Hi The same 20 or so ns delay in a saw would also apply to the saw (or tight filter) in some timing antennas. It also would apply to the saw(s) in some modules. Even if the tolerance is “only” a couple ns on each of them, you *could* have 3 or more in the chain.
Lots of numbers to crunch to get to 5 ns “absolute”. One could go grab a GPS simulator and start poking. First step would be to find a simulator that is spec’d for a < 5 ns tolerance on the PPS into GPS out. I do believe that rules out the eBay marvels that some of us have lying around ….. Simpler answer would be a quick “clock trip” with your car full of 5071’s …… hour drive over to NIST and then back home. That sounds practical for most of us :) :) Bob > On Feb 26, 2021, at 9:29 PM, John Ackermann N8UR <j...@febo.com> wrote: > > A while ago I tried doing a decidedly non-anechoic measurement with a VNA > exciter going to a 1500 MHz ground plane and the receiver connected to the > antenna (with a known delay cable) and I got a similar result, but there was > enough noise that I didn't think I could nail it down to within 10 ns. > > I've also measured GPS antenna splitters and they tend to have 20-ish ns > delays, mainly due to the SAW filters. I did surgery on an HP splitter to > remove the filters so it could be used for L1 and L2 and that dropped the > delay down to only 1 or 2 ns. > > So there's definitely lots of stuff to calibrate if you want to get accurate > time transfer. > > John > ---- > > On 2/26/21 8:02 PM, Michael Wouters wrote: >> 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 <j...@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 <j...@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. >>> >> _______________________________________________ >> 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.