Re: [time-nuts] PPS for NTP Server - How Close Is Good Enough?
Hal, what stopped me from going down the BBB path was the reports of RF noise, they supposedly create a lot of noise. Not acceptable in an HF environment. Google around about the RF noise with the BBB. mg NG7M On Sat, Jun 13, 2015 at 12:02 AM, Hal Murray hmur...@megapathdsl.net wrote: eds_equipm...@verizon.net said: Is it possible to modify the kernel so the USB is polled more often, and would that significantly reduce the jitter? Modifying the kernel may not be enough if the timing parameters are in the microcode for the USB device. Whether any improvement is significant probably depends upon your goals. It's unlikely to become a great NTP server. If I wanted a good low power NTP server, I'd probably start with a BeagleBone Black. I haven't seen a low cost no-assembly-required GPS board for the BBB (There is at least one GPS board for the BBB, but it includes a cell phone modem which doubles the cost.) I'd probably try the GPS breakout board from SparkFun. It should take 5 wires: power, ground, trans, recv, and PPS. (and then the appropriate software hacking) -- 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. -- M. George ___ 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] Raspberry Pi tweaks and custom kernel, was RE: PPS for NTP Server - How Close Is Good Enough?
Hi At best, simply because of the way that USB interface works, you can go from the ~1/2 ms range into the ~1/4 ms range. Rewriting the low level drivers may be required. This compares to an equivalent lag on a device with a built in ethernet of 0.001 ms. The easy thing to do is to simply kill off everything else that is running on the device. That goes double for anything running on USB (keyboards / mice etc). Since you can get boards with built in (integrated in the MCU) ethernet for $50, it’s not clear how much tweaking time this is worth. You don’t get any real use out of the Pi’s fancy graphics in this case. The board really is not optimized for doing this sort of thing. Also - check the threads on Pi heat sinking and boards burning out. If you plan to use this full time - invest the money in cooling now. Bob On Jun 13, 2015, at 2:06 AM, David J Taylor david-tay...@blueyonder.co.uk wrote: Hi Max! Thanks for the information, I was wondering if you had documented what you did to your Raspberry Pi so that it might be reproducible to someone like me (a newcomer time-nut and intermediate Linux user) ... you had said: [] Thanks so much for your assistance! Sorry if these questions have been posted before, but I am very curious about your setup as it nearly matches mine! -Randal r3 of CubeCentral === I would also like to know how to best tweak the Raspberry Pi 2 for best performance as an NTP server. Although I have been using Linux-based firmware in my routers for several years now, I have never actually worked In Linux before. I have gone through several tutorials on compiling a custom kernel, only one or two have actually ended in a compilation, but then I couldn't figure out where the kernel and modules were and get them onto the Pi. I have tried this under Ubuntu x64, Debian x64, and Mint 32 bit. So far Mint has been the best, I successfully compiled and I found the kernel, but cannot figure out where the modules are. Anybody suggest a really nice tutorial for learning this Linux stuff? My experience so far is really leading me to appreciate Windows. Thanks Ed === Randal, Ed, Just in case you missed it, I am also a beginner to Linux, so I documented my steps to get NTP working on the Raspberry Pi on my Web site. There's a quick-start guide here: http://www.satsignal.eu/ntp/Raspberry-Pi-quickstart.html and a more blog-like set of detailed notes here: http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html I hope they may be of some help. Typically I'm seeing well under 5 microsecond offsets reported by the RPi themselves: http://www.satsignal.eu/mrtg/performance_ntp.php although with different GPS devices, antennas, and system loads the performance does vary. The polled USB is, perhaps, the main limitation to the device as a server on the LAN, although my own tests have shown RMS offsets reported by a remote client on a quiet LAN of 39 microseconds and a jitter of 38 microseconds. Likely on a busier LAN the network itself might be the limiting factor. I am no longer convinced that there is a significant gain to to be had by recompiling the kernel, now that PPS support for interrupts is included in the current Raspbian kernels. I'm willing to be convinced otherwise, though. Recompiling is a long and painful process, and cross-compiling presents further problems! 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. ___ 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] time-nuts slow this week
Hello time-nuts list members, Part of this past week we have been experiencing a strange slowdown of the febo.com out-going time-nuts mail list server. This has caused postings (including this one?) to be delayed by hours, even tens of hours. We're still trying to figure it out. Thanks for your patience. Messages are not lost, as far as I know, but they take an unusual amount of time. If any of you host Mailman / Linux servers, please contact John (j...@febo.com) and me (t...@leapsecond.com) as we seek advice to figure out this unusual, persistent, annoying event. Note that https://www.febo.com/pipermail/time-nuts/2015-June/date.html#end is updated (within seconds) of any accepted posting to the list. So maybe it's not Mailman itself. Still, it takes many hours before the posting arrives by email Thanks, /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] Cheap 48V 2A power supply
BG Micro has some nice 48V 2A power supply modules for around $12. IEC power cord in (100-240V), 2.1mm barrel connector out. Seems to work well with my Nortel GPSDOs, but I haven't scoped the thing out for noise, etc. http://www.bgmicro.com/48v-2-08a-enclosed-power-supply-by-xp-power-2-5mm-right-angle-barrel-connector.aspx ___ 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] NTG550AA 1 PPS mod
kb...@n1k.org said: The very real question is still - which edge is correct? Has anybody seen a GPSDO where the leading edge of a narrow pulse wasn't the correct one? -- 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] Cheap 48V 2A power supply
Thanks Mark - Here is the data sheet: http://www.farnell.com/datasheets/1903642.pdf John K1AE -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Mark Sims Sent: Saturday, June 13, 2015 5:20 PM To: time-nuts@febo.com Subject: [time-nuts] Cheap 48V 2A power supply BG Micro has some nice 48V 2A power supply modules for around $12. IEC power cord in (100-240V), 2.1mm barrel connector out. Seems to work well with my Nortel GPSDOs, but I haven't scoped the thing out for noise, etc. http://www.bgmicro.com/48v-2-08a-enclosed-power-supply-by-xp-power-2-5mm-right-angle-barrel-connector.aspx ___ 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. --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus ___ 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?
Several time-nuts have asked about my setup, here are some details of what I changed in the kernel and in the NTP build... Make sure and use the default config for the Pi 2 CPU when setting up .config for the Linux kernel. Make sure you are actually seeing your new kernel after you copy it to the /boot directory... name it kernel7.img if you dont' override the file name in config.txt. Also make sure dynamic modules are working. Here are details about the Linux kernel I'm currently using: Over clocked params in /boot/config.txt: #uncomment to overclock the arm. 700 MHz is the default. arm_freq=900 core_freq=500 sdram_freq=500 over_voltage=3 force_turbo=1 use force_turbo, I don't think the overclock really did anything. I do have a very good 5v power supply and I'm not using a wall wart USB power supply. Here are the contents of my /boot/cmdline.txt: dwc_otg.lpm_enable=0 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait smsc95xx.turbo_mode=0 Use the smsc95xx option to drop the latency on the network interface. Before building the kernel, in menu_config, in kernel options, set the timer frequency to 1000HZ. In CPU Power Management CPU Frequency scaling, set the default CPUFreq governor to 'performance'. I'm using this kernel code: Linux raspi2 3.18.14-v7+ #6 SMP Sun May 31 22:32:33 MDT 2015 armv7l GNU/Linux When you compile NTP, after running .configure, manually edit config.h and set DEFAULT_HZ to 1000 and then compile NTP. On the Pi 2, it can handle 4000 interrupts per second, I'm not sure how the previous Pi versions performed on interrupts. Google around and see what else you can find for a low latency raspberry pi configuration. Here is my ntpq -crv output as of the time I wrote this email: 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=1.075, refid=GPS, reftime=d9241692.3770a686 Thu, Jun 11 2015 8:15:46.216, clock=d9241697.6570084f Thu, Jun 11 2015 8:15:51.396, peer=6887, tc=4, mintc=3, offset=-0.000472, frequency=-7.870, sys_jitter=0.001907, clk_jitter=0.002, clk_wander=0.000, tai=35, leapsec=20150701, expire=20151228 So the offset at the moment was 472ns. But again, the sys_jitter has never been lower that I have seen, than 1.907 us. On Sat, Jun 13, 2015 at 11:14 AM, M. George m.matthew.geo...@gmail.com wrote: Hal, what stopped me from going down the BBB path was the reports of RF noise, they supposedly create a lot of noise. Not acceptable in an HF environment. Google around about the RF noise with the BBB. mg NG7M On Sat, Jun 13, 2015 at 12:02 AM, Hal Murray hmur...@megapathdsl.net wrote: eds_equipm...@verizon.net said: Is it possible to modify the kernel so the USB is polled more often, and would that significantly reduce the jitter? Modifying the kernel may not be enough if the timing parameters are in the microcode for the USB device. Whether any improvement is significant probably depends upon your goals. It's unlikely to become a great NTP server. If I wanted a good low power NTP server, I'd probably start with a BeagleBone Black. I haven't seen a low cost no-assembly-required GPS board for the BBB (There is at least one GPS board for the BBB, but it includes a cell phone modem which doubles the cost.) I'd probably try the GPS breakout board from SparkFun. It should take 5 wires: power, ground, trans, recv, and PPS. (and then the appropriate software hacking) -- 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. -- M. George -- M. George ___ 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] My HP 5370B reads 6 nS out!
I just got a new (to me) HP 5370B and I wanted to try it out on the 1 PPS output from a Trimble Resolution T. Using 10K samples averaging it is always about 6 or 7 nS to high. Shouldn't this average toward zero? If I use no averaging it bounces around within the expected range. I have done this test using the internal oscillator and an external rubidium frequency standard. I get the about the same results in both cases. I did calibrate the OCXO in the 5370B using the rubidium standard and got it so that there is less than one cycle difference between the two over a period of a few hours. I have tried a number of GPS units with the same result. Could my rubidium oscillator be that far out? It is a FEI model FE5680A. Am I missing something? Pete. ___ 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] NTGS50AA 1 PPS mod
Hi Of course tomorrow you will stumble into a “great deal” on a complete cell site that needs a 9.8304 MHz clock :) One thing to watch: The pps you now have may or may not be deterministic in its relation to the every other second output. It also may or may not be in a fixed relation to GPS. I would bet money that it *is* in a fixed relation and that it’s actually better than the other signal. Just because I believe it to be true does not make it true. It needs to be checked against something else. Bob On Jun 13, 2015, at 1:56 PM, EB4APL eb4...@gmail.com wrote: Hi, I just finish the mod. It was easy, I cut the trace between TP14 and U405-6 and soldered a wire between TP14 and TP33. Now I have a pretty 1 PPS on J5, the old 9.8304 MHz output. The signal has 0-5 V levels, normally high with a 10 us pulse going down. In my unit this pulse leads the even second pulse by 539 ns. I will check if the Lady Heather command for compensating the cable length can be used to move this if somebody needs a more accurate epoch second. I have to use the 1PPS from my FE5680A as a reference but now it is disconnected. I have made a picture of the mod and I'll include it with my partial schematic (I made some advances there) and the list of the TP signals that I'm preparing for upload. I have checked that now I have also 4 additional 1 PPS outputs in the 110 pin connector J2. They are in the pins previously used by the SYS_CLK signal. They are differential LVDS as most of the signals on this interface. Regards, Ignacio El 13/06/2015 a las 1:14, Ed Armstrong escribió: Ignacio, I would very much appreciate a copy of whatever schematics you have, even if it is not guaranteed to be 100% accurate I agree with you that the 9.9804 Mhz is basically useless, while the even second pulse is merely almost useless. However, as you have apparently looked the board over more carefully than me, you probably already understand why I did it the way I did. The location of the two output circuits were very easy to find, the path from the connector to them is quite distinctive. I just needed to find out where the signal got into the output circuit from, and when I flipped the board over, the trace bringing in the even second pulse was extremely obvious. There was no obvious trace for the 9.9804, and I didn't feel like probing all over the place and looking up a lot of chip numbers to try to figure out where it came from, as I have a very unsteady hand which makes poking around in these closely spaced components an invitation to disaster. So I just went with the obvious. I found it interesting that the output circuit inverts the signal a few times. I actually would have preferred to invert it, so that the polarity was correct for a raspberry pie or a serial port under Windows, but it appeared some of the traces to do so were hidden in the layers of the board, and again the more I fool around the better my chance of shorting something out and becoming very unhappy. I will be anxious to hear how your version of the modification works out, please do keep us posted. I believe the antenna cable feed delay is going to work in the wrong direction here, I also seem to recall reading somewhere that the adjustment range may be limited. I did pretty much correct the offset by manually setting my position about 75M higher than what the device figured it to be, but I am concerned that would only be accurate for a satellite directly overhead, and may cause other inaccuracies by throwing off the geometry, especially for satellites close to the horizon. Based on what I am currently seeing from the Pi, I think the smart solution is to just ignore the offset altogether. Ed On 6/10/2015 11:30 AM, EB4APL wrote: Hi Ed, I am the one who discovered the 1PPS pulse while troubleshooting a NTG550AA. Instead of reuse 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 wrapping wire to joint TP14 to TP33 so the 1PPS will be at J5. I think that I will do the modification this weekend. 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. I had 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,
[time-nuts] hp 5061b replacement tube
Hello, I'm guessing I all ready know the answer to this but: A friend gave me a hp 5061b but in need a tube. Symmetricom was listing the price of a replacement at 35k before the go bought out by Microsemi. Given Microsemi has a tendency to rebrand equipment and then charge 4x the price, an official tube is likely a way non starter. Friend seemed to think there were other sources for tubes, but I am rather pessimistic. What do you think? Is this thing junk? I would hate to scrap it. Maybe use it to house a GPSDO. Link On Jun 12, 2015, at 6:55 AM, Cube Central cubecent...@gmail.com wrote: Hi Max! Thanks for the information, I was wondering if you had documented what you did to your Raspberry Pi so that it might be reproducible to someone like me (a newcomer time-nut and intermediate Linux user) ... you had said: 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. What tweaks? What options have you compiled? What are the gritty details of your setup? 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. what setting is this and how might I go about experimenting with it? Is that the flag3 option in the Generic NMEA GPS Receiver documented here? https://www.eecis.udel.edu/~mills/ntp/html/drivers/driver20.html snip 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. I see word HARDPPS in the driver you mentioned (https://www.eecis.udel.edu/~mills/ntp/html/drivers/driver30.html ) but that documentation is a bit scarce... Could you fill me in on how you have it set up? Is the PPSAPI also used for the Generic NMEA GPS Receiver (driver 20) or the PPS driver (driver 22)? Thanks so much for your assistance! Sorry if these questions have been posted before, but I am very curious about your setup as it nearly matches mine! -Randal r3 of CubeCentral ___ 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
Hello It also depends on which device primitives you can use. Xilinx spartan series has an SRL16, 16 bit shift register that can be ganged to form dividers / pre scalers. It only takes up one lut or slice, I forget which. Link On Jun 11, 2015, at 4:11 AM, Bob Camp kb...@n1k.org wrote: 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 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] NTG550AA 1 PPS mod
Ignacio, I would very much appreciate a copy of whatever schematics you have, even if it is not guaranteed to be 100% accurate I agree with you that the 9.9804 Mhz is basically useless, while the even second pulse is merely almost useless. However, as you have apparently looked the board over more carefully than me, you probably already understand why I did it the way I did. The location of the two output circuits were very easy to find, the path from the connector to them is quite distinctive. I just needed to find out where the signal got into the output circuit from, and when I flipped the board over, the trace bringing in the even second pulse was extremely obvious. There was no obvious trace for the 9.9804, and I didn't feel like probing all over the place and looking up a lot of chip numbers to try to figure out where it came from, as I have a very unsteady hand which makes poking around in these closely spaced components an invitation to disaster. So I just went with the obvious. I found it interesting that the output circuit inverts the signal a few times. I actually would have preferred to invert it, so that the polarity was correct for a raspberry pie or a serial port under Windows, but it appeared some of the traces to do so were hidden in the layers of the board, and again the more I fool around the better my chance of shorting something out and becoming very unhappy. I will be anxious to hear how your version of the modification works out, please do keep us posted. I believe the antenna cable feed delay is going to work in the wrong direction here, I also seem to recall reading somewhere that the adjustment range may be limited. I did pretty much correct the offset by manually setting my position about 75M higher than what the device figured it to be, but I am concerned that would only be accurate for a satellite directly overhead, and may cause other inaccuracies by throwing off the geometry, especially for satellites close to the horizon. Based on what I am currently seeing from the Pi, I think the smart solution is to just ignore the offset altogether. Ed On 6/10/2015 11:30 AM, EB4APL wrote: Hi Ed, I am the one who discovered the 1PPS pulse while troubleshooting a NTG550AA. Instead of reuse 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 wrapping wire to joint TP14 to TP33 so the 1PPS will be at J5. I think that I will do the modification this weekend. 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. I had 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. Probably the easier way to correct this is to use the command which sets the antenna cable delay and compensate for the difference. I don't have a full schematic, even I am not sure that the partial one is 100% correct but I can send it to anyone who wants it. 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
Re: [time-nuts] NTG550AA 1 PPS mod
Hi Ed, While your board is not exactly the same as mine I think that the schematics are almost identical but the TPs and probably the chip names has changed. I think that the main difference is that your unit can be powered with -48 V or +24 V and obviously the parts layout has changed. I have made a partial schematic and it is a work in progress but it has been quite useful for me so far. Since it was started when troubleshooting my board, I focused in certain areas and I still continue from time to time. The troubleshooting effort, while some initial success, was not able to get good results and now I have a dead board that I can trace for expanding the schematic without much care . I use Eagle to draw the schematic and I'm in the process of adding some chips to Eagle since they are not included in the standard library, when I finish I will add a new section which covers the signals that goes to and from the 110 pin connector J2. I think it will be ready in a couple of days. I plan to upload an Eagle .sch file and an image to Dropbox, I will inform you when it is ready. The Eagle file could be useful for continuing the reverse engineering effort. I'm working also in pictures of the board's top and bottom with the resistors and capacitors labeled according to the schematic, I registered the top with a mirror image of the bottom and this is a good way to find the correspondence of the vias but it is advancing at a slower pace, it takes a lot of time. Also I have made a table with the signals of all the the test points, I will also include this. I will keep you informed of the progress. regarding the delay, I checked that Lady Heather accepts both positive and negative delays, in fact cable delays are considered negative. I didn't checked that the board retards the pulses with positive values, I'll do it after the 1PPS mod but I think that this will work. I believe that the elevation trick is not a good idea, it will ruin the GPS receiver calculations, as you say it will work for 1 satellite view and only when it is exactly overhead. Best regards, Ignacio El 13/06/2015 a las 1:14, Ed Armstrong wrote: Ignacio, I would very much appreciate a copy of whatever schematics you have, even if it is not guaranteed to be 100% accurate I agree with you that the 9.9804 Mhz is basically useless, while the even second pulse is merely almost useless. However, as you have apparently looked the board over more carefully than me, you probably already understand why I did it the way I did. The location of the two output circuits were very easy to find, the path from the connector to them is quite distinctive. I just needed to find out where the signal got into the output circuit from, and when I flipped the board over, the trace bringing in the even second pulse was extremely obvious. There was no obvious trace for the 9.9804, and I didn't feel like probing all over the place and looking up a lot of chip numbers to try to figure out where it came from, as I have a very unsteady hand which makes poking around in these closely spaced components an invitation to disaster. So I just went with the obvious. I found it interesting that the output circuit inverts the signal a few times. I actually would have preferred to invert it, so that the polarity was correct for a raspberry pie or a serial port under Windows, but it appeared some of the traces to do so were hidden in the layers of the board, and again the more I fool around the better my chance of shorting something out and becoming very unhappy. I will be anxious to hear how your version of the modification works out, please do keep us posted. I believe the antenna cable feed delay is going to work in the wrong direction here, I also seem to recall reading somewhere that the adjustment range may be limited. I did pretty much correct the offset by manually setting my position about 75M higher than what the device figured it to be, but I am concerned that would only be accurate for a satellite directly overhead, and may cause other inaccuracies by throwing off the geometry, especially for satellites close to the horizon. Based on what I am currently seeing from the Pi, I think the smart solution is to just ignore the offset altogether. Ed On 6/10/2015 11:30 AM, EB4APL wrote: Hi Ed, I am the one who discovered the 1PPS pulse while troubleshooting a NTG550AA. Instead of reuse 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 wrapping wire to joint TP14 to TP33 so the 1PPS will be at J5. I think that I will do the modification this weekend. 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. I had not measured the time
Re: [time-nuts] Using CPLD/FPGA or similar for frequency
Hi The whole “weird primitives” thing is why I try to count this stuff in registers (flip flops) used rather than what ever neat name the marketing guys came up with this week that sounds better than “glob of stuff”. Bob On Jun 12, 2015, at 11:44 PM, lincoln linc...@ampmonkeys.com wrote: Hello It also depends on which device primitives you can use. Xilinx spartan series has an SRL16, 16 bit shift register that can be ganged to form dividers / pre scalers. It only takes up one lut or slice, I forget which. Link On Jun 11, 2015, at 4:11 AM, Bob Camp kb...@n1k.org wrote: 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 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] Raspberry Pi tweaks and custom kernel, was RE: PPS for NTP Server - How Close Is Good Enough?
Hi Max! Thanks for the information, I was wondering if you had documented what you did to your Raspberry Pi so that it might be reproducible to someone like me (a newcomer time-nut and intermediate Linux user) ... you had said: [] Thanks so much for your assistance! Sorry if these questions have been posted before, but I am very curious about your setup as it nearly matches mine! -Randal r3 of CubeCentral === I would also like to know how to best tweak the Raspberry Pi 2 for best performance as an NTP server. Although I have been using Linux-based firmware in my routers for several years now, I have never actually worked In Linux before. I have gone through several tutorials on compiling a custom kernel, only one or two have actually ended in a compilation, but then I couldn't figure out where the kernel and modules were and get them onto the Pi. I have tried this under Ubuntu x64, Debian x64, and Mint 32 bit. So far Mint has been the best, I successfully compiled and I found the kernel, but cannot figure out where the modules are. Anybody suggest a really nice tutorial for learning this Linux stuff? My experience so far is really leading me to appreciate Windows. Thanks Ed === Randal, Ed, Just in case you missed it, I am also a beginner to Linux, so I documented my steps to get NTP working on the Raspberry Pi on my Web site. There's a quick-start guide here: http://www.satsignal.eu/ntp/Raspberry-Pi-quickstart.html and a more blog-like set of detailed notes here: http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html I hope they may be of some help. Typically I'm seeing well under 5 microsecond offsets reported by the RPi themselves: http://www.satsignal.eu/mrtg/performance_ntp.php although with different GPS devices, antennas, and system loads the performance does vary. The polled USB is, perhaps, the main limitation to the device as a server on the LAN, although my own tests have shown RMS offsets reported by a remote client on a quiet LAN of 39 microseconds and a jitter of 38 microseconds. Likely on a busier LAN the network itself might be the limiting factor. I am no longer convinced that there is a significant gain to to be had by recompiling the kernel, now that PPS support for interrupts is included in the current Raspbian kernels. I'm willing to be convinced otherwise, though. Recompiling is a long and painful process, and cross-compiling presents further problems! 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] NTG550AA 1 PPS mod
I agree with you that the 9.9804 Mhz is basically useless, ... Is it really useless? How stable or clean is it? Would it be useful as the reference input to a DMTD? I believe the antenna cable feed delay is going to work in the wrong direction here Have you tried a negative number? Based on what I am currently seeing from the Pi, I think the smart solution is to just ignore the offset altogether. Or use ntpd's fudge -- 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] PPS for NTP Server - How Close Is Good Enough?
eds_equipm...@verizon.net said: Is it possible to modify the kernel so the USB is polled more often, and would that significantly reduce the jitter? Modifying the kernel may not be enough if the timing parameters are in the microcode for the USB device. Whether any improvement is significant probably depends upon your goals. It's unlikely to become a great NTP server. If I wanted a good low power NTP server, I'd probably start with a BeagleBone Black. I haven't seen a low cost no-assembly-required GPS board for the BBB (There is at least one GPS board for the BBB, but it includes a cell phone modem which doubles the cost.) I'd probably try the GPS breakout board from SparkFun. It should take 5 wires: power, ground, trans, recv, and PPS. (and then the appropriate software hacking) -- 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] NTG550AA 1 PPS mod
Hi On Jun 12, 2015, at 7:14 PM, Ed Armstrong eds_equipm...@verizon.net wrote: Ignacio, I would very much appreciate a copy of whatever schematics you have, even if it is not guaranteed to be 100% accurate I agree with you that the 9.9804 Mhz is basically useless, while the even second pulse is merely almost useless. However, as you have apparently looked the board over more carefully than me, you probably already understand why I did it the way I did. The location of the two output circuits were very easy to find, the path from the connector to them is quite distinctive. I just needed to find out where the signal got into the output circuit from, and when I flipped the board over, the trace bringing in the even second pulse was extremely obvious. There was no obvious trace for the 9.9804, and I didn't feel like probing all over the place and looking up a lot of chip numbers to try to figure out where it came from, as I have a very unsteady hand which makes poking around in these closely spaced components an invitation to disaster. So I just went with the obvious. I found it interesting that the output circuit inverts the signal a few times. I actually would have preferred to invert it, so that the polarity was correct for a raspberry pie or a serial port under Windows, but it appeared some of the traces to do so were hidden in the layers of the board, and again the more I fool around the better my chance of shorting something out and becoming very unhappy. I will be anxious to hear how your version of the modification works out, please do keep us posted. I believe the antenna cable feed delay is going to work in the wrong direction here, I also seem to recall reading somewhere that the adjustment range may be limited. I did pretty much correct the offset by manually setting my position about 75M higher than what the device figured it to be, Don’t do that :) The cable delay has far more range than you need for this sort of correction. It’s the ideal way to move the pulse around. It also is quite happy to be either negative or positive, so it can do a pulse offset either ahead or behind GPS. Changing the position does not put in a fixed time offset. Instead it adds an error to (almost) every datapoint you get. Since you are dealing with a 3 dimensional space, the error may be either towards or away from a given satellite. Yes some of those sat’s are out of your view. In your case the error varies from zero to 250 ns depending on the view angle. The net result will be a time solution that swings around a lot. The GPSDO will either try to follow this solution (and swing the frequency) or it will look at the data and toss the device into holdover. Exactly what the threshold of “I don’t like this location” varies a lot from manufacturer to manufacturer. The very real question is still - which edge is correct? Checking against the output of something like a cheap LEA-5T board would give you a quick way to work out what’s what. (You could equally well use an Oncore or any of the other boards out there). Until you have the output calibrated against some sort of independent reference, I would not worry a lot about correcting out a few hundred ns error when doing NTP. It’s small enough that measuring it directly inside NTP will just drive you crazy. Bob but I am concerned that would only be accurate for a satellite directly overhead, and may cause other inaccuracies by throwing off the geometry, especially for satellites close to the horizon. Based on what I am currently seeing from the Pi, I think the smart solution is to just ignore the offset altogether. Ed On 6/10/2015 11:30 AM, EB4APL wrote: Hi Ed, I am the one who discovered the 1PPS pulse while troubleshooting a NTG550AA. Instead of reuse 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 wrapping wire to joint TP14 to TP33 so the 1PPS will be at J5. I think that I will do the modification this weekend. 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. I had 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
Re: [time-nuts] hp 5061b replacement tube
Define 'needs a tube Paul Swed and I have 5061's and both are way past what most would consider needing a new tube. Search the archives on what we have done. I power mine up every 4 months and let it run for a few hours to a day. And once or twice a year. Last year mine has run for a couple weeks while using to do some experimenting. -pete On Fri, Jun 12, 2015 at 10:03 PM, lincoln linc...@ampmonkeys.com wrote: Hello, I'm guessing I all ready know the answer to this but: A friend gave me a hp 5061b but in need a tube. Symmetricom was listing the price of a replacement at 35k before the go bought out by Microsemi. Given Microsemi has a tendency to rebrand equipment and then charge 4x the price, an official tube is likely a way non starter. Friend seemed to think there were other sources for tubes, but I am rather pessimistic. What do you think? Is this thing junk? I would hate to scrap it. Maybe use it to house a GPSDO. Link On Jun 12, 2015, at 6:55 AM, Cube Central cubecent...@gmail.com wrote: Hi Max! Thanks for the information, I was wondering if you had documented what you did to your Raspberry Pi so that it might be reproducible to someone like me (a newcomer time-nut and intermediate Linux user) ... you had said: 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. What tweaks? What options have you compiled? What are the gritty details of your setup? 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. what setting is this and how might I go about experimenting with it? Is that the flag3 option in the Generic NMEA GPS Receiver documented here? https://www.eecis.udel.edu/~mills/ntp/html/drivers/driver20.html snip 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. I see word HARDPPS in the driver you mentioned ( https://www.eecis.udel.edu/~mills/ntp/html/drivers/driver30.html ) but that documentation is a bit scarce... Could you fill me in on how you have it set up? Is the PPSAPI also used for the Generic NMEA GPS Receiver (driver 20) or the PPS driver (driver 22)? Thanks so much for your assistance! Sorry if these questions have been posted before, but I am very curious about your setup as it nearly matches mine! -Randal r3 of CubeCentral ___ 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] hp 5061b replacement tube
Dead tube is a huge issue.At least for most of us finding a replacement tube is zero especially at a cost that is reasonable. I speculate that given the age of all 5061s pretty much all the tubes should be in very bad shape. They only had a life of 7 years and we are many years beyond that. I have done some craziness to get an alternate tube working. Like a new oven controller to actually raise the temp very carefully... But the tubes absolutely run out of Cs and thats that. I picked up a 5061 and it had a dead tube (Hey for $125 you get what you pay for) and another time-nut was kind enough to give me his dead tube. That started my 6 month journey to see if I could get a few Cs. And I did. Just a few but enough to ultimately lock and even today the unit will re-lock on its own after 24 or so hours. What a pain in the $%^. But heck I learned an awful lot from the effort. Jeeze are the 5061s heavy. So there you go hope you did not invest to much money. Further comment there is a good oven osc that would work well for a GPDSO. But there are also quite nice gpsdos on ebay for little money. Do not want to get into x is better then y discussion. But they do work draw little power and are just simply there and working. Happy to discuss off line. Regards Paul WB8TSL On Fri, Jun 12, 2015 at 10:03 PM, lincoln linc...@ampmonkeys.com wrote: Hello, I'm guessing I all ready know the answer to this but: A friend gave me a hp 5061b but in need a tube. Symmetricom was listing the price of a replacement at 35k before the go bought out by Microsemi. Given Microsemi has a tendency to rebrand equipment and then charge 4x the price, an official tube is likely a way non starter. Friend seemed to think there were other sources for tubes, but I am rather pessimistic. What do you think? Is this thing junk? I would hate to scrap it. Maybe use it to house a GPSDO. Link On Jun 12, 2015, at 6:55 AM, Cube Central cubecent...@gmail.com wrote: Hi Max! Thanks for the information, I was wondering if you had documented what you did to your Raspberry Pi so that it might be reproducible to someone like me (a newcomer time-nut and intermediate Linux user) ... you had said: 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. What tweaks? What options have you compiled? What are the gritty details of your setup? 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. what setting is this and how might I go about experimenting with it? Is that the flag3 option in the Generic NMEA GPS Receiver documented here? https://www.eecis.udel.edu/~mills/ntp/html/drivers/driver20.html snip 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. I see word HARDPPS in the driver you mentioned ( https://www.eecis.udel.edu/~mills/ntp/html/drivers/driver30.html ) but that documentation is a bit scarce... Could you fill me in on how you have it set up? Is the PPSAPI also used for the Generic NMEA GPS Receiver (driver 20) or the PPS driver (driver 22)? Thanks so much for your assistance! Sorry if these questions have been posted before, but I am very curious about your setup as it nearly matches mine! -Randal r3 of CubeCentral ___ 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] hp 5061b replacement tube
Hi We’ve had a cesium back for rebuild after the Microsemi merger. The price on a tube is still in the same vicinity. If you ship the Cs back to them, they will do a rebuild and drop the tube in. The price on that process is only firm once they see the actual device. So far our rebuilds all have come out at the $35K-ish price. Bob On Jun 12, 2015, at 10:03 PM, lincoln linc...@ampmonkeys.com wrote: Hello, I'm guessing I all ready know the answer to this but: A friend gave me a hp 5061b but in need a tube. Symmetricom was listing the price of a replacement at 35k before the go bought out by Microsemi. Given Microsemi has a tendency to rebrand equipment and then charge 4x the price, an official tube is likely a way non starter. Friend seemed to think there were other sources for tubes, but I am rather pessimistic. What do you think? Is this thing junk? I would hate to scrap it. Maybe use it to house a GPSDO. Link On Jun 12, 2015, at 6:55 AM, Cube Central cubecent...@gmail.com wrote: Hi Max! Thanks for the information, I was wondering if you had documented what you did to your Raspberry Pi so that it might be reproducible to someone like me (a newcomer time-nut and intermediate Linux user) ... you had said: 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. What tweaks? What options have you compiled? What are the gritty details of your setup? 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. what setting is this and how might I go about experimenting with it? Is that the flag3 option in the Generic NMEA GPS Receiver documented here? https://www.eecis.udel.edu/~mills/ntp/html/drivers/driver20.html snip 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. I see word HARDPPS in the driver you mentioned (https://www.eecis.udel.edu/~mills/ntp/html/drivers/driver30.html ) but that documentation is a bit scarce... Could you fill me in on how you have it set up? Is the PPSAPI also used for the Generic NMEA GPS Receiver (driver 20) or the PPS driver (driver 22)? Thanks so much for your assistance! Sorry if these questions have been posted before, but I am very curious about your setup as it nearly matches mine! -Randal r3 of CubeCentral ___ 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] NTGS50AA 1 PPS mod
Hi, I just finish the mod. It was easy, I cut the trace between TP14 and U405-6 and soldered a wire between TP14 and TP33. Now I have a pretty 1 PPS on J5, the old 9.8304 MHz output. The signal has 0-5 V levels, normally high with a 10 us pulse going down. In my unit this pulse leads the even second pulse by 539 ns. I will check if the Lady Heather command for compensating the cable length can be used to move this if somebody needs a more accurate epoch second. I have to use the 1PPS from my FE5680A as a reference but now it is disconnected. I have made a picture of the mod and I'll include it with my partial schematic (I made some advances there) and the list of the TP signals that I'm preparing for upload. I have checked that now I have also 4 additional 1 PPS outputs in the 110 pin connector J2. They are in the pins previously used by the SYS_CLK signal. They are differential LVDS as most of the signals on this interface. Regards, Ignacio El 13/06/2015 a las 1:14, Ed Armstrong escribió: Ignacio, I would very much appreciate a copy of whatever schematics you have, even if it is not guaranteed to be 100% accurate I agree with you that the 9.9804 Mhz is basically useless, while the even second pulse is merely almost useless. However, as you have apparently looked the board over more carefully than me, you probably already understand why I did it the way I did. The location of the two output circuits were very easy to find, the path from the connector to them is quite distinctive. I just needed to find out where the signal got into the output circuit from, and when I flipped the board over, the trace bringing in the even second pulse was extremely obvious. There was no obvious trace for the 9.9804, and I didn't feel like probing all over the place and looking up a lot of chip numbers to try to figure out where it came from, as I have a very unsteady hand which makes poking around in these closely spaced components an invitation to disaster. So I just went with the obvious. I found it interesting that the output circuit inverts the signal a few times. I actually would have preferred to invert it, so that the polarity was correct for a raspberry pie or a serial port under Windows, but it appeared some of the traces to do so were hidden in the layers of the board, and again the more I fool around the better my chance of shorting something out and becoming very unhappy. I will be anxious to hear how your version of the modification works out, please do keep us posted. I believe the antenna cable feed delay is going to work in the wrong direction here, I also seem to recall reading somewhere that the adjustment range may be limited. I did pretty much correct the offset by manually setting my position about 75M higher than what the device figured it to be, but I am concerned that would only be accurate for a satellite directly overhead, and may cause other inaccuracies by throwing off the geometry, especially for satellites close to the horizon. Based on what I am currently seeing from the Pi, I think the smart solution is to just ignore the offset altogether. Ed On 6/10/2015 11:30 AM, EB4APL wrote: Hi Ed, I am the one who discovered the 1PPS pulse while troubleshooting a NTG550AA. Instead of reuse 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 wrapping wire to joint TP14 to TP33 so the 1PPS will be at J5. I think that I will do the modification this weekend. 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. I had 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. Probably the easier way to correct this is to use the command which sets the antenna cable delay and compensate for the difference. I don't have a full schematic, even I am not sure that the partial one is 100% correct but I can send it to anyone who wants it. 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
