Re: [time-nuts] A small piece on HP's hydrogen maser in 1968
rich...@karlquist.com said: Solid dielectric cable and connectors of 3.5 mm size are mode limited to 18 GHz. That is why there is so much stuff rated at 18 GHz as opposed to 16 or 20 GHz. Thanks. That's what I was looking for. Wiki says that SMA works to 18 GHz and the 3.5 mm is good for 34 GHz. http://en.wikipedia.org/wiki/SMA_connector#Variations -- 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] DS3231m 1HZ output stability
Do you have a scope? Any overshoot/bounce crap? (Not likely with low power CMOS.) Attached is screenshot from USB-based scope. I'll going to switch wires to see any difference. -- WBW, V.P.attachment: gps2rtc.PNG___ 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] A small piece on HP's hydrogen maser in 1968
On 2/26/14 12:44 AM, Hal Murray wrote: rich...@karlquist.com said: Solid dielectric cable and connectors of 3.5 mm size are mode limited to 18 GHz. That is why there is so much stuff rated at 18 GHz as opposed to 16 or 20 GHz. Thanks. That's what I was looking for. Wiki says that SMA works to 18 GHz and the 3.5 mm is good for 34 GHz. http://en.wikipedia.org/wiki/SMA_connector#Variations And, as pointed out earlier, the market is smaller, so volumes are smaller, and driving the price down from being able to change to truly mass production is harder. There's also a manufacturing tolerance issue. The higher you go, the tighter the mechanical tolerances get. I suspect there is a huge amount of tooling out there for SMA connectors and other things of that size where the machining tolerances are good enough for SMA and 18GHz, but not good enough for higher. That drives all sorts of things. THere's also semiconductor parts. Lots and lots of stuff in the under 12-13 GHz range that are inexpensive. A fair amount up to 18-ish, and then it sort of falls off. There, it's driven by market, which in turn is driven by international allocations. DBS satellites at 12-13 GHz is a high volume market, so there's lots of things like MMIC low noise amplifiers. Likewise anything around 2.45 or 5.1-5.8 GHz. You see a big break in RF equipment model capability at 3GHz and 6GHz, and I suspect that's driven by the desire to test cellphones and wifi and BT (3 GHz) and 802.11a/802.11n, WiMax, etc at 6GHz. Parts that are cheap and easy to use lead to interesting products like the SignalHound spectrum analyzer, but I don't expect to see a 50GHz SignalHound any time soon. ($900 for 4.4 GHz, $2k for 12.4GHz). You could probably *build* a front end converter for a signal hound fairly inexpensively, but the parts for, say, 32 GHz would cost as much as the Signal Hound backend. ___ 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] DS3231m 1HZ output stability
To answering myself: I think nothing wrong with DS32XX. I hooked up GPS 1PPS output to the same timer (different channel) where I have 1PPS from RTC. Now I see something like this. # Delta GPS: 7330, Delta RTC: 7330 # Delta GPS: 7330, Delta RTC: 7329 # Delta GPS: 7330, Delta RTC: 7329 # Delta GPS: 7330, Delta RTC: 7330 # Delta GPS: 7330, Delta RTC: 7330 # Delta GPS: 405, Delta RTC: 705 # Delta GPS: 405, Delta RTC: 705 # Delta GPS: 7330, Delta RTC: 7330 Definitely something wrong with my code or the way how MCU handle different events (interrupts). Reggards, V.P. On 2014-02-25 17:32, Tom Van Baak wrote: I would like to ask if somebody did measurement for that Dallas DS32XX series chips. Is that 1PPS (1HZ square wave) stable there or it has some issues ? I am thinking that burp in my tests could be because of my poor code or may be because of DS32XX doing temperature conversion every second, which cause an impact to the 1HZ output. I would be interested to hear any information about. From the datasheet of DS3231m , that 1HZ from DS32XX should be stable. Both the GPS and DS32XX 1PPS should be fine. Are your free-run counters really free? It looks like a simple bug in your code. All this is very easy to debug if you have even the most basic frequency or time interval counter available to independently validate the GPS or the DS32XX 1PPS interval. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- WBW, V.P. ___ 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] Serial port splitter s/w
I'm running Meinberg NTP on the Windows 7 x64 machine to which my Thunderbolt is attached. I'd like to be able to share the serial port between LH and NTP so that I can run the machine as an NTP Stratum 1 server locked to the TB, and also be able to use LH to check things. I looked around the with Google, and saw *numerous serial port splitters. Which is recommended? Also what's the best way how to configure NTP to lock the the TB on a serial port? Do I need to modify the TB to deliver the PPS down one of the serial data lines or will NTP work well by parsing the NMEA time messages? Many thanks David Partridge ___ 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] Thermal Compensation: Digital vs Analog
I've been experimenting with digital thermal compensation on my GPSDO. The results have been favorable for a 14 bit dithered PWM-based DAC, but leaves a bit to be desired in the big picture. And it takes up a lot of program bytes on my PIC.. What's the general consensus on this? Should thermal compensation be completely analog? Bob - AE6RV ___ 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] A small piece on HP's hydrogen maser in 1968
Gravity Probe A used Hydrogen Masers to verify gravitational rate change. 1976 and suborbital, so not exactly the same as Red Shift mentioned in the HP note. I myself participated in a variation of Pound-Rebka-Snider (Mossbauer nuclear physics techniques) in the 1980's. On Mon, Feb 24, 2014 at 7:53 PM, Jim Lux jim...@earthlink.net wrote: On 2/24/14 8:17 AM, Poul-Henning Kamp wrote: In message CAA-F0u_jBZ5dyB+hacMwFPkz6VhFo7arZ+ jpsmhrt9uss2n...@mail.gmail.com , Pete Lancashire writes: http://www.hp.com/hpinfo/abouthp/histnfacts/ publications/measure/pdf/1968_09.pdf pages 8 9 As far as I know, those satellites never made it to orbit ? Wasn't that Gravity Probe B.. which finally launched in 2004, and had equivocal results. Also: You can just see the writer twist his brain in order to get to that final punch-line :-) ___ 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] Thermal Compensation: Digital vs Analog
On Wed, 26 Feb 2014 08:09:44 -0800 (PST) Bob Stewart b...@evoria.net wrote: I've been experimenting with digital thermal compensation on my GPSDO. The results have been favorable for a 14 bit dithered PWM-based DAC, but leaves a bit to be desired in the big picture. And it takes up a lot of program bytes on my PIC.. What's the general consensus on this? Should thermal compensation be completely analog? Out of pure interest. Could you elaborate what results you got? Ie. what does your GPSDO look like? How do you compensate for the temperature coefficient? How much did that improve performance compared to non-compensated operation? Did you try any other approaches? Why? Why not? Yes, i'm a curious mind :-) Thanks in advance Attila Kinali -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin ___ 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] Serial port splitter s/w
I'm running Meinberg NTP on the Windows 7 x64 machine to which my Thunderbolt is attached. I'd like to be able to share the serial port between LH and NTP so that I can run the machine as an NTP Stratum 1 server locked to the TB, and also be able to use LH to check things. I looked around the with Google, and saw *numerous serial port splitters. Which is recommended? Also what's the best way how to configure NTP to lock the the TB on a serial port? Do I need to modify the TB to deliver the PPS down one of the serial data lines or will NTP work well by parsing the NMEA time messages? Many thanks David Partridge = David, Can't comment on the COM port splitters. For best results with NTP you need a PPS signal on the RS-232 DCD line. Using NMEA alone is often worse than just Internet sync. Look for a white flash with my Serial Port LEDs program: http://www.satsignal.eu/software/net.htm#SerialPortLEDs The pulse needs to be rather more than a few microseconds - 100-200 milliseconds is typically used. Cheers, David -- 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] Thermal Compensation: Digital vs Analog
Hi Atilla, The GPSDO is VE2ZAZ's circuit with new code. It detects phase crossings to change the DAC, so it has a phase crossing for every update. I'm working on a TIC design but haven't started on the hardware. In the interim, I hooked up an LM34 thermistor and have been playing with that. In the 8 hour plot below, there are no frequency updates, only temperature updates. I've tried a rolling average, but it doesn't smooth it enough, so I'll have to try hysteresis next. The orange/green/blue line is the DAC. The red line is the thermistor. The cyan smear is the phase plot of 1PPS from my Adafruit (MT3339) against the OCXO (Trimble 34310-T). The units on the right correspond to the temperature - 100 degrees at the EFC divider directly beneath the OCXO. Also, they correspond to the wrapped phase, where 0-20 is 0-360 degrees. The OCXO is limited to a swing of about +/- 1.1Hz at the moment. http://www.evoria.net/AE6RV/TempComp/GPSDO.png In the plot below is the ADEV. Hopefully it's self explanatory. The phase has varied a bit more than 180 degrees during the test. http://www.evoria.net/AE6RV/TempComp/ADEV.png The biggest influence on temperature seems to be the low quality divider resistors in the EFC divider chain. I have new low TempCo resistors but I couldn't resist playing with these first. Without temperature compensation, phase would vary through about one cycle every change to the red (thermistor) line. Bob - AE6RV From: Attila Kinali att...@kinali.ch To: Bob Stewart b...@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wednesday, February 26, 2014 10:23 AM Subject: Re: [time-nuts] Thermal Compensation: Digital vs Analog On Wed, 26 Feb 2014 08:09:44 -0800 (PST) Bob Stewart b...@evoria.net wrote: I've been experimenting with digital thermal compensation on my GPSDO. The results have been favorable for a 14 bit dithered PWM-based DAC, but leaves a bit to be desired in the big picture. And it takes up a lot of program bytes on my PIC.. What's the general consensus on this? Should thermal compensation be completely analog? Out of pure interest. Could you elaborate what results you got? Ie. what does your GPSDO look like? How do you compensate for the temperature coefficient? How much did that improve performance compared to non-compensated operation? Did you try any other approaches? Why? Why not? Yes, i'm a curious mind :-) Thanks in advance Attila Kinali -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin ___ 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] Serial port splitter s/w
It's not going to work. If the purpose of running the Thunderbolt is only to drive NTP then you don't need LH. NTP's only tags the pulses to the nearest microsecond, nano sec on accuracy is lost on NTP. I'd even say the TB is the wrong GPS for NTP. It costs to much and uses to much power. But if you are also, or mainly, using the Thunderbolt for it's 10Mhz and NTP is a secondary function then a TB makes sense. Yes you NEED the PPS on the serial cable. Thunderbolts do not send NMEA. Thunderbolts send their own data format that is unique to Trimble. Don't modify the GPS receiver. Make a special cable adapter. When you do this pay attention to polarity of the PPS signal. It is easy to get it backwards. You want the raising edge of the TB pulse to interrupt the computer. It you invert the signal the wrong number of times the time will be off by the ouse length and I don't know if the pulse length is controlled to the level the leading edge is.Remember RS232 uses negative and positive voltage, data lines use negative logic, control lines positive. The TB's PPS is TTL level. Many rs232 ports do accept t/l level if you get the polariy correct. Again don't even bother to run an NTP server without PPS. You may as well just get time from some internet time servers. You can NOT control a GPS from two ports. Both NTP and LH will try to send commands to the GPS. Likely, almost certainly you need to build a small circuit board the has two connectors that face the TB (PPS and serial) and one that faces the computer. The little perfboard makes a neat way to or connect cables but you could solder up a y--cable The best thing to do is get a cheaper GPS, and one that uses less power to drive the NTP server. The old Motorola Oncore series are cheap and the new breed of very small GPSes are good too. DOn't spend more than $40 or $50 on a GPS to drive NTP as ,again NTP record microseconds. You could free up that Windows PC too. It is not the best platform for NTP. Asmall ARM based system (even the Rasbery Pi) will outperform a Windows based NTP server. and use a LOT less power (Power cost for a NTP server is more than you think, it came to about $300 a year for me if I used a standard PC and a thunderbolt. Switching to a very tiny ARM based system and a smaller GPS gave as good performance and power savings paid for the hardware in 1/2 a year. $.21/KWH about 170W and 8760 hours per year comes to a $300 power bill. My current system is powered by a 1000 mw plug-in power cube and does not need a cooling fan. On Wed, Feb 26, 2014 at 7:53 AM, David C. Partridge david.partri...@perdrix.co.uk wrote: I'm running Meinberg NTP on the Windows 7 x64 machine to which my Thunderbolt is attached. I'd like to be able to share the serial port between LH and NTP so that I can run the machine as an NTP Stratum 1 server locked to the TB, and also be able to use LH to check things. I looked around the with Google, and saw *numerous serial port splitters. Which is recommended? Also what's the best way how to configure NTP to lock the the TB on a serial port? Do I need to modify the TB to deliver the PPS down one of the serial data lines or will NTP work well by parsing the NMEA time messages? Many thanks David Partridge ___ 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] Serial port splitter s/w
Here is interesting topic about NTP on Raspberry PI (typical usage of ARM and Linux bread on top of it) http://www.synclab.org/?tag=testing Basically, TCP stack on ARM usually come from one source - its a Adam Dunken TCP stack. Then its is MII part and the hardware which doing Ethernet. In my opinion, MCU (ARM) could provide excellent Ethernet functions. However its far from serious dedicated ethernet controllers we could see in enterprise servers. Regards, V.P. On 2014-02-26 12:32, Chris Albertson wrote: It's not going to work. If the purpose of running the Thunderbolt is only to drive NTP then you don't need LH. NTP's only tags the pulses to the nearest microsecond, nano sec on accuracy is lost on NTP. I'd even say the TB is the wrong GPS for NTP. It costs to much and uses to much power. But if you are also, or mainly, using the Thunderbolt for it's 10Mhz and NTP is a secondary function then a TB makes sense. Yes you NEED the PPS on the serial cable. Thunderbolts do not send NMEA. Thunderbolts send their own data format that is unique to Trimble. Don't modify the GPS receiver. Make a special cable adapter. When you do this pay attention to polarity of the PPS signal. It is easy to get it backwards. You want the raising edge of the TB pulse to interrupt the computer. It you invert the signal the wrong number of times the time will be off by the ouse length and I don't know if the pulse length is controlled to the level the leading edge is.Remember RS232 uses negative and positive voltage, data lines use negative logic, control lines positive. The TB's PPS is TTL level. Many rs232 ports do accept t/l level if you get the polariy correct. Again don't even bother to run an NTP server without PPS. You may as well just get time from some internet time servers. You can NOT control a GPS from two ports. Both NTP and LH will try to send commands to the GPS. Likely, almost certainly you need to build a small circuit board the has two connectors that face the TB (PPS and serial) and one that faces the computer. The little perfboard makes a neat way to or connect cables but you could solder up a y--cable The best thing to do is get a cheaper GPS, and one that uses less power to drive the NTP server. The old Motorola Oncore series are cheap and the new breed of very small GPSes are good too. DOn't spend more than $40 or $50 on a GPS to drive NTP as ,again NTP record microseconds. You could free up that Windows PC too. It is not the best platform for NTP. Asmall ARM based system (even the Rasbery Pi) will outperform a Windows based NTP server. and use a LOT less power (Power cost for a NTP server is more than you think, it came to about $300 a year for me if I used a standard PC and a thunderbolt. Switching to a very tiny ARM based system and a smaller GPS gave as good performance and power savings paid for the hardware in 1/2 a year. $.21/KWH about 170W and 8760 hours per year comes to a $300 power bill. My current system is powered by a 1000 mw plug-in power cube and does not need a cooling fan. On Wed, Feb 26, 2014 at 7:53 AM, David C. Partridge david.partri...@perdrix.co.uk wrote: I'm running Meinberg NTP on the Windows 7 x64 machine to which my Thunderbolt is attached. I'd like to be able to share the serial port between LH and NTP so that I can run the machine as an NTP Stratum 1 server locked to the TB, and also be able to use LH to check things. I looked around the with Google, and saw *numerous serial port splitters. Which is recommended? Also what's the best way how to configure NTP to lock the the TB on a serial port? Do I need to modify the TB to deliver the PPS down one of the serial data lines or will NTP work well by parsing the NMEA time messages? Many thanks David Partridge ___ 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. -- WBW, V.P. ___ 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] Serial port splitter s/w
I have some problems with My 8505A Analyzer, it has no RF output, I checked the YTO and other frequency dividers and it appears to be OK some times there is RF output only it will not tune and it seems to cut out as I tune trough the frequency range. Thank You Sal C. Cornacchia Electronic RF Engineer Ret. On Wednesday, February 26, 2014 12:33:17 PM, Chris Albertson albertson.ch...@gmail.com wrote: It's not going to work. If the purpose of running the Thunderbolt is only to drive NTP then you don't need LH. NTP's only tags the pulses to the nearest microsecond, nano sec on accuracy is lost on NTP. I'd even say the TB is the wrong GPS for NTP. It costs to much and uses to much power. But if you are also, or mainly, using the Thunderbolt for it's 10Mhz and NTP is a secondary function then a TB makes sense. Yes you NEED the PPS on the serial cable. Thunderbolts do not send NMEA. Thunderbolts send their own data format that is unique to Trimble. Don't modify the GPS receiver. Make a special cable adapter. When you do this pay attention to polarity of the PPS signal. It is easy to get it backwards. You want the raising edge of the TB pulse to interrupt the computer. It you invert the signal the wrong number of times the time will be off by the ouse length and I don't know if the pulse length is controlled to the level the leading edge is. Remember RS232 uses negative and positive voltage, data lines use negative logic, control lines positive. The TB's PPS is TTL level. Many rs232 ports do accept t/l level if you get the polariy correct. Again don't even bother to run an NTP server without PPS. You may as well just get time from some internet time servers. You can NOT control a GPS from two ports. Both NTP and LH will try to send commands to the GPS. Likely, almost certainly you need to build a small circuit board the has two connectors that face the TB (PPS and serial) and one that faces the computer. The little perfboard makes a neat way to or connect cables but you could solder up a y--cable The best thing to do is get a cheaper GPS, and one that uses less power to drive the NTP server. The old Motorola Oncore series are cheap and the new breed of very small GPSes are good too. DOn't spend more than $40 or $50 on a GPS to drive NTP as ,again NTP record microseconds. You could free up that Windows PC too. It is not the best platform for NTP. Asmall ARM based system (even the Rasbery Pi) will outperform a Windows based NTP server. and use a LOT less power (Power cost for a NTP server is more than you think, it came to about $300 a year for me if I used a standard PC and a thunderbolt. Switching to a very tiny ARM based system and a smaller GPS gave as good performance and power savings paid for the hardware in 1/2 a year. $.21/KWH about 170W and 8760 hours per year comes to a $300 power bill. My current system is powered by a 1000 mw plug-in power cube and does not need a cooling fan. On Wed, Feb 26, 2014 at 7:53 AM, David C. Partridge david.partri...@perdrix.co.uk wrote: I'm running Meinberg NTP on the Windows 7 x64 machine to which my Thunderbolt is attached. I'd like to be able to share the serial port between LH and NTP so that I can run the machine as an NTP Stratum 1 server locked to the TB, and also be able to use LH to check things. I looked around the with Google, and saw *numerous serial port splitters. Which is recommended? Also what's the best way how to configure NTP to lock the the TB on a serial port? Do I need to modify the TB to deliver the PPS down one of the serial data lines or will NTP work well by parsing the NMEA time messages? Many thanks David Partridge ___ 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. ___ 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] Serial port splitter s/w
Ummm think you sent the question to the wrong group perhaps? On Wed, Feb 26, 2014 at 12:50 PM, corc...@yahoo.ca wrote: I have some problems with My 8505A Analyzer, it has no RF output, I checked the YTO and other frequency dividers and it appears to be OK some times there is RF output only it will not tune and it seems to cut out as I tune trough the frequency range. Thank You Sal C. Cornacchia Electronic RF Engineer Ret. On Wednesday, February 26, 2014 12:33:17 PM, Chris Albertson albertson.ch...@gmail.com wrote: It's not going to work. If the purpose of running the Thunderbolt is only to drive NTP then you don't need LH. NTP's only tags the pulses to the nearest microsecond, nano sec on accuracy is lost on NTP. I'd even say the TB is the wrong GPS for NTP. It costs to much and uses to much power. But if you are also, or mainly, using the Thunderbolt for it's 10Mhz and NTP is a secondary function then a TB makes sense. Yes you NEED the PPS on the serial cable. Thunderbolts do not send NMEA. Thunderbolts send their own data format that is unique to Trimble. Don't modify the GPS receiver. Make a special cable adapter. When you do this pay attention to polarity of the PPS signal. It is easy to get it backwards. You want the raising edge of the TB pulse to interrupt the computer. It you invert the signal the wrong number of times the time will be off by the ouse length and I don't know if the pulse length is controlled to the level the leading edge is.Remember RS232 uses negative and positive voltage, data lines use negative logic, control lines positive. The TB's PPS is TTL level. Many rs232 ports do accept t/l level if you get the polariy correct. Again don't even bother to run an NTP server without PPS. You may as well just get time from some internet time servers. You can NOT control a GPS from two ports. Both NTP and LH will try to send commands to the GPS. Likely, almost certainly you need to build a small circuit board the has two connectors that face the TB (PPS and serial) and one that faces the computer. The little perfboard makes a neat way to or connect cables but you could solder up a y--cable The best thing to do is get a cheaper GPS, and one that uses less power to drive the NTP server. The old Motorola Oncore series are cheap and the new breed of very small GPSes are good too. DOn't spend more than $40 or $50 on a GPS to drive NTP as ,again NTP record microseconds. You could free up that Windows PC too. It is not the best platform for NTP. Asmall ARM based system (even the Rasbery Pi) will outperform a Windows based NTP server. and use a LOT less power (Power cost for a NTP server is more than you think, it came to about $300 a year for me if I used a standard PC and a thunderbolt. Switching to a very tiny ARM based system and a smaller GPS gave as good performance and power savings paid for the hardware in 1/2 a year. $.21/KWH about 170W and 8760 hours per year comes to a $300 power bill. My current system is powered by a 1000 mw plug-in power cube and does not need a cooling fan. On Wed, Feb 26, 2014 at 7:53 AM, David C. Partridge david.partri...@perdrix.co.uk wrote: I'm running Meinberg NTP on the Windows 7 x64 machine to which my Thunderbolt is attached. I'd like to be able to share the serial port between LH and NTP so that I can run the machine as an NTP Stratum 1 server locked to the TB, and also be able to use LH to check things. I looked around the with Google, and saw *numerous serial port splitters. Which is recommended? Also what's the best way how to configure NTP to lock the the TB on a serial port? Do I need to modify the TB to deliver the PPS down one of the serial data lines or will NTP work well by parsing the NMEA time messages? Many thanks David Partridge ___ 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. ___ 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] Thermal Compensation: Digital vs Analog
Hi Bob, better use an FIR. Your rolling average didn't smooth out enough because it doesn't have a cutoff low enough. Hysteresis is not going to help here that I know of. Cheers, D. On Wed, Feb 26, 2014 at 6:05 PM, Bob Stewart b...@evoria.net wrote: Hi Atilla, The GPSDO is VE2ZAZ's circuit with new code. It detects phase crossings to change the DAC, so it has a phase crossing for every update. I'm working on a TIC design but haven't started on the hardware. In the interim, I hooked up an LM34 thermistor and have been playing with that. In the 8 hour plot below, there are no frequency updates, only temperature updates. I've tried a rolling average, but it doesn't smooth it enough, so I'll have to try hysteresis next. The orange/green/blue line is the DAC. The red line is the thermistor. The cyan smear is the phase plot of 1PPS from my Adafruit (MT3339) against the OCXO (Trimble 34310-T). The units on the right correspond to the temperature - 100 degrees at the EFC divider directly beneath the OCXO. Also, they correspond to the wrapped phase, where 0-20 is 0-360 degrees. The OCXO is limited to a swing of about +/- 1.1Hz at the moment. http://www.evoria.net/AE6RV/TempComp/GPSDO.png In the plot below is the ADEV. Hopefully it's self explanatory. The phase has varied a bit more than 180 degrees during the test. http://www.evoria.net/AE6RV/TempComp/ADEV.png The biggest influence on temperature seems to be the low quality divider resistors in the EFC divider chain. I have new low TempCo resistors but I couldn't resist playing with these first. Without temperature compensation, phase would vary through about one cycle every change to the red (thermistor) line. Bob - AE6RV From: Attila Kinali att...@kinali.ch To: Bob Stewart b...@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wednesday, February 26, 2014 10:23 AM Subject: Re: [time-nuts] Thermal Compensation: Digital vs Analog On Wed, 26 Feb 2014 08:09:44 -0800 (PST) Bob Stewart b...@evoria.net wrote: I've been experimenting with digital thermal compensation on my GPSDO. The results have been favorable for a 14 bit dithered PWM-based DAC, but leaves a bit to be desired in the big picture. And it takes up a lot of program bytes on my PIC.. What's the general consensus on this? Should thermal compensation be completely analog? Out of pure interest. Could you elaborate what results you got? Ie. what does your GPSDO look like? How do you compensate for the temperature coefficient? How much did that improve performance compared to non-compensated operation? Did you try any other approaches? Why? Why not? Yes, i'm a curious mind :-) Thanks in advance Attila Kinali -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin ___ 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] Serial port splitter s/w
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Re: [time-nuts] Thermal Compensation: Digital vs Analog
If you can understand the temperature effects and can model them accurately and you can measure temperatures and your DAC steps are small enough, then digital compensation can be perfect. But you are unlikely to meet all those conditions. In theory if the problem is that the voltage diver's ratio is a function of temperature then you can epoxy the LM34 to the divider and adjust the output of the DAC based on the current divider ratio. But in the real word you don't know the exact function or temperature and the DAC might have larger steps. I think the best plan is to reduce the source of the error, (the analog fix) Then if there is still any error source you can measure and model to that too. On Wed, Feb 26, 2014 at 8:09 AM, Bob Stewart b...@evoria.net wrote: I've been experimenting with digital thermal compensation on my GPSDO. The results have been favorable for a 14 bit dithered PWM-based DAC, but leaves a bit to be desired in the big picture. And it takes up a lot of program bytes on my PIC.. What's the general consensus on this? Should thermal compensation be completely analog? Bob - AE6RV ___ 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] Serial port splitter s/w
david.partri...@perdrix.co.uk said: I looked around the with Google, and saw *numerous serial port splitters. Which is recommended? If your lines are short, you don't need fancy hardware. The RS-232 driver will drive 2 lines. Just take 2 cables, cut them in half, connect the wires... Also what's the best way how to configure NTP to lock the the TB on a serial port? Do I need to modify the TB to deliver the PPS down one of the serial data lines or will NTP work well by parsing the NMEA time messages? Yes, you need to connect the PPS. You can get the PPS by just opening up the TB and soldering a wire from the BNC to the DB-9. You may/probably need a pulse stretcher. I have one TB where I changed the PPS wire to a diode and R/C. It's a kludge, but works. You can get a clean version from TAPR. It needs power. http://tapr.org/kits_fatpps.html TBs don't talk NMEA. Use the Palisade driver. The problem is that both LH and ntpd expect to talk to the TB. It may work if you let one of them listen to whatever traffic the other one generates. ntpd just sets it up so a couple of packet types get sent every second. If LH does something similar, it should work. (I think ntpd will ignore everything else. It it complains too loudly we can fix it.) -- 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] Serial port splitter s/w
On Wed, Feb 26, 2014 at 12:32 PM, Chris Albertson albertson.ch...@gmail.com wrote: You can NOT control a GPS from two ports. Both NTP and LH will try to send commands to the GPS. Actually the Palisades driver doesn't send commands to the Thunderbolt. It sends a single invalid command requesting auto messages and then parses the data stream. As long as primary timing packets are received it works. A Thunderbolt will wake up doing the right thing and if not I believe LH will correctly initialize it. The deeper point is correct and the Trimble devices I have experience with have ~100ms of jitter. Props to Jackson Labs -- my Fury has O(10) microseconds of jitter using NMEA messages. If only they were $100. ___ 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] Serial port splitter s/w
On Wed, Feb 26, 2014 at 9:53 AM, d0ct0r t...@patoka.org wrote: Here is interesting topic about NTP on Raspberry PI (typical usage of ARM and Linux bread on top of it) The article addresses using the Pi as an NTP server with stratum 0. In other words as an NTP server that uses another NTP server as its reference clock so it uses Ethernet for time transfer. In the OP's case he wants to build a Stratum = 0 server that uses GPS as a reference clock. Ethernet noise will not be an issue. The Pi might or might not be the best choise. There are now so many small and cheap ARM systems. You can even re-purpose an old ARM based router or small NAS. box. Except as an exercise there is almost no point any more using GPS to drive a local NTP server if you have a very good Internet connection. My fiber Internet connection is as good as Ethernet as the Pool Servers work well for me. Those using slower or a widely shared connection might not get as good a result. -- 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] Serial port splitter s/w
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Re: [time-nuts] Serial port splitter s/w
From: Chris Albertson [] Except as an exercise there is almost no point any more using GPS to drive a local NTP server if you have a very good Internet connection. My fiber Internet connection is as good as Ethernet as the Pool Servers work well for me. Those using slower or a widely shared connection might not get as good a result. Chris Albertson Redondo Beach, California === The Raspberry Pi with GPS/PPS certainly beats any internet connection I've ever had delivered to this house, though: http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html http://www.satsignal.eu/mrtg/performance_ntp.php Cheers, David -- 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] Serial port splitter s/w
On Wed, Feb 26, 2014 at 11:15 AM, David J Taylor david-tay...@blueyonder.co.uk wrote: The Raspberry Pi with GPS/PPS certainly beats any internet connection I've ever had delivered to this house, though: Yes it will. But the point of the server is to deliver time to other computers. The the measure is goodness is not the accuracy of your local NTP server but the accuracy of the client computers that use it. So if I point my desktop computer at a set of 5 to 7 Internet pool servers or it I point the same desktop to my local NTP server I don't se a lot of difference. With the notebook computer using WiFi I don't see any difference. This is what I moment by saying it is hardly worth it if you happen to have Ethernet-like connectivity all the way back to your ISP. Of douse many people don't and have to use DSL or Cable TV lines. The ARM has some real potential for time keeping. Inside the chip in addition to the ARM CPU are two RPU processors. Thee run at exactly 200MHz one instruction per cycle with very deterministic timing. They have access to all of the ARM memory and interrupts. They are in effect two micro controllers that are in addition to however many ARM cores there are. A really good project would be to move NTP's PPS timing to a PRU.But as I said the weak link is getting time OUT of the NTP server, not into it. But again the ARM is great for real time because it has both the ARM cores runnig Linux and the PRUs that you can program in assembly with deterministic timing. But as of today I don't think the PRUs are used for this but see below, lots of potential uses for building things like TICs http://processors.wiki.ti.com/index.php/Programmable_Realtime_Unit_Subsystem http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html http://www.satsignal.eu/mrtg/performance_ntp.php Cheers, David -- 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. -- 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] Serial port splitter s/w
From: Chris Albertson Sent: Wednesday, February 26, 2014 7:32 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Serial port splitter s/w On Wed, Feb 26, 2014 at 11:15 AM, David J Taylor david-tay...@blueyonder.co.uk wrote: The Raspberry Pi with GPS/PPS certainly beats any internet connection I've ever had delivered to this house, though: Yes it will. But the point of the server is to deliver time to other computers. The the measure is goodness is not the accuracy of your local NTP server but the accuracy of the client computers that use it. So if I point my desktop computer at a set of 5 to 7 Internet pool servers or it I point the same desktop to my local NTP server I don't se a lot of difference. With the notebook computer using WiFi I don't see any difference. This is what I moment by saying it is hardly worth it if you happen to have Ethernet-like connectivity all the way back to your ISP. Of douse many people don't and have to use DSL or Cable TV lines. The ARM has some real potential for time keeping. Inside the chip in addition to the ARM CPU are two RPU processors. Thee run at exactly 200MHz one instruction per cycle with very deterministic timing. They have access to all of the ARM memory and interrupts. They are in effect two micro controllers that are in addition to however many ARM cores there are. A really good project would be to move NTP's PPS timing to a PRU.But as I said the weak link is getting time OUT of the NTP server, not into it. But again the ARM is great for real time because it has both the ARM cores runnig Linux and the PRUs that you can program in assembly with deterministic timing. But as of today I don't think the PRUs are used for this but see below, lots of potential uses for building things like TICs http://processors.wiki.ti.com/index.php/Programmable_Realtime_Unit_Subsystem = Chris, even with Wi-Fi connected computers, mostly running Windows, there is a huge difference between talking to a stratum-1 server on my LAN compared to running just Internet servers. Our experiences differ, as I am on a cable modem connection from the UK's Virgin Media. Folks need to measure what performance they are getting and choose their own best path, otherwise it's guesswork. Cheers, David -- 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] Serial port splitter s/w
Chris, even with Wi-Fi connected computers, mostly running Windows, there is a huge difference between talking to a stratum-1 server on my LAN compared to running just Internet servers. Our experiences differ, as I am on a cable modem connection from the UK's Virgin Media. Folks need to measure what performance they are getting and choose their own best path, otherwise it's guesswork. Yes, exactly. It depends entirely on your internet connection. As soon as you get even slow 10Mb/s fiber the distinction between LAN and Internet starts to melt away. The problem with Cable TV is that it is a shared connection with who knows how many others. Shared media have collisions with back off and retries and are not deterministic. I do have a local NTP server. I had one back in the days of dial-up phone modems and still have one with my current fiber connection. I was just pointing out that the local NTP server is less useful as the Internet connections get better. Every few years I get motivated to improve the NTP server. The next step is for certain going to be to use the ARM's PRUs somehow. That would remove the effect of the OS from timing which is now the largest source of error. Cheers, David -- 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. -- 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] Serial port splitter s/w
On Wed, Feb 26, 2014 at 2:05 PM, Chris Albertson albertson.ch...@gmail.comwrote: Chris, even with Wi-Fi connected computers, mostly running Windows, there is a huge difference between talking to a stratum-1 server on my LAN compared to running just Internet servers. Our experiences differ, as I am on a cable modem connection from the UK's Virgin Media. Folks need to measure what performance they are getting and choose their own best path, otherwise it's guesswork. Yes, exactly. It depends entirely on your internet connection. As soon as you get even slow 10Mb/s fiber the distinction between LAN and Internet starts to melt away. The problem with Cable TV is that it is a shared connection with who knows how many others. Shared media have collisions with back off and retries and are not deterministic. Not generally with broadband. (True broadband that is, such as Internet-over-cable. I do find it annoying that all higher-speed, i.e. non-dial-up, access is referred to as broadband.) There are no collisions coming downstream because there is only one source -- the head end. There you just have variable queueing delays if a burst of traffic exceeding downstream capacity arrives at once. Collisions are possible on the upstream but less likely. I do have a local NTP server. I had one back in the days of dial-up phone modems and still have one with my current fiber connection. I was just pointing out that the local NTP server is less useful as the Internet connections get better. True, but far more deterministic. As you suggest, a local NTP server is independent of upstream traffic, queueing, and backoff/retry delays. Personally I would like to have a local stratum-1 source for that reason. -- Brian Lloyd, WB6RQN/J79BPL 706 Flightline Drive Spring Branch, TX 78070 br...@lloyd.com +1.916.877.5067 ___ 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] Question for Fluke 732A owners
Fluke used two different connector schemes for the DC input on 732A battery packs. The oldest units have a pair of banana jacks, and later units use a 3-pin connector made by Hypertronics. My question concerns only the latter (732A battery packs with the Hypertronics connectors). The Hypertronics contacts are interchangeable between the panel mount connector body and the plug body. It is customary to build the panel mount connectors with female contacts, and the plugs with male contacts. However, it appears that Fluke may have made at least some 732A battery packs with male contacts in the panel mount connectors. I'd be interested to know what is out there in the field. If you have a 732A battery module with the Hypertronics 3-pin connector, could you please look at the connector and let me know if the contacts are male or female? Just to be painfully clear, I'm referring to the gold-plated metal contacts only, not to the black plastic parts of the connector. The gold-plated metal contacts can be male (i.e., the metal part you can see is a solid pin) or female (i.e., the metal part you can see is a hole that will accept a pin). Thank you, 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] Serial port splitter s/w
You guys have me persuaded - I'll get a Raspberry Pi ... Regards, David Partridge -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of David J Taylor Sent: 26 February 2014 19:15 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Serial port splitter s/w The Raspberry Pi with GPS/PPS certainly beats any internet connection I've ever had delivered to this house, though: http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html http://www.satsignal.eu/mrtg/performance_ntp.php Cheers, David -- 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] Serial port splitter s/w
Serial outputs can usually drive several serial inputs if the cables are short (to avoid reflections). You can wire it yourself, serial out from the TB to both LH and NTP, serial in from LH only. David On 2/26/14 11:51 AM, David J Taylor wrote: I'm running Meinberg NTP on the Windows 7 x64 machine to which my Thunderbolt is attached. I'd like to be able to share the serial port between LH and NTP so that I can run the machine as an NTP Stratum 1 server locked to the TB, and also be able to use LH to check things. I looked around the with Google, and saw *numerous serial port splitters. Which is recommended? Also what's the best way how to configure NTP to lock the the TB on a serial port? Do I need to modify the TB to deliver the PPS down one of the serial data lines or will NTP work well by parsing the NMEA time messages? Many thanks David Partridge = David, Can't comment on the COM port splitters. For best results with NTP you need a PPS signal on the RS-232 DCD line. Using NMEA alone is often worse than just Internet sync. Look for a white flash with my Serial Port LEDs program: http://www.satsignal.eu/software/net.htm#SerialPortLEDs The pulse needs to be rather more than a few microseconds - 100-200 milliseconds is typically used. Cheers, David ___ 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] A small piece on HP's hydrogen maser in 1968
Hi One of the more common explanations for the 18 GHz “upper limit” is that the broad water vapor absorption peak at about 23 GHz made systems less practical as you went up from 18. I suspect the same water issues make certain types of parts more difficult to fabricate. Bob On Feb 26, 2014, at 9:01 AM, Jim Lux jim...@earthlink.net wrote: On 2/26/14 12:44 AM, Hal Murray wrote: rich...@karlquist.com said: Solid dielectric cable and connectors of 3.5 mm size are mode limited to 18 GHz. That is why there is so much stuff rated at 18 GHz as opposed to 16 or 20 GHz. Thanks. That's what I was looking for. Wiki says that SMA works to 18 GHz and the 3.5 mm is good for 34 GHz. http://en.wikipedia.org/wiki/SMA_connector#Variations And, as pointed out earlier, the market is smaller, so volumes are smaller, and driving the price down from being able to change to truly mass production is harder. There's also a manufacturing tolerance issue. The higher you go, the tighter the mechanical tolerances get. I suspect there is a huge amount of tooling out there for SMA connectors and other things of that size where the machining tolerances are good enough for SMA and 18GHz, but not good enough for higher. That drives all sorts of things. THere's also semiconductor parts. Lots and lots of stuff in the under 12-13 GHz range that are inexpensive. A fair amount up to 18-ish, and then it sort of falls off. There, it's driven by market, which in turn is driven by international allocations. DBS satellites at 12-13 GHz is a high volume market, so there's lots of things like MMIC low noise amplifiers. Likewise anything around 2.45 or 5.1-5.8 GHz. You see a big break in RF equipment model capability at 3GHz and 6GHz, and I suspect that's driven by the desire to test cellphones and wifi and BT (3 GHz) and 802.11a/802.11n, WiMax, etc at 6GHz. Parts that are cheap and easy to use lead to interesting products like the SignalHound spectrum analyzer, but I don't expect to see a 50GHz SignalHound any time soon. ($900 for 4.4 GHz, $2k for 12.4GHz). You could probably *build* a front end converter for a signal hound fairly inexpensively, but the parts for, say, 32 GHz would cost as much as the Signal Hound backend. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] GPSDO with all-digital phase/time measurement?
Hi everyone, I'm new to the list, and have been reading the recent threads on Arduino-based GPSDOs and the pros/cons of 10-kHz vs 1-Hz time pulses with interest. As I understand it, there are a couple of reasons why one needs a time-interval / phase measurement implemented outside the MCU: 1) Time resolution inside the MCU is limited by its clock period, which is much too coarse. The GPSDO would ping-pong within a huge dead zone. 2) Software tends to inject non-determinism into the timing. Are there others? I have no background or experience with PLLs/DLLs, so I'm really just feeling my way blindly here. That being said, I find myself wondering as follows: Suppose that we count OCXO cycles (at, say, 10 MHz) using one of the MCU's timer/counter peripherals, and periodically sample the counter value with an interrupt triggered on the rising edge of the GPS 1pps. Assume that this interrupt is the highest priority in the system, so that our measurement is fully deterministic, having only the +/- one cycle ambiguity inherent in the counting. Also assume that we keep the counter running continuously. At this point the time measurement is quite crude, with 100-ns resolution. But because we keep the counter running, the unknown residuals will keep accumulating, and we should be able to average out this quantization noise in the long run. That is, we can measure any T-second period to within 100 ns, so the resolution on a per-second basis becomes 100 ns / T. Is there any reason why this sort of processing cannot attain equivalent performance to the more conventional analog phase-detection approach? Thanks, Mark KJ6PC ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPSDO with all-digital phase/time measurement?
Hi Mark, Not to worry. It's not really too coarse. Your method is more than enough for millisecond or microsecond timing. Consider that everything about time frequency is merely an exponent; avoid fuzzy words like coarse or fine. Your approach will work just fine; many a GPSDO has been designed that way. If you measure your oscillator to a second using WWVB and make adjustments, or if you measure your oscillator to a millisecond using NTP and make adjustments, or if you measure your oscillator to a microsecond using GPS and make adjustments, it is really all the same thing. The exponent is different but the concept is the same. The final result depends on the time quality of the external 1PPS, the frequency quality of your oscillator, the resolution quality of your measurement, and the granularity of your adjustment. So every GPSDO works, the question is simply how well does it work? And does it meet your needs? For many applications 1 ms or 1 us timing accuracy is more than enough. For only a few applications does 100 ns or 50 ns matter. It gets much, much harder as you get into the double and single ns digit range. Several members on this list have developed GPSDO that are based on a MCU timestamping of 1PPS pulses. It works fine. Perfecting the tuning constants takes some time, and is somewhat dependent on your GPS receiver, your antenna, your location. Your oscillator, environment, and MCU also play a key part. But the art is to be able to *measure* all of this, to document it, to experiment, and to possibly improve on it over time. /tvb - Original Message - From: Mark Haun hau...@keteu.org To: time-nuts@febo.com Sent: Wednesday, February 26, 2014 1:51 PM Subject: [time-nuts] GPSDO with all-digital phase/time measurement? Hi everyone, I'm new to the list, and have been reading the recent threads on Arduino-based GPSDOs and the pros/cons of 10-kHz vs 1-Hz time pulses with interest. As I understand it, there are a couple of reasons why one needs a time-interval / phase measurement implemented outside the MCU: 1) Time resolution inside the MCU is limited by its clock period, which is much too coarse. The GPSDO would ping-pong within a huge dead zone. 2) Software tends to inject non-determinism into the timing. Are there others? I have no background or experience with PLLs/DLLs, so I'm really just feeling my way blindly here. That being said, I find myself wondering as follows: Suppose that we count OCXO cycles (at, say, 10 MHz) using one of the MCU's timer/counter peripherals, and periodically sample the counter value with an interrupt triggered on the rising edge of the GPS 1pps. Assume that this interrupt is the highest priority in the system, so that our measurement is fully deterministic, having only the +/- one cycle ambiguity inherent in the counting. Also assume that we keep the counter running continuously. At this point the time measurement is quite crude, with 100-ns resolution. But because we keep the counter running, the unknown residuals will keep accumulating, and we should be able to average out this quantization noise in the long run. That is, we can measure any T-second period to within 100 ns, so the resolution on a per-second basis becomes 100 ns / T. Is there any reason why this sort of processing cannot attain equivalent performance to the more conventional analog phase-detection approach? Thanks, Mark KJ6PC ___ 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] Serial port splitter s/w
On Wed, Feb 26, 2014 at 1:30 PM, David C. Partridge david.partri...@perdrix.co.uk wrote: You guys have me persuaded - I'll get a Raspberry Pi ... You might want to think a little more about which to get. The Pi is OK and will work fine but look at BeagleBone Black. It's a little nicer for hardware hackers. Cost is $5 different. You can read specs and the respective forums. One thing to watch out for is that all ARM boards run on 3.3 volts. The serial ports are 3.3 volts. Don't connect a 5 volt signal and certainly NOT a real RS232 level signal -- 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] GPSDO with all-digital phase/time measurement?
At this point the time measurement is quite crude, with 100-ns resolution. But because we keep the counter running, the unknown residuals will keep accumulating, and we should be able to average out this quantization noise What you are saying is With a long enough gate time you can measure frequency to any desired level of accuracy. For that to be true the frequency must remain stable over the long period you are averaging. For example let's say you average over 10 seconds. What happens of the nominal 10MHz oscillator ran at 10.1 Mhz for five seconds and then 9.9 Mhz for 5 seconds. You'd measure 10Mhz and be happy. So there is the problem. With long period averaging, you can only do it for so long as you trust the clock to not change. All the long gate time tells you is the AVERAGE so it only works of the change over the period is smooth and monotonic. If you want very good accuracy, say one part in 10^14 you can't get there by waiting days and weeks because the frequency will move while you are measuring it. The quicker way is to measure the phase. You can still do this digitally. Make a one bit measurement. zero if the phase leads, 1 if it lags and then over time you want the average to be 0.5 This works much faster because your controller does not have to wait for an entire cycle of error to accumulate. Your counting system would have to wait for a one cycle error and then make a very large and infrequent correction. It could work for some use cases. -- 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] GPSDO with all-digital phase/time measurement?
Hi Mark, I'm neither an engineer, nor an expert, but here are my comments. I think that the idea of 100ns/T is wrong. There are several variables that control accuracy, but the time between pulses from your OCXO (assuming no phase or frequency drift) isn't one of them. So, that gives 1/T. Here the problem is that T must get large before your accuracy can be good. You can achieve very good accuracy, but at the cost of waiting thousands of seconds between phase points; i.e. where your 1PPS coincides with the 10 millionth OCXO pulse. The theoretical maximum would be infinity, of course, but your oscillator won't be that stable. Another big problem is the accuracy of the 1PPS pulse. I'm using an Adafruit GPS receiver, and it's listed as accurate to within 10ns. And it is, but you have to be wary of exactly what that means. It doesn't mean +/- 5ns. So, as your 1PPS pulse bobs back and forth, you will often encounter an OCXO pulse up to 10ns early, or up to 10ns late. So, might you count 9,999,999 pulses from the OCXO immediately followed by 10,000,001 pulses. Neither of those, by itself is a signal to change the EFC voltage to your OCXO. In fact, it is normal for your count to alternate between the two for long periods, if you are very very close to exactly 10MHz, just from the quantization error on the 1PPS. It is also normal for 1/T to control the time between phase crossings. So you have to wait for two miscounts in a row in the same direction to make a change. And even then, you can't be 100% sure that it's not due to the quantization errors in your 1PPS signal. The better GPS receivers will output a quantization error value every second. But if you're using the 1/T method, there's nothing you can do with it, so you have to live with whatever quantization errors you get. Anyway, those are my experiences. Bob - AE6RV From: Mark Haun hau...@keteu.org To: time-nuts@febo.com Sent: Wednesday, February 26, 2014 3:51 PM Subject: [time-nuts] GPSDO with all-digital phase/time measurement? Hi everyone, I'm new to the list, and have been reading the recent threads on Arduino-based GPSDOs and the pros/cons of 10-kHz vs 1-Hz time pulses with interest. As I understand it, there are a couple of reasons why one needs a time-interval / phase measurement implemented outside the MCU: 1) Time resolution inside the MCU is limited by its clock period, which is much too coarse. The GPSDO would ping-pong within a huge dead zone. 2) Software tends to inject non-determinism into the timing. snip Thanks, Mark KJ6PC ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] frequency comparator reading question
Hello, I know this is really a basic question. I have a Fluke montronics frequency comparator. It has 2 inputs, one from my GPS and one from my DUT. After a given oscillator is warmed up, I can read the meter in parts 10 -X There are 2 meters, One for phase 0 to 360 degrees, and one for part to the -nth In the 10-9th position on the selector switch the a given oscillator will show a 0 to 360 degrees travel lets say in 1 second. So does that mean that the DUT is off frequency compared to the GPS input by 1 cycle in 1 billon? What if it takes 10 seconds to make the 0-360 excursion? 100 seconds? Paul A. Cianciolo W1VLF http://www.rescueelectronics.com/ Our business computer network is powered exclusively by solar and wind power. Converting Photons to Electrons for over 20 years ___ 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] A small piece on HP's hydrogen maser in 1968
___ 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] frequency comparator reading question
Hi Not having one here, about all I can guess is that there are 360 degrees in a cycle. If it’s going through 360 degrees in 10 seconds it’s 0.1 Hz off at what ever point it’s comparing. If it takes 100 seconds that’s 0.01 Hz. Yes I get this pesky decimal point stuff wrong from time to time ... Bob On Feb 26, 2014, at 9:19 PM, Paul A. Cianciolo pa...@snet.net wrote: Hello, I know this is really a basic question. I have a Fluke montronics frequency comparator. It has 2 inputs, one from my GPS and one from my DUT. After a given oscillator is warmed up, I can read the meter in parts 10 -X There are 2 meters, One for phase 0 to 360 degrees, and one for part to the -nth In the 10-9th position on the selector switch the a given oscillator will show a 0 to 360 degrees travel lets say in 1 second. So does that mean that the DUT is off frequency compared to the GPS input by 1 cycle in 1 billon? What if it takes 10 seconds to make the 0-360 excursion? 100 seconds? Paul A. Cianciolo W1VLF http://www.rescueelectronics.com/ Our business computer network is powered exclusively by solar and wind power. Converting Photons to Electrons for over 20 years ___ 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] frequency comparator reading question
Hello Bob, Thanks for the reality check. I just wanted to make sure , From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wednesday, February 26, 2014 10:16 PM Subject: Re: [time-nuts] frequency comparator reading question Hi Not having one here, about all I can guess is that there are 360 degrees in a cycle. If it’s going through 360 degrees in 10 seconds it’s 0.1 Hz off at what ever point it’s comparing. If it takes 100 seconds that’s 0.01 Hz. Yes I get this pesky decimal point stuff wrong from time to time ... Bob On Feb 26, 2014, at 9:19 PM, Paul A. Cianciolo pa...@snet.net wrote: Hello, I know this is really a basic question. I have a Fluke montronics frequency comparator. It has 2 inputs, one from my GPS and one from my DUT. After a given oscillator is warmed up, I can read the meter in parts 10 -X There are 2 meters, One for phase 0 to 360 degrees, and one for part to the -nth In the 10-9th position on the selector switch the a given oscillator will show a 0 to 360 degrees travel lets say in 1 second. So does that mean that the DUT is off frequency compared to the GPS input by 1 cycle in 1 billon? What if it takes 10 seconds to make the 0-360 excursion? 100 seconds? Paul A. Cianciolo W1VLF http://www.rescueelectronics.com/ Our business computer network is powered exclusively by solar and wind power. Converting Photons to Electrons for over 20 years ___ 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] 5370 processor boards available
On Feb 25, 2014, at 12:59 PM, John Seamons j...@jks.com wrote: I may have a solution for the power-off problem that doesn't involve batteries or supercaps. It has the added advantage of providing instant-on. From the latest documentation: One solution to the annoyance of having to halt the BBB before the instrument is powered off is simply to keep the BBB running by providing it a secondary source of power via the USB-mini port. The BBB already understands how to select between two sources of power: the USB-mini and +5V barrel connectors (the latter of which is actually being delivered from the 5370 via the board expansion connectors). The app detects when the instrument has powered down and resumes running when power is restored. USB power could come from an external USB hub or charger. You may have to obtain a longer USB cable than the one supplied. Be certain to only use the USB-mini connector that is adjacent to the Ethernet RJ45 connector. Do not use the USB-A connector on the other end of the board as that port will not accept input power. Some of you might even figure out how to derive +5V for the USB-mini cable from the 5370 oven power supply card that is always powered if the instrument is off but the line cord is plugged in. But beware of the potential problem of conducting noise from the BBB to the reference oscillator over such a connection. Some experimentation and measurement is necessary. The planned USB/Ethernet connector card that replaces the current HPIB one at the back-panel could host a voltage regulator. Aligator clip connections to the '+25V UNREG' and GND test points on the oven power supply would alleviate the need for any soldering. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPSDO with all-digital phase/time measurement?
Tom, I took his 100ns figure to be simply the period of 10MHz. He mentioned using an interrupt driven system, so the counts should not necessarily be limited to 100ns accuracy. At least on the PIC I'm using, the CCP and timer interrupts don't seem to be synchronous with the PIC clock. I could be mistaken. Bob From: Tom Van Baak t...@leapsecond.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wednesday, February 26, 2014 11:22 PM Subject: Re: [time-nuts] GPSDO with all-digital phase/time measurement? At this point the time measurement is quite crude, with 100-ns resolution. But because we keep the counter running, the unknown residuals will keep accumulating, and we should be able to average out this quantization noise in the long run. That is, we can measure any T-second period to within 100 ns, so the resolution on a per-second basis becomes 100 ns / T. No. The timing resolution per second is always 100 ns. You're probably thinking about average frequency, in which case dividing by T is sometimes valid, and it looks better and better as time goes by, usually. What saves you here is that your counter noise (100 ns) is likely greater than the quantization noise. So you can pretty much ignore the receiver 1PPS quantization noise. For people with much lower measurement noise (e.g., 1 ns) the quantization noise becomes a more important piece of the error pie. Try not to say average out; that sounds like it goes away over time or gets smaller. You're doing a timing measurement so the 100 ns measurement granularity is always there, on every measurement. Is there any reason why this sort of processing cannot attain equivalent performance to the more conventional analog phase-detection approach? All other factors equal, a GPSDO based on 100 ns measurement resolution can never attain the equivalent of a GPSDO based on 10 ns or 1 ns measurement resolution. Waiting shorter or longer doesn't change the RMS timing accuracy. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 5370 processor boards available
That fix presumes that the power line never quits at inappropriate times. This winter has provided me with ample reminders that power can go out anytime. I think a better solution would be to find a very large super cap and power the BBB from that while giving it a power fail interrupt to quickly sync the file system. -Chuck Harris John Seamons wrote: On Feb 25, 2014, at 12:59 PM, John Seamons j...@jks.com wrote: I may have a solution for the power-off problem that doesn't involve batteries or supercaps. It has the added advantage of providing instant-on. From the latest documentation: One solution to the annoyance of having to halt the BBB before the instrument is powered off is simply to keep the BBB running by providing it a secondary source of power via the USB-mini port. The BBB already understands how to select between two sources of power: the USB-mini and +5V barrel connectors (the latter of which is actually being delivered from the 5370 via the board expansion connectors). The app detects when the instrument has powered down and resumes running when power is restored. USB power could come from an external USB hub or charger. You may have to obtain a longer USB cable than the one supplied. Be certain to only use the USB-mini connector that is adjacent to the Ethernet RJ45 connector. Do not use the USB-A connector on the other end of the board as that port will not accept input power. Some of you might even figure out how to derive +5V for the USB-mini cable from the 5370 oven power supply card that is always powered if the instrument is off but the line cord is plugged in. But beware of the potential problem of conducting noise from the BBB to the reference oscillator over such a connection. Some experimentation and measurement is necessary. The planned USB/Ethernet connector card that replaces the current HPIB one at the back-panel could host a voltage regulator. Aligator clip connections to the '+25V UNREG' and GND test points on the oven power supply would alleviate the need for any soldering. ___ 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] Serial port splitter s/w
From: Chris Albertson You might want to think a little more about which to get. The Pi is OK and will work fine but look at BeagleBone Black. It's a little nicer for hardware hackers. Cost is $5 different. You can read specs and the respective forums. One thing to watch out for is that all ARM boards run on 3.3 volts. The serial ports are 3.3 volts. Don't connect a 5 volt signal and certainly NOT a real RS232 level signal === It would be interesting to see a performance comparison between the RPi and the BBB. when running NTP from a PPS signal. The RPi is much more popular and has a much wider user base, though. I've used mine for a 1.09 GHz ADS-B receiver (aircraft tracking), logging room temperature, as a wall-clock synced from NTP, of course, and for various other applications. The GPS units you can get these days support 3.3V operation so that's not a difficulty in practice. I've used these units for both with soldering and no soldering needed choices: With soldering: http://www.adafruit.com/products/746 No soldering required http://ava.upuaut.net/store/index.php?route=product/productpath=59_60product_id=95 Certainly, for external true RS-232 devices an interface is needed, but these can again be bought for the Raspberry Pi (data only): http://www.davidhunt.ie/?p=3091 http://www.abelectronics.co.uk/products/3/Raspberry-Pi/29/Serial-Pi-RS232-Interface Cheers, David -- 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] GPSDO with all-digital phase/time measurement?
b...@evoria.net said: At least on the PIC I'm using, the CCP and timer interrupts don't seem to be synchronous with the PIC clock. I could be mistaken. Unless you have a very strange architecture, it doesn't make sense for an interrupt to not be synchronous with the CPU clock. You are in the middle of an add instruction, and now you want to start an interrupt. What does that mean? I expect there is the standard 2 FF synchronizer on all the input pins. Things like the counter/timers run on the CPU clock, taking their input after the synchronizer. I don't remember seeing a data sheet that comes out and says that, but sometimes you can get some (strong?) hints with things like minimum pulse widths or max clock rate. -- 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.
