Re: [time-nuts] DIY FE-5680A lobotomy (disable temp compensation)
Is a heatpipe really appropriate for this application? The heatpipe expects that the heat source wants to burn up and so there's lots of heat available to vaporize the liquid in the pipe. It's not clear to me whether that situation exists with these Rb standards. My tests with an FE-5680A showed a maximum temperature of about 62C without a heatsink. That's far lower than a CPU or GPU. Some of them run at that temperature *with* the heatpipe. I think that a heatsink/fan (maybe from a video card) equipped with a PWM controller might be a better fit. Many of those combinations have a ducted fan to provide better control of the airflow. That would reduce the effects of drafts and convection. One nuisance with using a video card heatsink is that the back side typically has a raised area that contacts the GPU. For this application you'd have to have a flat back over the entire heatsink. Ed On 8/18/2014 6:58 PM, Angus wrote: On Fri, 04 Jul 2014 02:35:41 +0100, you wrote: Hi Bert, I am thinking about testing a heat pipe on a fan cooled setup I use. The first temp controlled chassis I did used a peltier and works very well, but was a lot more work to do and is much more power hungry. The main problem I find is not the temp controller itself, but rather the change in the temperature across the chassis as the ambient changes. However good the temp controller is, it only controls a single point, but other points further away from the sensing thermistor can vary a lot. I noticed you posted a picture of a heat pipe cooler a couple of weeks ago - did you happen to compare the temperature across the unit with direct fan cooling and the heat pipe cooler, or with different heat pipes? Angus. I finally got around to playing with a couple of laptop heat pipes, fixed to a 25x50x75mm block of aluminium which is fixed to the 12mm thick baseplate. On a quick test of it, a sensor near the end of the baseplate showed 1.5-2x greater variation with temperature compared with just having a fan blow directly onto the baseplate. The oscillator also had to be allowed to run a few degrees C hotter for the heatpipe coolers to work to the same max ambient temp. One cooler had two heatpipes with about 12cm between the aluminium block and the heatsink fins (cast in this case) The other had a single, wider heat pipe with about 5cm between the block and the heatsink (this time with a lot more fine fins) The second cooler was rather more efficient, allowing a extra degreee of cooling at the top end, but more problematic was that it entered 'bang-bang' mode with the analogue temperature controller even sooner, and the temperature fluctuations there were greater. Both were rather worse than with the fan just blowing onto the baseplate. Using a PWM fan controller would help a good bit, but getting more creative with a microcontroller would be better. That way you can give the fan a minimum of a small kick every so often, and vary the repetition rate as well as the duty cycle as more cooling is needed. With feedback from the fan and even air temperature monitoring, you could get a good idea of exactly how much cooling was being applied. Another problem is that the overall temp control range is lower with the coolers - barely 8-9 DegC compared with 12+ DegC with the fan blowing directly on the baseplate. That's mainly the result of the poorer cooling at the top end of the range. The Rb osc fitted during this test was a SA.22c which takes a good bit less power than a 5680A, and the fan blowing onto the baseplate was normally a 60mm one fitted about 50mm away from it. The baseplate was horizontal with the fan blowing onto it from below. Maybe fitting a heatsink directly onto the base would help further with the maximum temp, but it would increase the convection cooling at the minimum temp, reducing the overall benefit. It could also be more susceptible to drafts, and would make the fan control much more delicate. Anyway, that's the results I got with my setup. Other setups and more fine tuning could change things a good bit, but I just wanted to get an idea of how the two cooling methods compared on the same setup. Angus On Sat, 28 Jun 2014 12:37:37 -0400 (EDT), you wrote: Will someone beside us use heat pipe. Would love to have an impendent input. What does it take to get a test going. Scott has done a lot of work, how about some one else step up to the plate. There are a lot of time nuts out there with the 5680A,many for the first time will have a very good reference and some of our experts with proper equipment can make a big difference. Bert Kehren In a message dated 6/28/2014 12:20:12 P.M. Eastern Daylight Time, newell+timen...@n5tnl.com writes: At 04:32 AM 6/28/2014, wb6bnq wrote: monitoring process ? In other words have you traced out the connections to see what is driving the pin you think is the temperature input ? No. I've only traced back from the ADC input to the voltage divider.
[time-nuts] DIY FE-5680A lobotomy (disable temp compensation)
There is no question that direct fan control in combination with a heat sink is the best solution and we use it on FRK and M 100 with proper thermal insulation we get 0.01 C on the back plate and better than 0.1 C on the front. For us the FE 5680 A is not in that class so we looked for a solution that gives us 0.1 C. The shape of the FE 5680 does not lend itself easily for fan cooling if you want to mount it in a chassis horizontally, I did using two L shaped plates with a back plate heat sink and fan. How ever few have access to metal work and it gets quickly expensive. A picture is attached. I did extensive test with heat pipes first with a power resistor on a Alu plate followed by tests with a FRS, FE 5650 and FE 5680. You have to take in to consideration the function of the heat pipe in other words set the temperature of the base plate above the boiling point of the liquid. In my case 46 C was a good tradeoff between fan speed and operating range of the fan. To much heat pipe can also be a problem. No question a uprocessor controlled temperature control would be better, but till now typical time nuts, all talk while we have working analog circuits and boards. If worried about temperature change across the unit it can not be totally be eliminated but if important enclose the unit totally in foam. Easy when you use a heat pipe. I use a an 1/8 Alu base plate between the Rb and the heat pipe so I can also tap threads in to it to hold the heat pipe and I did away with the bottom plate of the FE 5680. Many options. Bert Kehren In a message dated 8/19/2014 3:02:49 A.M. Eastern Daylight Time, ed_pal...@sasktel.net writes: Is a heatpipe really appropriate for this application? The heatpipe expects that the heat source wants to burn up and so there's lots of heat available to vaporize the liquid in the pipe. It's not clear to me whether that situation exists with these Rb standards. My tests with an FE-5680A showed a maximum temperature of about 62C without a heatsink. That's far lower than a CPU or GPU. Some of them run at that temperature *with* the heatpipe. I think that a heatsink/fan (maybe from a video card) equipped with a PWM controller might be a better fit. Many of those combinations have a ducted fan to provide better control of the airflow. That would reduce the effects of drafts and convection. One nuisance with using a video card heatsink is that the back side typically has a raised area that contacts the GPU. For this application you'd have to have a flat back over the entire heatsink. Ed On 8/18/2014 6:58 PM, Angus wrote: On Fri, 04 Jul 2014 02:35:41 +0100, you wrote: Hi Bert, I am thinking about testing a heat pipe on a fan cooled setup I use. The first temp controlled chassis I did used a peltier and works very well, but was a lot more work to do and is much more power hungry. The main problem I find is not the temp controller itself, but rather the change in the temperature across the chassis as the ambient changes. However good the temp controller is, it only controls a single point, but other points further away from the sensing thermistor can vary a lot. I noticed you posted a picture of a heat pipe cooler a couple of weeks ago - did you happen to compare the temperature across the unit with direct fan cooling and the heat pipe cooler, or with different heat pipes? Angus. I finally got around to playing with a couple of laptop heat pipes, fixed to a 25x50x75mm block of aluminium which is fixed to the 12mm thick baseplate. On a quick test of it, a sensor near the end of the baseplate showed 1.5-2x greater variation with temperature compared with just having a fan blow directly onto the baseplate. The oscillator also had to be allowed to run a few degrees C hotter for the heatpipe coolers to work to the same max ambient temp. One cooler had two heatpipes with about 12cm between the aluminium block and the heatsink fins (cast in this case) The other had a single, wider heat pipe with about 5cm between the block and the heatsink (this time with a lot more fine fins) The second cooler was rather more efficient, allowing a extra degreee of cooling at the top end, but more problematic was that it entered 'bang-bang' mode with the analogue temperature controller even sooner, and the temperature fluctuations there were greater. Both were rather worse than with the fan just blowing onto the baseplate. Using a PWM fan controller would help a good bit, but getting more creative with a microcontroller would be better. That way you can give the fan a minimum of a small kick every so often, and vary the repetition rate as well as the duty cycle as more cooling is needed. With feedback from the fan and even air temperature monitoring, you could get a good idea of exactly how much cooling was being applied. Another problem is that the
Re: [time-nuts] MIT Flea
Thanks for the info. 73, Dick, W1KSZ On 8/17/2014 12:19 PM, paul swed wrote: I did see John scooting along the road. The gates had not opened yet. But did not see him after the gates did open. It was a fairly small crowd Regards Paul WB8TSL/1 On Sun, Aug 17, 2014 at 12:57 PM, Richard Solomon w1...@earthlink.net wrote: Speaking of the MIT Flea, I have not read anything from John Forster (sp ?) lately on any of his forums. I hope all is well with him. 73, Dick, W1KSZ On 8/16/2014 10:56 PM, bownes wrote: Apologies for to those not in New England or not going to the Flea. I'm heading out to the MIT Flea at oh-freaking-dark in the morning and I know there are often several time nuts who go. If you happen to see a guy wander by in a Horton Emergency Vehicles hat looking very tired, say Hi! ___ 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. ___ 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] MH370 Doppler
My understanding is that the BFO and BTO values are self reported from the SDU (Terminal in the aircraft) and they represent adjustments made by the SDU. If so the BFO value would be the AFC adjustment relative to the OCXO onboard. My contention is that if the investigators are assuming the OCXO is 2Hz high and reporting an +88Hz offset as 86Hz Doppler, what if in fact the OCXO is 10Hz high? Then the doppler is 78Hz and that means the velocity and location at each of the pings is way off. It would also be good to know if the terminal has any sort of holdover battery to keep it running. So far I have heard only that the IRU has battery. Even so, the terminal has possibly three power sources, left and right and APU busses. Unlikely as it seems, what if they ditched successfully at sea and the APU ran for hours? From: David I. Emeryd...@dieconsulting.com IIRC the plane is expected to adjust its burst uplink frequency and timing to come out right at the satellite receive antenna... thus compensating for the uplink Doppler at L band and the time delay too. But I do remember that the ground supplies feedback on the control channel as to how much the plane is off so it can adjust... Guess it might be time to dig out the docs again. -- Joe Leikhim Leikhim and Associates Communications Consultants Oviedo, Florida jleik...@leikhim.com 407-982-0446 WWW.LEIKHIM.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] Ublox neo-7M GPS
Good day all, On another list to which I subscribe, there has been chatter about the Ublox neo-7M GPS receiver. It seems that the device's configurable timepulse output is configurable from 0.25hz to 10 MHz as well as it's duty cycle and can also be set to be one condition when the GPS is not locked and a different condition when locked (i.e. 1 PPS if not locked, 10KHz when locked). This seems all too good to be true. Sounds like a very simple self-contained GPSDO. I don't know anything more about the device. I have just downloaded the documents and will be spending some time reading them. I am curious if any other list members were aware of this feature of this device and have had any first hand experiences with it. There is another model, the 7N. the 7M uses a simple crystal clock, the 7N a TXCO. Cheers, Graham ve3gtc This electronic message, as well as any transmitted files included in the electronic message, may contain privileged or confidential information and is intended solely for the use of the individual(s) or entity to which it is addressed. If you have received this electronic message in error please notify the sender immediately and delete the electronic message. Any unauthorized copying, disclosure or distribution of the electronic message is strictly forbidden. NAV CANADA accepts no liability for any damage caused by any virus and/or other malicious code transmitted by this electronic communication. Le présent message électronique et tout fichier qui peut y être joint peuvent contenir des renseignements privilégiés ou confidentiels destinés à l’usage exclusif des personnes ou des organismes à qui ils s’adressent. Si vous avez reçu ce message électronique par erreur, veuillez en informer l’expéditeur immédiatement et supprimez le. Toute reproduction, divulgation ou distribution du présent message électronique est strictement interdite. NAV CANADA n’assume aucune responsabilité en cas de dommage causé par tout virus ou autre programme malveillant transmis par ce message électronique. ___ 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] Ublox neo-7M GPS
Good day all, On another list to which I subscribe, there has been chatter about the Ublox neo-7M GPS receiver. It seems that the device's configurable timepulse output is configurable from 0.25hz to 10 MHz as well as it's duty cycle and can also be set to be one condition when the GPS is not locked and a different condition when locked (i.e. 1 PPS if not locked, 10KHz when locked). This seems all too good to be true. Sounds like a very simple self-contained GPSDO. I don't know anything more about the device. I have just downloaded the documents and will be spending some time reading them. I am curious if any other list members were aware of this feature of this device and have had any first hand experiences with it. There is another model, the 7N. the 7M uses a simple crystal clock, the 7N a TXCO. Cheers, Graham ve3gtc Graham, Take a look at the data sheet. The waveforms at frequencies other than 8 MHz (IIRC in other modules) and sub-multiples may not be all you desire. However, I would be delighted to see testing of this box by a qualified frequency-nut! http://www.u-blox.com/en/download/documents-a-resources/u-blox-7-gps-modules-resources.html http://www.u-blox.com/images/downloads/Product_Docs/NEO-7_DataSheet_%28GPS.G7-HW-11004%29.pdf http://www.u-blox.com/images/downloads/Product_Docs/u-blox7-V14_ReceiverDescriptionProtocolSpec_Public_%28GPS.G7-SW-12001%29.pdf 73, David GM8ARV -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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] Ublox neo-7M GPS
Graham, Those are not GPSDO's by definition. They are based on NCO technology. The difference being many orders of magnitude higher phase noise and ADEV noise. We tried to measure their phase noise and our TSC5125A could not even lock on to the 10MHz - they were so noisy. You can make a GPSDO out of them if you use a post filter oscillator loop locked with sufficient time constant (10s).. Sent From iPhone On Aug 19, 2014, at 9:20, Collins, Graham coll...@navcanada.ca wrote: Good day all, On another list to which I subscribe, there has been chatter about the Ublox neo-7M GPS receiver. It seems that the device's configurable timepulse output is configurable from 0.25hz to 10 MHz as well as it's duty cycle and can also be set to be one condition when the GPS is not locked and a different condition when locked (i.e. 1 PPS if not locked, 10KHz when locked). This seems all too good to be true. Sounds like a very simple self-contained GPSDO. I don't know anything more about the device. I have just downloaded the documents and will be spending some time reading them. I am curious if any other list members were aware of this feature of this device and have had any first hand experiences with it. There is another model, the 7N. the 7M uses a simple crystal clock, the 7N a TXCO. Cheers, Graham ve3gtc This electronic message, as well as any transmitted files included in the electronic message, may contain privileged or confidential information and is intended solely for the use of the individual(s) or entity to which it is addressed. If you have received this electronic message in error please notify the sender immediately and delete the electronic message. Any unauthorized copying, disclosure or distribution of the electronic message is strictly forbidden. NAV CANADA accepts no liability for any damage caused by any virus and/or other malicious code transmitted by this electronic communication. Le présent message électronique et tout fichier qui peut y être joint peuvent contenir des renseignements privilégiés ou confidentiels destinés à l’usage exclusif des personnes ou des organismes à qui ils s’adressent. Si vous avez reçu ce message électronique par erreur, veuillez en informer l’expéditeur immédiatement et supprimez le. Toute reproduction, divulgation ou distribution du présent message électronique est strictement interdite. NAV CANADA n’assume aucune responsabilité en cas de dommage causé par tout virus ou autre programme malveillant transmis par ce message électronique. ___ 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] Ublox neo-7M GPS
Said, Agreed, hence my reference as a very simple self-contained GPSDO. Even after a very quick first glance at the documentation it didn't seem like it would be much of threat to more traditional GPSDO's. It will be interesting to play around with and see what it can do. Cheers, Graham ve3gtc -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Said Jackson Sent: August-19-14 12:44 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Ublox neo-7M GPS Graham, Those are not GPSDO's by definition. They are based on NCO technology. The difference being many orders of magnitude higher phase noise and ADEV noise. We tried to measure their phase noise and our TSC5125A could not even lock on to the 10MHz - they were so noisy. You can make a GPSDO out of them if you use a post filter oscillator loop locked with sufficient time constant (10s).. Sent From iPhone On Aug 19, 2014, at 9:20, Collins, Graham coll...@navcanada.ca wrote: Good day all, On another list to which I subscribe, there has been chatter about the Ublox neo-7M GPS receiver. It seems that the device's configurable timepulse output is configurable from 0.25hz to 10 MHz as well as it's duty cycle and can also be set to be one condition when the GPS is not locked and a different condition when locked (i.e. 1 PPS if not locked, 10KHz when locked). This seems all too good to be true. Sounds like a very simple self-contained GPSDO. I don't know anything more about the device. I have just downloaded the documents and will be spending some time reading them. I am curious if any other list members were aware of this feature of this device and have had any first hand experiences with it. There is another model, the 7N. the 7M uses a simple crystal clock, the 7N a TXCO. Cheers, Graham ve3gtc This electronic message, as well as any transmitted files included in the electronic message, may contain privileged or confidential information and is intended solely for the use of the individual(s) or entity to which it is addressed. If you have received this electronic message in error please notify the sender immediately and delete the electronic message. Any unauthorized copying, disclosure or distribution of the electronic message is strictly forbidden. NAV CANADA accepts no liability for any damage caused by any virus and/or other malicious code transmitted by this electronic communication. Le présent message électronique et tout fichier qui peut y être joint peuvent contenir des renseignements privilégiés ou confidentiels destinés à l’usage exclusif des personnes ou des organismes à qui ils s’adressent. Si vous avez reçu ce message électronique par erreur, veuillez en informer l’expéditeur immédiatement et supprimez le. Toute reproduction, divulgation ou distribution du présent message électronique est strictement interdite. NAV CANADA n’assume aucune responsabilité en cas de dommage causé par tout virus ou autre programme malveillant transmis par ce message électronique. ___ 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] Ublox neo-7M GPS
Hi Graham, its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally adds/drops/extends/retards the phase of the output clock to achieve an average of number of desired clock cycles. This causes huge cycle-to-cycle phase jumps. One cycle maybe 100ns long, and the next adjacent cycle could only be 87ns long! Without filtering, I doubt the output is useful for much because it has phase jumps from cycle to cycle of 10's of nanoseconds or more. A true GPSDO (even the cheapest one) has cycle to cycle phase jumps of femtoseconds only due to oscillator jitter. You can easily make a GPSDO out of it though through a simple EXOR gate (74AC86), feeding a TCXO/VCXO through a low-pass filter, and designing a phase loop low-pass filter with less than say 10Hz bandwidth.. That approach has been discussed here in the past a couple of times and is very cost-effective. That is essentially what the Conner Winfield units do. The drawback is that you have very large phase and frequency jumps when going into and coming out of holdover on these units, because the unit does not have a holdover oscillator with any type of reasonable stability, and whatever high ADEV stability your filter oscillator has is lost due to the analog loop bandwidth of typically 10Hz meaning the internal $1 crystal of the GPS receiver itself determines ADEV. Bye, Said In a message dated 8/19/2014 10:03:27 Pacific Daylight Time, coll...@navcanada.ca writes: Said, Agreed, hence my reference as a very simple self-contained GPSDO. Even after a very quick first glance at the documentation it didn't seem like it would be much of threat to more traditional GPSDO's. It will be interesting to play around with and see what it can do. Cheers, Graham ve3gtc -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Said Jackson Sent: August-19-14 12:44 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Ublox neo-7M GPS Graham, Those are not GPSDO's by definition. They are based on NCO technology. The difference being many orders of magnitude higher phase noise and ADEV noise. We tried to measure their phase noise and our TSC5125A could not even lock on to the 10MHz - they were so noisy. You can make a GPSDO out of them if you use a post filter oscillator loop locked with sufficient time constant (10s).. Sent From iPhone On Aug 19, 2014, at 9:20, Collins, Graham coll...@navcanada.ca wrote: Good day all, On another list to which I subscribe, there has been chatter about the Ublox neo-7M GPS receiver. It seems that the device's configurable timepulse output is configurable from 0.25hz to 10 MHz as well as it's duty cycle and can also be set to be one condition when the GPS is not locked and a different condition when locked (i.e. 1 PPS if not locked, 10KHz when locked). This seems all too good to be true. Sounds like a very simple self-contained GPSDO. I don't know anything more about the device. I have just downloaded the documents and will be spending some time reading them. I am curious if any other list members were aware of this feature of this device and have had any first hand experiences with it. There is another model, the 7N. the 7M uses a simple crystal clock, the 7N a TXCO. Cheers, Graham ve3gtc This electronic message, as well as any transmitted files included in the electronic message, may contain privileged or confidential information and is intended solely for the use of the individual(s) or entity to which it is addressed. If you have received this electronic message in error please notify the sender immediately and delete the electronic message. Any unauthorized copying, disclosure or distribution of the electronic message is strictly forbidden. NAV CANADA accepts no liability for any damage caused by any virus and/or other malicious code transmitted by this electronic communication. Le présent message électronique et tout fichier qui peut y être joint peuvent contenir des renseignements privilégiés ou confidentiels destinés à l’ usage exclusif des personnes ou des organismes à qui ils s’adressent. Si vous avez reçu ce message électronique par erreur, veuillez en informer l’ expéditeur immédiatement et supprimez le. Toute reproduction, divulgation ou distribution du présent message électronique est strictement interdite. NAV CANADA n’assume aucune responsabilité en cas de dommage causé par tout virus ou autre programme malveillant transmis par ce message électronique. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow
Re: [time-nuts] Ublox neo-7M GPS
saidj...@aol.com said: its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally adds/drops/extends/retards the phase of the output clock to achieve an average of number of desired clock cycles. Is there something about the term GPSDO that says I have to do the D in the analog domain rather than the digital domain? I agree that current technology doesn't give results that are useful for many applications that currently use GPSDOs. What if the clock ran at a GHz? 10 GHz? Sure, it would have spurs, but would it be useful for some applications? Is a GPSDO still a GPSDO if the D/A driving the VCXO only has a few bits? How many bits does it need to be a real GPSDO? Is a battery powered wall clock listening to WWVB at 2 AM a WWVDO? It's got a pretty good ADEV if you go out far enough. -- These are my opinions. I hate spam. ___ 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] Ublox neo-7M GPS
Hal, I guess that depends on your definition of disciplined. The products that I am familiar with don't consider adjusting phase length of an asynchronously running oscillator on a cycle-to-cycle basis thousands of times per second to try to fit 10 million of them (or whatever your desired frequency is) disciplining. Best case you could call it phase/frequency hopping to try to achieve some sort of frequency average in my opinion. However if you used a DDS to adjust the frequency of an asynchronous clock digitally and control that frequency by digital adjustment that would be true disciplining of your frequency source. So analog versus digital has nothing to do with it. If your DAC had only a few bits you still would have many orders of magnitude less phase errors than the NCO approach; you can do the simple math: Let's say your VCXO had only 4 bits and a +/-20Hz frequency adjustment range. Pretty nasty considering any low-ball GPSDO these days has at least 21 bits EFC resolution. Now changing one LSB on our 4 bit DAC would thus result in a massive frequency change of +/-2.5Hz. This would result in a phase drift of 2.5E-07 or 250ns drift over ONE ENTIRE SECOND. That means 250ns divided by 10 Million (!!) cycles or a cycle to cycle change of only 25 femtoseconds when the DAC changes state. Theoretically that cycle length change would only happen ONCE if the system was a digital DDS type system. How does a single 25 femtoseconds cycle length change on our hypothetical 4 bit EFC DAC compare to a 10ns cycle to cycle change that happens thousands of times or more per second on typical NCO's? My point is we are talking performance differences of 5 or 6 orders of magnitude between a GPSDO (digital or analog) and an NCO. We are not comparing apples to apples. These are not even apples to oranges in my opinion. bye, Said In a message dated 8/19/2014 12:32:02 Pacific Daylight Time, hmur...@megapathdsl.net writes: saidj...@aol.com said: its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally adds/drops/extends/retards the phase of the output clock to achieve an average of number of desired clock cycles. Is there something about the term GPSDO that says I have to do the D in the analog domain rather than the digital domain? I agree that current technology doesn't give results that are useful for many applications that currently use GPSDOs. What if the clock ran at a GHz? 10 GHz? Sure, it would have spurs, but would it be useful for some applications? Is a GPSDO still a GPSDO if the D/A driving the VCXO only has a few bits? How many bits does it need to be a real GPSDO? Is a battery powered wall clock listening to WWVB at 2 AM a WWVDO? It's got a pretty good ADEV if you go out far enough. ___ 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] Ublox neo-7M GPS
Hal, as long as you maintain long-term phase lock it's a disciplined oscillator. So, yes, a carrier tracking WWVB receiver with sufficiently stable flywheel LO is a WWVBDO. Said, too-short or too-long 100 ns cycles is one thing. Still ok for many applications. But tell me more about extra or missing pulses in the ublox-7. That sounds like a show stopper to me. /tvb (i5s) On Aug 19, 2014, at 2:05 PM, Hal Murray hmur...@megapathdsl.net wrote: saidj...@aol.com said: its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally adds/drops/extends/retards the phase of the output clock to achieve an average of number of desired clock cycles. Is there something about the term GPSDO that says I have to do the D in the analog domain rather than the digital domain? I agree that current technology doesn't give results that are useful for many applications that currently use GPSDOs. What if the clock ran at a GHz? 10 GHz? Sure, it would have spurs, but would it be useful for some applications? Is a GPSDO still a GPSDO if the D/A driving the VCXO only has a few bits? How many bits does it need to be a real GPSDO? Is a battery powered wall clock listening to WWVB at 2 AM a WWVDO? It's got a pretty good ADEV if you go out far enough. -- These are my opinions. I hate spam. ___ 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] Ublox neo-7M GPS
Knowing a litle bit about semiconductor production it is safe to assume that all 7M series divvices have the same chip and during production at ublox some features are disabled or enabled. The result is one mask set one chip run and one inventory. I did see a recent announcement where a 7M can be used as a GPSDO one of the intended markets is micro cell sites.Will require an external XO. In the meantime we have been playing with a $ 15 M7 ublox that can be programmed from 1 pps to 1 KHz and use it in a PLL. I call it a GPS PLL and is mainly intended for Ham's. Clark had years ago a similar circuits we have added some mods. Using a Morion 89 we get better than 1 E-10 per second on first try.. There have been recent claims using 1000 seconds which is easy but this is per second. Next steps are more fine tuning and lower cost XO's. Maybe even a VCTCXO. As I said before intended for Ham's, field day, uwave and SDR. Not really a time nut unit, but low cost off the shelf standard parts and no adjustments all on a 5 X 5 cm board. With a Morion you have to start off with 15 V but there are OCXO's out there for 5 V. Ideal for fieldday 12 V. Bert Kehren In a message dated 8/19/2014 12:20:40 P.M. Eastern Daylight Time, coll...@navcanada.ca writes: Good day all, On another list to which I subscribe, there has been chatter about the Ublox neo-7M GPS receiver. It seems that the device's configurable timepulse output is configurable from 0.25hz to 10 MHz as well as it's duty cycle and can also be set to be one condition when the GPS is not locked and a different condition when locked (i.e. 1 PPS if not locked, 10KHz when locked). This seems all too good to be true. Sounds like a very simple self-contained GPSDO. I don't know anything more about the device. I have just downloaded the documents and will be spending some time reading them. I am curious if any other list members were aware of this feature of this device and have had any first hand experiences with it. There is another model, the 7N. the 7M uses a simple crystal clock, the 7N a TXCO. Cheers, Graham ve3gtc This electronic message, as well as any transmitted files included in the electronic message, may contain privileged or confidential information and is intended solely for the use of the individual(s) or entity to which it is addressed. If you have received this electronic message in error please notify the sender immediately and delete the electronic message. Any unauthorized copying, disclosure or distribution of the electronic message is strictly forbidden. NAV CANADA accepts no liability for any damage caused by any virus and/or other malicious code transmitted by this electronic communication. Le présent message électronique et tout fichier qui peut y être joint peuvent contenir des renseignements privilégiés ou confidentiels destinés à l’ usage exclusif des personnes ou des organismes à qui ils s’adressent. Si vous avez reçu ce message électronique par erreur, veuillez en informer l’ expéditeur immédiatement et supprimez le. Toute reproduction, divulgation ou distribution du présent message électronique est strictement interdite. NAV CANADA n’assume aucune responsabilité en cas de dommage causé par tout virus ou autre programme malveillant transmis par ce message électronique. ___ 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] Ublox neo-7M GPS
Hi Tom, last time I looked at these I tried figuring out what they were doing. It is very hard to get measurement data, our TSC did not converge on their signal, and looking at the output on a scope revealed only a bunch of crazy random phase jumps. I guess one could use a counter to measure how many time pulses are being sent in x seconds with x being a large number, or divide the output by 10 million and see how the pulse moves back and forth compared to the 1PPS UTC output.. Since I don't know the exact algorithm being used, I said adds/drops/extends/retards in my previous email. I did not mean to imply that the unit is doing all or any of those items. But that is exactly part of the problem isn't it, there is no clear description of what exactly is happening in the uBlox documents or the CW docs for that matter that I could find. I for one would not use that output to drive a processor or other digital device directly, who knows what happens if the processor sees a 100ns, then a 110ns, and then an 70ns pulse if it is only rated at 10MHz and 100ns pulse-width +/- a couple percent for example.. Without knowing the exact minimum phase time period specification that could come out of one of these NCO's, one should not properly use that signal in a digital design. My initial concern was that this is time-nuts, and we should call a GPSDO a GPSDO, and an NCO an NCO in my opinion. Nothing wrong with one or the other, but they sure are not the same thing - by 6 or more orders of magnitude in phase stability. We usually are concerned here about parts per trillion stability and accuracy, and now we are mixing things up that are millions of times worse than one another.. bye, Said In a message dated 8/19/2014 13:08:52 Pacific Daylight Time, t...@leapsecond.com writes: Hal, as long as you maintain long-term phase lock it's a disciplined oscillator. So, yes, a carrier tracking WWVB receiver with sufficiently stable flywheel LO is a WWVBDO. Said, too-short or too-long 100 ns cycles is one thing. Still ok for many applications. But tell me more about extra or missing pulses in the ublox-7. That sounds like a show stopper to me. /tvb (i5s) On Aug 19, 2014, at 2:05 PM, Hal Murray hmur...@megapathdsl.net wrote: saidj...@aol.com said: its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally adds/drops/extends/retards the phase of the output clock to achieve an average of number of desired clock cycles. Is there something about the term GPSDO that says I have to do the D in the analog domain rather than the digital domain? I agree that current technology doesn't give results that are useful for many applications that currently use GPSDOs. What if the clock ran at a GHz? 10 GHz? Sure, it would have spurs, but would it be useful for some applications? Is a GPSDO still a GPSDO if the D/A driving the VCXO only has a few bits? How many bits does it need to be a real GPSDO? Is a battery powered wall clock listening to WWVB at 2 AM a WWVDO? It's got a pretty good ADEV if you go out far enough. -- These are my opinions. I hate spam. ___ 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] Ublox neo-7M GPS
Hi They are constrained by the same basic TCXO issues that give you sawtooth correction. They do not use EFC to get the TCXO on frequency. With sawtooth they give you a word that lets you know what’s going on. With the NCO’s they often are doing very crude synthesis. They don’t put a $48 DDS chip in a $10 GPS module. If you put one on a spectrum analyzer, it’s not pretty …. Bob On Aug 19, 2014, at 5:46 PM, Said Jackson saidj...@aol.com wrote: Tom, Btw part of my frustration with this is that we sometimes get calls from customers asking why they need our or others' GPSDOs for a couple 100 dollars when they can buy a CW or uBlox doing the same thing for a fraction of the cost. Most of them come back to us after evaluating these NCOs and finding that its not the same thing. You get what you pay for I guess.. Said Sent From iPhone On Aug 19, 2014, at 13:01, Tom Van Baak (lab) t...@leapsecond.com wrote: Hal, as long as you maintain long-term phase lock it's a disciplined oscillator. So, yes, a carrier tracking WWVB receiver with sufficiently stable flywheel LO is a WWVBDO. Said, too-short or too-long 100 ns cycles is one thing. Still ok for many applications. But tell me more about extra or missing pulses in the ublox-7. That sounds like a show stopper to me. /tvb (i5s) On Aug 19, 2014, at 2:05 PM, Hal Murray hmur...@megapathdsl.net wrote: saidj...@aol.com said: its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally adds/drops/extends/retards the phase of the output clock to achieve an average of number of desired clock cycles. Is there something about the term GPSDO that says I have to do the D in the analog domain rather than the digital domain? I agree that current technology doesn't give results that are useful for many applications that currently use GPSDOs. What if the clock ran at a GHz? 10 GHz? Sure, it would have spurs, but would it be useful for some applications? Is a GPSDO still a GPSDO if the D/A driving the VCXO only has a few bits? How many bits does it need to be a real GPSDO? Is a battery powered wall clock listening to WWVB at 2 AM a WWVDO? It's got a pretty good ADEV if you go out far enough. -- These are my opinions. I hate spam. ___ 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. ___ 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] MH370 Doppler
As I understand it, Doppler will give you the magnitude of the velocity vector for an aircraft with respect to the satellite, but it won't give you the actual direction of the aircraft. Why does the stability of the oscillators matter if you can't determine the direction? Is there another satellite involved? Can you learn something if you assume a velocity for the aircraft? In which case the error in the assumed velocity would swamp the oscillator error, no? Bill Hawkins -Original Message- From: Joe Leikhim Sent: Monday, August 18, 2014 11:53 AM Is anyone paying attention to all the chatter about the lost aircraft MH370, Inmarsat's supposed flight tracks based on 6 or 7 pings (1 per hour), the Doppler shift (BFO) and transaction timing (BTO) etc?? Basically from my perspective they are putting too much stock into the Doppler which relies in part upon the stability of the satellite terminal in the 777 aircraft. My question is how stable an oscillator (reported OCXO - not confirmed) would be under the extremes of either or both a cabin fire or decompression event. There is a website (Duncan Steel Blog) where some math brains are trying to sort out the raw data provided by Inmarsat. They have made assumptions about the stability of the local oscillator in the satellite, but I think the aircraft satellite terminal's master oscillator is a variable they have pushed aside. ___ 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] MH370 Doppler
You CAN determine the ground track if you assume the altitude above sea level is constant and the aircraft's speed is also constant. But you are correct that Doppler alone would not be enough. The question I have to people here is: How does error in the dopler translate to error in the ground track. In other words what is the function that maps oscillator stability to distance on the ground. On Tue, Aug 19, 2014 at 3:25 PM, Bill Hawkins b...@iaxs.net wrote: As I understand it, Doppler will give you the magnitude of the velocity vector for an aircraft with respect to the satellite, but it won't give you the actual direction of the aircraft. Why does the stability of the oscillators matter if you can't determine the direction? Is there another satellite involved? Can you learn something if you assume a velocity for the aircraft? In which case the error in the assumed velocity would swamp the oscillator error, no? Bill Hawkins -Original Message- From: Joe Leikhim Sent: Monday, August 18, 2014 11:53 AM Is anyone paying attention to all the chatter about the lost aircraft MH370, Inmarsat's supposed flight tracks based on 6 or 7 pings (1 per hour), the Doppler shift (BFO) and transaction timing (BTO) etc?? Basically from my perspective they are putting too much stock into the Doppler which relies in part upon the stability of the satellite terminal in the 777 aircraft. My question is how stable an oscillator (reported OCXO - not confirmed) would be under the extremes of either or both a cabin fire or decompression event. There is a website (Duncan Steel Blog) where some math brains are trying to sort out the raw data provided by Inmarsat. They have made assumptions about the stability of the local oscillator in the satellite, but I think the aircraft satellite terminal's master oscillator is a variable they have pushed aside. ___ 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. -- Chris Albertson Redondo Beach, California ___ 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] MH370 Doppler
On Tue, Aug 19, 2014 at 12:08:24PM -0400, Joe Leikhim wrote: My understanding is that the BFO and BTO values are self reported from the SDU (Terminal in the aircraft) and they represent adjustments made by the SDU. If so the BFO value would be the AFC adjustment relative to the OCXO onboard. My contention is that if the investigators are assuming the OCXO is 2Hz high and reporting an +88Hz offset as 86Hz Doppler, what if in fact the OCXO is 10Hz high? Then the doppler is 78Hz and that means the velocity and location at each of the pings is way off. Clearly they have a history of the MH370 Aero Clasic terminal measured burst frequency at the ground earth station and the BFO value the SDU reports it used WHEN the aircraft was on the ground before it took off and WHEN it was being tracked by radar/mode-s/ads-b and was in a known position going at a known velocity on a known heading.This should presumably allow determination of the baseline OCXO long term error, and some indication of its short term drift as well. Whether that particular SDU attempts to use any form of EFC of its OCXO based on measured satellite L band downlink frequency error corrected for doppler or not I do not know. It is quite possible that any correction for OCXO error is just a value factored into computing the BFO to use and not used for actually correcting the standard with a EFC DAC. If that is true then the drift should be presumably be pretty typical of the class of OCXO used in the SDU which I suspect should be fairly small once it warms up - over a 6-8 hour period after warmup. And there may be some history of that particular terminal from previous flights to validate this. Of course if environment significantly changes the drift performance of that particular OCXO it is possible that temperature, or pressure or power conditions were so different on the fatal flight that the drift might be larger and unknown in character... not sure. It is an error to consider of course. Not clear to me how carefully it has been or what possible factors have been considered. But surely the folks doing the analysis know about these issues. -- Dave Emery N1PRE/AE, d...@dieconsulting.com DIE Consulting, Weston, Mass 02493 An empty zombie mind with a forlorn barely readable weatherbeaten 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in celebration of what could have been, but wasn't and is not to be now either. ___ 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] Ublox neo-7M GPS
I recall when the LEA-M8F was announced that they mentioned a VCTCXO and maybe I wrongly assumed that they used it for sawtooth correction they also mention ability to control in addition an external OCXO. I previously suggested using saw tooth correction information to tune a TCXO but that would require a GPS module with sawtooth information and than it would be simpler to just use a PIC and delay chip. Still do not understand why no one took me up on the offer of chips and PCB. I guess time nuts like to talk about it but not fix it. How many receivers are out there. Bert Kehren. In a message dated 8/19/2014 5:51:30 P.M. Eastern Daylight Time, kb...@n1k.org writes: Hi They are constrained by the same basic TCXO issues that give you sawtooth correction. They do not use EFC to get the TCXO on frequency. With sawtooth they give you a word that lets you know what’s going on. With the NCO’s they often are doing very crude synthesis. They don’t put a $48 DDS chip in a $10 GPS module. If you put one on a spectrum analyzer, it’s not pretty …. Bob On Aug 19, 2014, at 5:46 PM, Said Jackson saidj...@aol.com wrote: Tom, Btw part of my frustration with this is that we sometimes get calls from customers asking why they need our or others' GPSDOs for a couple 100 dollars when they can buy a CW or uBlox doing the same thing for a fraction of the cost. Most of them come back to us after evaluating these NCOs and finding that its not the same thing. You get what you pay for I guess.. Said Sent From iPhone On Aug 19, 2014, at 13:01, Tom Van Baak (lab) t...@leapsecond.com wrote: Hal, as long as you maintain long-term phase lock it's a disciplined oscillator. So, yes, a carrier tracking WWVB receiver with sufficiently stable flywheel LO is a WWVBDO. Said, too-short or too-long 100 ns cycles is one thing. Still ok for many applications. But tell me more about extra or missing pulses in the ublox-7. That sounds like a show stopper to me. /tvb (i5s) On Aug 19, 2014, at 2:05 PM, Hal Murray hmur...@megapathdsl.net wrote: saidj...@aol.com said: its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally adds/drops/extends/retards the phase of the output clock to achieve an average of number of desired clock cycles. Is there something about the term GPSDO that says I have to do the D in the analog domain rather than the digital domain? I agree that current technology doesn't give results that are useful for many applications that currently use GPSDOs. What if the clock ran at a GHz? 10 GHz? Sure, it would have spurs, but would it be useful for some applications? Is a GPSDO still a GPSDO if the D/A driving the VCXO only has a few bits? How many bits does it need to be a real GPSDO? Is a battery powered wall clock listening to WWVB at 2 AM a WWVDO? It's got a pretty good ADEV if you go out far enough. -- These are my opinions. I hate spam. ___ 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. ___ 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] Ublox neo-7M GPS
Does anyone have a neo-7M and an HP 5371A or a 5372A Analyzer? Use the Histogram Time Interval function to measure a block of samples. That will show the length of the samples with a resolution of 200 ps. That's what I did a couple of years ago when I analyzed the Navsync CW-12 with the old and new firmware. http://www.febo.com/pipermail/time-nuts/2012-January/062913.html Remember the explanation of a GPSDO's Adev curve. At low values of Tau, the value is determined by the oscillator (whether OCXO or TCXO). At high values of Tau, the value is determined by the GPS system. I think of 'The GPS Line'. It's a line on the Adev graph that passes through 1e-10 @ 100 sec. with a slope of -1. Use a *really* fat pencil when you draw the line! Every GPSDO follows that line - nothing exists to the right of it. The oscillator determines where the curve for that particular GPSDO is on the left side of the line. When the oscillator performance hits the GPS Line, the graph turns down and to the right and follows the line. Since an NCO (Navsync, Ublox, whatever) has no internal oscillator, it just follows the GPS Line. That means that at a Tau of 1 sec. the Adev can't be any better than 1e-8. A low clock speed could make it worse due to limited resolution on the step size. Said's GPSTCXO has a nice TCXO oscillator which gives an Adev two orders of magnitude better than that at 1 second, but that difference disappears at 100 sec. Most GPSDO's use an OCXO which give even better performance at 1 sec. but eventually, the GPS line corrals everyone and imposes similar performance. For any particular application, the user has to decide what level of performance is necessary. If an NCO is good enough with it's cycle-to-cycle anomalies and limited low Tau performance, use it. If not, move up to a real GPSDO. Ed On 8/19/2014 3:23 PM, saidj...@aol.com wrote: Hi Tom, last time I looked at these I tried figuring out what they were doing. It is very hard to get measurement data, our TSC did not converge on their signal, and looking at the output on a scope revealed only a bunch of crazy random phase jumps. I guess one could use a counter to measure how many time pulses are being sent in x seconds with x being a large number, or divide the output by 10 million and see how the pulse moves back and forth compared to the 1PPS UTC output.. Since I don't know the exact algorithm being used, I said adds/drops/extends/retards in my previous email. I did not mean to imply that the unit is doing all or any of those items. But that is exactly part of the problem isn't it, there is no clear description of what exactly is happening in the uBlox documents or the CW docs for that matter that I could find. I for one would not use that output to drive a processor or other digital device directly, who knows what happens if the processor sees a 100ns, then a 110ns, and then an 70ns pulse if it is only rated at 10MHz and 100ns pulse-width +/- a couple percent for example.. Without knowing the exact minimum phase time period specification that could come out of one of these NCO's, one should not properly use that signal in a digital design. My initial concern was that this is time-nuts, and we should call a GPSDO a GPSDO, and an NCO an NCO in my opinion. Nothing wrong with one or the other, but they sure are not the same thing - by 6 or more orders of magnitude in phase stability. We usually are concerned here about parts per trillion stability and accuracy, and now we are mixing things up that are millions of times worse than one another.. bye, Said In a message dated 8/19/2014 13:08:52 Pacific Daylight Time, t...@leapsecond.com writes: Hal, as long as you maintain long-term phase lock it's a disciplined oscillator. So, yes, a carrier tracking WWVB receiver with sufficiently stable flywheel LO is a WWVBDO. Said, too-short or too-long 100 ns cycles is one thing. Still ok for many applications. But tell me more about extra or missing pulses in the ublox-7. That sounds like a show stopper to me. /tvb (i5s) On Aug 19, 2014, at 2:05 PM, Hal Murray hmur...@megapathdsl.net wrote: saidj...@aol.com said: its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally adds/drops/extends/retards the phase of the output clock to achieve an average of number of desired clock cycles. Is there something about the term GPSDO that says I have to do the D in the analog domain rather than the digital domain? I agree that current technology doesn't give results that are useful for many applications that currently use GPSDOs. What if the clock ran at a GHz? 10 GHz? Sure, it would have spurs, but would it be useful for some applications? Is a GPSDO still a GPSDO if the D/A driving the VCXO only has a few
Re: [time-nuts] Ublox neo-7M GPS
Hi There are only two things they can be doing (since it’s not a tuned oscillator). 1) It’s a true DDS with a D/A on the output and you need to put a filter on it before you can do anything at all with it. 2) It’s a pulse drop / add NCO that drops or adds at the 20 to 30 ns level (28 to 50 MHz TCXO). Those are the only two choices there are. Both have significant issues as RF signal sources. Bob On Aug 19, 2014, at 7:11 PM, Ed Palmer ed_pal...@sasktel.net wrote: Does anyone have a neo-7M and an HP 5371A or a 5372A Analyzer? Use the Histogram Time Interval function to measure a block of samples. That will show the length of the samples with a resolution of 200 ps. That's what I did a couple of years ago when I analyzed the Navsync CW-12 with the old and new firmware. http://www.febo.com/pipermail/time-nuts/2012-January/062913.html Remember the explanation of a GPSDO's Adev curve. At low values of Tau, the value is determined by the oscillator (whether OCXO or TCXO). At high values of Tau, the value is determined by the GPS system. I think of 'The GPS Line'. It's a line on the Adev graph that passes through 1e-10 @ 100 sec. with a slope of -1. Use a *really* fat pencil when you draw the line! Every GPSDO follows that line - nothing exists to the right of it. The oscillator determines where the curve for that particular GPSDO is on the left side of the line. When the oscillator performance hits the GPS Line, the graph turns down and to the right and follows the line. Since an NCO (Navsync, Ublox, whatever) has no internal oscillator, it just follows the GPS Line. That means that at a Tau of 1 sec. the Adev can't be any better than 1e-8. A low clock speed could make it worse due to limited resolution on the step size. Said's GPSTCXO has a nice TCXO oscillator which gives an Adev two orders of magnitude better than that at 1 second, but that difference disappears at 100 sec. Most GPSDO's use an OCXO which give even better performance at 1 sec. but eventually, the GPS line corrals everyone and imposes similar performance. For any particular application, the user has to decide what level of performance is necessary. If an NCO is good enough with it's cycle-to-cycle anomalies and limited low Tau performance, use it. If not, move up to a real GPSDO. Ed On 8/19/2014 3:23 PM, saidj...@aol.com wrote: Hi Tom, last time I looked at these I tried figuring out what they were doing. It is very hard to get measurement data, our TSC did not converge on their signal, and looking at the output on a scope revealed only a bunch of crazy random phase jumps. I guess one could use a counter to measure how many time pulses are being sent in x seconds with x being a large number, or divide the output by 10 million and see how the pulse moves back and forth compared to the 1PPS UTC output.. Since I don't know the exact algorithm being used, I said adds/drops/extends/retards in my previous email. I did not mean to imply that the unit is doing all or any of those items. But that is exactly part of the problem isn't it, there is no clear description of what exactly is happening in the uBlox documents or the CW docs for that matter that I could find. I for one would not use that output to drive a processor or other digital device directly, who knows what happens if the processor sees a 100ns, then a 110ns, and then an 70ns pulse if it is only rated at 10MHz and 100ns pulse-width +/- a couple percent for example.. Without knowing the exact minimum phase time period specification that could come out of one of these NCO's, one should not properly use that signal in a digital design. My initial concern was that this is time-nuts, and we should call a GPSDO a GPSDO, and an NCO an NCO in my opinion. Nothing wrong with one or the other, but they sure are not the same thing - by 6 or more orders of magnitude in phase stability. We usually are concerned here about parts per trillion stability and accuracy, and now we are mixing things up that are millions of times worse than one another.. bye, Said In a message dated 8/19/2014 13:08:52 Pacific Daylight Time, t...@leapsecond.com writes: Hal, as long as you maintain long-term phase lock it's a disciplined oscillator. So, yes, a carrier tracking WWVB receiver with sufficiently stable flywheel LO is a WWVBDO. Said, too-short or too-long 100 ns cycles is one thing. Still ok for many applications. But tell me more about extra or missing pulses in the ublox-7. That sounds like a show stopper to me. /tvb (i5s) On Aug 19, 2014, at 2:05 PM, Hal Murray hmur...@megapathdsl.net wrote: saidj...@aol.com said: its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally
Re: [time-nuts] Ublox neo-7M GPS
Hi If you have to womp up a MCU anyway, there is no reason to put in a delay chip. It’s easier / faster / more accurate to just do it all in the MCU. You have to write and maintain custom code either way. Bob On Aug 19, 2014, at 7:53 PM, ewkeh...@aol.com wrote: I recall when the LEA-M8F was announced that they mentioned a VCTCXO and maybe I wrongly assumed that they used it for sawtooth correction they also mention ability to control in addition an external OCXO. I previously suggested using saw tooth correction information to tune a TCXO but that would require a GPS module with sawtooth information and than it would be simpler to just use a PIC and delay chip. Still do not understand why no one took me up on the offer of chips and PCB. I guess time nuts like to talk about it but not fix it. How many receivers are out there. Bert Kehren. In a message dated 8/19/2014 5:51:30 P.M. Eastern Daylight Time, kb...@n1k.org writes: Hi They are constrained by the same basic TCXO issues that give you sawtooth correction. They do not use EFC to get the TCXO on frequency. With sawtooth they give you a word that lets you know what’s going on. With the NCO’s they often are doing very crude synthesis. They don’t put a $48 DDS chip in a $10 GPS module. If you put one on a spectrum analyzer, it’s not pretty …. Bob On Aug 19, 2014, at 5:46 PM, Said Jackson saidj...@aol.com wrote: Tom, Btw part of my frustration with this is that we sometimes get calls from customers asking why they need our or others' GPSDOs for a couple 100 dollars when they can buy a CW or uBlox doing the same thing for a fraction of the cost. Most of them come back to us after evaluating these NCOs and finding that its not the same thing. You get what you pay for I guess.. Said Sent From iPhone On Aug 19, 2014, at 13:01, Tom Van Baak (lab) t...@leapsecond.com wrote: Hal, as long as you maintain long-term phase lock it's a disciplined oscillator. So, yes, a carrier tracking WWVB receiver with sufficiently stable flywheel LO is a WWVBDO. Said, too-short or too-long 100 ns cycles is one thing. Still ok for many applications. But tell me more about extra or missing pulses in the ublox-7. That sounds like a show stopper to me. /tvb (i5s) On Aug 19, 2014, at 2:05 PM, Hal Murray hmur...@megapathdsl.net wrote: saidj...@aol.com said: its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally adds/drops/extends/retards the phase of the output clock to achieve an average of number of desired clock cycles. Is there something about the term GPSDO that says I have to do the D in the analog domain rather than the digital domain? I agree that current technology doesn't give results that are useful for many applications that currently use GPSDOs. What if the clock ran at a GHz? 10 GHz? Sure, it would have spurs, but would it be useful for some applications? Is a GPSDO still a GPSDO if the D/A driving the VCXO only has a few bits? How many bits does it need to be a real GPSDO? Is a battery powered wall clock listening to WWVB at 2 AM a WWVDO? It's got a pretty good ADEV if you go out far enough. -- These are my opinions. I hate spam. ___ 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. ___ 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] MH370 Doppler
I raised this on the Duncan Steel website and was pretty much blown off. Oh there is a nice stable OCXO aboard etc. Well DUHH yes there is an OCXO aboard and if it is good to -20 to +75C, or just -20 to +60C and there is a huge fire raging around it for an hour, and then perhaps later the plane decompresses at 32,000 feet and ice forms inside the aircraft that all has to be a factor to consider. The ATSB (Australian NTSB) report is mute on this as well. Plus the Doppler reports are only every hour or so, so there isn't much of a trendline. But some interesting excursions. I was surprised no time-nuts have ventured over to that blog. David I. Emery wrote: Of course if environment significantly changes the drift performance of that particular OCXO it is possible that temperature, or pressure or power conditions were so different on the fatal flight that the drift might be larger and unknown in character... not sure. It is an error to consider of course. Not clear to me how carefully it has been or what possible factors have been considered. But surely the folks doing the analysis know about these issues. -- Joe Leikhim Leikhim and Associates Communications Consultants Oviedo, Florida jleik...@leikhim.com 407-982-0446 WWW.LEIKHIM.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.
Re: [time-nuts] Cutler NAA on 24.0kHz....
Did measure NAA near Boston 8000uv using a dipole for 80 meters. Looking at various vlf receivers it looks like a LPF or maybe a BPF filter to a ne602 mixer followed by a tl081opamp LPF makes a direct conversion receiver. Then hit the tracor d-msk-r. Regards Paul WB8TSL On Mon, Aug 18, 2014 at 2:34 PM, Charles Steinmetz csteinm...@yandex.com wrote: Paul wrote: Nat Semi App Note 72 page 18, par. 6.4 shows the configuration for bandpass active filter. This matches the last LM3900 stage, so you would seem to be correct. The shift in filter frequency for 200bps is because the higher modulation rate results in a greater frequency shift. It's like 50hz instead of the 25hz of the 100bps rate. Robert wrote: It's simple, but not obvious. The LM3900 is a Norton amplifier, and while it has differential inputs they are current driven. * * * Both the upper amplifier and the second lower amplifier have 1M feedback resistors, and + inputs fed 10V by 1M bias resistors. That would bias the output at near the supply rail, turning these stages into something like half-wave rectifiers. Since the first lower stage has a 2M bias resistor it idles at about half supply, and behaves as a simple inverter. * * * combining the two outputs produces a negative going full wave rectification of the signal. The fourth LM3900 stage looks like an inverting bandpass filter, but I'd have to dig out some reference books to determine its behavior in more detail. As f or the 100-200 switch I'm confused, why would the bandpass frequency be lowered for the higher modulation rate? The circuit as a whole operates as a frequency doubler using full-wave rectification and filtering. The rx LO is 100Hz below the nominal carrier frequency, so in normal (non-MSK) mode, the IF frequency is 100Hz. Referring to the MSK addendum, a received 200 baud MSK signal is 50Hz below nominal, and a 100 baud MSK signal is 25Hz below nominal. With the LO 100 Hz below nominal, this makes the IF frequency 50Hz when receiving a 200 baud MSK signal, and 75 Hz when receiving a 100 baud MSK signal. After doubling, these become 100 Hz (200 baud) and 150 Hz (100 baud), so the BPF is switchable between 100Hz and 150Hz. They used a FET to chop the 150Hz (100 baud) signal with a 50Hz square wave. I can't say I'm impressed with the design, even for the era. The whole instrument is built mostly with LM3900s, which makes it thousands (maybe even millions) of times noisier than it would be if it had been properly designed with standard op-amps. It may work more or less, but it's a fugly way to get there. There are other questionable choices (like the FET chopper, an overall design that depends on lots of one-shots, etc.). The designers knew about the LM301 (there is one in the unit), so there was really no excuse for using LM3900s. Yeah, the 301 was more expensive -- but this was supposed to be a state-of-the-art measuring device for characterizing good OCXOs down to PPB or below. I simulated the MSK board in LTspice. Let me know (OFFLIST ONLY, please) if you would like the files to play with (662kB ZIP file). (Note that these won't do you any good if you're not an LTspice user.) Again, please do not clutter the list with requests for files -- OFFLIST ONLY, please (check your headers carefully before you hit Send). Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/ mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Ublox neo-7M GPS
I have a dozen ublox max-7's on hand and should have suitable PCB's for the analysis in a couple of days. Unfortunately I don't have the analyser, the test kit is currently limited to a HP5834A recently calibrated to Rb and a 100MHz DSO so probably not what your looking for. Let me know if I can help though. On Wed, Aug 20, 2014 at 9:11 AM, Ed Palmer ed_pal...@sasktel.net wrote: Does anyone have a neo-7M and an HP 5371A or a 5372A Analyzer? Use the Histogram Time Interval function to measure a block of samples. That will show the length of the samples with a resolution of 200 ps. That's what I did a couple of years ago when I analyzed the Navsync CW-12 with the old and new firmware. -- -- Teach your kids Science, or somebody else will :/ ja...@ball.net vk2...@google.com callsign: vk2vjb ___ 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] Ublox neo-7M GPS
Bert wrote: I guess time nuts like to talk about it but not fix it. Will you PLEASE quit beating this tired old drum? All of us know this is your opinion, although many of us have other explanations for the phenomena you think it explains. We do not need you to repeat it every time you post, and it is offensive. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] MH370 Doppler
The total Doppler in this case is on the order of 100 Hz. The tiny frequency shifts of an out of spec OCXO is just to small to measure. The data says at UTC 18:30 the shift was in the mid range and was about 175Hz. Assume the OCXO drifts 10 parts per million. That is a lot for an OCXO. But maybe the effect is only about 50 feet on the ground. The OCXO error of even 1E-5 is just not very important as it does not move the aircrafts ground track enough to matter. On Tue, Aug 19, 2014 at 6:26 PM, Joe Leikhim jleik...@leikhim.com wrote: I raised this on the Duncan Steel website and was pretty much blown off. Oh there is a nice stable OCXO aboard etc. Well DUHH yes there is an OCXO aboard and if it is good to -20 to +75C, or just -20 to +60C and there is a huge fire raging around it for an hour, and then perhaps later the plane decompresses at 32,000 feet and ice forms inside the aircraft that all has to be a factor to consider. The ATSB (Australian NTSB) report is mute on this as well. Plus the Doppler reports are only every hour or so, so there isn't much of a trendline. But some interesting excursions. I was surprised no time-nuts have ventured over to that blog. David I. Emery wrote: Of course if environment significantly changes the drift performance of that particular OCXO it is possible that temperature, or pressure or power conditions were so different on the fatal flight that the drift might be larger and unknown in character... not sure. It is an error to consider of course. Not clear to me how carefully it has been or what possible factors have been considered. But surely the folks doing the analysis know about these issues. -- Joe Leikhim Leikhim and Associates Communications Consultants Oviedo, Florida jleik...@leikhim.com 407-982-0446 WWW.LEIKHIM.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. -- Chris Albertson Redondo Beach, California ___ 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.
