optical fiber? Hi all, I have to carry a 10 MHz standard frequency signal inside an EMC screened room via fiber optic cable. ___ 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] GPS Valid Fix Detector
I worked wtih a GPS module that would spit out all zeros for lat/long if there was no fix, and another that would spit out the coordinates for the manufacturer's office. It'll probably be hard to weed out every special case, but with the code, any of us can easily just modify it for our own needs. Thank you for taking the time to at least get *me* started :) You saved me a lot of trouble. -Bob On Mon, Nov 24, 2008 at 3:00 AM, Ulrich Bangert [EMAIL PROTECTED]wrote: Peter, in general NMEA decoding involves 1) Message type detection 2) End of message detection 4) Checksum test 5) Looking for what is to be found between comma N and comma N+1, having in mind that there may also be NOTHING. Best regards Ulrich Bangert -Ursprungliche Nachricht- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Im Auftrag von Yuri Ostry Gesendet: Montag, 24. November 2008 04:21 An: Peter Putnam; Discussion of precise time and frequency measurement Betreff: Re: [time-nuts] GPS Valid Fix Detector Hello, Monday, November 24, 2008, 1:08:45, Peter Putnam wrote: P Greetings, P For those interested in a very simple means of determining if the P NMEA data stream from a GPS receiver contains valid fix data, I offer P design details for a Valid Fix detector that runs in a Microchip P 12F629, an 8-pin DIP device. P No other components are required if the GPS receiver provides CMOS P output levels: P http://www.ni6e.com/time/GPS_Valid_Fix.html P Regards, P Peter Looks like your firmware will need some correction, as there is a lot of NMEA variations... Below is examples of GPRMC sentences from several different GPS receivers. You'll need to pick character after second comma, not by particular offset, to be compatible. uBlox LEA4A (firmware 4): $GPRMC,214541.00,A,5558.55936,N,03709.54595,E,1.116,104.33,120 107,,,A*6A Trimble Pathfinder Pro XR $GPRMC,050945.00,A,3504.227794,N,13545.810149,E,000.0,57.1,140 302,6.5,W,A*12 Garmin GPS III Plus $GPRMC,031655,A,3404.456,N,13531.788,E,000.0,360.0,110101,006.8,W*6D Garmin GPSMAP 76S $GPRMC,040014,A,4242.0410,N,14134.2795,E,1.4,51.0,010802,8.0,W,A*35 Blue Logger GPS (Something from Japan) $GPRMC,021803.751,A,3501.5666,N,13546.9457,E,0.00,212.31,110604,,*07 uBlox SBR-LS (firmware 3.01) $GPRMC,051250.00,A,5558.55523,N,03709.54211,E,1.177,229.34,080 705,,,A*6E GlobalSat BT-338 (SiRF) $GPRMC,100643.000,A,5522.9036,N,03710.1282,E,0.16,119.11,200507,,*0D -- Best regards, Yuri mailto:[EMAIL PROTECTED] ___ 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] 10 MHz over optical fiber?
In message [EMAIL PROTECTED], Marco IK1ODO -2 writes: Hi all, I have to carry a 10 MHz standard frequency signal inside an EMC screened room via fiber optic cable. Not willing to re-invent the wheel, do something like an optical standard frequency link exist on the market? I think it is possible to use standard 100MB LAN transceivers, and POF. Phase noise requirements are not very stringent, and the distance is in the order of some tens of meters. HP used to have kits consisting of transmitter + receiver + plastic fiber in various lengths. HParchive.org has a service note that explains how to use that for reference frequency distribution. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [EMAIL PROTECTED] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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] 10 MHz over optical fiber?
At 16.41 24/11/2008, you wrote: Why fibre optic? You'll only need to convert back to copper when you get it in there (unless the kit that needs the 10Mhz reference has optical 10MHz in), and if you do that you may as well just take it in there using high quality coax (say RG-400U) and a bulkhead connector in the wall of the room. Dave Dave, the customer wants no bulkheads and asks specifically for an optical connection. The signal will be, of course, be converted back to electrical inside the room. Marco ___ 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] position determination over short distance
Her's another approach, see: http://www.youtube.com/watch?v=FBy_e4yvqhQ Regards, Bob Martinson, N1VQR -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of EB4APL Sent: Monday, November 24, 2008 9:20 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] position determination over short distance Of course you can use any of the standard photogrammetric tecniques and programs. Even you can do it automatically using image correlation to find the paralax and hence the distance. But I have a simpler and cheaper (and also accurate) solution: Put a transmiting coil in the object to be measured, about 1-2 cm diameter, 0.5 cm high (I don´t remember the frequency now, it is quite low but it doesn't matter). Lay a receiving antenna grid of vertical and horizontal wires, spaced about 1 cm, in a surface below the object. Scan the antennas noting the amplitudes an phases on the 4 or 6 horizontal and vertical wires surrounding the Tx coil in each moment . Calculate the position in real time (you obtain a precision of about 0.1 mm if the antenna surface is calibrated) Sound complicated? buy a digitizing tablet (used ones are really cheap). This is how these things works. Regards, Ignacio Cembreros Lux, James P wrote: There's a fair amount of F/OSS software from JPL available to do this sort of calibration. It's used to calibrate cameras used on Mars rovers, among other things. The target pattern for calibration is a bunch of big circular dots on a background. On 11/23/08 7:56 PM, Bruce Griffiths [EMAIL PROTECTED] wrote: Tom Van Baak wrote: I need to determine the position of a instrument with a 1mm accuracy or less. The instrument is not connected to a mechanical device but is separate independent. The surface which the instrument is positioned on is close to the size of a 11x11 square. 1 mm or better accuracy on a 300x300 mm surface can be obtained with a cheap webcam mounted above the surface and a little bit a creative software. /tvb Dont forget to calibrate the camera distortion and ensure that this doesnt over over time. i.e. lock the focus and ensure the camera position, tilt etc with respect to the reference surface do not vary. Bruce ___ 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] 10 MHz over optical fiber?
I'm looking for the same thing, but between buildings over singlemode fiber. I have not evaluated any of these but I've been looking at: http://www.terahertztechnologies.com http://www.highlandtechnology.com/ http://www.luxlink.com/ Scott Marco IK1ODO -2 wrote: Hi all, I have to carry a 10 MHz standard frequency signal inside an EMC screened room via fiber optic cable. Not willing to re-invent the wheel, do something like an optical standard frequency link exist on the market? I think it is possible to use standard 100MB LAN transceivers, and POF. Phase noise requirements are not very stringent, and the distance is in the order of some tens of meters. Marco IK1ODO / AI4YF ___ 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] 10 MHz over optical fiber?
We do lots of this sort of thing at JPL. But the high precision does come at a cost.. Here's a paper from Bob Tjoelker and colleagues.. http://ipnpr.jpl.nasa.gov/progress_report/42-167/167C.pdf There are various off the shelf products too, (you could buy a receiver and transmitter module from Ortel, for instance) James Lux, P.E. Task Manager, SOMD Software Defined Radios Flight Communications Systems Section Jet Propulsion Laboratory 4800 Oak Grove Drive, Mail Stop 161-213 Pasadena, CA, 91109 +1(818)354-2075 phone +1(818)393-6875 fax -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Scott Mace Sent: Monday, November 24, 2008 8:37 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] 10 MHz over optical fiber? I'm looking for the same thing, but between buildings over singlemode fiber. I have not evaluated any of these but I've been looking at: http://www.terahertztechnologies.com http://www.highlandtechnology.com/ http://www.luxlink.com/ Scott Marco IK1ODO -2 wrote: ___ 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] Oncore question
Hi Arnold, not sure what voltage the crystal stops at, that is probably different unit-to-unit. It happens on the M12+, it may not happen on other Oncores. As someone else mentioned, if you only use the Li battery during power outages, it will probably last a very long time, years and years. It's mostly an issue when the unit is un-powered, in storage. bye, Said In a message dated 11/23/2008 13:05:10 Pacific Standard Time, [EMAIL PROTECTED] writes: Hi Said, thank you very much for the additional clarification, very interesting behaviour. I think this does confirm roughly my assumption. When only pwr fails for a few hours (intermittant) have to be taken into account, super caps may be good for safe work during several hours up to perhaps 24 hours, but not beyond, is that right? Do you know at what voltage the clock does resign? Perhaps this could be improved with a software solving the recovery problem when repowering the RX. You describe that using LiIon batteries are not yet the ideal way, but why cannot higher capacities come into play (space should be not the problem for on ground use in fix stations)? regards, Arnold ___ 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] GPSDO using 100Hz
Hi, Sorry, I don't know how to reply to a post using the digest. But my question is if 100Hz or 10KHz are available from a GPS unit, where do they come from? Does that mean there is a 10MHz oscillator somewhere on the pcb that is just divided down? If so, then adding another PLL loop to control an external 10MHz crystal will just add additional noise, jitter, variable phase offset, etc. If there is already a 10MHz oscillator, wouldn't it be simpler to add a buffer like paralleled sections of a 74AC04 to the source, and drive a 50 ohm coax directly? Regards, Mike Monett ___ 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] 10 MHz over optical fiber?
You might look at video fiber optic transmitter/receiver. I used one once to carry a certain telemetry signal for the same reasons your are looking for. The fiber optics were analog in this case and rated from 30 hz to 10 Mhz at 1 volt P-P. We had to attenuate the signal going into the transmitter and we had to amplify the receiver. Our run was around 400 feet. The signal to noise ratio was somewhere around 55 db. ___ 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] GPSDO using 100Hz
Mike Neither do I, know how to reply to a post that is. This may be the blind leading the blind and end up in some unknown place. True it would be simpler to use the High freq Osc directly but it would not be accurate. The problem with just using the High freq as you suggested is that it is not at any known, exact or even constant frequency. The divider number can change for each low freq cycle. Example if the master freq was say 0.2520 Hz high then every forth second the divider would add 1 extra divide count and every 500th second it would divide by an additional extra clock time, therefore skipping 11 divides every 500 seconds. Regards, Warren - Original Message - From: Mike Monett [EMAIL PROTECTED] To: time-nuts@febo.com Sent: Monday, November 24, 2008 9:02 AM Subject: Re: [time-nuts] GPSDO using 100Hz Hi, Sorry, I don't know how to reply to a post using the digest. But my question is if 100Hz or 10KHz are available from a GPS unit, where do they come from? Does that mean there is a 10MHz oscillator somewhere on the pcb that is just divided down? If so, then adding another PLL loop to control an external 10MHz crystal will just add additional noise, jitter, variable phase offset, etc. If there is already a 10MHz oscillator, wouldn't it be simpler to add a buffer like paralleled sections of a 74AC04 to the source, and drive a 50 ohm coax directly? Regards, Mike Monett ___ 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] GPSDO using 100Hz
Mike Monett wrote: Hi, Sorry, I don't know how to reply to a post using the digest. But my question is if 100Hz or 10KHz are available from a GPS unit, where do they come from? Does that mean there is a 10MHz oscillator somewhere on the pcb that is just divided down? If so, then adding another PLL loop to control an external 10MHz crystal will just add additional noise, jitter, variable phase offset, etc. If there is already a 10MHz oscillator, wouldn't it be simpler to add a buffer like paralleled sections of a 74AC04 to the source, and drive a 50 ohm coax directly? Regards, Mike Monett ___ Few GPS receivers other than Geodetic receivers and the Novatel Superstar use 10MHz crystal oscillators. In particular neither the the M12+T nor the Resolution-T uses a 10MHz crystal Bruce ___ 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] GPSDO using 100Hz
WarrenS Email wrote: Bruce Griffiths answered: Its difficult to make much useful comment as you provide few measured results. With an M12+T or equivalent the ADEV of the PPS output (without sawtooth correction) goes below 1E-10 at Tau 200 sec or so. Thus with an optimized GPSDO it wont take an hour or so to achieve 1E-10 stability. However a single shot phase error measurement system resolution of around 1ns or so is usually required. Take a look at the GPSDO ADEV plots at: http://www.leapsecond.com/pages/gpsdo/ Where the ADEV for various GPSDO remains below 1E-11 over the Tau range of [0.1s, 100,000s] The achievable performance also depends a great deal on the quality of the OCXO used in the GPSDO. If the digital phase error measurement techniques you have been comparing your system with have inadequate resolution it will tale longer for the measured ADEV to fall below 1E-10. If the OCXO used has a relatively high ADEV at low values of tau then it may well required averaging over very long time intervals to achieve an ADEV below 1E-10. More detail is required before an analysis of the performance of your system is possible. Bruce * Bruce, Thanks for the feedback, Good information to know, but you seemed to missed my point and question. Yes I am comparing to SIMPLE, and home built type, non optimized, trackers like Brooks Shera's 10 Mhz GPS Frequency Standard. I understand, and even wrote, NIST reports about a 10ns uncertainty with a 10 minute average, which would give a 1e-8 / 600, or 1.5 parts in 1E-11 possible in 600 seconds, 1e-10 in 100 seconds. Its safe to assume NIST is not using Shera's unit, which I believe adds an additional 24 ns or is it 41.7 ns uncertainty to each 1 second reading. Besides asking if anyone is using the 100Hz output, I would like to ask why don't the generally available GPSDO use the 100Hz, which can give about 1 ns of certainly with a simple PLL and analog RC filter, instead of the using the 1 sec which has more like 100 ns of uncorrected uncertainty in it and must use a processor? Also I should comment that on LeapSecond.com http://www.leapsecond.com/pages/gpsdo/ you stated where the ADEV for various GPSDO remains below 1E-11 over the Tau range of [0.1s, 100,000s]. This Tau has NOTHING to do with the tracking time constant that the GPSDO is set to, which is usually recommended to be set for a TC of several hours for optimal results. BTW most of what they have plotted is the results of NOT setting the GPSDO tracking TC slow enough. This is why the Allan Deviation increases in the tracking mode at mid averaging times. The 1 second GPS tracking signal is adding noise, which pretty much makes my point that 1 PPS signal is not so good to use if you want good fast results. Warren Warren The optimum loop time constant depends on the quality of the local oscillator and the GPS timing receiver timing signals. A time constant of several hours is only useful with a very high quality OCXO. The 100Hz output of an M12+T is phase jerked into alignment with the the second once every second as is the 10kHz output from Jupiter-T GPS receiver. The variable pulse width of the 100Hz (and 10kHz) outputs do no favours to an XOR phase detector, its better to use the leading edges of these signals. When one uses a low resolution phase detector with dither as in the Brooks Shera circuit then making 100 or 10,000 measurements of the phase error every second can, if the dither is of the right form, improve the effective resolution. However surely the timing quantisation error of the leading edges of the 100Hz (or 10kHz) outputs limits the potential improvement? One can do much better with an inexpensive processor with little external hardware other than a high resolution DACX (even that can be implemented in software and hardware within the processor together with a couple of opamps). Bruce ___ 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] GPSDO using 100Hz
Sorry my example should of said skip 126 cycles every 500 seconds (500/4 +1) - Original Message - From: WarrenS [EMAIL PROTECTED] To: time-nuts@febo.com Sent: Monday, November 24, 2008 10:27 AM Subject: Re: [time-nuts] GPSDO using 100Hz Mike Neither do I, know how to reply to a post that is. This may be the blind leading the blind and end up in some unknown place. True it would be simpler to use the High freq Osc directly but it would not be accurate. The problem with just using the High freq as you suggested is that it is not at any known, exact or even constant frequency. The divider number can change for each low freq cycle. Example if the master freq was say 0.2520 Hz high then every forth second the divider would add 1 extra divide count and every 500th second it would divide by an additional extra clock time, therefore skipping 11 divides every 500 seconds. Regards, Warren - Original Message - From: Mike Monett [EMAIL PROTECTED] To: time-nuts@febo.com Sent: Monday, November 24, 2008 9:02 AM Subject: Re: [time-nuts] GPSDO using 100Hz Hi, Sorry, I don't know how to reply to a post using the digest. But my question is if 100Hz or 10KHz are available from a GPS unit, where do they come from? Does that mean there is a 10MHz oscillator somewhere on the pcb that is just divided down? If so, then adding another PLL loop to control an external 10MHz crystal will just add additional noise, jitter, variable phase offset, etc. If there is already a 10MHz oscillator, wouldn't it be simpler to add a buffer like paralleled sections of a 74AC04 to the source, and drive a 50 ohm coax directly? Regards, Mike Monett ___ 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] GPSDO using 100Hz
WarrenS Email wrote: Bruce, Thanks for the feedback, Good information to know, but you seemed to missed my point and question. in it and must use a processor? Also I should comment that on LeapSecond.com http://www.leapsecond.com/pages/gpsdo/ you stated where the ADEV for various GPSDO remains below 1E-11 over the Tau range of [0.1s, 100,000s]. This Tau has NOTHING to do with the tracking time constant that the GPSDO is set to, which is usually recommended to be set for a TC of several hours for optimal results. BTW most of what they have plotted is the results of NOT setting the GPSDO tracking TC slow enough. This is why the Allan Deviation increases in the tracking mode at mid averaging times. The 1 second GPS tracking signal is adding noise, which pretty much makes my point that 1 PPS signal is not so good to use if you want good fast results. Warren Analog time constants of several hours are generally considered impractical due to the lack of suitable low noise components principally high value resistors and capacitors. So how do you propose to get around this with an analog control loop? Bruce ___ 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] LPRO-101 HELP
Hi Gents, Just fired up my LPRO-101, bought a year ago or more on Ebay from Switzerland and found unserviceable It is a 24V vesion and upon switching ON only 0,47A is the current consumption and the 10MHz wondering up/down and never stops. No lock. Suspect the Heating part is defective Anybody having more info or circuit diagram where to look?? Thanks in advance. Rgds Ernie ___ 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] 10 MHz over optical fiber?
Hi Marco , You might try firecoms if it's not too hot in there. (plastic) Steve --- On Mon, 11/24/08, Marco IK1ODO -2 [EMAIL PROTECTED] wrote: From: Marco IK1ODO -2 [EMAIL PROTECTED] Subject: [time-nuts] 10 MHz over optical fiber? To: Discussion of precise time and frequency measurement time-nuts@febo.com Date: Monday, November 24, 2008, 7:31 AM Hi all, I have to carry a 10 MHz standard frequency signal inside an EMC screened room via fiber optic cable. Not willing to re-invent the wheel, do something like an optical standard frequency link exist on the market? I think it is possible to use standard 100MB LAN transceivers, and POF. Phase noise requirements are not very stringent, and the distance is in the order of some tens of meters. Marco IK1ODO / AI4YF ___ 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] 10 MHz over optical fiber?
Thanks to all for the quick answers and all the info. As usual, time-nuts is a great resource :-) Marco IK1ODO ___ 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] GPSDO using 100Hz
WarrenS Email wrote: Bruce, Thanks for the feedback, Good information to know, but you seemed to missed my point and question. in it and must use a processor? Also I should comment that on LeapSecond.com http://www.leapsecond.com/pages/gpsdo/ you stated where the ADEV for various GPSDO remains below 1E-11 over the Tau range of [0.1s, 100,000s]. This Tau has NOTHING to do with the tracking time constant that the GPSDO is set to, which is usually recommended to be set for a TC of several hours for optimal results. BTW most of what they have plotted is the results of NOT setting the GPSDO tracking TC slow enough. This is why the Allan Deviation increases in the tracking mode at mid averaging times. The 1 second GPS tracking signal is adding noise, which pretty much makes my point that 1 PPS signal is not so good to use if you want good fast results. Warren Analog time constants of several hours are generally considered impractical due to the lack of suitable low noise components principally high value resistors and capacitors. So how do you propose to get around this with an analog control loop? Bruce * Bruce In answer to your question of : how do you propose to get around this with an analog control loop? Short answer is: By using the 100Hz output pulses, instead of the 1 PPS. What I have found is that it takes about the same number of total pulses for a given accuracy whether it is 1 Hz or 100 Hz. SO by using the 100Hz signal, the time Constant can go down by nearly 2 decades. What I have also found is that a 100 seconds RC TC, which is very practical for analog, gives pretty good results AND of course this whole discussion only applies to errors caused by the 100 ns pulse jitter and not the 10ns GPS jitter, and it does not apply if you are using the 1Hz offset correction to get each down to 1 ns, etc. This is for the basic GPS tracker that does not use the sawtooth correction. The reason this works is because it is easy enough to get about a 1ns uncertainty for a 1 sec average using the 100 Hz instead of the nearer 100ns uncertainty of the 1 PPS. (Note what I am talking about is Typical performance. Worse case, a couple times a day it has some other problems, that I would love to discuses with you, under an advanced topic, if we can ever get that far) Under another subject, You said in one of your other post that the 100hz is not useful for an XOR phase detector because only one of its edges are known. Sorry, I thought we where above that kind of basic information exchange. I just took it that everyone that cares, knows the 100Hz has to be divided by 2 (using the correct edge) before it is feed to a simple XOR phase detector. So a 100 Hz XOR phase detector runs with 50 Hz square wave inputs and gives out a 100Hz, 50% duty cycle square wave at lock. (And has a very low gain, which is why I don't use it for low frequencies) Warren ___ 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] HP 53131A question
Thanks Magnus and Tom, you clarified more than enough. 73, Antonio I8IOV ___ 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] GPSDO using 100Hz
Mike Neither do I, know how to reply to a post that is. This may be the blind leading the blind and end up in some unknown place. True it would be simpler to use the High freq Osc directly but it would not be accurate. The problem with just using the High freq as you suggested is that it is not at any known, exact or even constant frequency. The divider number can change for each low freq cycle. Example if the master freq was say 0.2520 Hz high then every forth second the divider would add 1 extra divide count and every 500th second it would divide by an additional extra clock time, therefore skipping 11 divides every 500 seconds. Regards, Warren Warren, thanks for the reply. When you say The divider number can change, what oscillator are you referring to? Is this the cheap crystal oscillator in the GPS unit? If so, is it adjusting the timing of the 100Hz pulses the same way as it adjusts the 1PPS? It doesn't seem it could do it any other way. If that's true, how does it do the calculation for each 1Hz message from the GPS decode? Does it put out 100 pulses using the same timing info, and repeat the next cycle with a different timing? Then the sawtooth would be a group of 100 pulses, then another group shifted slightly in phase. Heh - that would be fun for a PLL to track:) Another alternative would be to repeat the calculation for each pulse and shift them according to where they are in the cycle. This would be a much nicer signal for a PLL to work with. It might take a lot of calculations, but I suppose a lookup table would reduce the workload on the processor and leave enough cpu cycles for other tasks. Can you tell if any of the above methods are used in your system? Thanks, Mike Monett ___ 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] Oncore question
Thanks to all those who replie don this subject. I'm using an old VP Oncore purely for timing. The situation where the RTC stops at low voltage but the memory lingers on resulting in the wrong time for the Almanac is a fascinating one of which I was not aware. I may do some experiments to see at what voltage the RTC stops. In the meantime the discussion prompted a baord redesign to find some real estate for a Li cell :-) Thanks again, Morris ___ 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] GPSDO using 100Hz
Mike Neither do I, know how to reply to a post that is. This may be the blind leading the blind and end up in some unknown place. True it would be simpler to use the High freq Osc directly but it would not be accurate. The problem with just using the High freq as you suggested is that it is not at any known, exact or even constant frequency. The divider number can change for each low freq cycle. Example if the master freq was say 0.2520 Hz high then every forth second the divider would add 1 extra divide count and every 500th second it would divide by an additional extra clock time, therefore skipping 11 divides every 500 seconds. Regards, Warren Warren, thanks for the reply. When you say The divider number can change, what oscillator are you referring to? Is this the cheap crystal oscillator in the GPS unit? If so, is it adjusting the timing of the 100Hz pulses the same way as it adjusts the 1PPS? It doesn't seem it could do it any other way. If that's true, how does it do the calculation for each 1Hz message from the GPS decode? Does it put out 100 pulses using the same timing info, and repeat the next cycle with a different timing? Then the sawtooth would be a group of 100 pulses, then another group shifted slightly in phase. Heh - that would be fun for a PLL to track:) Another alternative would be to repeat the calculation for each pulse and shift them according to where they are in the cycle. This would be a much nicer signal for a PLL to work with. It might take a lot of calculations, but I suppose a lookup table would reduce the workload on the processor and leave enough cpu cycles for other tasks. Can you tell if any of the above methods are used in your system? Thanks, Mike Monett Mike Note: I gave you a simple example of why it is not possible to just buffer the High Freq osc . The actual working get a bit more complicated. In short when it is time to give out the next pulse whether it is 1 Hz or 100 Hz It sends it outs as close as possible to the correct time, using some internal clock. What I have seen on the Oncore is that this causes a peak of +- 50ns of jitter. It works the same with the 100Hz or the 1 Hz, both have the same peak to peak rising edge jitter, which is different for each pulse sent. The 1Hz timing error message it sends out has little to do with the 100 Hz timing. And is not relevant when using the 100Hz except for a few advanced alising issues. I hope that answers your questions. Can I ask why the interest? Warren ___ 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] GPSDO using 100Hz
Warren The optimum loop time constant depends on the quality of the local oscillator and the GPS timing receiver timing signals. A time constant of several hours is only useful with a very high quality OCXO. The 100Hz output of an M12+T is phase jerked into alignment with the the second once every second as is the 10kHz output from Jupiter-T GPS receiver. The variable pulse width of the 100Hz (and 10kHz) outputs do no favours to an XOR phase detector, its better to use the leading edges of these signals. When one uses a low resolution phase detector with dither as in the Brooks Shera circuit then making 100 or 10,000 measurements of the phase error every second can, if the dither is of the right form, improve the effective resolution. However surely the timing quantisation error of the leading edges of the 100Hz (or 10kHz) outputs limits the potential improvement? One can do much better with an inexpensive processor with little external hardware other than a high resolution DACX (even that can be implemented in software and hardware within the processor together with a couple of opamps). Bruce ** Bruce It would seem we are now in agreement and on the same track in most areas. B) A time constant of several hours is only useful with a very high quality OCXO. Agree, a High quality Osc needs a long TC or else it will degrade the noise performance. On the other hand if using a short time constant (for whatever reason) there is little need for a high quality OCXO. A short term stable osc will give about the same results. AND if you don't care about short term noise such as when you are only averaging the counts over say an hour or a day, to compare small phase shifts to get very accurate frequency results, then any OSC even the most crappy VCO will do if it is updated fast enough to keep it from skipping counts. B) The variable pulse width of the 100Hz (and 10kHz) outputs do no favours to an XOR phase detector, its better to use the leading edges of these signals. We agree again, That is why they MUST be divided by two first, using the correct edge. B) making 100 or 10,000 measurements of the phase error every second can, if the dither is of the right form, improve the effective resolution. However surely the timing quantisation error of the leading edges of the 100Hz (or 10kHz) outputs limits the potential improvement? Yep, there is a limit to how much improvement is available, It can not get better than perfect. The rule of thumb is the improvement is the square root of the number of samples for random noise. For the non random noise of the 100 Hz the improvement can be anywhere from Zero to 1/number of samples. Typically I'm seeing about a 50 to one improvement, with a worse case of no improvement for short periods lasting under a minute (without the addition of a simple processor) B) One can do much better with an inexpensive processor... I completely agree. One can always do better with something. But my point is One can do 'good enough' for many applications with a lot less. B) with little external hardware other than a high resolution DAC (even that can be implemented in software and hardware within the processor together with a couple of opamps). Don't even need that much, most of the time, by providing a seldom changed course adjustment along with the fine adjustment. Warren ___ 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] GPSDO using 100Hz
WarrenS wrote: Bruce It would seem we are now in agreement and on the same track in most areas. We probably always have been, but this certainly wasn't clear from the original posting. B) A time constant of several hours is only useful with a very high quality OCXO. Agree, a High quality Osc needs a long TC or else it will degrade the noise performance. On the other hand if using a short time constant (for whatever reason) there is little need for a high quality OCXO. A short term stable osc will give about the same results. AND if you don't care about short term noise such as when you are only averaging the counts over say an hour or a day, to compare small phase shifts to get very accurate frequency results, then any OSC even the most crappy VCO will do if it is updated fast enough to keep it from skipping counts. B) The variable pulse width of the 100Hz (and 10kHz) outputs do no favours to an XOR phase detector, its better to use the leading edges of these signals. We agree again, That is why they MUST be divided by two first, using the correct edge. It is very important to give such detail on this list as the knowledge/experience of the list members varies so widely. The last thing one wants to happen is for someone to blindly rush ahead and use an XOR phase detector without first dividing the the 100Hz or 10kHz by 2 and then wonder why the performance isnt that good. Providing such detail also engenders more confidence in the soundness of the method. B) making 100 or 10,000 measurements of the phase error every second can, if the dither is of the right form, improve the effective resolution. However surely the timing quantisation error of the leading edges of the 100Hz (or 10kHz) outputs limits the potential improvement? Yep, there is a limit to how much improvement is available, It can not get better than perfect. The rule of thumb is the improvement is the square root of the number of samples for random noise. For the non random noise of the 100 Hz the improvement can be anywhere from Zero to 1/number of samples. Typically I'm seeing about a 50 to one improvement, with a worse case of no improvement for short periods lasting under a minute (without the addition of a simple processor) If the phase error counter clock should ever injection lock to the OCXO or the GPS timing receiver output, then the averaging will fail. If this clock is sufficiently noisy or is phase dithered sufficiently with random noise then this wont happen. B) One can do much better with an inexpensive processor... I completely agree. One can always do better with something. But my point is One can do 'good enough' for many applications with a lot less. B) with little external hardware other than a high resolution DAC (even that can be implemented in software and hardware within the processor together with a couple of opamps). Don't even need that much, most of the time, by providing a seldom changed course adjustment along with the fine adjustment. Warren Bruce ___ 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] GPSDO using 100Hz
Bruce wrote: Analog time constants of several hours are generally considered impractical due to the lack of suitable low noise components principally high value resistors and capacitors. So how do you propose to get around this with an analog control loop? Bruce Not that I'm recommending this approach, but for general info, Digikey sells a 1 Farad 5.5V cap for about $7.00CAD in singles: http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=131084;keywords=1%20farad A time constant of 1 hr would need a 3.6k resistor. That's not bad. I have some 5 Farad caps that might be even better. The typical leakage spec for electrolytics is I = K * C * V where C = capacitance in Farads V = applied voltage K = 0.002 for low leakage electrolytic caps, 0.02 for standard I have measured K values of 7e-7 for double layer caps. This is much, much better than any electrolytic I have ever seen. This enabled some advanced silver ion generators using differentiation that could not be done with electrolytics. The typical frequency response rolls off above a few hundred Hz. This is of little consequence in timing circuits intended for several hours duration. But I'd go with a digital approach for a low frequency PLL. Mike Monett ___ 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] GPSDO using 100Hz
B) The variable pulse width of the 100Hz (and 10kHz) outputs do no favours to an XOR phase detector, its better to use the leading edges of these signals. We agree again, That is why they MUST be divided by two first, using the correct edge. I'm not convinced that would cure the problem. Yes, it would correct for pulses that weren't a perfect 1:1 mark-space ratio, but assuming the shape is constant, surely that isn't a problem? However, when a +/- 50ns step was inserted, surely the effect of that would at best be halved by dividing the 100Hz by two? Peter Vince ___ 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] GPSDO using 100Hz
Mike Note: I gave you a simple example of why it is not possible to just buffer the High Freq osc . The actual working get a bit more complicated. In short when it is time to give out the next pulse whether it is 1 Hz or 100 Hz It sends it outs as close as possible to the correct time, using some internal clock. What I have seen on the Oncore is that this causes a peak of +- 50ns of jitter. It works the same with the 100Hz or the 1 Hz, both have the same peak to peak rising edge jitter, which is different for each pulse sent. The 1Hz timing error message it sends out has little to do with the 100 Hz timing. And is not relevant when using the 100Hz except for a few advanced alising issues. I hope that answers your questions. Can I ask why the interest? Warren Ok, it seems they are calculating the best time for each 100Hz pulse individually. That makes life a bit easier for a PLL. My interest is I have a totally new way of locking to the 1PPS pulse that should improve the performance dramatically. The question is would it also work with a 100Hz signal. The answer is yes. It would also work with a 10KHz signal, but this would require a bit more horsepower. I was planning on using a simple inexpensive microprocessor for everything but I don't know if it would be fast enough to do 10KHz. But there's not many of those around anymore, are there? Best Regards, Mike Monett ___ 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] GPSDO using 100Hz
Mike Monett wrote: Warren Ok, it seems they are calculating the best time for each 100Hz pulse individually. That makes life a bit easier for a PLL. Not according to the datasheets which imply the phase of the 100Hz (or 10kHz) burst is adjusted once per second. This should be very easy to verify if the leading edges of individual pulses are time stamped with sufficient resolution. My interest is I have a totally new way of locking to the 1PPS pulse that should improve the performance dramatically. The question is would it also work with a 100Hz signal. The answer is yes. It would also work with a 10KHz signal, but this would require a bit more horsepower. I was planning on using a simple inexpensive microprocessor for everything but I don't know if it would be fast enough to do 10KHz. But there's not many of those around anymore, are there? Best Regards, Mike Monett Bruce ___ 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] GPSDO using 100Hz
Peter Vince wrote: B) The variable pulse width of the 100Hz (and 10kHz) outputs do no favours to an XOR phase detector, its better to use the leading edges of these signals. We agree again, That is why they MUST be divided by two first, using the correct edge. I'm not convinced that would cure the problem. Yes, it would correct for pulses that weren't a perfect 1:1 mark-space ratio, but assuming the shape is constant, surely that isn't a problem? However, when a +/- 50ns step was inserted, surely the effect of that would at best be halved by dividing the 100Hz by two? Peter Vince Not so as only the divide by 2 transition that occurs on the second will have its delay with respect to the previous transition adjusted by 50ns. The subsequent 99 transitions (or transitions with 10kHz output) will occur at intervals of 10ms (or 100uS with 10kHz output). The pulse duty cycle isn't necessarily constant (datasheet specs for the pulse width tend to be somewhat ambiguous) and usually the pulse width of the pulse preceding the second differs. The spec for the M12+T is: The 100Hz pulses are high for a period of 2-3ms in duration except for the pulse that immediately preceding the second which is 6-7 ms in duration. A 1millisec tolerance in pulse width is comparatively large. A pulse width variation of 1ms or so should be relatively easy to measure. Bruce ___ 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] GPSDO using 100Hz
Bruce My Oncore's phase is definitely different on each 100Hz cycle. A digital storage scope shows it very well. Some things that come to mine: 1) Not all Oncores are the same, mine is an old 8 channel one. (Don't remember the number, it is the one with the sawtooth capability) 2) The actual error amount is updated each 1 sec and the processors still dithers that to get the 100 Hz to be close to the correct value 3) Other TBD Warren *** Mike Monett wrote: Warren Ok, it seems they are calculating the best time for each 100Hz pulse individually. That makes life a bit easier for a PLL. Not according to the datasheets which imply the phase of the 100Hz (or 10kHz) burst is adjusted once per second. This should be very easy to verify if the leading edges of individual pulses are time stamped with sufficient resolution. My interest is I have a totally new way of locking to the 1PPS pulse that should improve the performance dramatically. The question is would it also work with a 100Hz signal. The answer is yes. It would also work with a 10KHz signal, but this would require a bit more horsepower. I was planning on using a simple inexpensive microprocessor for everything but I don't know if it would be fast enough to do 10KHz. But there's not many of those around anymore, are there? Best Regards, Mike Monett Bruce ___ 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] GPSDO using 100Hz
Besides asking if anyone is using the 100Hz output, I would like to ask why don't the generally available GPSDO use the 100Hz, which can give about 1 ns of certainly with a simple PLL and analog RC filter, instead of the using the 1 sec which has more like 100 ns of uncorrected uncertainty in it and must use a processor? Where do you get your 1 ns and 100 ns figures? Have you actually measured these values? Also, over what time average (tau) are you assuming this level of resolution? Also I should comment that on LeapSecond.com http://www.leapsecond.com/pages/gpsdo/ you stated where the ADEV for various GPSDO remains below 1E-11 over the Tau range of [0.1s, 100,000s]. This Tau has NOTHING to do with the tracking time constant that the GPSDO is set to, which is usually recommended to be set for a TC of several hours for optimal results. For ideal results start with the TC = the tau where the ADEV of the GPS engine phase detector crosses the ADEV of the OCXO. However there are other practical considerations. BTW most of what they have plotted is the results of NOT setting the GPSDO tracking TC slow enough. This is why the Allan Deviation increases in the tracking mode at mid averaging times. The 1 second GPS tracking signal is adding noise, which pretty much makes my point that 1 PPS signal is not so good to use if you want good fast results. Warren At short averaging intervals when there is a phase difference it is easy for the GPSDO to assume the OCXO is stable and the GPS engine has noise. So you average more samples. At long averaging intervals when there is a phase difference is it easy for the GPSDO to assume the GPS engine is more correct and the OCXO has drifted. So you steer using EFC. At the tau of the ideal TC, the GPSDO sees an average phase difference but can't totally blame either the OCXO or GPS for the error. By definition at this tau, half the noise is due to each subsystem. Hence you nearly always see an ADEV hump that goes above where you'd really like it. Best case sqrt(2). The ADEV hump itself is not indication of a mistuned TC; it is an indication that the GPSDO is working correctly. You can move the hump left and right and distort its shape by changing the TC. In practice I suspect most commercial GPSDO have a TC that appears too low for your liking. I can discuss why if you wish. /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] GPSDO using 100Hz
WarrenS wrote: Bruce My Oncore's phase is definitely different on each 100Hz cycle. A digital storage scope shows it very well. Some things that come to mine: 1) Not all Oncores are the same, mine is an old 8 channel one. (Don't remember the number, it is the one with the sawtooth capability) 2) The actual error amount is updated each 1 sec and the processors still dithers that to get the 100 Hz to be close to the correct value 3) Other TBD Warren *** Warren This raises some questions on the interpreatation of the M12+T and Jupiter-T receiver specs. Some measurements are required in order to settle the questions once and for all. Can anyone that has either or both of these receivers make the required measurements? I have both receivers, but no way of making the required measurements (timestamping the leading edge transitions of the 100Hz or 10kHz edges using a digital scope or other means). Bruce ___ 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] 10 MHz over optical fiber?
Marco IK1ODO -2 skrev: Hi all, I have to carry a 10 MHz standard frequency signal inside an EMC screened room via fiber optic cable. Not willing to re-invent the wheel, do something like an optical standard frequency link exist on the market? Yes. I know of several commecial systems. If you only need to do a short jump, then using fairly basic E/O-O/E equipment should work well enought. It all depends if you want/can to roll your own or need to buy a finished product (aka buy this, and you will be fine!). Stay of plastic fiber if you can. Go multimode at least. I think it is possible to use standard 100MB LAN transceivers, and POF. Phase noise requirements are not very stringent, and the distance is in the order of some tens of meters. 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] GPSDO using 100Hz
Bruce wrote: Analog time constants of several hours are generally considered impractical due to the lack of suitable low noise components principally high value resistors and capacitors. So how do you propose to get around this with an analog control loop? Not too many years ago, high-impedance op-amps and teflon capacitors were the way to do this. The op-amp companies had application notes discussing soakage/dielectric absorption in these circuits. 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.
Re: [time-nuts] 10 MHz over optical fiber?
Yes. I know of several commecial systems. If you only need to do a short jump, then using fairly basic E/O-O/E equipment should work well enought. It all depends if you want/can to roll your own or need to buy a finished product (aka buy this, and you will be fine!). Magnus, what's the typical noise floor, tempco or drift of cheap (i.e., non JPL-level) fiber distribution systems like this? Is it less than regular coax, or phase stabilized heliax? At 100 m lengths? /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] GPSDO using 100Hz
This raises some questions on the interpreatation of the M12+T and Jupiter-T receiver specs. Some measurements are required in order to settle the questions once and for all. Can anyone that has either or both of these receivers make the required measurements? We know the sawtooth correction message only comes once a second, for both receivers, right? That may be a clue. /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] GPSDO using 100Hz
Warren, This is what I believe, feel free to set me straight :-) The 100Hz is done by synthesis from the GPS receiver's crystal oscillator, which is usually not on a harmonic of 100Hz, at least not precisely (cheap crystal) so the receiver will usually generate each pulse to the best of it's ability to line up to 100Hz (so these will have somewhat deterministic jitter due to the difference between 100Hz and the divided crystal), and only once per second will try to align the average pulse train to GPS. There is pure jitter 99 times out of a hundred, and actual correction the 1/100 time. The advantage is that the once-per-second correction is burried under (spread by would be a better term) a fair amount of 100Hz noise, so it's probably easier to filter, allowing the use of a faster filter than a 1 PPS output for the same level of 1 PPS attenuation. You can't use the scope to determine if the jitter is pure jitter or a GPS correction, but I bet a TIC feeding a PC would. The point is that older receivers in particular simply don't have the horseower to update the timing solutions 100 times/second, or 10,000 times per second. Didier KO4BB -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of WarrenS Sent: Monday, November 24, 2008 6:48 PM To: Discussion of precise time and frequency measurement Subject: [time-nuts] GPSDO using 100Hz Bruce My Oncore's phase is definitely different on each 100Hz cycle. A digital storage scope shows it very well. Some things that come to mine: 1) Not all Oncores are the same, mine is an old 8 channel one. (Don't remember the number, it is the one with the sawtooth capability) 2) The actual error amount is updated each 1 sec and the processors still dithers that to get the 100 Hz to be close to the correct value 3) Other TBD Warren *** Mike Monett wrote: Warren Ok, it seems they are calculating the best time for each 100Hz pulse individually. That makes life a bit easier for a PLL. Not according to the datasheets which imply the phase of the 100Hz (or 10kHz) burst is adjusted once per second. This should be very easy to verify if the leading edges of individual pulses are time stamped with sufficient resolution. My interest is I have a totally new way of locking to the 1PPS pulse that should improve the performance dramatically. The question is would it also work with a 100Hz signal. The answer is yes. It would also work with a 10KHz signal, but this would require a bit more horsepower. I was planning on using a simple inexpensive microprocessor for everything but I don't know if it would be fast enough to do 10KHz. But there's not many of those around anymore, are there? Best Regards, Mike Monett Bruce ___ 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. -- No virus found in this incoming message. Checked by AVG. Version: 7.5.549 / Virus Database: 270.9.9/1809 - Release Date: 11/24/2008 9:03 AM ___ 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] 10 MHz over optical fiber?
Hi; This may fit your needs, Wenzel made a 10MHz reference that was disciplined thru fiber. I am currently using one. It could be easily modified to use battery power. It had very low phase noise. Thomas Knox NIST 4475 Whitney Place Boulder Colorado 80305 1-303-554-0307 [EMAIL PROTECTED] Quoting Magnus Danielson [EMAIL PROTECTED]: Marco IK1ODO -2 skrev: Hi all, I have to carry a 10 MHz standard frequency signal inside an EMC screened room via fiber optic cable. Not willing to re-invent the wheel, do something like an optical standard frequency link exist on the market? Yes. I know of several commecial systems. If you only need to do a short jump, then using fairly basic E/O-O/E equipment should work well enought. It all depends if you want/can to roll your own or need to buy a finished product (aka buy this, and you will be fine!). Stay of plastic fiber if you can. Go multimode at least. I think it is possible to use standard 100MB LAN transceivers, and POF. Phase noise requirements are not very stringent, and the distance is in the order of some tens of meters. 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. ___ 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] GPSDO using 100Hz
Tom Van Baak wrote: This raises some questions on the interpreatation of the M12+T and Jupiter-T receiver specs. Some measurements are required in order to settle the questions once and for all. Can anyone that has either or both of these receivers make the required measurements? We know the sawtooth correction message only comes once a second, for both receivers, right? That may be a clue. /tvb Tom The picket fence technique can be used to timestamp the leading edges of the 100Hz (or 10kHz for the Jupiter -T) outputs. The 100Hz signal being used to start the TIC whilst a 1kHz signal derived from a low noise OCXO output is used to STOP the TIC. Sawtooth error should then be able to be derived from the measurements after removing phase wraps. ADEV could then be plotted for Tau ranging from 10ms to say 100s. With a 10KHz signal the STOP input frequency would need to be around 100KHz or so. Any known frequency = 2*(Start frequency) will suffice. Bruce ___ 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] GPSDO using 100Hz
Warren Answers and comments to /tvb below in the text. Besides asking if anyone is using the 100Hz output, I would like to ask why don't the generally available GPSDO use the 100Hz, which can give about 1 ns of certainly with a simple PLL and analog RC filter, instead of the using the 1 sec which has more like 100 ns of uncorrected uncertainty in it and must use a processor? Where do you get your 1 ns and 100 ns figures? Have you actually measured these values? Also, over what time average (tau) are you assuming this level of resolution? 1 ns and 100ns are measured Values of the nominal phase Jitter over a few seconds. Long enough to let the Phase cycle thru a couple of its sawtooth cycles, and short enough so as not to include the added GSP signal errors. The values are pretty much independent of time, as long as the time is not too long or too short. The GPS signal errors that I see are around 10 ns over about a 10 + seconds period, with short excursions (no more than a few seconds) of up to an additional to 30 ns. Also I should comment that on LeapSecond.com http://www.leapsecond.com/pages/gpsdo/ you stated where the ADEV for various GPSDO remains below 1E-11 over the Tau range of [0.1s, 100,000s]. This Tau has NOTHING to do with the tracking time constant that the GPSDO is set to, which is usually recommended to be set for a TC of several hours for optimal results. For ideal results start with the TC = the tau where the ADEV of the GPS engine phase detector crosses the ADEV of the OCXO. However there are other practical considerations. Yes we agree on this, and this is somewhere between an hour and a day for good osc. (and as short as a few seconds for some special applications). BTW most of what they have plotted is the results of NOT setting the GPSDO tracking TC slow enough. This is why the Allan Deviation increases in the tracking mode at mid averaging times. The 1 second GPS tracking signal is adding noise, which pretty much makes my point that 1 PPS signal is not so good to use if you want good fast results. Warren At short averaging intervals when there is a phase difference it is easy for the GPSDO to assume the OCXO is stable and the GPS engine has noise. So you average more samples. At long averaging intervals when there is a phase difference is it easy for the GPSDO to assume the GPS engine is more correct and the OCXO has drifted. So you steer using EFC. At the tau of the ideal TC, the GPSDO sees an average phase difference but can't totally blame either the OCXO or GPS for the error. By definition at this tau, half the noise is due to each subsystem. Hence you nearly always see an ADEV hump that goes above where you'd really like it. Best case sqrt(2). The ADEV hump itself is not indication of a mistuned TC; it is an indication that the GPSDO is working correctly. You can move the hump left and right and distort its shape by changing the TC. In practice I suspect most commercial GPSDO have a TC that appears too low for your liking. I can discuss why if you wish. /tvb Thanks, Good information to remember. Note that in many of the units shown, the tracking hump is more like 4 to one instead of 1.5 to one. I would love to know the 'can Discuss more' reasons Warren ___ 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] GPSDO using 100Hz
Tom Van Baak wrote: This raises some questions on the interpreatation of the M12+T and Jupiter-T receiver specs. Some measurements are required in order to settle the questions once and for all. Can anyone that has either or both of these receivers make the required measurements? We know the sawtooth correction message only comes once a second, for both receivers, right? That may be a clue. /tvb Tom The picket fence technique can be used to timestamp the leading edges of the 100Hz (or 10kHz for the Jupiter -T) outputs. The 100Hz signal being used to start the TIC whilst a 1kHz signal derived from a low noise OCXO output is used to STOP the TIC. Sawtooth error should then be able to be derived from the measurements after removing phase wraps. ADEV could then be plotted for Tau ranging from 10ms to say 100s. With a 10KHz signal the STOP input frequency would need to be around 100KHz or so. Any known frequency = 2*(Start frequency) will suffice. Bruce Bruce OR on the 100Hz signal, not the 10Khz, can I use a digital scope that can log data time values between say the rise time and a marker, for each sweep. For the most part, the phase jitter on for the Oncore can be seen easily at 100 Hz output by just waiting until the sawtooth jitter frequency is down to below about 5 Hz. Something else you said, I did not know was that the 100rd pulse is time stamped by extending it length, Something I've always seen, but did not know the extended time was anything more than random. Next time I have it scoped, I'll check and see if the 1 Hz reported error is for that pulse while in the 100 Hz mode. Warren ___ 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.
