[time-nuts] Rubidium Cesium video
For those of you who are both chemists and time nuts, here's an amazing video about rubidium and cesium... http://video.google.com/videoplay?docid=-2134266654801392897 Do any of the UK readers know the background to this? /tvb ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Rubidium Cesium video
At 11:18 PM -0700 10/28/06, Tom Van Baak wrote: For those of you who are both chemists and time nuts, here's an amazing video about rubidium and cesium... http://video.google.com/videoplay?docid=-2134266654801392897 Do any of the UK readers know the background to this? /tvb Marvelous video! But it's perfectly harmless in a clock, right? Right? -- --David Forbes, Tucson, AZ http://www.cathodecorner.com/ ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] looking for HP 3738A external pin connections or schematic
I believe he means the HP 3783A in the Subject Rob K -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Dr Bruce Griffiths Sent: 28 October 2006 23:46 To: Eric Haskell; Discussion of precise time and frequency measurement Subject: Re: [time-nuts] looking for HP 3738A external pin connections or schematic Eric Haskell wrote: I purchased this item to ebay to play with the YIG. Can anyone help with proper voltages to apply to this unit and which pins they go to? Eric Haskell KC4YOE ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts Eric What item, no link to anything in post?? Bruce ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Halloween
Back to good ol' UTC here in the UK this morning!! -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Bill Hawkins Sent: 29 October 2006 05:42 To: Discussion of precise time and frequency measurement Subject: [time-nuts] Halloween Stumbled on the Rocky Horror Show, which seems to have become timeless. The song Let's do the time warp again seems appropriate for the USA time-change Sunday. It's just a jump to the left, put your hands on your hips, do the pelvic thrust, let's do the time warp again. Something about anticipation, come on up to the lab, let's see what's on the slab ... and so on. Pardon me if it only has a little bit to do with precision time, but it's that time of year. Regards, Bill Hawkins -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.1.408 / Virus Database: 268.13.17/505 - Release Date: 10/27/2006 ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Rubidium Cesium video
Hadn't seen this before. Great stuff!! Presenter is Richard Hammond affectionately known by associates as The Hamster because of his diminutive size. Just out of hospital after crashing a jet powered car at 300+ MPH while filming BBC TV's Top Gear (compulsive viewing and hugely popular programme for car enthusiast). As you say across the pond.. One crazy dude!! Rob Kimberley -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Tom Van Baak Sent: 29 October 2006 06:19 To: Discussion of precise time and frequency measurement Subject: [time-nuts] Rubidium Cesium video For those of you who are both chemists and time nuts, here's an amazing video about rubidium and cesium... http://video.google.com/videoplay?docid=-2134266654801392897 Do any of the UK readers know the background to this? /tvb ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Rubidium Cesium video
Forgot to mention that Brainiacs was a fun science programme for kids that went out a couple of years back in the UK. Rob K -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Tom Van Baak Sent: 29 October 2006 06:19 To: Discussion of precise time and frequency measurement Subject: [time-nuts] Rubidium Cesium video For those of you who are both chemists and time nuts, here's an amazing video about rubidium and cesium... http://video.google.com/videoplay?docid=-2134266654801392897 Do any of the UK readers know the background to this? /tvb ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Rubidium Cesium video
Harmless when you use the right isotope!! Rob K -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of David Forbes Sent: 29 October 2006 07:14 To: time-nuts@febo.com Subject: Re: [time-nuts] Rubidium Cesium video At 11:18 PM -0700 10/28/06, Tom Van Baak wrote: For those of you who are both chemists and time nuts, here's an amazing video about rubidium and cesium... http://video.google.com/videoplay?docid=-2134266654801392897 Do any of the UK readers know the background to this? /tvb Marvelous video! But it's perfectly harmless in a clock, right? Right? -- --David Forbes, Tucson, AZ http://www.cathodecorner.com/ ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] GPS vagaries and binary interface
Didier Juges wrote: Dr Bruce Griffiths wrote: Didier Alternative GPSDO solution Divide the 10MHz reference by 32 resync the output to 10MHz with a fast D flipflop and then divide the D flipflop output by 4 using a 2 bit switchtail ring (Johnson) counter. Low pass filter the outputs of both divide by 4 counter flipflops with identical filters. OK, I follow even if I am not sure where this is leading... Anything magic about 32, other than it's probably the smallest division that may not immediately result in rollover when the OCXO is cold? Based on yesterday's experiment, my OCXO rolled over once while warming up with a division ratio of 128. A few more chips are not a real problem. I like the 74F161, they are fast and synchronous. If I could find 74F162's, that would be the best, or I can program the 161s as decade counters, but it's more work. Use ACMOS flipflops in the ring counter so the sine wave output amplitude is reasonably stable. Of course, TTL outputs are anything but stable. This should produce 2 nominally quadrature sinewave outputs at (10/128) MHz. Use 2 12 bit ADCs (eg AD7942) to sample the 2 quadrature sinewaves on the leading edge of the GPS receiver PPS signal. The ADC readings can be processed to derive the phase angle at the PPS edge. A resolution of 10ns or better is readily achieved. This is more than adequate for most current GPS receivers. If you are worried about the stability of the low pass filter phase shifts just use another pair of ADCs to sample the 2 sinewaves at 10/128 MHz.or a submultiple thereof. The difference between the 2 phase angles will be independent of the filter phase shifts. That would be a software interpolator? I like that approach because it reduces the hardware to a relative minimum, compared to the Brooke Shera approach, and puts the complexity in software. Regarding your next message recommending to use a dual channel ADC, I agree, even though it may be simpler to use SH devices with the built-in multiplexed ADC of the microprocessor. I have a few monolithic Burr Brown devices that have a small aperture gate, I forgot how much. This sounds very interesting, but it won't be an evening project :-) I don't do PICs (no development tools, no code bank). I do not have the tools to do PLDs either. My favorite uCs are 8051s, particularly the Silabs parts. I also have access to a good C compiler and I have written a lot of 8051 code. I do not know how these parts fare as timing chips. They are plenty fast though, some run at a 100 MHz clock, with many instructions taking one clock. Bruce ___ Thanks again for many thought provoking ideas. Didier ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts Didier Nothing too critical about divide by 32. A quadrature phased sinewave pair frequency of about 100 KHz is about the lowest with which its possible to achieve a resolution of better than about 10ns with a relatively inexpensive 12 bit ADC. The period of the reference sinewave has to be large enough to accomodate the GPS receiver PPS jitter and the OCXO wander whilst locked over the loop time constant (~ 1000 sec). Doing PLDs is easy just choose one that can be programmed over a JTAG interface. Bit banging on a PC parallel port can then be used to program the PLD in circuit. A simple interface (1 chip) between the parallel port and the JTAG port is required. That only leaves the software to find. Of course if you forgo correcting for harmonics and dc offset then the logic complexity is reasonably small. Easily implemented using readily available CMOS chips. It doesn't really matter what processor you use as long as its fast enough to do the job with some margin to spare for enhancements. Even the 8051 chips of 25 years ago are probably fast enough. The reason I didn't suggest sample and holds to do the simultaneous sampling is that its difficult to get high performance standalone sample and holds these days. Its just more cost effective to use a pair of ADCs. Bruce ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] GPS vagaries and binary interface
Didier Juges wrote: Dr Bruce Griffiths wrote: Didier Juges wrote: That's the impression I am getting. I do not know if any of the GPSDO that I have seen described in recent literature take care of this properly. It seems when the GPS goes nuts, the 1 PPS goes quite a bit out of normal range, so it should not take too much processing power to determine if it's in range or not. Of course, an analog solution would require many more parts to do that determination, filtering and switching, so it seems the most *practical* way to implement a GPSDO is with a uC of some sort. The uC could even monitor what's coming out of the GPS receiver's serial port and open the loop if there are not enough satellites in range. Didier KO4BB ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts On further reflection a slower 2 channel simultaneous sampling ADC (eg AD7862 200ps aperture delay mismatch, 100ps sampling jitter ) with matched ADC gains and aperture delays is a better fit when sampling the nominally quadrature phased sinewaves. To assist in filtering out spurious data a coarse (1us resolution??) phase derived by sampling a digital counter can be used to detect when the GPS PPS pulse timing deteriorates. When using a timing GPS receiver with TRAIM enabled this elaboration is not necessary. It only remains to measure the quadrature phase error and amplitude mismatch errors of the nominally quadrature phased sinewaves. This can be done by taking a burst of calibration samples triggered by the PPS input (after synchronising it to the reference clock). Equivalent time sampling techniques can be used to take samples with an effective spacing of one reference oscillator period (100ns) throughout the sinewave cycle. A total of 64/128 samples is a sufficient number to allow the dc offset, the amplitude and phase offset of the fundamental, as well as the and amplitudes and phases of the at least the first 16/32 harmonics for each of the 2 nominally quadrature phased waveforms to be determined. Since the processor only need process a few (~100??) samples each second almost anything that can read and process the ADC samples fast enough (1 sample burst /sec) should suffice. Residual ADC distortion, gain mismatch and aperture delay mismatch can be combined with the equivalent sinewave errors, the actual source of these errors doesn't really matter too much as long as their effect on the phase measurements can be corrected. The required logic can easily be implemented using a small programmable gate array or equivalent device. Bruce ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts Bruce, If we AC couple the sinewaves to the ADCs with a common reference at mid-point to the Vref, we should not have to worry too much about the mismatched amplitudes unless they are really far apart, since we are only trying to get the zero crossing. If we have enough samples near that point, the amplitude errors should be negligible. On the other hand, wouldn't time sampling introduce additional errors? As I pointed out in the previous messages, I do not have the tools or the experience with programmable logic. It seems to me that interpolation is probably more easily done in software anyhow (unless you use a fairly large PLD) because of the resources they use, but I may be mistaken. However I need to check if the uC/ADC can run fast enough to make this work. More food for thought, and more research... Didier ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts Didier No we are not looking to sample at the sinewave zero crossing. We are trying to measure the sine wave phase at the sampling instant or equivalently the time from the previous zero crossing to the sampling instant. If we sample the 2 quadrature sinewaves then have two samples Asin(theta), Acos(theta) where theta is the phase angle. The particular quadrant can be determined from the signs of the sine and cosine terms. Then the phase angle is given by the arc tangent of the ratio of the sine and cosine samples. Bruce ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Halloween
Rob Kimberley wrote: Back to good ol' UTC here in the UK this morning!! -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Bill Hawkins Sent: 29 October 2006 05:42 To: Discussion of precise time and frequency measurement Subject: [time-nuts] Halloween Stumbled on the Rocky Horror Show, which seems to have become timeless. The song Let's do the time warp again seems appropriate for the USA time-change Sunday. It's just a jump to the left, put your hands on your hips, do the pelvic thrust, let's do the time warp again. Something about anticipation, come on up to the lab, let's see what's on the slab ... and so on. Pardon me if it only has a little bit to do with precision time, but it's that time of year. Regards, Bill Hawkins -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.1.408 / Virus Database: 268.13.17/505 - Release Date: 10/27/2006 ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts There is a bronze statue (of riffraff?) commemorating this play/film in town (Hamilton NZ) Richard OBrien the author/playwright was born here. Bruce. ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Allan Deviation - more data: GPS1PPS against OCXO/128
Bruce, If GPSDO did some statistical filtering instead of just blindly accepting all PPS signals as valid and usable such dropouts would cease to be much of a problem. There's no substitute for a a correctly engineered design with an appropriate tracking loop bandwidth and statistical filtering of outliers. A good crystal will drift very little over half an hour or so when the GPS derived PPS signal may be unreliable. I have read lots of intelligent stuff from you in the last weeks that makes you a brother in mind, but let me explicitely say THANKS for this one. I have been using robust statistical methods in my own GPSDO design since years now. Every new second I compute the median over some hundred seconds of past phase data and after that i compute the MAD (median absolute deviation) over the same period. The MAD is is a measure for the width of the statistical distribution as is the standard deviation. Unlike the standard deviation, is it completely insensible to outliers itself. 99% of normal data are within +/-5 MAD around the median so once you have performed the math it is really easy to detect outliers. Since the algorithm needs a certain amount of RAM and sheer processing power this is not easily done with single-chip-processors. Thank you for pointing at the fact that sometimes a certain complexity of hardware and software is necessary to get a job done and that the quality of a GPSDO cannot be measured in term of lowcheap parts count as seems to be a quite common opinion. Best regards Ulrich Bangert -Ursprüngliche Nachricht- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Im Auftrag von Dr Bruce Griffiths Gesendet: Samstag, 28. Oktober 2006 23:46 An: [EMAIL PROTECTED]; Discussion of precise time and frequency measurement Betreff: Re: [time-nuts] Allan Deviation - more data: GPS1PPS against OCXO/128 kd7ts wrote: Didier Juges wrote: There are sudden increases in noise (bursts that last from seconds to minutes) on the plots I posted. I believe the sudden and drastic increase in noise at times comes from the GPS loosing lock. At the moment, I cannot hook up the computer to the GPS and verify, but I will do that later. I have a Brooks Shera GPSDO that exhibited similar symptoms. The phase showed huge jumps around 4:00 - 4:30 every morning. The PLL loop might, or might not recover, but usually didn't. I didn't have the time to spend troubleshooting, and we seldom ran tests overnight, so I just lived with it for more than 5 years. I retired recently and finally had the time to devote to finding the problem. It was so easy, it is almost embarassing. I picked up another GPSDO system based on a Jupiter GPS engine and an Isotemp ovenized 10 MHz oscillator with EFC. It was the antenna I purchased to go with this, that turned out to be the useful missing piece of the puzzle. I swapped antennas between the two units to compare the SS numbers reported by the Motorola UT+. They appeared to be about the same, so I swapped them back. This continued for another week or so, and I exhausted all remaining possibilities. I swapped the two patch antennas again, but this time I let it run for a week. I never observed the problem during this time, so I replaced the patch antenna (cheap) with a Symmetricomm antenna that is commonly used on Cell sites. The system has been 100% for about 3 weeks now. I beleve the Symmetricomm antenna has much better filtering, and because it has an N connector, I was able to use a longer cable, with lower loss and better mounting location. Watching the SS numbers reported by the UT+ did not provide any insight. They were generally between 43 and 47 and tracking 8 with the patch antenna. I have been watching the numbers for about 2 weeks with the Symmetricomm antenna connected, and they show between 47 and 52 and tracking 8. I can only speculate on the exact mechanism, but it appears that the system is functioning properly. It is the station reference for 10 and 24 GHz transverters and a DSP-10 IF rig. We have 5 of these GPSDO units in the area, and all I ever heard was, well mine runs just fine ! Mike KD7TS ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts Good timing antennas have built in ceramic or equivalent bandpass filters to minimise the effect of interference. A patch antenna is not as satisfactory as a quadrifilar helix or a choke ring ground plane antenna for accurate timing purposes. If GPSDO did some statistical filtering instead of just blindly accepting all PPS signals as valid and usable such dropouts would cease to be much of a problem. There's no substitute for a a correctly engineered design with an appropriate tracking
Re: [time-nuts] More Allan deviation data
Hi Didier, you may use the DRIFT section of the graphic editor of PLOTTER to remove a phase drift due to a constant frequency offset as seen in this data, with the result that you get more visual resolution out of it, as in the attached PDF. 73 de Ulrich, DF6JB -Ursprüngliche Nachricht- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Im Auftrag von Didier Juges Gesendet: Sonntag, 29. Oktober 2006 06:32 An: !Time Nuts Betreff: [time-nuts] More Allan deviation data I moved the GPS antenna as high as I could in the shack (instead of on a shelf at eye level) and it seems to have significantly improved the signal. Here is the latest plot of the HP10811 against the GPS, unlocked. http://www.ko4bb.com/Test_Equipment/HP10811-GPS-10-29.png (sorry the screen shot is cropped at the bottom) and the data file is at http://www.ko4bb.com/Test_Equipment/HP10811-GPS-10-29.dat Didier KO4BB ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts Counter.pdf Description: Adobe PDF document ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] More Allan deviation data
I had to stack up frequency counters on top of frequency counters (to measure time difference and each input frequency simultaneously - 3 counters) and the last one on the top, a HP 5334B, was fairly high and just about level with the antenna, about 2 feet away. I found out that if I stood in line with the antenna and the counter, my shadow would significantly affect the cleanliness of the 1 PPS, so I moved the antenna just under the ceiling and the problem went away. Amazing! Didier Rob Kimberley wrote: Interesting to know what obstructions you cleared by moving it higher. May have been getting some multipath from something on the antenna's apparent horizon. Rob K ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Rubidium Cesium video
From: Rob Kimberley [EMAIL PROTECTED] Subject: Re: [time-nuts] Rubidium Cesium video Date: Sun, 29 Oct 2006 07:59:04 - Message-ID: ![EMAIL PROTECTED] Harmless when you use the right isotope!! Not entierly. You end up with quite strong base which can cause you severe burns. Toss a piece of Caesium in water and you can etch glas with it. Anyway, you probably want to neutrilize it. In UK will probably heavy showers of acid rain clean things up fairly quickly. :P I still want to know where you can get it. :-) Cheers, Magnus ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Rubidium Cesium video
--- Tom Van Baak [EMAIL PROTECTED] wrote: For those of you who are both chemists and time nuts, here's an amazing video about rubidium and cesium... http://video.google.com/videoplay?docid=-2134266654801392897 Very impressive. Though I read a story somewhere that they faked the results for dramatic effect, for the cameras. /b Access over 1 million songs - Yahoo! Music Unlimited (http://music.yahoo.com/unlimited) ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Rubidium Cesium video
One word: Cool!! John Tom Van Baak said the following on 10/29/2006 01:18 AM: For those of you who are both chemists and time nuts, here's an amazing video about rubidium and cesium... http://video.google.com/videoplay?docid=-2134266654801392897 Do any of the UK readers know the background to this? /tvb ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] GPS vagaries and binary interface
Didier Juges wrote: Dr Bruce Griffiths wrote: Didier Alternative GPSDO solution Divide the 10MHz reference by 32 resync the output to 10MHz with a fast D flipflop and then divide the D flipflop output by 4 using a 2 bit switchtail ring (Johnson) counter. Low pass filter the outputs of both divide by 4 counter flipflops with identical filters. OK, I follow even if I am not sure where this is leading... Anything magic about 32, other than it's probably the smallest division that may not immediately result in rollover when the OCXO is cold? Based on yesterday's experiment, my OCXO rolled over once while warming up with a division ratio of 128. A few more chips are not a real problem. I like the 74F161, they are fast and synchronous. If I could find 74F162's, that would be the best, or I can program the 161s as decade counters, but it's more work. Use ACMOS flipflops in the ring counter so the sine wave output amplitude is reasonably stable. Of course, TTL outputs are anything but stable. This should produce 2 nominally quadrature sinewave outputs at (10/128) MHz. Use 2 12 bit ADCs (eg AD7942) to sample the 2 quadrature sinewaves on the leading edge of the GPS receiver PPS signal. The ADC readings can be processed to derive the phase angle at the PPS edge. A resolution of 10ns or better is readily achieved. This is more than adequate for most current GPS receivers. If you are worried about the stability of the low pass filter phase shifts just use another pair of ADCs to sample the 2 sinewaves at 10/128 MHz.or a submultiple thereof. The difference between the 2 phase angles will be independent of the filter phase shifts. That would be a software interpolator? I like that approach because it reduces the hardware to a relative minimum, compared to the Brooke Shera approach, and puts the complexity in software. Regarding your next message recommending to use a dual channel ADC, I agree, even though it may be simpler to use SH devices with the built-in multiplexed ADC of the microprocessor. I have a few monolithic Burr Brown devices that have a small aperture gate, I forgot how much. This sounds very interesting, but it won't be an evening project :-) I don't do PICs (no development tools, no code bank). I do not have the tools to do PLDs either. My favorite uCs are 8051s, particularly the Silabs parts. I also have access to a good C compiler and I have written a lot of 8051 code. I do not know how these parts fare as timing chips. They are plenty fast though, some run at a 100 MHz clock, with many instructions taking one clock. Bruce ___ Thanks again for many thought provoking ideas. Didier ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts If they have built in hardware to sample the count of a counter on the edge of an external pulse then they may be very useful. Another technique to reduce the amount of filtering required somewhat is to feed a square wave of 50% duty cycle into a shift register say 12 bits long clocked synchronously at 8x the input square wave frequency. The outputs of the first 8 stages can be added using a set of suitable resistors so that a 16 step approximation to a sine wave is formed at the resistor summing node. The quadrature phase sine wave can be formed by resistively summing the outputs of the last 8 stages of the 12 bit shift register. If the resistor values are correctly proportioned the 3rd, 5th etc harmonics can be nulled and less filtering of the sine and cosine waves is required. The approximation to sine and cosine waves improves as the shift register length is increased and the shift register is clocked with a higher frequency synchronous clock. However using 2 sets of 8 resistors with a 12 bit shift register is probably a reasonable compromise between the complexity of the resistor arrays and the complexity of the analog low pass filters. An even better approximation is possible if a pair of DAC and a sine lookup tables is employed. However the added cost and complexity is probably difficult to justify. Bruce ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Allan Deviation - more data: GPS1PPS against OCXO/128
Ulrich Bangert wrote: Bruce, If GPSDO did some statistical filtering instead of just blindly accepting all PPS signals as valid and usable such dropouts would cease to be much of a problem. There's no substitute for a a correctly engineered design with an appropriate tracking loop bandwidth and statistical filtering of outliers. A good crystal will drift very little over half an hour or so when the GPS derived PPS signal may be unreliable. I have read lots of intelligent stuff from you in the last weeks that makes you a brother in mind, but let me explicitely say THANKS for this one. I have been using robust statistical methods in my own GPSDO design since years now. Every new second I compute the median over some hundred seconds of past phase data and after that i compute the MAD (median absolute deviation) over the same period. The MAD is is a measure for the width of the statistical distribution as is the standard deviation. Unlike the standard deviation, is it completely insensible to outliers itself. 99% of normal data are within +/-5 MAD around the median so once you have performed the math it is really easy to detect outliers. Since the algorithm needs a certain amount of RAM and sheer processing power this is not easily done with single-chip-processors. Thank you for pointing at the fact that sometimes a certain complexity of hardware and software is necessary to get a job done and that the quality of a GPSDO cannot be measured in term of lowcheap parts count as seems to be a quite common opinion. Best regards Ulrich Bangert -Ursprüngliche Nachricht- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Im Auftrag von Dr Bruce Griffiths Gesendet: Samstag, 28. Oktober 2006 23:46 An: [EMAIL PROTECTED]; Discussion of precise time and frequency measurement Betreff: Re: [time-nuts] Allan Deviation - more data: GPS1PPS against OCXO/128 kd7ts wrote: Didier Juges wrote: There are sudden increases in noise (bursts that last from seconds to minutes) on the plots I posted. I believe the sudden and drastic increase in noise at times comes from the GPS loosing lock. At the moment, I cannot hook up the computer to the GPS and verify, but I will do that later. I have a Brooks Shera GPSDO that exhibited similar symptoms. The phase showed huge jumps around 4:00 - 4:30 every morning. The PLL loop might, or might not recover, but usually didn't. I didn't have the time to spend troubleshooting, and we seldom ran tests overnight, so I just lived with it for more than 5 years. I retired recently and finally had the time to devote to finding the problem. It was so easy, it is almost embarassing. I picked up another GPSDO system based on a Jupiter GPS engine and an Isotemp ovenized 10 MHz oscillator with EFC. It was the antenna I purchased to go with this, that turned out to be the useful missing piece of the puzzle. I swapped antennas between the two units to compare the SS numbers reported by the Motorola UT+. They appeared to be about the same, so I swapped them back. This continued for another week or so, and I exhausted all remaining possibilities. I swapped the two patch antennas again, but this time I let it run for a week. I never observed the problem during this time, so I replaced the patch antenna (cheap) with a Symmetricomm antenna that is commonly used on Cell sites. The system has been 100% for about 3 weeks now. I beleve the Symmetricomm antenna has much better filtering, and because it has an N connector, I was able to use a longer cable, with lower loss and better mounting location. Watching the SS numbers reported by the UT+ did not provide any insight. They were generally between 43 and 47 and tracking 8 with the patch antenna. I have been watching the numbers for about 2 weeks with the Symmetricomm antenna connected, and they show between 47 and 52 and tracking 8. I can only speculate on the exact mechanism, but it appears that the system is functioning properly. It is the station reference for 10 and 24 GHz transverters and a DSP-10 IF rig. We have 5 of these GPSDO units in the area, and all I ever heard was, well mine runs just fine ! Mike KD7TS ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts Good timing antennas have built in ceramic or equivalent bandpass filters to minimise the effect of interference. A patch antenna is not as satisfactory as a quadrifilar helix or a choke ring ground plane antenna for accurate timing purposes. If GPSDO did some statistical filtering instead of just blindly accepting all PPS signals as valid and usable such dropouts would cease to be much of a problem. There's no substitute for a a correctly
Re: [time-nuts] looking for HP 3738A external pin connections or schematic
I was talking about a HP 3738A which is a YIG LO module for a HP 3730A down converter. However, I apologize, the post is was topic. I meant to post to the Microwave mailing list and was not paying attention. Eric Haskell KC4YOE - Original Message - From: Dr Bruce Griffiths [EMAIL PROTECTED] To: Eric Haskell [EMAIL PROTECTED]; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Saturday, October 28, 2006 4:46 PM Subject: Re: [time-nuts] looking for HP 3738A external pin connections or schematic Eric Haskell wrote: I purchased this item to ebay to play with the YIG. Can anyone help with proper voltages to apply to this unit and which pins they go to? Eric Haskell KC4YOE ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts Eric What item, no link to anything in post?? Bruce ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] More Allan deviation data
Ulrich Bangert wrote: Hi Didier, you may use the DRIFT section of the graphic editor of PLOTTER to remove a phase drift due to a constant frequency offset as seen in this data, with the result that you get more visual resolution out of it, as in the attached PDF. 73 de Ulrich, DF6JB Ulrich, I ran the OCXO with the new antenna location overnight, except that the laptop went to sleep some time in the night, so I have lost several hours of data, which may explain the sudden slope change in the plot below (I need to save timestamps I guess). However, the remaining data is good I think. There was no sudden noise, and about 5 phase jumps due to the OCXO drifting during the observation period. I downloaded the latest version of Plotter (10-27) and it's all there. I was able to quickly remove the phase jumps when the OCXO drifted past the divided down period, and then remove the remaining slow drift. What a nice piece of software! (even the menu now has a *normal* File-Open :-) The latest plots are at the usual place: http://www.ko4bb.com/Test_Equipment/HP10811-GPS_10-29-2.png http://www.ko4bb.com/Test_Equipment/HP10811-GPS_10-29-2_Allan.png Now that the data collection method seems to be getting close, I wonder how I should use the data, and what it means. The Allan deviation seems to taper around e-10 at 1000 seconds, then it looks like it wants to keep getting lower. As a reminder, this is the HP10811 against the GPS receiver. I am not sure what I should expect? Didier PS: I am still planning to measure ambient temperature at the same time as I collect TI, via the GPIB, using a HP 3478A voltmeter and a thermistor. This way, I should be able to correlate frequency changes and temperature changes. I assume I can tell Plotter to ignore the temperature field or display it with its own scaling. Should I use a specific character as field delimiter? (such as a comma, or just spaces?) (In the short term, temperature data will be thermistor values, until I write the code to convert in degrees. ) Also, if I use time stamps, should I use field delimiter between the time stamp and the data? What is the time stamps are discontinuous (as if the laptop falls asleep again), will that mess up Plotter? ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
[time-nuts] Programmable delay 1 ns - 1 msec for sale
I noticed the top item here, in case anybody is interested: http://www.testequipmentcanada.com/new20060705.html W2791 BERKELEY NUCLEONICS 7065-2 MISCDIGITAL DELAY GENERATOR PROGRAMMABLE DELAY OF 1 NANOSEC TO 999.999 MICROSEC 19 5 21 $325.00 (That's canadian dollars) -- 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 https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Rubidium Cesium video
Rasputin Novgorod wrote: --- Tom Van Baak [EMAIL PROTECTED] wrote: For those of you who are both chemists and time nuts, here's an amazing video about rubidium and cesium... http://video.google.com/videoplay?docid=-2134266654801392897 Very impressive. Though I read a story somewhere that they faked the results for dramatic effect, for the cameras. Yep. According to badscience.net they faked the cesium explosion. If the rubidium was real it was definitely impressive. ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Rubidium Cesium video
In message [EMAIL PROTECTED], Gary Chatters writes: For those of you who are both chemists and time nuts, here's an amazing video about rubidium and cesium... http://video.google.com/videoplay?docid=-2134266654801392897 Very impressive. Though I read a story somewhere that they faked the results for dramatic effect, for the cameras. Yep. According to badscience.net they faked the cesium explosion. If the rubidium was real it was definitely impressive. See counter-demonstration here: http://www.theodoregray.com/PeriodicTable/AlkaliBangs/index.html -- 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 https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] More Allan deviation data
Didier, (even the menu now has a *normal* File-Open :-) you take the credit for this! 73 de Ulrich, DF6JB -Ursprüngliche Nachricht- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Im Auftrag von Didier Juges Gesendet: Sonntag, 29. Oktober 2006 15:22 An: Discussion of precise time and frequency measurement Betreff: Re: [time-nuts] More Allan deviation data Ulrich Bangert wrote: Hi Didier, you may use the DRIFT section of the graphic editor of PLOTTER to remove a phase drift due to a constant frequency offset as seen in this data, with the result that you get more visual resolution out of it, as in the attached PDF. 73 de Ulrich, DF6JB Ulrich, I ran the OCXO with the new antenna location overnight, except that the laptop went to sleep some time in the night, so I have lost several hours of data, which may explain the sudden slope change in the plot below (I need to save timestamps I guess). However, the remaining data is good I think. There was no sudden noise, and about 5 phase jumps due to the OCXO drifting during the observation period. I downloaded the latest version of Plotter (10-27) and it's all there. I was able to quickly remove the phase jumps when the OCXO drifted past the divided down period, and then remove the remaining slow drift. What a nice piece of software! (even the menu now has a *normal* File-Open :-) The latest plots are at the usual place: http://www.ko4bb.com/Test_Equipment/HP10811- GPS_10-29-2.png http://www.ko4bb.com/Test_Equipment/HP10811-GPS_10-29-2_Allan.png Now that the data collection method seems to be getting close, I wonder how I should use the data, and what it means. The Allan deviation seems to taper around e-10 at 1000 seconds, then it looks like it wants to keep getting lower. As a reminder, this is the HP10811 against the GPS receiver. I am not sure what I should expect? Didier PS: I am still planning to measure ambient temperature at the same time as I collect TI, via the GPIB, using a HP 3478A voltmeter and a thermistor. This way, I should be able to correlate frequency changes and temperature changes. I assume I can tell Plotter to ignore the temperature field or display it with its own scaling. Should I use a specific character as field delimiter? (such as a comma, or just spaces?) (In the short term, temperature data will be thermistor values, until I write the code to convert in degrees. ) Also, if I use time stamps, should I use field delimiter between the time stamp and the data? What is the time stamps are discontinuous (as if the laptop falls asleep again), will that mess up Plotter? ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Allan Deviation - moredata: GPS1PPS against OCXO/128
Hi Bruce, I read your paper in the AMSAT Journal and believe that an English translation of this would be very informative to those who cant read German. Please allow me to ask: Did you get it from my homepage or did you have a printed version of it?? Best regards Ulrich Bangert -Ursprüngliche Nachricht- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Im Auftrag von Dr Bruce Griffiths Gesendet: Sonntag, 29. Oktober 2006 14:37 An: Discussion of precise time and frequency measurement Betreff: Re: [time-nuts] Allan Deviation - moredata: GPS1PPS against OCXO/128 Ulrich Bangert wrote: Bruce, If GPSDO did some statistical filtering instead of just blindly accepting all PPS signals as valid and usable such dropouts would cease to be much of a problem. There's no substitute for a a correctly engineered design with an appropriate tracking loop bandwidth and statistical filtering of outliers. A good crystal will drift very little over half an hour or so when the GPS derived PPS signal may be unreliable. I have read lots of intelligent stuff from you in the last weeks that makes you a brother in mind, but let me explicitely say THANKS for this one. I have been using robust statistical methods in my own GPSDO design since years now. Every new second I compute the median over some hundred seconds of past phase data and after that i compute the MAD (median absolute deviation) over the same period. The MAD is is a measure for the width of the statistical distribution as is the standard deviation. Unlike the standard deviation, is it completely insensible to outliers itself. 99% of normal data are within +/-5 MAD around the median so once you have performed the math it is really easy to detect outliers. Since the algorithm needs a certain amount of RAM and sheer processing power this is not easily done with single-chip-processors. Thank you for pointing at the fact that sometimes a certain complexity of hardware and software is necessary to get a job done and that the quality of a GPSDO cannot be measured in term of lowcheap parts count as seems to be a quite common opinion. Best regards Ulrich Bangert -Ursprüngliche Nachricht- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Im Auftrag von Dr Bruce Griffiths Gesendet: Samstag, 28. Oktober 2006 23:46 An: [EMAIL PROTECTED]; Discussion of precise time and frequency measurement Betreff: Re: [time-nuts] Allan Deviation - more data: GPS1PPS against OCXO/128 kd7ts wrote: Didier Juges wrote: There are sudden increases in noise (bursts that last from seconds to minutes) on the plots I posted. I believe the sudden and drastic increase in noise at times comes from the GPS loosing lock. At the moment, I cannot hook up the computer to the GPS and verify, but I will do that later. I have a Brooks Shera GPSDO that exhibited similar symptoms. The phase showed huge jumps around 4:00 - 4:30 every morning. The PLL loop might, or might not recover, but usually didn't. I didn't have the time to spend troubleshooting, and we seldom ran tests overnight, so I just lived with it for more than 5 years. I retired recently and finally had the time to devote to finding the problem. It was so easy, it is almost embarassing. I picked up another GPSDO system based on a Jupiter GPS engine and an Isotemp ovenized 10 MHz oscillator with EFC. It was the antenna I purchased to go with this, that turned out to be the useful missing piece of the puzzle. I swapped antennas between the two units to compare the SS numbers reported by the Motorola UT+. They appeared to be about the same, so I swapped them back. This continued for another week or so, and I exhausted all remaining possibilities. I swapped the two patch antennas again, but this time I let it run for a week. I never observed the problem during this time, so I replaced the patch antenna (cheap) with a Symmetricomm antenna that is commonly used on Cell sites. The system has been 100% for about 3 weeks now. I beleve the Symmetricomm antenna has much better filtering, and because it has an N connector, I was able to use a longer cable, with lower loss and better mounting location. Watching the SS numbers reported by the UT+ did not provide any insight. They were generally between 43 and 47 and tracking 8 with the patch antenna. I have been watching the numbers for about 2 weeks with the Symmetricomm antenna connected, and they show between 47 and 52 and tracking 8. I can only speculate on the exact mechanism, but it appears that the system is functioning properly. It is the station reference for 10 and 24 GHz transverters and a DSP-10 IF rig.
Re: [time-nuts] Programmable delay 1 ns - 1 msec for sale
Please see their home page. W.J. Ford closed for business on Oct First. There is a link to an auction outfit. Bill Hawkins -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Poul-Henning Kamp Sent: Sunday, October 29, 2006 12:50 PM To: time-nuts@febo.com Subject: [time-nuts] Programmable delay 1 ns - 1 msec for sale I noticed the top item here, in case anybody is interested: http://www.testequipmentcanada.com/new20060705.html W2791 BERKELEY NUCLEONICS 7065-2 MISCDIGITAL DELAY GENERATOR PROGRAMMABLE DELAY OF 1 NANOSEC TO 999.999 MICROSEC 19 5 21 $325.00 (That's canadian dollars) -- 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 https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Allan Deviation - moredata: GPS1PPS against OCXO/128
Ulrich Bangert wrote: Hi Bruce, I read your paper in the AMSAT Journal and believe that an English translation of this would be very informative to those who cant read German. Please allow me to ask: Did you get it from my homepage or did you have a printed version of it?? Best regards Ulrich Bangert -Ursprüngliche Nachricht- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Im Auftrag von Dr Bruce Griffiths Gesendet: Sonntag, 29. Oktober 2006 14:37 An: Discussion of precise time and frequency measurement Betreff: Re: [time-nuts] Allan Deviation - moredata: GPS1PPS against OCXO/128 Ulrich Bangert wrote: Bruce, If GPSDO did some statistical filtering instead of just blindly accepting all PPS signals as valid and usable such dropouts would cease to be much of a problem. There's no substitute for a a correctly engineered design with an appropriate tracking loop bandwidth and statistical filtering of outliers. A good crystal will drift very little over half an hour or so when the GPS derived PPS signal may be unreliable. I have read lots of intelligent stuff from you in the last weeks that makes you a brother in mind, but let me explicitely say THANKS for this one. I have been using robust statistical methods in my own GPSDO design since years now. Every new second I compute the median over some hundred seconds of past phase data and after that i compute the MAD (median absolute deviation) over the same period. The MAD is is a measure for the width of the statistical distribution as is the standard deviation. Unlike the standard deviation, is it completely insensible to outliers itself. 99% of normal data are within +/-5 MAD around the median so once you have performed the math it is really easy to detect outliers. Since the algorithm needs a certain amount of RAM and sheer processing power this is not easily done with single-chip-processors. Thank you for pointing at the fact that sometimes a certain complexity of hardware and software is necessary to get a job done and that the quality of a GPSDO cannot be measured in term of lowcheap parts count as seems to be a quite common opinion. Best regards Ulrich Bangert -Ursprüngliche Nachricht- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Im Auftrag von Dr Bruce Griffiths Gesendet: Samstag, 28. Oktober 2006 23:46 An: [EMAIL PROTECTED]; Discussion of precise time and frequency measurement Betreff: Re: [time-nuts] Allan Deviation - more data: GPS1PPS against OCXO/128 kd7ts wrote: Didier Juges wrote: There are sudden increases in noise (bursts that last from seconds to minutes) on the plots I posted. I believe the sudden and drastic increase in noise at times comes from the GPS loosing lock. At the moment, I cannot hook up the computer to the GPS and verify, but I will do that later. I have a Brooks Shera GPSDO that exhibited similar symptoms. The phase showed huge jumps around 4:00 - 4:30 every morning. The PLL loop might, or might not recover, but usually didn't. I didn't have the time to spend troubleshooting, and we seldom ran tests overnight, so I just lived with it for more than 5 years. I retired recently and finally had the time to devote to finding the problem. It was so easy, it is almost embarassing. I picked up another GPSDO system based on a Jupiter GPS engine and an Isotemp ovenized 10 MHz oscillator with EFC. It was the antenna I purchased to go with this, that turned out to be the useful missing piece of the puzzle. I swapped antennas between the two units to compare the SS numbers reported by the Motorola UT+. They appeared to be about the same, so I swapped them back. This continued for another week or so, and I exhausted all remaining possibilities. I swapped the two patch antennas again, but this time I let it run for a week. I never observed the problem during this time, so I replaced the patch antenna (cheap) with a Symmetricomm antenna that is commonly used on Cell sites. The system has been 100% for about 3 weeks now. I beleve the Symmetricomm antenna has much better filtering, and because it has an N connector, I was able to use a longer cable, with lower loss and better mounting location. Watching the SS numbers reported by the UT+ did not provide any insight. They were generally between 43 and 47 and tracking 8 with the patch antenna. I have been watching the numbers for about 2
