Re: [time-nuts] Using CPLD/FPGA or similar for frequency
On Tue, Jun 9, 2015 at 11:40 AM, Alan Ambrose alan.ambr...@anagram.net wrote: How about a 1pS resolution TIC? :) Or a 12 digit frequency counter? :) :) It's not a proper time-nut project unless there's a nutty element... Well, how complex? Front end with a fast ADC and make a DSP DMTD device? In terms of simpler things that (AFAIK) one can't go out and buy: a TIC with 4 or 8 inputs would be an interesting piece of time nut gear.even if it was 'just' 1ns resolution Surplus lab TICs are easily had but become quite a pile of equipment when you want to concurrently measure a half dozen oscillators. ___ 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] PPS for NTP Server - How Close Is Good Enough?
Hi Be careful of “single source” comparisons. When running with one reference, NTP is really measuring the reference against it’s self. It’s analogous to using a frequency counter to check it’s own reference. It *does* indeed check a number of things. It’s not really checking everything. An overly simple way to look at it: NTP is running a PLL, it “locks” a (software based) oscillator to the reference. With a single reference, it’s comparing the output of that PLL to the input to the PLL. The obvious way to get around this is to have multiple references coming into NTP. That’s easy if you want “less stable” references. It’s more money if you want to duplicate the GPS you have. After that it’s a matter of telling NTP which sources to discipline to and which to simply observe. Bob On Jun 11, 2015, at 12:05 AM, M. George m.matthew.geo...@gmail.com wrote: Here is what I have been able to do with a Motorola Oncore UT+ that I got from Bob Stewart awhile back. This is with a Raspberry PI 2 with a number of tweaks and a custom compiled kernel. Nothing too drastic... plus the current Dev version of NTP compile on the Raspberry PI. I'm getting better results letting ntpd discipline the clock over doing kernel discipline... not surprising because the algorithms in the ntpd code are much more sophisticated than the Linux kernel pps code... ntpd discipline provides much lower jitter in my experience. I'm rambling at this point, but the following samples are with a $30 antenna on the peak of my roof with LMR-400 solid conductor coax at a length of 70 ft. ~1.2 ns per foot delay based on the LMR-400 specs and nice low loss. I'm running the coax into an 8 way antenna splitter etc... nothing that anyone else hasn't done before here. The Raspberry PI 2 in this case is under load too as part of the www.pool.ntp.org pool: time.nc7j.com if you want to sync against it. As everyone else has mentioned, it's total overkill for NTP, but I'm just interested in tweaking and seeing how good I can get for fun more than anything else... i.e. time-nut obsession. I'm pretty happy with the following under load with www.pool.ntp.org set at 25MB of bandwidth which controls the traffic to my Pi 2 running NTP. It's taking a lot of traffic per second... the CPU for ntpd on the Pi is still low at around .5% to 1% of one core on the Pi 2. Here is a block of offsets from a loopstat file, and yes I cherry picked a nice block in the low nano seconds, but it rarely shows an offset into the micro seconds over time.. these are 16 second samples of the offsets... -0.00225 -0.00273 0.00094 0.00328 -0.00155 -0.00042 -0.00169 0.00323 0.00038 -0.00312 -0.00675 -0.00036 0.00213 -0.00193 0.5 -0.00503 -0.00154 -0.00179 -0.00321 0.00096 -0.00119 -0.00173 Not too shabby for a killer deal on an Oncore UT+ for $5 from Bob! I'm running the PPS out of the UT+ through a level converter to get the ~3.3v PPS output... the serial output on the UT+ is also going through a level converter direct into the Pi 2. Using the oncore 127.127.30.0 ntpd driver and again, i'm not using hardpps kernel discipline. Anyway, users on the other end are at the mercy of the network latency and noise etc... but I'm serving up some pretty consistent time references, considering the Pi 2 was $35... and the only one that really cares is me... I'm trying to masquerade as a nerdy wana-b time-nut. I think NTP is a great place to start... if you want to toy around and tinker, plus provide a service to the rest of the Internet by joining www.pool.ntp.org and sharing your obsession with time. Max NG7M ___ 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] Using CPLD/FPGA or similar for frequency
Hi Depending on which chip you are using and how big it is, you can get into the 150 to 500 ps range running a carry chain as a TDC.That’s without getting into things like hand routing and temperature / voltage issues. How big a chip you need will be a function of how high you can get the internal PLL to run while packing a bunch of stuff in the chip. If you can hit 400 MHz, each carry chain will need to handle a bit more than 2.5 ns, but probably less than 5 ns. You can do that with a carry chain a few hundred bits long. There is a bit of handwaving already so this is indeed a guess rather than a design. If you run 320 bit chains and 8 inputs, you will need 2.5K registers for the carry chains. You also will need about 200 registers for the support of each chain, so that adds another 1.6K registers. Something in the 5K register range is a possible way to go for 8 inputs. Bob On Jun 11, 2015, at 2:04 AM, Gregory Maxwell gmaxw...@gmail.com wrote: On Tue, Jun 9, 2015 at 11:40 AM, Alan Ambrose alan.ambr...@anagram.net wrote: How about a 1pS resolution TIC? :) Or a 12 digit frequency counter? :) :) It's not a proper time-nut project unless there's a nutty element... Well, how complex? Front end with a fast ADC and make a DSP DMTD device? In terms of simpler things that (AFAIK) one can't go out and buy: a TIC with 4 or 8 inputs would be an interesting piece of time nut gear.even if it was 'just' 1ns resolution Surplus lab TICs are easily had but become quite a pile of equipment when you want to concurrently measure a half dozen oscillators. ___ 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] Firmware for TymServe 2100
Does anyone have v4.1 of the firmware for the 2100 they wouldn't mind sending me? With the new Heol GPS receivers on the way I would like to test it on the different firmware versions but I can only seem to find my v3.1. Respectfully, Sean Gallagher Malware Analyst 571-340-3475 ___ 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] PPS for NTP Server - How Close Is Good Enough?
Hi Ed, I have started another thread under the name NTG550AA 1 PPS mod for finding the subject easier and I include here my thoughts about this modification. I am the one who discovered the 1PPS pulse while troubleshooting a NTG550AA. For me I don't imagine any future use of the X8 Chip signal but having the even second output could be useful, at least to see the difference with the 1 PPS. Instead of removing the 1/2 PPS output and missing this signal, my plan is to recycle the 9.8304 MHz output circuitry and connector, the circuits are almost identical. So I will cut the trace that goes from TP14 to U405 pin 6 and also use a wire to joint TP14 to TP33 so the 1PPS will be at J5. I think that I will do the modification this weekend and will post the results and pictures. I have not measured the time difference yet, but I made a partial schematic of the board for my troubleshooting and there I see that the 1/2 PPS signal is synchronized with the 19.6608 signal that is the source for the 8X Chip ( 9.8304 MHz), this is done in U405B . The period of this signal is about 50 ns and this is the origin of the 1/2 PPS width. The 19.6608 MHz oscillator is phase locked somewhere to the 10 MHz oscillator thus it is as stable as this one. I think that using the other half of U405, which actually is used to divide by 2 the 19.6608 MHz signal, could render the 1 PPS synchronized with the 1/2 PPS and also with the same width but probably this is overkill and an easier way to adjust this is to use the command which sets the antenna cable delay and compensate for the difference. Checking the specs documentation of a very close cousin of this board, the GSBW50AA, I found the requirement for the even second pulse: +/-1 μs traceable to and synchronous with GPS Time Even_Second with at least one satellite in view. In fact this is something not easy to measure unless you have a calibrated 1 PPS source. Another spec states The falling edge of Even_Second shall occur 0-5 ns after the falling edge of SYS_CLK. (the 9.8304 MHz signal that is used as the clock reference in the CDMA system). This specs are the reason why the even second pulse is synchronized to the SYS_CLK as I said before. So my opinion is that the difference that you measured is not relevant because we can not be sure about the even second accuracy and if we need to be sure of the absolute time we will need to compare the 1 PPS output against a calibrated source, maybe another GPSDO that has been compared with a known standard and compensated for the antenna cable delay. Of course for a NTP server you have more than enough. As I said in the other post I have a partial schematic of the board, ask me if you want a copy. Best regards, Ignacio El 10/06/2015 a las 6:30, Ed Armstrong wrote: Hi, this is my first post ever to a mailing list, so if I'm doing anything wrong please be gentle with your corrections :-) A short time ago I purchased a Nortel/Trimble NTGS50AA GPSTM, I'm sure many on this list are familiar with it. At the time of purchase, my only interest was the 10 MHz output, for use with my HP5328b frequency counter and perhaps in the future also my signal generator. No question here, it just works great as is. However, it certainly seems best to leave these devices powered up all the time. OK, now were getting close to my question. The unit pulls about 10-11 watts, which is really not very much. But it kinda bugs me to have it sit there using electric and basically doing nothing when I'm not using it. So, I bought a Raspberry Pi 2 with the intent of using it as an NTP server. I can't really say I'm enjoying my intro to Linux a whole lot, but I'll get there. It still needs some work, but it does function with the PPS output from an Adafruit ultimate GPS, which I bought for testing this and possibly building my own GPSDO in the future. The NTGS50AA is a very capable device, but unfortunately it does not have a PPS output. Instead it has an even second output, which goes low for approximately 50 ns. The falling edge of this pulse marks the beginning of the second. During my search for a solution to this, I came across a post from this mailing list which I believe was discussing repair of one of these units. Someone in that post mentioned that there was a PPS signal at test point 33 which went low for about 10 µs. Thank you, that saves me a lot of probing. The first thing I did was verify that this pulse did exist, then I decided to examine it a little closer. I kind of suspected that it may have been a rather raw pulse as received from the satellites. I found out that is not correct, once the unit successfully phase locks, this PPS signal is very accurately tied to the 10 MHz output, even when the unit goes into holdover mode. I was very happy about this :-) Next step was to see how accurately it was synced to the even second pulse. The bad news is that it does not occur
Re: [time-nuts] Firmware for TymServe 2100
Sean, I have it (but not with me) and can send it directly to you this evening. I will also gladly post if anyone else is interested. Gerhard R Wittreich, P.E. On Thu, Jun 11, 2015 at 9:38 AM, Sean Gallagher s...@wetstonetech.com wrote: Does anyone have v4.1 of the firmware for the 2100 they wouldn't mind sending me? With the new Heol GPS receivers on the way I would like to test it on the different firmware versions but I can only seem to find my v3.1. Respectfully, Sean Gallagher Malware Analyst 571-340-3475 ___ 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] z3801a - serial help and for sale
Thanks for the suggestions! It turns out the answer was my serial dongle was failing. *head bonk* I swapped it out for another FDTI-based dongle and suddenly there's a happy working z3801a. Before I throw it on eBay, would anyone like a working (yay!) z3801a modified to take mains power? I'll throw in a little puck antenna and a homebrewed rs232 db25-to-db9 cable. Pictures as per my previous email about it. (please CC: me on reply -- I'm stuck in digest subscription and having issues.) ((No 'issues' jokes, please. :)) I'll note there's a risk that putting the switcher in it causes added noise. I haven't measured it precisely enough to tell. I didn't need nanoseconds for what I was using it for, but I did want it to be pain-free to plug in and use. -Dave … On Thu, Jun 11, 2015 at 1:18 AM time-nuts-requ...@febo.com wrote: -- Forwarded message -- From: James C Cotton jim.cot...@wmich.edu To: Discussion of precise time and frequency measurement time-nuts@febo.com Cc: Date: Wed, 10 Jun 2015 16:26:17 -0400 (EDT) Subject: Re: [time-nuts] z3801a - serial help and for sale. David, Using a USB dongle with an Apple Mac Laptop works fine for me. The chip is a FTDI FT232BL. Drivers from the FTDI site. In terminal or console use one of the following commands: [generic $5 dongle with no serial number] cd /dev screen tty.usbserial [xs880 with a serial number, http://www.usconverters.com/usb-serial-adapter-xs880] cd /dev screen tty.usbserial-A101OFXZ Having one (or more) with a serial number(s) allows several to work at the same time... I use the same USB-serial converters on windows PCs too. Jim -- Forwarded message -- From: Scott McGrath scmcgr...@gmail.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Cc: Date: Wed, 10 Jun 2015 16:50:51 -0400 Subject: Re: [time-nuts] z3801a - serial help and for sale. Try going through all the speeds starting at 300. Sounds like a baud rate mismatch to me from the symptoms Also try 8 bits 1 stop no parity Content by Scott Typos by Siri On Jun 10, 2015, at 10:28 AM, David Andersen d...@pobox.com wrote: I'm throwing my hands up in the air - I don't have the time to wrestle my silly mac into trying to talk to the box, unless someone has quick advice on something I might be doing wrong. z3801a, jumpered to RS232, modified with an internal switching power supply (see photos below). Power light comes on, unit is outputting stable 10MHz. Doesn't GPS lock, but that makes sense, since I haven't been able to issue a SURVEY command and I don't live where I used to. The internal green status light is blinking (as normal), suggesting that it's probably happy and I'm an idiot for not being able to make it work, but I don't vouch for anything about it past the 10mhz being there. The double-oven oscillator is clearly happy given the 10mhz (compared against a working Thunderbolt). Hooked up a serial cable at 19200, 7, O, 1, but only got a garbled little prompt back - no response to standard z3801a commands. I *think* I have the cable configured properly. I opened it up and checked the RS232 jumpers and they're correct. I'm open to advice on getting the serial working under my Mac or Linux, or anyone who wants to relieve me of the burden of z3801a ownership and take a risk that it's a fixer-upper. :-) I suspect that in some previous life, I switched it over into a binary mode of some sort while using it to sync something, but I can't for the life of me remember what I might have done. Some reasonable price plus shipping and it's all yours... I'm trying to de-clutter in preparation for a sabbatical on the other side of the country. Pictures: https://www.dropbox.com/s/ursszjgie8m1xj8/2015-06-09%2011.57.16.jpg?dl=0 https://www.dropbox.com/s/it8d2f65ztn4rkq/2015-06-09%2011.57.24.jpg?dl=0 https://www.dropbox.com/s/1p1g6xrapzdmvzh/2015-06-09%2011.59.56.jpg?dl=0 Thanks! -Dave ___ 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. -- Forwarded message -- From: Bob Camp kb...@n1k.org To: Discussion of precise time and frequency measurement time-nuts@febo.com Cc: Date: Wed, 10 Jun 2015 17:27:36 -0400 Subject: Re: [time-nuts] z3801a - serial help and for sale. Hi Normal drill for this sort of thing: 1) First connect the serial dongle back to back (output to input) and make sure it gives you back what you type in. If not, find another dongle. 2) Check the output levels from the Z3801 with a scope. It should be swinging at least +/- 5V and more like +/-12. The key thing here is that the swing is the same in both directions. Then, in combination, try each of the following: 3) Try the usual
Re: [time-nuts] PPS for NTP Server - How Close Is Good Enough?
Hi Bob, yes I'm including several other sources and usually about 3 are getting included in the discipline of the local clock. Here is my ntpq -pcrl output at the time I wrote this message. pi@raspi2 ~ $ ntpq -pcrl remote refid st t when poll reach delay offset jitter == LOCAL(0).LOCL. 10 l 20h 6400.0000.000 0.000 oGPS_ONCORE(0) .GPS.0 l 13 16 3770.0000.000 0.002 +time-c.timefreq .ACTS. 1 u2 64 377 21.373 -0.344 0.504 +utcnist2.colora .ACTS. 1 u3 64 377 22.2620.144 1.720 +india.colorado. .NIST. 1 u 48 64 377 22.2360.188 0.122 -time-a.timefreq .ACTS. 1 u 27 64 377 21.566 -0.595 0.405 associd=0 status=0419 leap_none, sync_uhf_radio, 1 event, leap_armed, version=ntpd 4.3.37@1.2483-o Thu Jun 11 00:12:07 UTC 2015 (1), processor=armv7l, system=Linux/3.18.14-v7+, leap=00, stratum=1, precision=-19, rootdelay=0.000, rootdisp=1.195, refid=GPS, reftime=d9246d02.38389bc3 Thu, Jun 11 2015 14:24:34.219, clock=d9246d0f.92141a9c Thu, Jun 11 2015 14:24:47.570, peer=6887, tc=4, mintc=3, offset=0.000163, frequency=-7.742, sys_jitter=0.001907, clk_jitter=0.002, clk_wander=0.000, tai=35, leapsec=20150701, expire=20151228 I have been careful to try and tweak the time1 offset to get a reasonable offset against the reference servers that show something less than 1ms over time. Shortly I'll have another GPS / M12+ up and running on another PI that I can use as a local reference along with other NTP servers over the internet. As you can see, the PPM frequency on this Pi is still showing -7.742. I assume that is if it was undisciplined? I have wondered about that. Matt On Thu, Jun 11, 2015 at 4:59 AM, Bob Camp kb...@n1k.org wrote: Hi Be careful of “single source” comparisons. When running with one reference, NTP is really measuring the reference against it’s self. It’s analogous to using a frequency counter to check it’s own reference. It *does* indeed check a number of things. It’s not really checking everything. An overly simple way to look at it: NTP is running a PLL, it “locks” a (software based) oscillator to the reference. With a single reference, it’s comparing the output of that PLL to the input to the PLL. The obvious way to get around this is to have multiple references coming into NTP. That’s easy if you want “less stable” references. It’s more money if you want to duplicate the GPS you have. After that it’s a matter of telling NTP which sources to discipline to and which to simply observe. Bob On Jun 11, 2015, at 12:05 AM, M. George m.matthew.geo...@gmail.com wrote: Here is what I have been able to do with a Motorola Oncore UT+ that I got from Bob Stewart awhile back. This is with a Raspberry PI 2 with a number of tweaks and a custom compiled kernel. Nothing too drastic... plus the current Dev version of NTP compile on the Raspberry PI. I'm getting better results letting ntpd discipline the clock over doing kernel discipline... not surprising because the algorithms in the ntpd code are much more sophisticated than the Linux kernel pps code... ntpd discipline provides much lower jitter in my experience. I'm rambling at this point, but the following samples are with a $30 antenna on the peak of my roof with LMR-400 solid conductor coax at a length of 70 ft. ~1.2 ns per foot delay based on the LMR-400 specs and nice low loss. I'm running the coax into an 8 way antenna splitter etc... nothing that anyone else hasn't done before here. The Raspberry PI 2 in this case is under load too as part of the www.pool.ntp.org pool: time.nc7j.com if you want to sync against it. As everyone else has mentioned, it's total overkill for NTP, but I'm just interested in tweaking and seeing how good I can get for fun more than anything else... i.e. time-nut obsession. I'm pretty happy with the following under load with www.pool.ntp.org set at 25MB of bandwidth which controls the traffic to my Pi 2 running NTP. It's taking a lot of traffic per second... the CPU for ntpd on the Pi is still low at around .5% to 1% of one core on the Pi 2. Here is a block of offsets from a loopstat file, and yes I cherry picked a nice block in the low nano seconds, but it rarely shows an offset into the micro seconds over time.. these are 16 second samples of the offsets... -0.00225 -0.00273 0.00094 0.00328 -0.00155 -0.00042 -0.00169 0.00323 0.00038 -0.00312 -0.00675 -0.00036 0.00213 -0.00193 0.5 -0.00503 -0.00154 -0.00179 -0.00321 0.00096 -0.00119 -0.00173 Not too shabby for a killer deal on an Oncore UT+ for $5 from Bob! I'm running the PPS out of the UT+
Re: [time-nuts] z3801a - serial help and for sale
Where on the planet are you? I'm in UK so if you are in USA shipping will make it uneconomic. Regards, David Partridge -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of David Andersen Sent: 11 June 2015 21:39 To: time-nuts@febo.com Subject: Re: [time-nuts] z3801a - serial help and for sale Thanks for the suggestions! It turns out the answer was my serial dongle was failing. *head bonk* I swapped it out for another FDTI-based dongle and suddenly there's a happy working z3801a. Before I throw it on eBay, would anyone like a working (yay!) z3801a modified to take mains power? I'll throw in a little puck antenna and a homebrewed rs232 db25-to-db9 cable. Pictures as per my previous email about it. (please CC: me on reply -- I'm stuck in digest subscription and having issues.) ((No 'issues' jokes, please. :)) I'll note there's a risk that putting the switcher in it causes added noise. I haven't measured it precisely enough to tell. I didn't need nanoseconds for what I was using it for, but I did want it to be pain-free to plug in and use. -Dave … On Thu, Jun 11, 2015 at 1:18 AM time-nuts-requ...@febo.com wrote: -- Forwarded message -- From: James C Cotton jim.cot...@wmich.edu To: Discussion of precise time and frequency measurement time-nuts@febo.com Cc: Date: Wed, 10 Jun 2015 16:26:17 -0400 (EDT) Subject: Re: [time-nuts] z3801a - serial help and for sale. David, Using a USB dongle with an Apple Mac Laptop works fine for me. The chip is a FTDI FT232BL. Drivers from the FTDI site. In terminal or console use one of the following commands: [generic $5 dongle with no serial number] cd /dev screen tty.usbserial [xs880 with a serial number, http://www.usconverters.com/usb-serial-adapter-xs880] cd /dev screen tty.usbserial-A101OFXZ Having one (or more) with a serial number(s) allows several to work at the same time... I use the same USB-serial converters on windows PCs too. Jim -- Forwarded message -- From: Scott McGrath scmcgr...@gmail.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Cc: Date: Wed, 10 Jun 2015 16:50:51 -0400 Subject: Re: [time-nuts] z3801a - serial help and for sale. Try going through all the speeds starting at 300. Sounds like a baud rate mismatch to me from the symptoms Also try 8 bits 1 stop no parity Content by Scott Typos by Siri On Jun 10, 2015, at 10:28 AM, David Andersen d...@pobox.com wrote: I'm throwing my hands up in the air - I don't have the time to wrestle my silly mac into trying to talk to the box, unless someone has quick advice on something I might be doing wrong. z3801a, jumpered to RS232, modified with an internal switching power supply (see photos below). Power light comes on, unit is outputting stable 10MHz. Doesn't GPS lock, but that makes sense, since I haven't been able to issue a SURVEY command and I don't live where I used to. The internal green status light is blinking (as normal), suggesting that it's probably happy and I'm an idiot for not being able to make it work, but I don't vouch for anything about it past the 10mhz being there. The double-oven oscillator is clearly happy given the 10mhz (compared against a working Thunderbolt). Hooked up a serial cable at 19200, 7, O, 1, but only got a garbled little prompt back - no response to standard z3801a commands. I *think* I have the cable configured properly. I opened it up and checked the RS232 jumpers and they're correct. I'm open to advice on getting the serial working under my Mac or Linux, or anyone who wants to relieve me of the burden of z3801a ownership and take a risk that it's a fixer-upper. :-) I suspect that in some previous life, I switched it over into a binary mode of some sort while using it to sync something, but I can't for the life of me remember what I might have done. Some reasonable price plus shipping and it's all yours... I'm trying to de-clutter in preparation for a sabbatical on the other side of the country. Pictures: https://www.dropbox.com/s/ursszjgie8m1xj8/2015-06-09%2011.57.16.jpg? dl=0 https://www.dropbox.com/s/it8d2f65ztn4rkq/2015-06-09%2011.57.24.jpg? dl=0 https://www.dropbox.com/s/1p1g6xrapzdmvzh/2015-06-09%2011.59.56.jpg? dl=0 Thanks! -Dave ___ 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. -- Forwarded message -- From: Bob Camp kb...@n1k.org To: Discussion of precise time and frequency measurement time-nuts@febo.com Cc: Date: Wed, 10 Jun 2015 17:27:36 -0400 Subject: Re: [time-nuts] z3801a - serial help and for sale. Hi Normal drill for this sort of thing: 1) First connect the
Re: [time-nuts] PPS for NTP Server - How Close Is Good Enough?
Here is what I have been able to do with a Motorola Oncore UT+ that I got from Bob Stewart awhile back. This is with a Raspberry PI 2 with a number of tweaks and a custom compiled kernel. Nothing too drastic... plus the current Dev version of NTP compile on the Raspberry PI. I'm getting better results letting ntpd discipline the clock over doing kernel discipline... not surprising because the algorithms in the ntpd code are much more sophisticated than the Linux kernel pps code... ntpd discipline provides much lower jitter in my experience. I'm rambling at this point, but the following samples are with a $30 antenna on the peak of my roof with LMR-400 solid conductor coax at a length of 70 ft. ~1.2 ns per foot delay based on the LMR-400 specs and nice low loss. I'm running the coax into an 8 way antenna splitter etc... nothing that anyone else hasn't done before here. The Raspberry PI 2 in this case is under load too as part of the www.pool.ntp.org pool: time.nc7j.com if you want to sync against it. As everyone else has mentioned, it's total overkill for NTP, but I'm just interested in tweaking and seeing how good I can get for fun more than anything else... i.e. time-nut obsession. I'm pretty happy with the following under load with www.pool.ntp.org set at 25MB of bandwidth which controls the traffic to my Pi 2 running NTP. It's taking a lot of traffic per second... the CPU for ntpd on the Pi is still low at around .5% to 1% of one core on the Pi 2. Here is a block of offsets from a loopstat file, and yes I cherry picked a nice block in the low nano seconds, but it rarely shows an offset into the micro seconds over time.. these are 16 second samples of the offsets... -0.00225 -0.00273 0.00094 0.00328 -0.00155 -0.00042 -0.00169 0.00323 0.00038 -0.00312 -0.00675 -0.00036 0.00213 -0.00193 0.5 -0.00503 -0.00154 -0.00179 -0.00321 0.00096 -0.00119 -0.00173 Not too shabby for a killer deal on an Oncore UT+ for $5 from Bob! I'm running the PPS out of the UT+ through a level converter to get the ~3.3v PPS output... the serial output on the UT+ is also going through a level converter direct into the Pi 2. Using the oncore 127.127.30.0 ntpd driver and again, i'm not using hardpps kernel discipline. Anyway, users on the other end are at the mercy of the network latency and noise etc... but I'm serving up some pretty consistent time references, considering the Pi 2 was $35... and the only one that really cares is me... I'm trying to masquerade as a nerdy wana-b time-nut. I think NTP is a great place to start... if you want to toy around and tinker, plus provide a service to the rest of the Internet by joining www.pool.ntp.org and sharing your obsession with time. Max NG7M ___ 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] PPS for NTP Server - How Close Is Good Enough?
Hi Comparing a GPS to a series of “over the net” sources will always make the GPS look good. NTP is usually smart enough to figure out that the GPS is the one it wants and lock in on it. The ppm’s at the bottom are talking about the software PLL and how it’s offset from your computer’s local clock. It’s telling you what it’s best guess is at the frequency of the oscillator on your Pi. It’s a guess until you can do enough work to be sure that NTP isn’t being messed up by something else going on in the system. Bob On Jun 11, 2015, at 4:32 PM, M. George m.matthew.geo...@gmail.com wrote: Hi Bob, yes I'm including several other sources and usually about 3 are getting included in the discipline of the local clock. Here is my ntpq -pcrl output at the time I wrote this message. pi@raspi2 ~ $ ntpq -pcrl remote refid st t when poll reach delay offset jitter == LOCAL(0).LOCL. 10 l 20h 6400.0000.000 0.000 oGPS_ONCORE(0) .GPS.0 l 13 16 3770.0000.000 0.002 +time-c.timefreq .ACTS. 1 u2 64 377 21.373 -0.344 0.504 +utcnist2.colora .ACTS. 1 u3 64 377 22.2620.144 1.720 +india.colorado. .NIST. 1 u 48 64 377 22.2360.188 0.122 -time-a.timefreq .ACTS. 1 u 27 64 377 21.566 -0.595 0.405 associd=0 status=0419 leap_none, sync_uhf_radio, 1 event, leap_armed, version=ntpd 4.3.37@1.2483-o Thu Jun 11 00:12:07 UTC 2015 (1), processor=armv7l, system=Linux/3.18.14-v7+, leap=00, stratum=1, precision=-19, rootdelay=0.000, rootdisp=1.195, refid=GPS, reftime=d9246d02.38389bc3 Thu, Jun 11 2015 14:24:34.219, clock=d9246d0f.92141a9c Thu, Jun 11 2015 14:24:47.570, peer=6887, tc=4, mintc=3, offset=0.000163, frequency=-7.742, sys_jitter=0.001907, clk_jitter=0.002, clk_wander=0.000, tai=35, leapsec=20150701, expire=20151228 I have been careful to try and tweak the time1 offset to get a reasonable offset against the reference servers that show something less than 1ms over time. Shortly I'll have another GPS / M12+ up and running on another PI that I can use as a local reference along with other NTP servers over the internet. As you can see, the PPM frequency on this Pi is still showing -7.742. I assume that is if it was undisciplined? I have wondered about that. Matt On Thu, Jun 11, 2015 at 4:59 AM, Bob Camp kb...@n1k.org wrote: Hi Be careful of “single source” comparisons. When running with one reference, NTP is really measuring the reference against it’s self. It’s analogous to using a frequency counter to check it’s own reference. It *does* indeed check a number of things. It’s not really checking everything. An overly simple way to look at it: NTP is running a PLL, it “locks” a (software based) oscillator to the reference. With a single reference, it’s comparing the output of that PLL to the input to the PLL. The obvious way to get around this is to have multiple references coming into NTP. That’s easy if you want “less stable” references. It’s more money if you want to duplicate the GPS you have. After that it’s a matter of telling NTP which sources to discipline to and which to simply observe. Bob On Jun 11, 2015, at 12:05 AM, M. George m.matthew.geo...@gmail.com wrote: Here is what I have been able to do with a Motorola Oncore UT+ that I got from Bob Stewart awhile back. This is with a Raspberry PI 2 with a number of tweaks and a custom compiled kernel. Nothing too drastic... plus the current Dev version of NTP compile on the Raspberry PI. I'm getting better results letting ntpd discipline the clock over doing kernel discipline... not surprising because the algorithms in the ntpd code are much more sophisticated than the Linux kernel pps code... ntpd discipline provides much lower jitter in my experience. I'm rambling at this point, but the following samples are with a $30 antenna on the peak of my roof with LMR-400 solid conductor coax at a length of 70 ft. ~1.2 ns per foot delay based on the LMR-400 specs and nice low loss. I'm running the coax into an 8 way antenna splitter etc... nothing that anyone else hasn't done before here. The Raspberry PI 2 in this case is under load too as part of the www.pool.ntp.org pool: time.nc7j.com if you want to sync against it. As everyone else has mentioned, it's total overkill for NTP, but I'm just interested in tweaking and seeing how good I can get for fun more than anything else... i.e. time-nut obsession. I'm pretty happy with the following under load with www.pool.ntp.org set at 25MB of bandwidth which controls the traffic to my Pi 2 running NTP. It's taking a lot of traffic per second... the CPU for ntpd on the Pi is still low at around .5% to 1% of one core on the Pi 2. Here is a block of offsets from a
Re: [time-nuts] z3801a - serial help and for sale
I modified one of my 3801s by placing a home brew linear power supply in it and a regular 3 connector AC plug in place of the 48 volt one. The power supply with the transformers was a tight fit, but I managed. It has been working fine for about 12 years. I also replaced the solid top cover with a fine mesh copper cover to get rid of the extra heat. Regards - Mike . Mike B. Feher, EOZ Inc. 89 Arnold Blvd. Howell, NJ, 07731 732-886-5960 office 908-902-3831 cell -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of David Andersen Sent: Thursday, June 11, 2015 4:39 PM To: time-nuts@febo.com Subject: Re: [time-nuts] z3801a - serial help and for sale Thanks for the suggestions! It turns out the answer was my serial dongle was failing. *head bonk* I swapped it out for another FDTI-based dongle and suddenly there's a happy working z3801a. Before I throw it on eBay, would anyone like a working (yay!) z3801a modified to take mains power? I'll throw in a little puck antenna and a homebrewed rs232 db25-to-db9 cable. Pictures as per my previous email about it. (please CC: me on reply -- I'm stuck in digest subscription and having issues.) ((No 'issues' jokes, please. :)) I'll note there's a risk that putting the switcher in it causes added noise. I haven't measured it precisely enough to tell. I didn't need nanoseconds for what I was using it for, but I did want it to be pain-free to plug in and use. -Dave ___ 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] Using CPLD/FPGA or similar for frequency
Hi, So that turns into 2 games: How fast can you count? How many digits can you get in 1 second? A clever interpolator for frequency or TIC would kill it - for TIC essentially a PICTIC on steroids. The PICTIC does 19pS with a 10 bit ADC and a 66MHz clock, an SR620 does 4pS with a 12 bit ADC and an 80 MHz clock - so ... cough ... Spartan 3E at 256MHz with 16 bit ADC - and 1pS should be easy Alan ___ 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.
