[time-nuts] Novatel ProPak-V3 GPSDO

[Ole Petter Ronningen]

Bob,

Perhaps my subject line should have been "Novatel ProPak-V3 and TAIPPP" - I
got the unit primarily to play around with PPP and time transfer. I was
unaware of the GPSDO-functionality when I got it, but I thought it was kind
of neat and at least worth testing. Will report back if I get any useful
results on that front.

But, as you rightly point out, the licenses to get L1/L2/L5 GPS+GLONASS and
so on are *not* cheap - and I am not at all clear on exactly which (if any)
firmware options are required to get PPP working properly in a timing
context.

I am therefore exploring the possibility to get useful performance on
L1-only - and there is at least a couple of papers[1] on that subject. It
would seem that L1 code+carrier tracking, combined with SBAS (or,
preferably, other precise corrections) in post processing will get the
PPP-solutions a lot closer to L1/L2 than I would have expected!

I assume that this accuracy in position will directly transfer over to
solving for time. If this is indeed the case, anyone with a cesium (or
perhaps even a rubidium) and one of these receivers could compare their
frequency-sources to e.g. USNO. It might take several days or weeks to get
any meaningful precision, and it would be post-processing all the way, but
still useful if the frequency source is stable enough. (And if not
particularly useful, then at least interesting!)

It is quite possible that other (more reasonably priced) receivers will
also produce useful precision in this setting. The referenced paper makes a
point that the reported levels of accuracy depend on "high grade equipment"
- but I am not clear on which properties distinguish "high grade" from "low
grade" in this context - multipath is mentioned. I have a uBlox that will
output raw measurements, and I may try to compare the two.

The receivers used in time transfer needs to be code+carrier tracking. It
needs to be driven by the frequency source to be calibrated, and according
to what scant information I have found, also needs a PPS input from the
local clock. I am unsure about that last requirement, I do not fully
understand the reasoning - but I *think* it is required to align "time" (as
opposed to only frequency). It may be that lack of PPS input on the
receiver can be compensated for with an external TI counter. It may also be
that it is possible to "calibrate" only frequency, and leave the PPS to its
own devices.

But we'll see how it progresses - away from the "lab" at the moment, so
it's all based on reading papers and guessing. (Which is at least half the
fun!)

BR,
Ole

1. Wanninger, L. Hesselbarth, A., "SBAS Based Single and Dual Frequency
Precise Point Positioning" and "SBAS Orbit and Satellite Clock Corrections
for Precise Point Positioning"


On Fri, Dec 25, 2015 at 6:19 PM, Bob Camp <kb8tq at n1k.org> wrote:

> Hi
>
> I think you will find the Novatel OEM cards inside a number of L1/L2
> timing receiver designs. The
> cost for the basic card is not crazy if bought surplus. Doing the *full*
> set of firmware / software
> upgrades to make them “work right’ is more expensive than some new
> automobiles. If you
> decide to go that way, it’s almost as cheap to buy the brand new V6 board
> plus the software as
> to upgrade an old one. The advantage is that the new boards have a bit
> more processing
> horsepower on them.
>
> If you run them as “L1 only” devices, the Novatel cards do not have much
> (if any) advantage
> over the other boards out there. Since they fetch a premium price surplus,
> their bang for the
> buck factor on L1 is not very good. Something like a TBolt is a cheaper /
> “at least as good”
> alternative.
>
> I do not know of any of the precision timing people who use the charge
> pump output of the
> board for their systems. They pretty much all team the board up with some
> sort of cpu board
> (single board computer) and let it do the heavy lifting and data
> collection. The full implementation
> then is the Novatel card, the CPU card, and a custom board for the GPSDO /
> measurement
> system.
>
> This is by no means a knock on the Novatel cards. They are *very* good
> devices. The gotcha
> is the fact that they need a lot of firmware “unlocks” to do all the good
> stuff they are capable of.
> With the *full* set of unlocks the newest cards are (when they come out)
> likely the best thing you
> can buy for this sort of thing when teamed up with a capable computer.
>
> Bob
>
>
> > On Dec 25, 2015, at 6:35 AM, Ole Petter Ronningen <opronningen at gmail.com>
> wrote:
> >
> > Hello
> >
> > I'm sure many of you have noticed quite a few surplus NOS Novatel OEM-V3
> > L1-only units appearing on eBay lately. Reading the firmware manual, it
> > seems the ProPak is capable of steering an external oscillator with the
> > addition of a filtered chargepump circuit. Has anyone made any
> experiments
> > using this functionality?
> >
> > Also, a couple of labs (APL and USNO) use ProPak-V3 receivers to
> > participate in TAI, by the use of PPP. BIPM has a little information
> about
> > the ProPak (calibration procedures), but other than that I have not found
> > much information about the configuration of the receiver in this
> particular
> > setting. Any clues would be appreciated.
> >
> > (In case anyone is interested - the receiver can be software upgraded to
> > also track L2 - the license is north of USD2K..)
> >
> > Thanks,
> > Ole
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