The F10T looks interesting, but from the datasheet it is missing a few
maybe important features compared to the ZED-F9T:

-- L1/L5 bands only (no L2 option)
-- only one TIMEPULSE output (could be a very big deal)
-- only one EXTINT input (probably not a big deal)
-- I/O appears to be solely via one UART -- no native USB, no I2C/SPI

A lot of the pins used in the NEO-M8/9 modules are listed as "reserved".
I don't know whether the limitations are the result of cramming a
dual-freq receiver into the NEO form factor, of if they're for product
differentiation.

John

On 6/21/23 10:00, Erik Kaashoek via time-nuts wrote:

Hi All;
There is one NEO F10T breakout board I have seen.
https://www.ardusimple.com/product/simplegnss-timing/
[https://www.ardusimple.com/wp-content/uploads/2023/04/NEO-F10T_top.jpg]https://www.ardusimple.com/product/simplegnss-timing/
simpleGNSShttps://www.ardusimple.com/product/simplegnss-timing/
L1/L5/E5a GNSS receiver with submeter location accuracy, nanosecond timing accuracy and RAW data for postprocessing PPK. Based on u-blox NEO-F10T.
www.ardusimple.com
UBLOX has a eval software that is very useful, but has a few bugs.l
Cheers;

Tom Knox
SR Test and Measurement Engineer
Phoenix Research
4870 Meredith Way Apt 102
Boulder, Co 80303
Formerly of:
357 Fox Lane
Superior Co 80027
303-554-0307
actast@hotmail.com

https://www.thedenverchannel.com/news/marshall-fire/superior-man-moving-forward-after-losing-dream-research-lab-during-marshall-fire

"Peace is not the absence of violence, but the presence of Justice" Both MLK and Albert Einstein

From: John Ackermann N8UR via time-nuts time-nuts@lists.febo.com
Sent: Wednesday, June 21, 2023 8:37 AM
To: time-nuts@lists.febo.com time-nuts@lists.febo.com
Cc: John Ackermann N8UR jra@febo.com
Subject: [time-nuts] Re: What GNSS module to buy for a good time reference?

The F10T looks interesting, but from the datasheet it is missing a few
maybe important features compared to the ZED-F9T:

-- L1/L5 bands only (no L2 option)
-- only one TIMEPULSE output (could be a very big deal)
-- only one EXTINT input (probably not a big deal)
-- I/O appears to be solely via one UART -- no native USB, no I2C/SPI

A lot of the pins used in the NEO-M8/9 modules are listed as "reserved".
I don't know whether the limitations are the result of cramming a
dual-freq receiver into the NEO form factor, of if they're for product
differentiation.

John

On 6/21/23 10:00, Erik Kaashoek via time-nuts wrote:

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

On 6/21/23 7:37 AM, John Ackermann N8UR via time-nuts wrote:

I'm not sure no L2 is such a big deal - going forward, people are
pushing to L5. It's better protected spectrum management (adjacent user)
wise, it has 3dB more power than L1, and longer spreading codes.   The
only hiccup is that it's only live on 17-18 satellites, 24 by 2025.  L2
has less power than L1, but the longer codes for L2C should make up
for that.

A question would be whether a L1, L2 receiver uses the L2C, or whether
they are just doing phase retrieval on the L2 unmodulated carrier (older
satellites). Or some sort of codeless processing.

There's also a somewhat wider spread between L1 and L5, so in theory,
you could do better ionospheric corrections.

L1 - 1575.42

L2c - 1227.6

L5 - 1176.45

John, thanks

Could you elaborate a bit on these points:

-- L1/L5 bands only (no L2 option)
I read the amount of satellites transmitting L5 is a bit lower compared to
L2, are there other reasons why L2 is important? I guess one would have to
choose between L2 or L5 anyway in configuring a F9T, anything else?

-- only one TIMEPULSE output (could be a very big deal)
I failed to understand why this may be a big deal, can you explain?

Erik.

On 6/21/23 13:11, Erik Kaashoek via time-nuts wrote:

In the future, L5 will be a solid choice for the second frequency, and
it's fine now if you want only real-time results.  But the NRCan
post-processing service currently does not use L5 in its corrections so
you won't be able to upload RINEX files to get back precise location
information or clock offsets.  At some point, I'm sure they will process
L5 but that's not the case yet.  (Last time I checked they ignored L5
data included in an L1/L2/L5 RINEX, and I haven't been able to find
anything on the web indicating that they've started.)

One of the neat things about the prior u-blox timing receivers (and some
of the non-timing ones as well) is that they have two independent
timepulse outputs that can be programmed to RF frequencies (as high as
25 MHz for some).  You can use one output for PPS, and the other to
generate an RF signal that can be used, with appropriate cleanup as the
phase noise/jitter is horrible, as a frequency reference.  There are a
couple of modern GPSDO designs that take advantage of this, using the
second TP output to drive a Silicon Labs jitter attenuator/synthesizer chip.

Without the second TP signal, you can do PPS or RF but not both.

John

Hi

The “big deal” with no L2 is fairly simple:

One of the great things about dual freq modules is the ability to send off data
and very quickly get back a corrected version. If you use NRCan, this includes
clock corrections. They are good to the ~ 0.1 ns level. You can get to < 1x10^-14
in less than a day.

The problem is, the free correction services (at the moment) are L1 / L2 based.
For whatever reason, they don’t (yet) understand L5. That may change, or it
may not change. Right now, it’s the way it is ….

If you want to go crazy, the Mosaic-T is the best of the best in terms of GNSS
modules at the moment. They apparently are well aware of this and charge
accordingly. You can buy a lot of F9T’s for the price of one Mosaic-T.

Bob

On 6/21/23 10:11 AM, Erik Kaashoek via time-nuts wrote:

Today, there are fewer L5 than L2, but that's rapidly changing. And L5
gives you better performance, so you get a better result with fewer
satellites being tracked.

"L2 unmodulated carrier"?  As in a CW tone?

Dana

On Wed, Jun 21, 2023 at 12:13 PM Lux, Jim via time-nuts <
time-nuts@lists.febo.com> wrote:

On 6/23/23 2:09 PM, Dana Whitlow via time-nuts wrote:

P/Y code on I, nothing on Q (so "bpsk" as opposed to QPSK).  The table
says "unmodulated"

talking about GNSS, someone here might know....

I have a problem which I can see either one hemisphere or the other, but
not both simultaneously  - from the one antenna.

It takes two antennas. Consequently, my 3D fixes are in the toilet.

Is there a mode where two receivers  separately correlate all the sats
they can see independently and then talk to each other to use the sats
from the 'other' receiver to get a better all sky 3D fix ? or get 
enough raw data out of them and post process elsewhere ?

glen.

On 22/06/2023 10:31 am, Lux, Jim via time-nuts wrote:

On 6/29/23 10:36 PM, glen english LIST via time-nuts wrote:

Not easily - you might be better off just running the two antennas into
a power combiner.

But, there's a variety of software that will take raw observables and
combine them to make a single fix.  GipsyX at JPL does this, but it is
non-trivial to do.

There's also RTGx (Real Time Gipsy) which can probably do it on the fly
(RTGx is part of GIPSYx). Or, at least, I know it can combine
observables from the signals from multiple antennas at the same time. 
Granted it's all one receiver, usually, with multiple input channels,
but I'm pretty sure that RTGx doesn't care - it would help if both
receivers share a common clock.  (isn't that a particularly Time-Nuts
kind of statement in general)?

https://gipsyx.jpl.nasa.gov/

In theory, if you've got a research application, you can get a free
non-commercial license from JPL.

You can get a pdf from here:

https://www.sciencedirect.com/science/article/pii/S0273117720302532

Willy Bertiger, Yoaz Bar-Sever, Angie Dorsey, Bruce Haines, Nate Harvey,
Dan Hemberger, Michael Heflin, Wenwen Lu, Mark Miller, Angelyn W. Moore,
Dave Murphy, Paul Ries, Larry Romans, Aurore Sibois, Ant Sibthorpe, Bela
Szilagyi, Michele Vallisneri, Pascal Willis,

GipsyX/RTGx, a new tool set for space geodetic operations and research,

Advances in Space Research,
Volume 66, Issue 3,
2020,
Pages 469-489,
ISSN 0273-1177,
https://doi.org/10.1016/j.asr.2020.04.015.

Full disclosure, I'm the project manager of NASA's SunRISE mission:
we're using RTGx on board the six space vehicles AND doing post
processing of the observables on the ground to get position to ~1 meter
and time to ~1 ns. The Precision Orbit Determination (POD) also uses
GIPSYx/RTGx, and gives us the clock bias estimate. SunRISE is a
constellation of 6 small space vehicles (called the observatory) that
will record radio signals between 100 kHz and 23 MHz in an orbit about
300km above GEO.  The six space vehicles fly about 1-15 km apart, and we
use interferometery to image the source of RF from Type II and Type III
bursts from the Sun. Type IIs come with CMEs.  We're launching in 2025,
theoretically.  The space vehicles are all built and tested, and are
basically in storage "waiting for our ride". Basically in the last few
weeks.

There will be some papers coming out over the next months (SmallSat in
August, BigSky in March) describing various aspects of how the design
came together and was tested. There's been a series of papers at BigSky,
and a set of 4 posters at AGU last year that describe it fairly well.

Giving plenty of credit to Time-Nuts - the conversations on this list
have been invaluable in feeding into making SunRISE a reality.  After
all, what we're doing with SunRISE is basically a GPS observed
oscillator (we don't adjust the oscillator), and there's been a LOT of
discussion on the list about that.  In fact, those discussions are
partly why we don't discipline - we don't have to worry about backing
out the disciplining.

And if that's not cool enough - We've been working on concepts for
50-100 satellites out at L4 or L5, and there's no handy GNSS out there
for position nav and timing. So now, we need to know relative position
to a meter, time to a nanosecond, and orientation relative to the sky,
completely within the observatory in space.

Solar radio bursts are bright (up to 40 dB over galactic background),
and the Sun doesn't put out much energy in that band, except from the
bursts.  But there's a lot of interest in low frequency radio astronomy
for planetary, or beyond solar system - you can't observe it from the
Earth's surface, because the ionosphere either blocks it, or is
sufficiently non-isotropic that imaging doesn't work.

Hi

This is sort of several questions rolled into one. Various answers:

1. Are there dual antenna receivers? Sure there are/ They assume you can see all the
   sats from both antennas at the same time.

2. Can you get 3D fixes from multiple independent antennas? Sure, but not with a stock
   receiver. The delays and phase shifts into multiple receivers from multiple inputs via multiple
   cables really mess with things.

3. Can receivers chat with each other? Yes, it’s RTK mode. Like 1 above to be useful, it
   wants both receivers looking at the same set of sat’s.

Bottom line, AFIK, you need an antenna that can see at least 4 sats all at the same time. It
needs to do that long enough to get a reasonable location fix. Once you have that fix, you
can go over to fixed location / timing mode. That will give you timing information. This mode
is not available on all GPS receivers or modules.

Bob

Thanks for the replies so far. and very Interesting Jim !

application is improve the GPS fix for field portable installed
TABS/conspicuity in experimental aircraft with metal skins or carbon
fibre skins. In a nutshell they broadcast a 1 sec intervals on ADSB 1090
MHz the posiiton, and info) . they are usually suction cup fitted.

There are conspicuity units that suction cup to the inside rear window
and they are terrible for fix, +/- 300m in H, +/- 200m in V.  even worse
if a high wing and a wing in the way that is full of fuel .

It's passable on the front of the instrument panel at the forward end
where it can see a fair bit of the sky through the windshield, but not
great for vis, and also affects compass swing . The units are very
popular with recreational experimental, and assist to avoid traffic.

Real TSO GPS require GPS antenna on the top of the skin to get an all
sky view.  (like my PA28)

Possible solution is 2 or 3  antennas looking at different parts of the
sky but my feeling is most likely just one antenna on either side window
left and right would eb a substantial improvement. I am yet to
QUANTIITIVELY see exactly why it is so poor- I need to put one of my
UBLOX radios there in the device's place and get some data.

sidenote - As an RF guy, I would have thought combining the signal from
both GPS antenna (downstream of their LNAs)  would lead to a fair bit of
infighting, and be highly sub optimal  . maybe not as bad as I imagine.

-glen

On 1/07/2023 8:35 am, Lux, Jim via time-nuts wrote:

On 6/30/23 4:52 PM, glen english LIST via time-nuts wrote:

Assuming the feedlines are equal length, and you combine them. You'll
get classic grating lobes where one is exactly in or out of phase with
the other.  BUT.. since the pattern is already rolling off (a typical
patch has a 90-100 degree HPBW), both of them are fairly far down at the
"dividing line" equi distant, so it may not be as bad as you think.

This is easy to model in a spreadsheet - Just assume the antenna has a
cos^2(theta) kind of pattern and then calculate the sum of the two
signals (including the phase difference for the angle off vertical,
which depends on the spacing between the antennas).

There's enough other lumps and bumps in the pattern from surroundings,
the grating lobes might be in the same general magnitude.   Or just try it.

One thing to watch out for: if you're using antennas with built in LNAs

• it's easy to build an oscillator - the amplified output of antenna 1
  goes through the splitter and comes out the port to antenna 2 and if the
  reverse isolation of the LNA isn't good enough, it radiates back to
  antenna 1.  Fortunately, the antennas are narrow band, so it might not
  happen to oscillate.  But if you get weird results, try covering one of
  the antennas with aluminum foil (or absorber, if you have some).

And these days, you can get a spectrum analyzer that goes up to 2GHz for
about $100  - it's not awesome, but it sure would see an oscillation at
GPS frequencies, and would prevent all the GPS users around you from
hunting you down like a rogue wolf.

Hi Jim

Seems this question of mine is well covered in  the ether.

Yes, might not be as bad as I think. I'll write a program to compute
various scenarios and also will be interested to see how the fixes get
affected  with loss of signal over some AZEL patch of the sky.

The other thing- these narrowband antennas, over 24 MHz ish, I would
suspect they are NOT phase  coherent, and that a combined pair of
signals over identical sky would be anythign but flat frequency response.

Yes, - the LNA. some of these have 40dB gain, golly. I have some 1500
MHz ferrite isolators, also. probably unnecessary as you say depends on
the S12 for the LNA   and thus the match the antenas see into the
splitter is likely important. Have spec-an to 50 GHz so.....

Time now I think to set up a couple of receivers and get some raw data.,
and compare with single receiver and combined antenna. Patch antennas
generally suck I find for all the usual reasons, I am a fan of
quadrafilar helicies.... but patches are a dime a dozen and 3what is in
use,  so that's what I will use for the tests and report back.

-glen

On 30/06/2023 06:36, glen english LIST via time-nuts wrote:

Geln,

Assuming you mean half-hemisphere....

Why not get a receiver capable of all three main systems - GPS, Galileo, and
Beidou - and configured to use them.  As Bob said, all you need is a reasonable
number of satellites, and receiving all three systems increases the changes of
that happening.

Getting both the 2.3 and 1.5 GHz signals can increase accuracy as well.

Perhaps you need something better than that can provide - I don't know.

Cheers,
David

SatSignal Software - Quality software for you
Web: https://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv

On 6/30/23 6:40 PM, glen english LIST via time-nuts wrote:

Oh, they're probably phase coherent "enough" - and it may not make much
difference.

Say your antennas are separated by a meter - that's 5 wavelengths at L
band (20cm). If they were ideal, you'd get a series of fans to form
grating lobes - the fans would be long in the direction crossing the
line between antennas, and narrow in the direction parallel to the
baseline between antennas.

Non ideal antennas make the grating lobes wiggle or be wavy along their
long axis. Of course what YOU care about are the nulls (and to a lesser
extent the phase smoothness as you traverse the pattern).  I've looked a
lot of these kind of models and your saving grace is that the nulls are
deep only when the signals from the antennas are equal strength, which
doesn't really happen much.

If you were trying to do real time kinematic surveying to millimeters,
and are depending on smooth phase response - yeah, probably not going to
work.  Those folks obsess about apparent phase center displacements of
millimeters over a hemisphere.  Good multiband choke ring or artichoke
antennas are where it's at.

Or, if you need precise position calculation, then the "multiple
receivers and post process" is probably a better approach, because that
can explicitly address that the antennas are not co located.

Indeed - sounds like fun.

I'll bet if you get raw observables out of your receiver, you could
probably sort them (based on the look direction to each SV) into which
antenna is more likely, and then run them through any of the online
processors with some excision of "observations likely to be wonky"

(Which is a lot of work, but..)

Hi Jim

In this case +/- 30m in H and +/- 15m in V would be quite acceptable. A
bit of calculator work and I would be able to determine the minimum
spatial diversity required for those fixes.

yeah the overlap at 0dB ratio  would be  very low or zero. except  for
regions of the lobe that are way down in sensitivity (far down enough
that they may not be included in the solution- IIRC L1 = 30dB is
available fo an isotropic antenna  which provides for substantial off
axis resolution PROVIDING the spreading gain substantially exceeds that,
which it does not  - L1 chip rate 1 Mcps, data =50bps, so gain ~13dB 
ALTHOUGH I see L5 has 10x the chipping rate with consumate increases in
spreading gain, so L5 should be in theory able to provide more fixes as
a higher wanted/unwanted ratio is possible. substantial. wow L5 is good.).

So, the multi antenna combination likely works OK for this application
where antennas have true diversity of sky view.

 Now, some research and I find that the multi receiver solution is
supported using the UBLOX RTK toolkit and the raw output receivers , and
less work to do using the full raw which includes the pseudoranges for
the 9 series.  That would seem a simple solution for high performance fixes.

On 2/07/2023 2:42 am, Lux, Jim via time-nuts wrote:

On 7/1/23 9:42 AM, Lux, Jim via time-nuts wrote:

Here's some samples with the two antennas (cos^2() pattern) angled at 0
(both pointing at zenith), 45 and 60 degrees off zenith. The two
antennas are 5 wavelengths apart (1 meter for 1500 MHz L1)

I clamped the antenna patterns at -20dB (in reality it would be some
sort of weird pattern with lots of lobes and nulls, but all small)

Python code to generate it also attached.

As I needed the accurate PPS in the coming weeks I decided to go for the
ZED-F9T L1/L2 and if all is well it will arrive tomorrow.
Now I need to understand how all this "postprocessing" works.
Some questions:

1: The ublox tools show ability to output basic or full raw data and there
are various scripts  to convert ublox data to Rinex and there are some
websites listing the commands required to get the required output but is
there a dummy's guide somewhere on how to get the RINEX data from the
ZED-F9T in the correct version/format for the postprocessing?

2: NRCan seems to process only for Canada (according to their website,
correct???). Auspos is listed as processing for the whole world. There are
some others. What would be a recommended service? I'm located in Europe.

Erik.

Op wo 21 jun 2023 om 19:34 schreef Bob Camp via time-nuts <
time-nuts@lists.febo.com>:

Hi Erik --

The ZED-F9T will give you about the best (lowest jitter) PPS accuracy of
any of the modestly priced modules, but I don't think post-processing
the results will help you with timing.

You can use the u-blox RAWX message to output raw data which can then be
converted to RINEX format by one of several means, and then send the
RINEX file for processing (or process it yourself with something like
RTKLIB).  The results will give you highly accurate position
information, usually better with longer observation times.

But the ZED-F9T uses a free-running TCXO for its clock, and can't accept
an external reference source.  As a result, the clock data returned from
the post processing service is pretty much meaningless because of the
TCXO inaccuracy and instability.

By contrast, the clock results from receivers that are locked to a
quality external reference can be used to determine both time and
frequency offset and stability down to parts in 10e-15 over long intervals.

I am not sure which post-processing site is best for Europe.  I don't
think that NRCan has any boundary restrictions (I use them in the U.S.)
but I don't know if their algorithms cross continents.

In a roundabout way, you can improve your PPS performance by getting a
good post-processed receiver position, and using that as the ZED-F9T's
fixed location mode position.  The closer your stated position is to
actual, the better the PPS results (though a few centimeters won't make
much difference).  But that's the only timing benefit post-processing
provides for the ZED-F9T.

John

On 7/2/23 11:09, Erik Kaashoek via time-nuts wrote:

On 7/2/23 8:09 AM, Erik Kaashoek via time-nuts wrote:

JPL has automated precise positioning service. They say it's free.  I've
not used it.

https://pppx.gdgps.net//

/APPS/accepts GPS measurement files, and applies the most advanced GPS
positioning technology from NASA’s Jet Propulsion Laboratory to estimate
the position of your GPS receivers, whether they are static, in motion,
on the ground, or in the air. APPS employs:

  *

    Real-time GPS orbit and clock products from JPL’sGDGPS
    <http://www.gdgps.net/>System

  *

    JPL’s daily and weekly precise GPS orbit and clock products

  *

    JPL’s GipsyX/RTGx software for processing the GPS measurements

So, what would you recommend for a lower cost module that accepts an external reference and has reasonable jitter when using an external reference? (I’m specifically calling that out assuming that either a rubidium or excellent quartz oscillator is available because I’m not necessarily concerned with jitter while using an internal reference).

If considering dual band receivers, is the answer different?

Do you have any opinions or experience to share with respect to Navsparq modules? On paper, the specifications are awesome for the price, most (maybe all) support binary output, are supported by open-source libraries, and have rtk options amenable to using dual receivers for spatial orientation. They seem almost too good to be true.

From: John Ackermann N8UR via time-nuts time-nuts@lists.febo.com
Sent: Sunday, July 2, 2023 10:41:37 AM
To: time-nuts@lists.febo.com time-nuts@lists.febo.com
Cc: John Ackermann N8UR jra@febo.com
Subject: [time-nuts] Re: What GNSS module to buy for a good time reference?

Hi Erik --

The ZED-F9T will give you about the best (lowest jitter) PPS accuracy of
any of the modestly priced modules, but I don't think post-processing
the results will help you with timing.

You can use the u-blox RAWX message to output raw data which can then be
converted to RINEX format by one of several means, and then send the
RINEX file for processing (or process it yourself with something like
RTKLIB).  The results will give you highly accurate position
information, usually better with longer observation times.

But the ZED-F9T uses a free-running TCXO for its clock, and can't accept
an external reference source.  As a result, the clock data returned from
the post processing service is pretty much meaningless because of the
TCXO inaccuracy and instability.

By contrast, the clock results from receivers that are locked to a
quality external reference can be used to determine both time and
frequency offset and stability down to parts in 10e-15 over long intervals.

I am not sure which post-processing site is best for Europe.  I don't
think that NRCan has any boundary restrictions (I use them in the U.S.)
but I don't know if their algorithms cross continents.

In a roundabout way, you can improve your PPS performance by getting a
good post-processed receiver position, and using that as the ZED-F9T's
fixed location mode position.  The closer your stated position is to
actual, the better the PPS results (though a few centimeters won't make
much difference).  But that's the only timing benefit post-processing
provides for the ZED-F9T.

John

On 7/2/23 11:09, Erik Kaashoek via time-nuts wrote:

time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com

John,
Thanks for the reply. The accurate position info to improve the PPS is
indeed the goal. This should allow using the ZED-F9T PPS as reference
for checking the absolute phase accuracy of the PPS from a cheap GPS.
I did not try if google earth or open street map can provide any
accuracy in location.  The pin in google earth seems to have a
resolution of about 50 cm and I can position it on top of my GPS antenna
but I'm not sure how accurate google positions their photos.
Going back in time shows most of the newer high resolution photo's are
positioned the same within 50cm, others are shifted up to 10 meters.
Erik.

On 2-7-2023 17:41, John Ackermann N8UR via time-nuts wrote:

Hi

I think you will find that NRCan is legally a traceable source of data for Canada and
will supply information that links to their national geodetic system. Like John, I use their
service here in the US with no issues. I believe they will happily process data from
anywhere.

Many folks have gone looking for a similar service in Europe. We have two here in the
US for positioning, as you have found, there is one in Australia. The only one that feeds
back a nice easy to use timing result is NRCan.

In terms of a low jitter PPS for testing, your typical GPSDO produces a better 1 PPS than
one of these modules. In terms of “on time” the module wins. However there are a lot of
fun and games to get form that time pulse to something like UTC.

You can indeed use a “sawtooth corrected” pps out of a F9T to compare it’s internal clock
to a standard you already own. Then you can compare that record to an after the fact
processed file on the F9T RINEX data to work out what’s what.

Off to the cookbook:

1. First you need an ok L1/L2 antenna. $100 or so will get you one from China. Note
   that a proper “antenna descriptor” may not be available for a low cost antenna. This
   can tangle things a bit. ( = they may want a descriptor )

2. Next you need an antenna location with a reasonable view of the sky. Being able
   to see from due east , around past due south to due west and down to about 20
   degrees is in the “great” category if you are in Europe.

3. Get things running and make sure all is well.

4. As John mentioned, the uBlox tools can grab a RINEX file for you. It will save it
   to disk. Everything but the header should be fine. Do a one hour file.

5. Head over to the NRCan website. Sign up for a user / password combo. Without
   that, you can’ t put in data.

6. Upload your file and look at the error message (if any) that comes back. They may
   want info in the header that isn’t there. A text editor will let you put in this or that.
   Possible things they might not like:

   Antenna description, if yours does not have an official designator just put in one that looks close
   Sat system names, at one time uBlox and NRCan didn’t quite agree on this. That may not be true today
   User name, site description, antenna offset …

Once the one hour file works, you know what to do with the header from then on.
If you are lucky, there may be fields in the F9T or uBlox tools to correct things. If not,
you edit each file.

7. If you are looking at a local standard, you take your log of PPS and sawtooth information
   and process it against the clock file that comes back in the zip file from NRCan.

Alternatives that let you put in a 10 MHz reference and get back data referenced to it:

1. Trimble NetRS. Prices vary from $150 to $900 depending on when you look. At anything
   below $250 they are a good deal. They may need a new flash memory card to get running.
   The latest firmware is free on the web so there is no reason to get this or that version.

2. Septentrio Mosaic-T dev kit. You just went up over $1K.

3. Trimble NetR9. Prices range from $1200 to $3000. There are various models. The T1 is
   the top of the line. The T3 is the basic one. They all will accept a 10 MHz in.

All three of these devices have a web interface to make configuration somewhat easier. All
can take a pretty normal 10 MHz sine wave source as a reference input. All can put out /
take in a pps signal. The Mosaic-T does a better job if you plan on doing this.

The NetRS is GPS only. The Mosaic-T will work with any GNSS system that is currently
deployed. The NetR9 will do various systems depending on which one you get and what
options are installed. They all will do GPS.

At the moment NRCan only does corrections on GPS and Glonass. Will they add more systems
in the future? Who knows ….. Last time I checked the US correction services only ran GPS.
It’s been a few years since I used them, that may have changed.

Bob

I'm not aware of anything in the ZED-F9T price range that accepts an
external reference.

The closest I know of is the Septentrio Mosaic-T, but the last I heard
the evaluation board was >$1K and I don't think you can buy the bare
modules in one-off quantities.  You can buy a bunch of ZED-F9Ts for
that, but it is thoroughly modern and works really well.  Any completely
packaged receiver with similar capabilities will cost several time that.

As Bob mentioned, there are some used dual frequency receivers that can
do this.  The ones likely to be <$1K are the Trimble NetRS and the
Ashtech Z12 or variants.  The NetRS works pretty well and are easy to
configure and (relatively) easy to get raw observations out of.

The Ashtechs are really, really ancient and very proprietary, and a lot
of them don't work anymore.  I got a couple going, and wrote some python
to convert their serial data stream into RINEX, but I can't really
recommend anyone go down that road these days.  The NetRS is a much less
painful choice.

Now, for those who have are really nuts (time or otherwise), if you take
the lid off a ZED-F9T module, you will see among the three or four ICs
there a separate TCXO.  Don't ask me how I know this; it's not pretty.

Anyway, in theory you could remove that oscillator (I think it's ~60
MHz) and feed in an external reference there.  I don't know anyone who's
tried that, and I don't know if the software has the right hooks to do
anything useful with it.

The Navspark dual-freq is designed for portable RTK applications and
probably does pretty well at that, but from the not-that-great
documentation, its timing performance looks to be pretty basic.  I could
be wrong, but I don't think it supports a 0-D timing mode.

John

On 7/2/23 12:31, Ed Marciniak wrote:

Hi

If position is the only goal (obviously it’s not ….) then things are a bit more simple:

These days, NRCan will accept a single frequency Rinex file. You no longer must
have dual freq. device. Plug in any of the uBlox devices to your antenna. Use their
tools to record a couple of days worth of data. Send that off to them.

You do have a F9 coming in, use it and record a day’s worth of data. With
a reasonable antenna, the answer should be good to a few mm.

One of last night’s runs here claims a 7mm x 5mm error in X and Y. Height comes
in at 22 mm. This is from their “ultra rapid” solution set. If I resubmit in a couple weeks,
they will have a better solution to work off of and that should reduce all those errors.

Anything else you plug into the same cable will use the antenna location, you only
need to do this “survey” process once.

Is the antenna stable to mm? Is the answer really good to that level? That’s all
open to debate. One could also wonder about the antenna mount …. Fortunately,
at 3 ns/m, you don’t really need a location that is good to < 10 cm.

If we’re talking about real time PPS, things like the ionosphere and troposphere
get into the act. Correction services can help with this. Dual frequency measurements
also can help. Wider frequency spread is better in that case. ( so L1 to L5 is a
better bet than L1 to L2). Some dual freq devices have the correction calculations
built in, others don’t.

Last time I played with a F9T (which was a while back) it did not have the ability
to do the calculations internally. That could easily have changed with newer firmware.
It also might be dependent on the unit being L1/L5 vs L1/L2. I have not dug into
them for a while.

Bob