[time-nuts] Re: Use of dual frequency GPS for NTP server and other purposes

[Todd Smith]

Hello Tim,

I know many people have had problems in contacting Jackson Labs, but when I
called them I was able to get someone to call me back.  they are in Las
Vegas so keep that in mind when you call them.

I paid $365 a unit plus a 2% CC fee and I installed two units just
purchased in 2 Syncserver S300 and it is a drop in replacement.  I plugged
the new receiver into my laptop using USB and configured the settings that
I wanted.  (GPS, SBAS, QZSS and Galileo, since I am using an
original Symmetricom GPS antenna)

After I configured the DIP switches so that SRAM settings were to be used
on power-up; I powered the receiver down and unbolted the S300.  I took
screws out of the top and took the lid off.  My Furuno receiver was secured
by 4 screws and standoffs.  I unscrewed the screws and unplugged the GPS
antenna lead going to the BNC connector.  I gently pulled up in the
receiver since it is plugged into the motherboard by a 10 pin Motorola
connector. I used the existing screws and standoffs from the orginial
Furuno receiver and plugged the new one in making sure that the pins
aligned on the motherboard.  Plugged the GPS lead back in and powered up
the Syncserver.  Pretty straight forward, nothing special I had to do.

Out of the box, the Jackson labs receiver is setup for GPS, SBAS, QZSS and
Glosnoss.  I didn't think my antenna would work for Glosnoss so I chose
Galileo instead.  You could also choose Beidou if you had the antenna for
it.  Any 2 GNSS can be active at a time and the Syncserver doesn't know the
difference.  It just sees more satellites at a time now.  In my case, my
S300 didn't have room between the power supply and the receiver to leave
the USB cable plugged in all of the time so I needed to config it before I
installed it.  In a different case, you could leave the USB cable plugged
in and extract timing or position information from it if you wished and
bypass or supplement your Syncserver.

The manual on Jackson Labs site was very useful to me as well as tech
support to answer some questions.  I am not affiliated even though almost
all of my posts recently have been about the Jackson Labs receiver.  I am
just a satisfied customer since my Furuno rolled over on Sept 18 2022 at
00:00 UTC

Todd


On Wed, Oct 5, 2022 at 11:34 AM Tim Lister <listertim at gmail.com> wrote:

> On Wed, Oct 5, 2022 at 7:43 AM Todd Smith <tssmith2002 at gmail.com> wrote:
> >
> > As has been mentioned on the list recently, Jackson Labs builds a M12M
> multi-GNSS receiver that is a drop-in replacement for the Furuno receivers
> that are in the Syncservers that you are running right now.
>
> Any idea on pricing and whether it's just a plug-in replacement or
> involves more serious surgery ? I've never had much luck in the past
> getting replies from Jackson Labs.
>
> >
> > If I am not mistaken, Galileo uses close enough frequency to GPS that
> you can reuse the existing GPS antenna and receive both systems with a
> multi-GNSS receiver like the Jackson Labs units.
> >
> > Todd
> >
> > On Tue, Oct 4, 2022 at 9:29 PM Bob kb8tq via time-nuts <
> time-nuts at lists.febo.com> wrote:
> >>
> >> Hi
> >>
> >> > On Oct 4, 2022, at 8:33 PM, Tim Lister <listertim at gmail.com> wrote:
> >> >
> >> > On Tue, Oct 4, 2022 at 4:57 PM Bob kb8tq <kb8tq at n1k.org> wrote:
> >> >>
> >> >> Hi
> >> >>
> >> >> The main issue with using the output of a GPS receiver directly is
> >> >> dropouts. They can be caused by a variety of things. When the GPS
> >> >> “goes away” you loose all timing information.  Do these various
> things
> >> >> ( jamming, birds, lightning, …..) impact you? If they do, depending
> on
> >> >> just how the loss of timing impacts you, you do or don’t have a
> problem.
> >> >>
> >> >> Into an NTP server, the impact will still be there. How great an
> impact
> >> >> it is depends a *lot* on what the next level source going into the
> server
> >> >> is. The commercial NTP gizmos tend to have things like OCXO’s or Rb
> >> >> standards in them. That gives them a bit better performance than a
> >> >> typical DIY computer based NTP server.
> >> >
> >> > Yes they would definitely impact us. I neglected to mention that we
> >> > have the rubidium oscillator option as backup in these units to
> >> > provide holdover. Mostly to provide insurance/holdover for the case
> >> > that weather takes out the antenna to give time to ship a replacement
> >> > out from HQ in CA to whichever site was affected. Given that one of
> >> > the time servers provides the IRIG-B signal for the 400 Hz control
> >> > loop for the drives for a ~20 ton 2-meter diameter telescope, I'm not
> >> > keen on a homebrew Raspberry Pi solution however much I like them for
> >> > my own time-nut home use...
> >>
> >> So indeed, having timing drop out is not a good thing ….
> >>
> >> >
> >> >>
> >> >> If you *do* go with a dual freq GPS, you can do a very good job of
> working
> >> >> out the location of your antenna. With some effort that can improve
> the
> >> >> net timing accuracy. If post processing timing correction is ok in
> this
> >> >> case, that also is a lot easier / more accurate with a full set of
> dual freq
> >> >> GPS data to correct against.
> >> >
> >> > A "real time" (latency ~<30 minutes) measure of the PWV would be
> >> > helpful for scheduling/optimization of observations but there's also
> >> > likely to be value in an improved value for use during later analysis
> >> > at timescale >12 hours. Haven't done enough reading around of the
> >> > literature on determining PWV from GPS to get a sense of where the
> >> > error budget and improvements lie. I'm assuming something like a 48
> >> > hour initial survey and having that post processed by e.g. the NRCan
> >> > PPP service after the final GPS orbits are available would likely be a
> >> > benefit but unclear how having a proper geodetic phase center vs a
> >> > $200 bullet L1/L2/L5 antenna matters. Similarly it's not clear to me
> >> > how much improvement in the water vapor determination comes from the
> >> > increasingly precise (but increasingly delayed) GPS orbit products -
> >> > it may be e.g. the Ultra Rapids are Good Enough.
> >>
> >> For about $100 ( delivered ) you can get a “pretty good” Chinese multi
> >> band antenna. It’s not as good as fancy $2,000 antenna, but it’s way
> >> better than a hockey puck. With that and a week’s data into NRCan
> >> (it’s free ….. ) you can be pretty sure of your location to < 10 CM.
> That’s
> >> good enough to “not matter” for timing.
> >>
> >> >>
> >> >> So, when it works, you might be down into the < 10 ns range. When
> that
> >> >> bird sits on that antenna …. microseconds …. takes a nap …
> milliseconds ….
> >> >
> >> > We're not an optical observatory so not in the pulsars & masers
> >> > category. Driving demand on accuracy for us is normally very close,
> >> > fast moving Near Earth Objects which can move at several hundred
> >> > arcseconds/minute. If we don't want the timing uncertainty to degrade
> >> > the position accuracy by more than the star catalog does, then we need
> >> > timing precision in the ~1-10ms range. Determining diameters from
> >> > occultations of stars by Kuiper Belt Objects, which have a transverse
> >> > velocity of ~15 km/s, leads to similar requirements.
> >>
> >> The advantages of all this stuff ( single band vs multi band ) are in
> the < 100 ns
> >> range. If you do a good job on the single frequency stuff ( sawtooth
> correction ….)
> >> the improvement is < 20 ns.  There is a footnote down somewhere that
> mentions
> >> some sort of “99.9% of the time” stuff. There are unusual solar events
> that can
> >> push things well above the 20 ns range.
> >>
> >> Yes, there are other factors. There is another chunk for GPS <-> UTC.
> There also
> >> is a chunk for antenna / cable delays and the like. This stuff impacts
> both approaches.
> >> Normally that all should be < 100 ns. The delay part should be stable
> to < 20 ns in
> >> a typical setup.
> >>
> >> >>
> >> >> Lots of tradeoffs.
> >> >
> >> > As always, tempered often by a lack of funds.
> >>
> >> Somehow money always matters :)
> >>
> >> Bob
> >>
> >> >
> >> > Tim
> >> >
> >> >>
> >> >> Bob
> >> >>
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