[time-nuts] Re: Comparison/evaluation of u-blox timing receivers

[Avamander]

Hi,

I hope you don't mind me starting a "newcomer" thread based on your
sentence: "with a GPSDO, finding one that’s got a clean output is not at
all easy".

Are there any up-to-date resources that would provide such information
about a larger selection of GPSDOs?

Are there any GPSDOs that people really recommend purchasing right now,
costing say up to $500? Or is the "just build your own" approach the most
cost-effective way?

P.S: "Study John Vig's Introduction to Quartz Frequency Standards" link on
http://www.leapsecond.com/time-nuts.htm is broken

On Tue, Aug 24, 2021 at 3:20 PM Bob kb8tq <kb8tq at n1k.org> wrote:

> Hi
>
> The problem with the approach used in the basic GPS / GNSS modules is
> that the TCXO is not tuned on frequency. Even with an integer relation to
> the
> internal oscillator, you still see the pulse drop / pulse add into the
> divider. The
> result is that they are noisy.
>
> There are a couple of modules that *do* tune the frequency. ( as noted in
> the
> paper). There the very coarse DAC used is what gets you in terms of noise.
> Again, it’s regardless of output frequency. The signal *is* cleaner, it’s
> just not
> as clean as what most folks are looking for.
>
> Even with a GPSDO, finding one that’s got a clean output is not at all
> easy.
> Yes, this all depends a lot on just what you mean by clean. It normally
> comes
> up in the context of folks wanting to run radios at microwaves. Indeed the
> normal answer there is that you use multiple oscillators in your multiplier
> chain.
>
> Bob
>
> > On Aug 24, 2021, at 7:18 AM, Marek Doršic <marek.dorsic at gmail.com>
> wrote:
> >
> > Hello,
> >
> >  thank you for sharing valuable comprehensive comparisions.
> >
> > In the high timepulse rate experiment, have you also investigated other
> rates than the standard 10 MHz? Most Ublox receivers use 48MHz internal
> clock thus the 10MHz timepulse must be missing some of the clock pulses
> which generates additional jitter. 8MHz or 12MHz rates which are integer
> divisions might have cleaner output.
> >
> >  .marek
> >
> >> On 24 Aug 2021, at 03:51, John Ackermann N8UR <jra at febo.com> wrote:
> >>
> >> In 2020 I did an extensive evaluation of the timing ability of the
> u-blox LEA-M8F, NEO-M8N, NEO-M8T, NEO-M9N, ZED-F9P, and ZED-F9T.  The work
> was made possible by support from the HamSci consortium (
> https://hamsci.org) under NSF grants supporting HamSci activities.
> >>
> >> I was sure I'd posted about the paper on time-nuts, but I can't find
> any record that I did, so this is a belated announcement.  It's available
> for download from
> >>
> >>
> https://hamsci.org/sites/default/files/publications/2020_TAPR_DCC/N8UR_GPS_Evaluation_August2020.pdf
> >>
> >> As BobC says, "Lots of fun!"
> >>
> >> John
> >>
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