[time-nuts] U-blox teaser

[Michael Wouters]

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 at 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 at 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
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