Re: [time-nuts] Is it sensible to update every few seconds from NTP server?
On 08/11/12 09:14, Poul-Henning Kamp wrote: In messageCANX10hBat1ie0Rx_bS+X1dqGGLTPx5xCz2=typp_uvwgu-m...@mail.gmail.com , David Kirkby writes: If the local NTP implementation on the machine has a marginally competent PLL, updating more than once per minute will just increase the noise. If the local NTP implementation is really SNTP which steps the clock, then you should find a better one, if what you need is good timekeeping. In addition, if many people ask the same server at a relatively high rate, it's approximating DDOS. I'd expect that kernel FLL/PLL be included and used. Shifting from the default SNTP to NTP with set-only is of only marginal improvement at best, but with the dangerous notion that you fixed it. If you read up on NTP, there are articles (you find them through http://www.ntp.org) describing the properties of some (now old) OS clocks and their behaviour. Similar is to be expected for default Windows behaviour as well as many virtual machines. I think the old articles is good to raise the awareness, but I can't recall similar for the modern situation, but I am sure someone here have seen them. Make sure the OS (kernel-support + NTP configuration) you are using provides you with the stability you need. Does someone holds a Best Current Practice for various OSes? Cheers, Magnus ___ 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] Is it sensible to update every few seconds from NTP server?
In message CANX10hBat1ie0Rx_bS+X1dqGGLTPx5xCz2=typp_uvwgu-m...@mail.gmail.com , David Kirkby writes: If the local NTP implementation on the machine has a marginally competent PLL, updating more than once per minute will just increase the noise. If the local NTP implementation is really SNTP which steps the clock, then you should find a better one, if what you need is good timekeeping. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Is it sensible to update every few seconds from NTP server?
On 7 November 2012 22:52, David davidwh...@gmail.com wrote: Some finicky software becomes upset if time is stepped backwards too far. Although noting to dowith my original post, if I set the time too far back on a CentOs 5 (Redhat clone), it will not boot properly next time, as it detects the file sytem was last mounted in the future. So one has to run fsck to get the system to boot properly. Anyway, I'll find out what my friend is using. 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.
Re: [time-nuts] Is it sensible to update every few seconds from NTP server?
Hi There are two different things being used here. One is SNTP - a one way time set and forget approach. The other is NTP - a client / server setup that creates a disciplined local clock in software. You get SNTP data from an NTP server, but that doesn't make it NTP. It's still SNTP. Since you pick a NTP server when you do SNTP setup people get confused. Rapid poling with SNTP is silly. Back a few thousand years ago :), desktop / laptop cpu horsepower for NTP was an issue. That hasn't been true for at least 15 years. You are doing heavy duty DSP to run any of these modes. If your CPU can do that, NTP is not going to be an issue. I doubt you will even *see* the CPU percentage used by NTP on a modern machine. Bob On Nov 7, 2012, at 10:04 PM, Christopher Brown cbr...@woods.net wrote: There are 2 different things here. Setting the time based on a single query. Disciplining the local clock Many of the built in NTP clients just Set the time every X Setting one of these to SET the local clock every X seconds is a less than good thing. If you timing needs are loose, let the client _set_ the time once an hour or day. If you need tight timing, install a full NTP setup. Normally this means... Host starts up Host performs a _set_ to get the time within a few tens of ms Host then fires up a proper ntp server, with a list of remote service. This talks to all of the provided servers, figures the local osc offset, compensates and keeps everything in-line. This is a much better (and more stable) setup than hard setting the clock every 4 seconds On 11/7/12 12:41 PM, David Kirkby wrote: Someone at my radio club uses some mode of operation where accurate time is required. He said the standard Windoze clock does not keep sufficiently accurate, so he has software which updates from an NTP server every 4 seconds or so. It's not exactly a denial of service (DOS) attack, but seems almost close to it in NTP terms to me. I can't really believe updating every few seconds is sensible myself, but he assures me it works very well. (I'm rather hoping it does not use a stratum 1 server!) I'm sure someone will say if you want accurate time on a PC, to use some combination of GPS, rubidium or OCXO with a 1 pps pulse and a serial port on a FreeBSD or similar computer. But that's probably not practical if your software only works on Windoze. Any comments? Dave, G8WRB. ___ 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] Is it sensible to update every few seconds from NTP server?
Someone at my radio club uses some mode of operation where accurate time is required. He said the standard Windoze clock does not keep sufficiently accurate, so he has software which updates from an NTP server every 4 seconds or so. It's not exactly a denial of service (DOS) attack, but seems almost close to it in NTP terms to me. I can't really believe updating every few seconds is sensible myself, but he assures me it works very well. (I'm rather hoping it does not use a stratum 1 server!) I'm sure someone will say if you want accurate time on a PC, to use some combination of GPS, rubidium or OCXO with a 1 pps pulse and a serial port on a FreeBSD or similar computer. But that's probably not practical if your software only works on Windoze. Any comments? Dave, G8WRB. ___ 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] Is it sensible to update every few seconds from NTP server?
Some Windows NTP clients like Tardis can calculate and implement a clock frequency adjustment instead of stepping the clock if the time adjustment is below a specified limit. If he was using an application that was upset by the time being stepped, then that might allow less frequent updates. If he is polling that often to maintain accurate time, then I would assume he is using a local known to be accurate NTP server. There are Windows NTP clients which will synchronize to GPS PPS time. That should be better than stock hardware and Windows can handle anyway. Something like a Garmin GPS18 is specified to be within 1uS and has a pulse to pulse jitter in the 10s of nanoseconds. On Wed, 7 Nov 2012 21:41:36 +, David Kirkby david.kir...@onetel.net wrote: Someone at my radio club uses some mode of operation where accurate time is required. He said the standard Windoze clock does not keep sufficiently accurate, so he has software which updates from an NTP server every 4 seconds or so. It's not exactly a denial of service (DOS) attack, but seems almost close to it in NTP terms to me. I can't really believe updating every few seconds is sensible myself, but he assures me it works very well. (I'm rather hoping it does not use a stratum 1 server!) I'm sure someone will say if you want accurate time on a PC, to use some combination of GPS, rubidium or OCXO with a 1 pps pulse and a serial port on a FreeBSD or similar computer. But that's probably not practical if your software only works on Windoze. Any comments? Dave, G8WRB. ___ 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] Is it sensible to update every few seconds from NTP server?
Interesting I am unaware of any amateur service requiring that tight of a timing relationship. At least modern PC clocks do not drift that badly in a few minutes. So it is pretty odd. Without further detail I am at a loss for why you need to do that. Maybe he is tinkering with spreadspectrum? Regards Paul On Wed, Nov 7, 2012 at 5:04 PM, David davidwh...@gmail.com wrote: Some Windows NTP clients like Tardis can calculate and implement a clock frequency adjustment instead of stepping the clock if the time adjustment is below a specified limit. If he was using an application that was upset by the time being stepped, then that might allow less frequent updates. If he is polling that often to maintain accurate time, then I would assume he is using a local known to be accurate NTP server. There are Windows NTP clients which will synchronize to GPS PPS time. That should be better than stock hardware and Windows can handle anyway. Something like a Garmin GPS18 is specified to be within 1uS and has a pulse to pulse jitter in the 10s of nanoseconds. On Wed, 7 Nov 2012 21:41:36 +, David Kirkby david.kir...@onetel.net wrote: Someone at my radio club uses some mode of operation where accurate time is required. He said the standard Windoze clock does not keep sufficiently accurate, so he has software which updates from an NTP server every 4 seconds or so. It's not exactly a denial of service (DOS) attack, but seems almost close to it in NTP terms to me. I can't really believe updating every few seconds is sensible myself, but he assures me it works very well. (I'm rather hoping it does not use a stratum 1 server!) I'm sure someone will say if you want accurate time on a PC, to use some combination of GPS, rubidium or OCXO with a 1 pps pulse and a serial port on a FreeBSD or similar computer. But that's probably not practical if your software only works on Windoze. Any comments? Dave, G8WRB. ___ 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] Is it sensible to update every few seconds from NTP server?
Some finicky software becomes upset if time is stepped backwards too far. I have seen PC hardware clocks that drifted 30 seconds a day but that only matters during a restart. The more common problem involves OS time drift, often amounting to seconds per minute, caused by bad System Management Mode code leading to lost interrupts or other problems. A BIOS update or fiddling with the CPU power management usually fixes that. On Wed, 7 Nov 2012 17:11:26 -0500, paul swed paulsw...@gmail.com wrote: Interesting I am unaware of any amateur service requiring that tight of a timing relationship. At least modern PC clocks do not drift that badly in a few minutes. So it is pretty odd. Without further detail I am at a loss for why you need to do that. Maybe he is tinkering with spreadspectrum? Regards Paul On Wed, Nov 7, 2012 at 5:04 PM, David davidwh...@gmail.com wrote: Some Windows NTP clients like Tardis can calculate and implement a clock frequency adjustment instead of stepping the clock if the time adjustment is below a specified limit. If he was using an application that was upset by the time being stepped, then that might allow less frequent updates. If he is polling that often to maintain accurate time, then I would assume he is using a local known to be accurate NTP server. There are Windows NTP clients which will synchronize to GPS PPS time. That should be better than stock hardware and Windows can handle anyway. Something like a Garmin GPS18 is specified to be within 1uS and has a pulse to pulse jitter in the 10s of nanoseconds. On Wed, 7 Nov 2012 21:41:36 +, David Kirkby david.kir...@onetel.net wrote: Someone at my radio club uses some mode of operation where accurate time is required. He said the standard Windoze clock does not keep sufficiently accurate, so he has software which updates from an NTP server every 4 seconds or so. It's not exactly a denial of service (DOS) attack, but seems almost close to it in NTP terms to me. I can't really believe updating every few seconds is sensible myself, but he assures me it works very well. (I'm rather hoping it does not use a stratum 1 server!) I'm sure someone will say if you want accurate time on a PC, to use some combination of GPS, rubidium or OCXO with a 1 pps pulse and a serial port on a FreeBSD or similar computer. But that's probably not practical if your software only works on Windoze. Any comments? Dave, G8WRB. ___ 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] Is it sensible to update every few seconds from NTP server?
Sure enough every 4 seconds would work, as would every 2 seconds. But I bet every 1000 seconds would work as well. We need some more details but it seem he has something badly misconfigured if 4 seconds updates are required. On Wed, Nov 7, 2012 at 1:41 PM, David Kirkby david.kir...@onetel.netwrote: Someone at my radio club uses some mode of operation where accurate time is required. He said the standard Windoze clock does not keep sufficiently accurate, so he has software which updates from an NTP server every 4 seconds or so. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Is it sensible to update every few seconds from NTP server?
We had a presentation at our radio club several months ago on digital HF modes, and part of the presentation was on JT65 and apparently it needs a precise synchronized time fix on both ends for an exchange to occur. I do not recollect all of the details that were presented, but they did say that the default windows time keeper is not accurate enough, and advocated installing a third party ntp client that updates (way too) frequently. -Brian On Wed, 2012-11-07 at 16:52 -0600, David wrote: Some finicky software becomes upset if time is stepped backwards too far. I have seen PC hardware clocks that drifted 30 seconds a day but that only matters during a restart. The more common problem involves OS time drift, often amounting to seconds per minute, caused by bad System Management Mode code leading to lost interrupts or other problems. A BIOS update or fiddling with the CPU power management usually fixes that. On Wed, 7 Nov 2012 17:11:26 -0500, paul swed paulsw...@gmail.com wrote: Interesting I am unaware of any amateur service requiring that tight of a timing relationship. At least modern PC clocks do not drift that badly in a few minutes. So it is pretty odd. Without further detail I am at a loss for why you need to do that. Maybe he is tinkering with spreadspectrum? Regards Paul On Wed, Nov 7, 2012 at 5:04 PM, David davidwh...@gmail.com wrote: Some Windows NTP clients like Tardis can calculate and implement a clock frequency adjustment instead of stepping the clock if the time adjustment is below a specified limit. If he was using an application that was upset by the time being stepped, then that might allow less frequent updates. If he is polling that often to maintain accurate time, then I would assume he is using a local known to be accurate NTP server. There are Windows NTP clients which will synchronize to GPS PPS time. That should be better than stock hardware and Windows can handle anyway. Something like a Garmin GPS18 is specified to be within 1uS and has a pulse to pulse jitter in the 10s of nanoseconds. On Wed, 7 Nov 2012 21:41:36 +, David Kirkby david.kir...@onetel.net wrote: Someone at my radio club uses some mode of operation where accurate time is required. He said the standard Windoze clock does not keep sufficiently accurate, so he has software which updates from an NTP server every 4 seconds or so. It's not exactly a denial of service (DOS) attack, but seems almost close to it in NTP terms to me. I can't really believe updating every few seconds is sensible myself, but he assures me it works very well. (I'm rather hoping it does not use a stratum 1 server!) I'm sure someone will say if you want accurate time on a PC, to use some combination of GPS, rubidium or OCXO with a 1 pps pulse and a serial port on a FreeBSD or similar computer. But that's probably not practical if your software only works on Windoze. Any comments? Dave, G8WRB. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Is it sensible to update every few seconds from NTP server?
On 7 November 2012 23:28, bjon...@mindspring.com wrote: We had a presentation at our radio club several months ago on digital HF modes, and part of the presentation was on JT65 and apparently it needs a precise synchronized time fix on both ends for an exchange to occur. I do not recollect all of the details that were presented, but they did say that the default windows time keeper is not accurate enough, and advocated installing a third party ntp client that updates (way too) frequently. -Brian I think it might be JT65 he is using. I know he said that if your time was accurate to 1 ms, and someone elses 2 ms, you have a higher chance of making the QSO. Hence there is a need for accurate timing. (I'm not sure he said those exact figures of 1 and 2 ms, but the general point was that it needed to be accuate, and increased accuracy gave a higher chance of making the QSO). But the whole idea of getting time from an internet time server every few seconds seemed odd to me. He is not using any local time server. I'll try to find out what mode he is using, and what software to correct his time. 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.
Re: [time-nuts] Is it sensible to update every few seconds from NTP server?
Based on a sample of one (my NTP), I can hold the clock frequency to 0.1PPM. Seems to me you could compute the adjustment requirements from such a number. -Original Message- From: Chris Albertson albertson.ch...@gmail.com Sender: time-nuts-boun...@febo.com Date: Wed, 7 Nov 2012 15:02:41 To: Discussion of precise time and frequency measurementtime-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Is it sensible to update every few seconds from NTP server? Sure enough every 4 seconds would work, as would every 2 seconds. But I bet every 1000 seconds would work as well. We need some more details but it seem he has something badly misconfigured if 4 seconds updates are required. On Wed, Nov 7, 2012 at 1:41 PM, David Kirkby david.kir...@onetel.netwrote: Someone at my radio club uses some mode of operation where accurate time is required. He said the standard Windoze clock does not keep sufficiently accurate, so he has software which updates from an NTP server every 4 seconds or so. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Is it sensible to update every few seconds from NTP server?
Hi I think you would do a lot better with a cheap GPS rather than fiddling with NTP for this level of timing. No real need for a GPSDO, just the raw pps and time of day straight out of the GPS. Probably no need for a timing grade GPS, just one with a PPS. Bob On Nov 7, 2012, at 6:47 PM, David Kirkby david.kir...@onetel.net wrote: On 7 November 2012 23:28, bjon...@mindspring.com wrote: We had a presentation at our radio club several months ago on digital HF modes, and part of the presentation was on JT65 and apparently it needs a precise synchronized time fix on both ends for an exchange to occur. I do not recollect all of the details that were presented, but they did say that the default windows time keeper is not accurate enough, and advocated installing a third party ntp client that updates (way too) frequently. -Brian I think it might be JT65 he is using. I know he said that if your time was accurate to 1 ms, and someone elses 2 ms, you have a higher chance of making the QSO. Hence there is a need for accurate timing. (I'm not sure he said those exact figures of 1 and 2 ms, but the general point was that it needed to be accuate, and increased accuracy gave a higher chance of making the QSO). But the whole idea of getting time from an internet time server every few seconds seemed odd to me. He is not using any local time server. I'll try to find out what mode he is using, and what software to correct his time. 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 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] Is it sensible to update every few seconds from NTP server?
David, What mode is your friend using that he finds the need to do an ntp update every 4 seconds? I'm familiar with JT65 , but that does fine with a +/- 1 second error. -Jeff W7WWA ___ 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] Is it sensible to update every few seconds from NTP server?
Hi JT65 needs at most +/- 0.5 seconds. Just about any proper NTP running continuously on a Windows machine will do far better than that. There's no need for massive update rates to make it all happen. Bob On Nov 7, 2012, at 8:00 PM, Jeff Stevens j...@mossycup.com wrote: David, What mode is your friend using that he finds the need to do an ntp update every 4 seconds? I'm familiar with JT65 , but that does fine with a +/- 1 second error. -Jeff W7WWA ___ 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] Is it sensible to update every few seconds from NTP server?
That sounds odd, as most radios take tens of millisecond, if not hundreds to switch from transmit to receive and back in any mode other than break-in CW. Further JT65 is used with propagation modes that typically do not have a stable or predictable propagation time like moonbounce or meteor scatter, so I don't understand why mS timing would be necessary? I must be missing something. Didier KO4BB Didier Sent from my Droid Razr 4G LTE wireless tracker. -Original Message- From: David Kirkby david.kir...@onetel.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wed, 07 Nov 2012 5:47 PM Subject: Re: [time-nuts] Is it sensible to update every few seconds from NTP server? On 7 November 2012 23:28, bjon...@mindspring.com wrote: We had a presentation at our radio club several months ago on digital HF modes, and part of the presentation was on JT65 and apparently it needs a precise synchronized time fix on both ends for an exchange to occur. I do not recollect all of the details that were presented, but they did say that the default windows time keeper is not accurate enough, and advocated installing a third party ntp client that updates (way too) frequently. -Brian I think it might be JT65 he is using. I know he said that if your time was accurate to 1 ms, and someone elses 2 ms, you have a higher chance of making the QSO. Hence there is a need for accurate timing. (I'm not sure he said those exact figures of 1 and 2 ms, but the general point was that it needed to be accuate, and increased accuracy gave a higher chance of making the QSO). But the whole idea of getting time from an internet time server every few seconds seemed odd to me. He is not using any local time server. I'll try to find out what mode he is using, and what software to correct his time. 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 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] Is it sensible to update every few seconds from NTP server?
The symbol time for JT65 is 2.69 baud or 0.372 seconds so one symbol is about 70,000 miles of propagation. The information I found online says synchronization needs to be within 1 or 2 seconds for decoding and closer is better. http://www.qsl.net/zs2pe/VHF/Downloads/JT65%20Technical%20Specs.txt If the OS clock was screwed up because of the issues I mentioned earlier, synchronizing every few seconds might be needed to make it work. I sure would try fiddling with CPU power management though to fix it. On Wed, 7 Nov 2012 19:42:38 -0600, shali...@gmail.com wrote: That sounds odd, as most radios take tens of millisecond, if not hundreds to switch from transmit to receive and back in any mode other than break-in CW. Further JT65 is used with propagation modes that typically do not have a stable or predictable propagation time like moonbounce or meteor scatter, so I don't understand why mS timing would be necessary? I must be missing something. Didier KO4BB Didier Sent from my Droid Razr 4G LTE wireless tracker. -Original Message- From: David Kirkby david.kir...@onetel.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Wed, 07 Nov 2012 5:47 PM Subject: Re: [time-nuts] Is it sensible to update every few seconds from NTP server? On 7 November 2012 23:28, bjon...@mindspring.com wrote: We had a presentation at our radio club several months ago on digital HF modes, and part of the presentation was on JT65 and apparently it needs a precise synchronized time fix on both ends for an exchange to occur. I do not recollect all of the details that were presented, but they did say that the default windows time keeper is not accurate enough, and advocated installing a third party ntp client that updates (way too) frequently. -Brian I think it might be JT65 he is using. I know he said that if your time was accurate to 1 ms, and someone elses 2 ms, you have a higher chance of making the QSO. Hence there is a need for accurate timing. (I'm not sure he said those exact figures of 1 and 2 ms, but the general point was that it needed to be accuate, and increased accuracy gave a higher chance of making the QSO). But the whole idea of getting time from an internet time server every few seconds seemed odd to me. He is not using any local time server. I'll try to find out what mode he is using, and what software to correct his time. 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 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] Is it sensible to update every few seconds from NTP server?
On 11/7/12 5:42 PM, shali...@gmail.com wrote: That sounds odd, as most radios take tens of millisecond, if not hundreds to switch from transmit to receive and back in any mode other than break-in CW. Further JT65 is used with propagation modes that typically do not have a stable or predictable propagation time like moonbounce or meteor scatter, so I don't understand why mS timing would be necessary? I must be missing something. maybe some form of Coherent or very low speed CW or equivalent, where you use an external reference to get symbol timing. Say you were sending at 1 bit per second, using a 1 PPS as your symbol clock. You send a sync pattern at the beginning, then free run for the message. Don't forget that the implementation may be very unsophisticated or adopted/modified from some hardware design where the timing was counted down from a good clock, and now it's just a slavish copy in software. ___ 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] Is it sensible to update every few seconds from NTP server?
There are 2 different things here. Setting the time based on a single query. Disciplining the local clock Many of the built in NTP clients just Set the time every X Setting one of these to SET the local clock every X seconds is a less than good thing. If you timing needs are loose, let the client _set_ the time once an hour or day. If you need tight timing, install a full NTP setup. Normally this means... Host starts up Host performs a _set_ to get the time within a few tens of ms Host then fires up a proper ntp server, with a list of remote service. This talks to all of the provided servers, figures the local osc offset, compensates and keeps everything in-line. This is a much better (and more stable) setup than hard setting the clock every 4 seconds On 11/7/12 12:41 PM, David Kirkby wrote: Someone at my radio club uses some mode of operation where accurate time is required. He said the standard Windoze clock does not keep sufficiently accurate, so he has software which updates from an NTP server every 4 seconds or so. It's not exactly a denial of service (DOS) attack, but seems almost close to it in NTP terms to me. I can't really believe updating every few seconds is sensible myself, but he assures me it works very well. (I'm rather hoping it does not use a stratum 1 server!) I'm sure someone will say if you want accurate time on a PC, to use some combination of GPS, rubidium or OCXO with a 1 pps pulse and a serial port on a FreeBSD or similar computer. But that's probably not practical if your software only works on Windoze. Any comments? Dave, G8WRB. ___ 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.
