FWIW. No detailed content, and a rather quick read. "Five key trends in GPS". https://www.u-blox.com/en/blogs/insights/five-key-trends-gps

It's interesting that they talk about the F9 receivers offering 5 ns absolute time accuracy. Does anyone know of tests confirming that, and what sort of care was required in the setup to get there? John ---- On 2/26/21 9:34 AM, Robert LaJeunesse wrote: > FWIW. No detailed content, and a rather quick read. "Five key trends in GPS". > > https://www.u-blox.com/en/blogs/insights/five-key-trends-gps > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. >

Hi I can’t think of many antennas (multi band or single band) that claim to know their delay to < 5 ns. Simply having a *differential* delay spec of < 5 ns is quite good. Same thing with delay ripple, you see specs out to around 15 ns on a lot of antennas. None of this is getting you to the actual total delay of the antenna. It’s a pretty good bet that number is a bit larger than either of these. Some of the ripple probably comes out in the standard modeling. I’m not sure that the differential delay is taken out that way. Total delay, not taken out in any obvious fashion ( at least that I can see). If the F9 has a built in antenna database, that’s not mentioned in the doc’s. Any benefit from the corrections would have to be part of post processing. No, that’s not the same as talking about the F9 it’s self doing X ns, but it would be part of any practical system trying to get close to 5 ns absolute accuracy. 5 ns *relative* accuracy between two F9’s? I probably could buy that if the appropriate one sigma / on a clear day / with the wind in the right direction sort of qualifiers are attached. Bob > On Feb 26, 2021, at 4:27 PM, John Ackermann N8UR <jra@febo.com> wrote: > > It's interesting that they talk about the F9 receivers offering 5 ns absolute time accuracy. Does anyone know of tests confirming that, and what sort of care was required in the setup to get there? > > John > ---- > > On 2/26/21 9:34 AM, Robert LaJeunesse wrote: >> FWIW. No detailed content, and a rather quick read. "Five key trends in GPS". >> https://www.u-blox.com/en/blogs/insights/five-key-trends-gps >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there.

John, if you look back at the recent GPSDO discussion initiated by "dandober" in hpaligent keysight group, you'll see a post by Leo Bodnar, linking a Ublox model here https://www.u-blox.com/sites/default/files/products/documents/LEA-M8F_DataSheet_%28UBX-14001772%29.pdf I looked it up, and I recall the PPS timing spec is +/- 5 nSec. After I studied it some, I replied back "Thanks Leo, that's a great example of what I've been picturing. This is from the data sheet, regarding the PPS output: "After an initial phase of acquisition the time-pulse becomes essentially jitter-free, generated coherently from the built-in reference oscillator and guaranteeing an exact number of reference frequency cycles between each time-pulse." It looks like this is an implementation of what we've talked about here before a few times, for saw-tooth error reduction. BTW I didn't call it "1PPS" above, because it can be programmed for different rates - I don't recall what they are. BTW, did dandober ever sign up here? Ed

Hi Would not “absolute” timing be referenced to UTC? (or something similar) Bob > On Feb 26, 2021, at 5:37 PM, ed breya <eb@telight.com> wrote: > > John, if you look back at the recent GPSDO discussion initiated by "dandober" in hpaligent keysight group, you'll see a post by Leo Bodnar, linking a Ublox model here > > https://www.u-blox.com/sites/default/files/products/documents/LEA-M8F_DataSheet_%28UBX-14001772%29.pdf > > I looked it up, and I recall the PPS timing spec is +/- 5 nSec. After I studied it some, I replied back > > "Thanks Leo, that's a great example of what I've been picturing. This is from the data sheet, regarding the PPS output: > > "After an initial phase of acquisition the time-pulse becomes essentially jitter-free, generated coherently from the built-in reference oscillator and guaranteeing an exact number of reference frequency cycles between each time-pulse." > > It looks like this is an implementation of what we've talked about here before a few times, for saw-tooth error reduction. BTW I didn't call it "1PPS" above, because it can be programmed for different rates - I don't recall what they are. > > BTW, did dandober ever sign up here? > > Ed > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there.

They're claiming "even better than" 5 ns for relative time, which given the 4 ns jitter seems at least sort-of reasonable. But until someone shows me otherwise, I'm still thinking that getting better than 25 ns absolute accuracy is a pretty good day's work. John ---- On 2/26/21 5:26 PM, Bob kb8tq wrote: > Hi > > I can’t think of many antennas (multi band or single band) that claim to know their > delay to < 5 ns. Simply having a *differential* delay spec of < 5 ns is quite good. > Same thing with delay ripple, you see specs out to around 15 ns on a lot of antennas. > None of this is getting you to the actual total delay of the antenna. It’s a pretty good > bet that number is a bit larger than either of these. > > Some of the ripple probably comes out in the standard modeling. I’m not sure that > the differential delay is taken out that way. Total delay, not taken out in any obvious > fashion ( at least that I can see). If the F9 has a built in antenna database, that’s not > mentioned in the doc’s. Any benefit from the corrections would have to be part of > post processing. > > No, that’s not the same as talking about the F9 it’s self doing X ns, but it would be part > of any practical system trying to get close to 5 ns absolute accuracy. > > 5 ns *relative* accuracy between two F9’s? I probably could buy that if the appropriate > one sigma / on a clear day / with the wind in the right direction sort of qualifiers are > attached. > > Bob > >> On Feb 26, 2021, at 4:27 PM, John Ackermann N8UR <jra@febo.com> wrote: >> >> It's interesting that they talk about the F9 receivers offering 5 ns absolute time accuracy. Does anyone know of tests confirming that, and what sort of care was required in the setup to get there? >> >> John >> ---- >> >> On 2/26/21 9:34 AM, Robert LaJeunesse wrote: >>> FWIW. No detailed content, and a rather quick read. "Five key trends in GPS". >>> https://www.u-blox.com/en/blogs/insights/five-key-trends-gps >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@lists.febo.com >>> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. >

You have to be careful comparing the LEA-M8F with other GPS units. It does have low jitter because the "TIMEPULSE" signal is derived from the TCXO which is locked to the GPS time mark. But their claim of "essentially jitter free" depends on your definition of "essentially" -- attached is a comparison of LEA-M8F PPS jitter vs. NEO-M8T and ZED-F9T raw, and NEO-M8T and ZED-F9T sawtooth corrected PPS. The M8F is definitely better than the raw M8T and even the raw F9T, but the corrected M8T and F9T are both much better than the M8F. And the M8F does *not* have sawtooth correction available. So, it's a neat implementation and has some applications (basically as a modest performance 30.72 MHz GPSDO), but TANSTAAFL. John ---- On 2/26/21 5:37 PM, ed breya wrote: > John, if you look back at the recent GPSDO discussion initiated by > "dandober" in hpaligent keysight group, you'll see a post by Leo Bodnar, > linking a Ublox model here > > https://www.u-blox.com/sites/default/files/products/documents/LEA-M8F_DataSheet_%28UBX-14001772%29.pdf > > > I looked it up, and I recall the PPS timing spec is +/- 5 nSec. After I > studied it some, I replied back > > "Thanks Leo, that's a great example of what I've been picturing. This is > from the data sheet, regarding the PPS output: > > "After an initial phase of acquisition the time-pulse becomes > essentially jitter-free, generated coherently from the built-in > reference oscillator and guaranteeing an exact number of reference > frequency cycles between each time-pulse." > > It looks like this is an implementation of what we've talked about here > before a few times, for saw-tooth error reduction. BTW I didn't call it > "1PPS" above, because it can be programmed for different rates - I don't > recall what they are. > > BTW, did dandober ever sign up here? > > Ed > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there.

That's how I'd interpret it. ⁣Get BlueMail for Android ​ On Feb 26, 2021, 7:42 PM, at 7:42 PM, Bob kb8tq <kb8tq@n1k.org> wrote: >Hi > >Would not “absolute” timing be referenced to UTC? (or something >similar) > >Bob > >> On Feb 26, 2021, at 5:37 PM, ed breya <eb@telight.com> wrote: >> >> John, if you look back at the recent GPSDO discussion initiated by >"dandober" in hpaligent keysight group, you'll see a post by Leo >Bodnar, linking a Ublox model here >> >> >https://www.u-blox.com/sites/default/files/products/documents/LEA-M8F_DataSheet_%28UBX-14001772%29.pdf >> >> I looked it up, and I recall the PPS timing spec is +/- 5 nSec. After >I studied it some, I replied back >> >> "Thanks Leo, that's a great example of what I've been picturing. This >is from the data sheet, regarding the PPS output: >> >> "After an initial phase of acquisition the time-pulse becomes >essentially jitter-free, generated coherently from the built-in >reference oscillator and guaranteeing an exact number of reference >frequency cycles between each time-pulse." >> >> It looks like this is an implementation of what we've talked about >here before a few times, for saw-tooth error reduction. BTW I didn't >call it "1PPS" above, because it can be programmed for different rates >- I don't recall what they are. >> >> BTW, did dandober ever sign up here? >> >> Ed >> >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe, go to >http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. > > >_______________________________________________ >time-nuts mailing list -- time-nuts@lists.febo.com >To unsubscribe, go to >http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >and follow the instructions there.

Typical L1 antenna delays range from 20 to 70 ns. I know of only one antenna for which a delay is given by the vendor and the technique used was just to measure the electronic delay ie by injecting a signal into the circuit. To do it properly, you need a setup in a microwave anechoic chamber with transmitting antenna etc. The practical difference may be small though, 1 or 2 ns ( sample of one antenna!). Cheers Michael On Sat, 27 Feb 2021 at 11:42 am, John Ackermann N8UR <jra@febo.com> wrote: > They're claiming "even better than" 5 ns for relative time, which given > the 4 ns jitter seems at least sort-of reasonable. But until someone > shows me otherwise, I'm still thinking that getting better than 25 ns > absolute accuracy is a pretty good day's work. > > John > ---- > > On 2/26/21 5:26 PM, Bob kb8tq wrote: > > Hi > > > > I can’t think of many antennas (multi band or single band) that claim to > know their > > delay to < 5 ns. Simply having a *differential* delay spec of < 5 ns is > quite good. > > Same thing with delay ripple, you see specs out to around 15 ns on a lot > of antennas. > > None of this is getting you to the actual total delay of the antenna. > It’s a pretty good > > bet that number is a bit larger than either of these. > > > > Some of the ripple probably comes out in the standard modeling. I’m not > sure that > > the differential delay is taken out that way. Total delay, not taken out > in any obvious > > fashion ( at least that I can see). If the F9 has a built in antenna > database, that’s not > > mentioned in the doc’s. Any benefit from the corrections would have to > be part of > > post processing. > > > > No, that’s not the same as talking about the F9 it’s self doing X ns, > but it would be part > > of any practical system trying to get close to 5 ns absolute accuracy. > > > > 5 ns *relative* accuracy between two F9’s? I probably could buy that if > the appropriate > > one sigma / on a clear day / with the wind in the right direction sort > of qualifiers are > > attached. > > > > Bob > > > >> On Feb 26, 2021, at 4:27 PM, John Ackermann N8UR <jra@febo.com> wrote: > >> > >> It's interesting that they talk about the F9 receivers offering 5 ns > absolute time accuracy. Does anyone know of tests confirming that, and > what sort of care was required in the setup to get there? > >> > >> John > >> ---- > >> > >> On 2/26/21 9:34 AM, Robert LaJeunesse wrote: > >>> FWIW. No detailed content, and a rather quick read. "Five key trends > in GPS". > >>> https://www.u-blox.com/en/blogs/insights/five-key-trends-gps > >>> _______________________________________________ > >>> time-nuts mailing list -- time-nuts@lists.febo.com > >>> To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > >>> and follow the instructions there. > >> > >> _______________________________________________ > >> time-nuts mailing list -- time-nuts@lists.febo.com > >> To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > >> and follow the instructions there. > > > > > > _______________________________________________ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. >

On 2/26/21 4:00 PM, John Ackermann N8UR wrote: > They're claiming "even better than" 5 ns for relative time, which > given the 4 ns jitter seems at least sort-of reasonable.  But until > someone shows me otherwise, I'm still thinking that getting better > than 25 ns absolute accuracy is a pretty good day's work. > > John > ---- And if the jitter is uniformly distributed (i.e. 1 clock cycle of some sort) - then the sd is 1/sqrt(12) of the extremes, so a "max uncertainty" of 5ns, is more like a 1.5 ns 1 sigma.