LJ
Lux, Jim
Sun, Jul 2, 2023 9:08 PM
On 7/2/23 9:45 AM, Bob Camp via time-nuts wrote:
Hi
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
JPL runs all GNSS constellations. On SunRISE we were planning on
augmenting GPS with GLONASS, but we ran out of time/money to implement
that in the receiver. And had we a receiver that could do GALILEO we
could have run that. Not so sure about BEIDOU, given the "thou shalt not
collaborate with Chinese" laws (Wolf amendment). I suppose there's no
collaboration - we get the signals, we process them, we determine an
orbit, and then we can process it.
On 7/2/23 9:45 AM, Bob Camp via time-nuts wrote:
> Hi
>
> 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
JPL runs all GNSS constellations. On SunRISE we were planning on
augmenting GPS with GLONASS, but we ran out of time/money to implement
that in the receiver. And had we a receiver that could do GALILEO we
could have run that. Not so sure about BEIDOU, given the "thou shalt not
collaborate with Chinese" laws (Wolf amendment). I suppose there's no
collaboration - we get the signals, we process them, we determine an
orbit, and then we can process it.
EM
Ed Marciniak
Mon, Jul 3, 2023 6:22 AM
Navsparq has the NS-T but that's single band, so no further value discussing in this context.
A look at the Trimble NetRS reveals it's PPS output has 40 ns resolution and says several external factors limit accuracy to +-1 microsecond. While 40ns would come from a 25 MHz clock, it seems to be common reference frequencies are 19.2,26,38.4 MHz. Perhaps it's not exactly 40ns. Elsewhere the manual claims position 5mm+1ppm horizontal and 10mm+1ppm vertical accuracy, which probably represents a fairly decent internal receiver frequency reference. That doesn't seem directly useful for time and frequency but it's interesting for other purposes.
Ah, well...thanks for the interesting reading material the conversation generated.
From: John Ackermann N8UR jra@febo.com
Sent: Sunday, July 2, 2023 3:00:37 PM
To: Ed Marciniak ed@nb0m.org; Discussion of precise time and frequency measurement time-nuts@lists.febo.com
Subject: Re: [time-nuts] Re: What GNSS module to buy for a good time reference?
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:
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:
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
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
Navsparq has the NS-T but that's single band, so no further value discussing in this context.
A look at the Trimble NetRS reveals it's PPS output has 40 ns resolution and says several external factors limit accuracy to +-1 microsecond. While 40ns would come from a 25 MHz clock, it seems to be common reference frequencies are 19.2,26,38.4 MHz. Perhaps it's not exactly 40ns. Elsewhere the manual claims position 5mm+1ppm horizontal and 10mm+1ppm vertical accuracy, which probably represents a fairly decent internal receiver frequency reference. That doesn't seem directly useful for time and frequency but it's interesting for other purposes.
Ah, well...thanks for the interesting reading material the conversation generated.
________________________________
From: John Ackermann N8UR <jra@febo.com>
Sent: Sunday, July 2, 2023 3:00:37 PM
To: Ed Marciniak <ed@nb0m.org>; Discussion of precise time and frequency measurement <time-nuts@lists.febo.com>
Subject: Re: [time-nuts] Re: What GNSS module to buy for a good time reference?
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:
> 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:
>> 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
>>>
>>> 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
>>>
>>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts@lists.febo.com
>> To unsubscribe send an email to time-nuts-leave@lists.febo.com
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe send an email to time-nuts-leave@lists.febo.com
MB
Mete Balci
Mon, Jul 3, 2023 6:32 AM
I also tried using F9T in different ways, and because of my poor antenna
location it was not successful but the most easy to setup and understand
for me was real-time PPP with BKG Ntrip Client. If I remember right, it can
output RTCM and this can be used directly.
I also have Mosaic-X5, and it is naturally better than ublox (~4x more
expensive) but I think the sensitivity of ublox is higher, so with a poor
antenna location ublox is working actually better.
At the end the best solution for my poor location was using the GPS in the
mobile phone, because of AGPS I think, it seems to work better and can get
<10m. I also checked local so-called height control points and surveying
maps to get close to 1m.
The cheapest proper antenna I could find for multi-band and also with
parameters for RINEX was Tallysman TW7972, which has calibration files at
geodesy@noaa.
Mete
On Mon, 3 Jul 2023 at 01:24, Lux, Jim via time-nuts <
time-nuts@lists.febo.com> wrote:
On 7/2/23 9:45 AM, Bob Camp via time-nuts wrote:
Hi
At the moment NRCan only does corrections on GPS and Glonass. Will they
in the future? Who knows ….. Last time I checked the US correction
It’s been a few years since I used them, that may have changed.
Bob
JPL runs all GNSS constellations. On SunRISE we were planning on
augmenting GPS with GLONASS, but we ran out of time/money to implement
that in the receiver. And had we a receiver that could do GALILEO we
could have run that. Not so sure about BEIDOU, given the "thou shalt not
collaborate with Chinese" laws (Wolf amendment). I suppose there's no
collaboration - we get the signals, we process them, we determine an
orbit, and then we can process it.
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
I also tried using F9T in different ways, and because of my poor antenna
location it was not successful but the most easy to setup and understand
for me was real-time PPP with BKG Ntrip Client. If I remember right, it can
output RTCM and this can be used directly.
I also have Mosaic-X5, and it is naturally better than ublox (~4x more
expensive) but I think the sensitivity of ublox is higher, so with a poor
antenna location ublox is working actually better.
At the end the best solution for my poor location was using the GPS in the
mobile phone, because of AGPS I think, it seems to work better and can get
<10m. I also checked local so-called height control points and surveying
maps to get close to 1m.
The cheapest proper antenna I could find for multi-band and also with
parameters for RINEX was Tallysman TW7972, which has calibration files at
geodesy@noaa.
Mete
On Mon, 3 Jul 2023 at 01:24, Lux, Jim via time-nuts <
time-nuts@lists.febo.com> wrote:
> On 7/2/23 9:45 AM, Bob Camp via time-nuts wrote:
> > Hi
> >
> > 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
>
>
> JPL runs all GNSS constellations. On SunRISE we were planning on
> augmenting GPS with GLONASS, but we ran out of time/money to implement
> that in the receiver. And had we a receiver that could do GALILEO we
> could have run that. Not so sure about BEIDOU, given the "thou shalt not
> collaborate with Chinese" laws (Wolf amendment). I suppose there's no
> collaboration - we get the signals, we process them, we determine an
> orbit, and then we can process it.
>
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe send an email to time-nuts-leave@lists.febo.com
JA
John Ackermann N8UR
Mon, Jul 3, 2023 12:23 PM
One interesting note -- the survey/geodetic receivers (at least the
older ones) don't pay a lot of attention to the PPS output, as their
main use is gathering raw observation data for external processing.
Reading between the lines in some of the manuals, they were thinking of
the PPS more for event tagging or triggering a sensor, than as a high
quality time source.
John
On 7/3/23 02:22, Ed Marciniak wrote:
Navsparq has the NS-T but that's single band, so no further value
discussing in this context.
A look at the Trimble NetRS reveals it's PPS output has 40 ns resolution
and says several external factors limit accuracy to +-1 microsecond.
While 40ns would come from a 25 MHz clock, it seems to be common
reference frequencies are 19.2,26,38.4 MHz. Perhaps it's not exactly
40ns. Elsewhere the manual claims position 5mm+1ppm horizontal and
10mm+1ppm vertical accuracy, which probably represents a fairly decent
internal receiver frequency reference. That doesn't seem directly useful
for time and frequency but it's interesting for other purposes.
Ah, well...thanks for the interesting reading material the conversation
generated.
From: John Ackermann N8UR jra@febo.com
Sent: Sunday, July 2, 2023 3:00:37 PM
To: Ed Marciniak ed@nb0m.org; Discussion of precise time and
frequency measurement time-nuts@lists.febo.com
Subject: Re: [time-nuts] Re: What GNSS module to buy for a good time
reference?
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:
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:
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
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
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
One interesting note -- the survey/geodetic receivers (at least the
older ones) don't pay a lot of attention to the PPS output, as their
main use is gathering raw observation data for external processing.
Reading between the lines in some of the manuals, they were thinking of
the PPS more for event tagging or triggering a sensor, than as a high
quality time source.
John
----
On 7/3/23 02:22, Ed Marciniak wrote:
> Navsparq has the NS-T but that's single band, so no further value
> discussing in this context.
>
> A look at the Trimble NetRS reveals it's PPS output has 40 ns resolution
> and says several external factors limit accuracy to +-1 microsecond.
> While 40ns would come from a 25 MHz clock, it seems to be common
> reference frequencies are 19.2,26,38.4 MHz. Perhaps it's not exactly
> 40ns. Elsewhere the manual claims position 5mm+1ppm horizontal and
> 10mm+1ppm vertical accuracy, which probably represents a fairly decent
> internal receiver frequency reference. That doesn't seem directly useful
> for time and frequency but it's interesting for other purposes.
>
> Ah, well...thanks for the interesting reading material the conversation
> generated.
>
>
> ------------------------------------------------------------------------
> *From:* John Ackermann N8UR <jra@febo.com>
> *Sent:* Sunday, July 2, 2023 3:00:37 PM
> *To:* Ed Marciniak <ed@nb0m.org>; Discussion of precise time and
> frequency measurement <time-nuts@lists.febo.com>
> *Subject:* Re: [time-nuts] Re: What GNSS module to buy for a good time
> reference?
> 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:
>> 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:
>>> 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
>>>>
>>>> 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
>>>>
>>>>
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts@lists.febo.com
>>> To unsubscribe send an email to time-nuts-leave@lists.febo.com
>> _______________________________________________
>> time-nuts mailing list -- time-nuts@lists.febo.com
>> To unsubscribe send an email to time-nuts-leave@lists.febo.com
BC
Bob Camp
Mon, Jul 3, 2023 12:50 PM
Hi
The way one uses a NetRS in this application is to feed it a local
10 MHz reference. With the proper settings, the data it records is
referenced directly to that source. You can get < 100 ps resolution
and < 1x10^-14 one day frequency this way.
Other than a few devices in the $20K price range, pretty much all
GNSS gizmos have limited (+/- nanoseconds) resolution on their
PPS outputs. The same “feed it a 10 MHz source” approach is
how this is done on a lot of devices.
Bob
On Jul 3, 2023, at 2:22 AM, Ed Marciniak via time-nuts time-nuts@lists.febo.com wrote:
Navsparq has the NS-T but that's single band, so no further value discussing in this context.
A look at the Trimble NetRS reveals it's PPS output has 40 ns resolution and says several external factors limit accuracy to +-1 microsecond. While 40ns would come from a 25 MHz clock, it seems to be common reference frequencies are 19.2,26,38.4 MHz. Perhaps it's not exactly 40ns. Elsewhere the manual claims position 5mm+1ppm horizontal and 10mm+1ppm vertical accuracy, which probably represents a fairly decent internal receiver frequency reference. That doesn't seem directly useful for time and frequency but it's interesting for other purposes.
Ah, well...thanks for the interesting reading material the conversation generated.
From: John Ackermann N8UR jra@febo.com
Sent: Sunday, July 2, 2023 3:00:37 PM
To: Ed Marciniak ed@nb0m.org; Discussion of precise time and frequency measurement time-nuts@lists.febo.com
Subject: Re: [time-nuts] Re: What GNSS module to buy for a good time reference?
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:
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:
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
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
Hi
The way one uses a NetRS in this application is to feed it a local
10 MHz reference. With the proper settings, the data it records is
referenced directly to that source. You can get < 100 ps resolution
and < 1x10^-14 one day frequency this way.
Other than a few devices in the $20K price range, pretty much all
GNSS gizmos have limited (+/- nanoseconds) resolution on their
PPS outputs. The same “feed it a 10 MHz source” approach is
how this is done on a lot of devices.
Bob
> On Jul 3, 2023, at 2:22 AM, Ed Marciniak via time-nuts <time-nuts@lists.febo.com> wrote:
>
> Navsparq has the NS-T but that's single band, so no further value discussing in this context.
>
> A look at the Trimble NetRS reveals it's PPS output has 40 ns resolution and says several external factors limit accuracy to +-1 microsecond. While 40ns would come from a 25 MHz clock, it seems to be common reference frequencies are 19.2,26,38.4 MHz. Perhaps it's not exactly 40ns. Elsewhere the manual claims position 5mm+1ppm horizontal and 10mm+1ppm vertical accuracy, which probably represents a fairly decent internal receiver frequency reference. That doesn't seem directly useful for time and frequency but it's interesting for other purposes.
>
> Ah, well...thanks for the interesting reading material the conversation generated.
>
>
> ________________________________
> From: John Ackermann N8UR <jra@febo.com>
> Sent: Sunday, July 2, 2023 3:00:37 PM
> To: Ed Marciniak <ed@nb0m.org>; Discussion of precise time and frequency measurement <time-nuts@lists.febo.com>
> Subject: Re: [time-nuts] Re: What GNSS module to buy for a good time reference?
>
> 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:
>> 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:
>>> 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
>>>>
>>>> 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
>>>>
>>>>
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts@lists.febo.com
>>> To unsubscribe send an email to time-nuts-leave@lists.febo.com
>> _______________________________________________
>> time-nuts mailing list -- time-nuts@lists.febo.com
>> To unsubscribe send an email to time-nuts-leave@lists.febo.com
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe send an email to time-nuts-leave@lists.febo.com
LJ
Lux, Jim
Mon, Jul 3, 2023 1:07 PM
On 7/2/23 11:22 PM, Ed Marciniak via time-nuts wrote:
Navsparq has the NS-T but that's single band, so no further value discussing in this context.
A look at the Trimble NetRS reveals it's PPS output has 40 ns resolution and says several external factors limit accuracy to +-1 microsecond. While 40ns would come from a 25 MHz clock, it seems to be common reference frequencies are 19.2,26,38.4 MHz. Perhaps it's not exactly 40ns. Elsewhere the manual claims position 5mm+1ppm horizontal and 10mm+1ppm vertical accuracy, which probably represents a fairly decent internal receiver frequency reference. That doesn't seem directly useful for time and frequency but it's interesting for other purposes.
Ah, well...thanks for the interesting reading material the conversation generated.
A lot of receivers choose a clock rate so that when the signal is
sampled at that rate, it aliases down to a convenient place.
1575.42 is a bit higher than 41 * 38.4, and so forth.
What you want is the alias to be far enough from zero that the largest
possible Doppler keeps the carrier at a positive frequency.
5mm + 1 ppm of distance is a typical spec for differential GPS surveying.
On 7/2/23 11:22 PM, Ed Marciniak via time-nuts wrote:
> Navsparq has the NS-T but that's single band, so no further value discussing in this context.
>
> A look at the Trimble NetRS reveals it's PPS output has 40 ns resolution and says several external factors limit accuracy to +-1 microsecond. While 40ns would come from a 25 MHz clock, it seems to be common reference frequencies are 19.2,26,38.4 MHz. Perhaps it's not exactly 40ns. Elsewhere the manual claims position 5mm+1ppm horizontal and 10mm+1ppm vertical accuracy, which probably represents a fairly decent internal receiver frequency reference. That doesn't seem directly useful for time and frequency but it's interesting for other purposes.
>
> Ah, well...thanks for the interesting reading material the conversation generated.
>
A lot of receivers choose a clock rate so that when the signal is
sampled at that rate, it aliases down to a convenient place.
1575.42 is a bit higher than 41 * 38.4, and so forth.
What you want is the alias to be far enough from zero that the largest
possible Doppler keeps the carrier at a positive frequency.
5mm + 1 ppm of distance is a typical spec for differential GPS surveying.
TA
Thomas Abbott
Mon, Jul 3, 2023 6:31 PM
if you take the lid off a ZED-F9T module, you will see among the
three or four ICs there a separate TCXO.
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
Someone tried that with a NEO-6M, it is messy but quite beautiful:
- HP10811 10 MHz oscillator,
- 26 MHz synthesizer from this
- uBlox NEO-6M with internal crystal removed
- microcontroller gently steering the master oscillator
- using standard messages from the GPS - first the reported freq accuracy
to get it close to the right frequency, and then the TPQerr for phase lock.
Detailed write-up here:
http://lea.hamradio.si/~s57uuu/mischam/gpsy/index.html#self
In the end I don't think its frequency stability will be better than a
regular GPSDO, it just needs no TIC. This guy wasn't so interested in
absolute time, but if you added one more PPS input/output for once-off
sync, the clock data from the NRCAN PPP would now accurately reflect the
time error of the oscillator.
You could also run the whole thing off your master reference, without
steering it, and the same would apply. You'd have to once find the
relationship between GPS time and one of your 10 MHz edges, maybe using the
PPS output. The post-processing would tell you the clock error over time. I
suppose it would work with the F9T.
I found the F9T timepulse was degraded from ~1 ns RMS (short term) to ~10
ns, if the temperature was changing quickly, or if there was any vibration.
So it might perform even better with a more stable reference.
Thomas
On Sun, 2 Jul 2023 at 13:04, John Ackermann N8UR via time-nuts <
time-nuts@lists.febo.com> wrote:
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
> if you take the lid off a ZED-F9T module, you will see among the
> three or four ICs there a separate TCXO.
>
> 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
Someone tried that with a NEO-6M, it is messy but quite beautiful:
- HP10811 10 MHz oscillator,
- 26 MHz synthesizer from this
- uBlox NEO-6M with internal crystal removed
- microcontroller gently steering the master oscillator
- using standard messages from the GPS - first the reported freq accuracy
to get it close to the right frequency, and then the TPQerr for phase lock.
Detailed write-up here:
http://lea.hamradio.si/~s57uuu/mischam/gpsy/index.html#self
In the end I don't think its frequency stability will be better than a
regular GPSDO, it just needs no TIC. This guy wasn't so interested in
absolute time, but if you added one more PPS input/output for once-off
sync, the clock data from the NRCAN PPP would now accurately reflect the
time error of the oscillator.
You could also run the whole thing off your master reference, without
steering it, and the same would apply. You'd have to once find the
relationship between GPS time and one of your 10 MHz edges, maybe using the
PPS output. The post-processing would tell you the clock error over time. I
suppose it would work with the F9T.
I found the F9T timepulse was degraded from ~1 ns RMS (short term) to ~10
ns, if the temperature was changing quickly, or if there was any vibration.
So it might perform even better with a more stable reference.
Thomas
On Sun, 2 Jul 2023 at 13:04, John Ackermann N8UR via time-nuts <
time-nuts@lists.febo.com> wrote:
> 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
> ----
>
>
G
glenlist
Tue, Jul 4, 2023 9:25 AM
Hi Jim
the 45/60deg is certainly useful. the gain might not be identical (or
could use a pad say 3dB gain difference) and so that of course with
reduce the overhead null depth. I'll do some calcs..
On 2/07/2023 10:28 am, Lux, Jim via time-nuts wrote:
On 7/1/23 9:42 AM, Lux, Jim via time-nuts wrote:
On 6/30/23 6:40 PM, glen english LIST via time-nuts wrote:
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.
Hi Jim
the 45/60deg is certainly useful. the gain might not be identical (or
could use a pad say 3dB gain difference) and so that of course with
reduce the overhead null depth. I'll do some calcs..
On 2/07/2023 10:28 am, Lux, Jim via time-nuts wrote:
> On 7/1/23 9:42 AM, Lux, Jim via time-nuts wrote:
>> On 6/30/23 6:40 PM, glen english LIST via time-nuts wrote:
>>> 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.
>
