Re: [time-nuts] u-blox "naked" chips - anyone brave enough to try them?

[Bob Camp]

Hi


> On Jun 15, 2016, at 7:44 PM, Attila Kinali  wrote:
> 
> On Wed, 15 Jun 2016 18:43:38 -0400
> Bob Camp  wrote:
> 
>>> Same as above.
>>> If you lock the VCXO to an OCXO, this will be much better.
>> 
>> Each time you steer the OCXO to lock things up, you will degrade both it’s 
>> ADEV and it’s 
>> phase noise. If the GPS drops out when you do this …. the GPSDO never locks 
>> up.
> 
> Yes, sure. The ADEV of an OCXO will turn upwards again at taus somehwere
> around 10 to 1000 seconds. The loop bandwidth of the PLL that locks the OCXO
> to GPS should be in the same range in order not to degrade the short term
> stability of the OCXO. Also the PLL should have a rather damped behaviour
> in order to average out the "phase jumps" resulting from the jitter of
> the GPS PPS.
> 
> If these two points are not taken care of, then yes, the ADEV, resp the
> phase stability will degrate and thus can cause the GPS receiver to lose
> track of the satellites.

If you take data on the ADEV and phase noise of the OCXO during the initial 
lock / aggressive
steering phase of the process … it’s a lot worse than a minor tip up at 100 
seconds.

Bob


> 
> 
>   Attila Kinali
> -- 
> Malek's Law:
>Any simple idea will be worded in the most complicated way.
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Re: [time-nuts] u-blox "naked" chips - anyone brave enough to try them?

[Attila Kinali]

On Wed, 15 Jun 2016 18:43:38 -0400
Bob Camp  wrote:

> > Same as above.
> > If you lock the VCXO to an OCXO, this will be much better.
> 
> Each time you steer the OCXO to lock things up, you will degrade both it’s 
> ADEV and it’s 
> phase noise. If the GPS drops out when you do this …. the GPSDO never locks 
> up.

Yes, sure. The ADEV of an OCXO will turn upwards again at taus somehwere
around 10 to 1000 seconds. The loop bandwidth of the PLL that locks the OCXO
to GPS should be in the same range in order not to degrade the short term
stability of the OCXO. Also the PLL should have a rather damped behaviour
in order to average out the "phase jumps" resulting from the jitter of
the GPS PPS.

If these two points are not taken care of, then yes, the ADEV, resp the
phase stability will degrate and thus can cause the GPS receiver to lose
track of the satellites.


Attila Kinali
-- 
Malek's Law:
Any simple idea will be worded in the most complicated way.
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Re: [time-nuts] u-blox "naked" chips - anyone brave enough to try them?

[Bob Camp]

Hi

> On Jun 15, 2016, at 9:22 AM, Attila Kinali  wrote:
> 
> On Wed, 15 Jun 2016 07:03:28 -0400
> Bob Camp  wrote:
> 
> 
>> If you feed the chip with your local reference: 
>> 
>> 1) You need to synthesize a signal at the expected frequency (26 MHz, 48 MHz 
>> … whatever)
> 
> 26MHz is rather benign to generate. Either use TCXO that has already
> 26MHz (e.g. ASVTX-09 from Abracon are readily available) or lock some VCXO
> to an OCXO of your choise using a simple divider+XOR based PLL.
> If you feel like it you could even use a tiny FPGA (ICE40 come to mind)
> to implement the PLL and get more flexibility.
> 
>> 2) The signal needs to be low phase noise (per the chip set specs)
> 
> The specs of the oscillator used in the LEA modules is pretty much standard.
> Not a great oscillator, but not a bad one either. The above mentioned
> ASVTX-09 is in the same ballpark.
> 
>> 3) The signal needs to be constrained for ADEV (per the chip set specs)
> 
> Same as above.
> If you lock the VCXO to an OCXO, this will be much better.

Each time you steer the OCXO to lock things up, you will degrade both it’s ADEV 
and it’s 
phase noise. If the GPS drops out when you do this …. the GPSDO never locks up.

Bob

> 
> 
>   Attila Kinali
> 
> -- 
> It is upon moral qualities that a society is ultimately founded. All 
> the prosperity and technological sophistication in the world is of no 
> use without that foundation.
> -- Miss Matheson, The Diamond Age, Neil Stephenson

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Re: [time-nuts] u-blox "naked" chips - anyone brave enough to try them?

[Attila Kinali]

On Wed, 15 Jun 2016 07:03:28 -0400
Bob Camp  wrote:


> If you feed the chip with your local reference: 
> 
> 1) You need to synthesize a signal at the expected frequency (26 MHz, 48 MHz 
> … whatever)

26MHz is rather benign to generate. Either use TCXO that has already
26MHz (e.g. ASVTX-09 from Abracon are readily available) or lock some VCXO
to an OCXO of your choise using a simple divider+XOR based PLL.
If you feel like it you could even use a tiny FPGA (ICE40 come to mind)
to implement the PLL and get more flexibility.
 
> 2) The signal needs to be low phase noise (per the chip set specs)

The specs of the oscillator used in the LEA modules is pretty much standard.
Not a great oscillator, but not a bad one either. The above mentioned
ASVTX-09 is in the same ballpark.

> 3) The signal needs to be constrained for ADEV (per the chip set specs)

Same as above.
If you lock the VCXO to an OCXO, this will be much better.


Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] u-blox "naked" chips - anyone brave enough to try them?

[Bob Camp]

Hi

If you feed the chip with your local reference: 

1) You need to synthesize a signal at the expected frequency (26 MHz, 48 MHz … 
whatever)

2) The signal needs to be low phase noise (per the chip set specs)

3) The signal needs to be constrained for ADEV (per the chip set specs)

All of that may or may not be as simple as measuring the phase.

Bob

> On Jun 15, 2016, at 5:11 AM, Attila Kinali  wrote:
> 
> On Wed, 15 Jun 2016 09:44:15 +0200
> Mike Cook  wrote:
> 
>> Certainly cheap…. BUT
>> 
>> On the ublox site there is a table indicating that the KT is a standard 
>> precision engine. On the same table, the UBX-M8030-KT-FT is required for 
>> timing:
> 
> Oops! Missed that one! Sorry!
> 
> How about using an UBX-G6010 [1] then? They are also available for <5USD/pcs.
> Apparently, it is possible to enable various commands with the 6th gen
> chips [2] and there is some RAW message enabled firmware available[3]
> 
>> So, they may be cheap, very cheap, but are they really what a TN would want?
> 
> Maybe? :-)
> Given the amoount of people who use modules without even sawtooth correction
> and still get pretty good results, it might be promising. At the very least
> you could get around measuring the PPS directly and instead, just use the
> sawtooth correction message to know how far you've drifted
> 
> 
>   Attila Kinali
> 
> 
> [1] 
> http://innovictor.com/pdf/UBXG6010_UBXG600_UBXG0010_DataSheet_GPS%20G6-X-09004_Confidential.pdf
> [2] http://wiki.openstreetmap.org/wiki/UbloxRAW#U-BLOX6
> [3] 
> http://gps.0xdc.ru/static/ublox/device/Navilock%20NL-602U/patched/NL602-patched-fw.bin
> 
> -- 
> It is upon moral qualities that a society is ultimately founded. All 
> the prosperity and technological sophistication in the world is of no 
> use without that foundation.
> -- Miss Matheson, The Diamond Age, Neil Stephenson
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Re: [time-nuts] u-blox "naked" chips - anyone brave enough to try them?

[Attila Kinali]

On Wed, 15 Jun 2016 09:44:15 +0200
Mike Cook  wrote:

> Certainly cheap…. BUT
> 
> On the ublox site there is a table indicating that the KT is a standard 
> precision engine. On the same table, the UBX-M8030-KT-FT is required for 
> timing:

Oops! Missed that one! Sorry!

How about using an UBX-G6010 [1] then? They are also available for <5USD/pcs.
Apparently, it is possible to enable various commands with the 6th gen
chips [2] and there is some RAW message enabled firmware available[3]

> So, they may be cheap, very cheap, but are they really what a TN would want?

Maybe? :-)
Given the amoount of people who use modules without even sawtooth correction
and still get pretty good results, it might be promising. At the very least
you could get around measuring the PPS directly and instead, just use the
sawtooth correction message to know how far you've drifted


Attila Kinali


[1] 
http://innovictor.com/pdf/UBXG6010_UBXG600_UBXG0010_DataSheet_GPS%20G6-X-09004_Confidential.pdf
[2] http://wiki.openstreetmap.org/wiki/UbloxRAW#U-BLOX6
[3] 
http://gps.0xdc.ru/static/ublox/device/Navilock%20NL-602U/patched/NL602-patched-fw.bin

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] u-blox "naked" chips - anyone brave enough to try them?

[Mike Cook]

Certainly cheap…. BUT

On the ublox site there is a table indicating that the KT is a standard 
precision engine. On the same table, the UBX-M8030-KT-FT is required for timing:

< 
https://www.u-blox.com/sites/default/files/GNSS-Chips_Linecard_%28UBX-13004716%29.pdf
 >
< 
https://www.u-blox.com/sites/default/files/products/documents/UBX-M8030-KT-FT_ProductSummary_%28UBX-14001605%29.pdf
 >

So, they may be cheap, very cheap, but are they really what a TN would want?

Hope that helps.
Mike



> Le 15 juin 2016 à 01:38, Attila Kinali  a écrit :
> 
> Moin,
> 
> Some of you might know that the u-blox chips are available in small
> quantities and for quite cheap too. Just go to aliexpress or taobao
> and type in "UBX-G7020" or "UBX-M8030" and you will get plenty of
> results. My guess is, that these chips are leftovers from cellphone
> production that get sold off close at wholesale price (I've seen
> that with other chips as well). So it is likely that these are 
> actually genuine chips.
> 
> Now, the documentation for those chips is not that readily available.
> But fret not! Some of it can be found if you look hard enough. At least
> for the G7020. I think, this information should be enough for anyone
> who wants to build his own GPSDO with Trimble like oscillator control
> (ie that the reference oscillator of the GPS module is steered directly).
> 
> The UBX-M8030-KT, which would be a timing chip and thus for sure
> support the RAW data commandos, is unfortunately quite google proof.
> At least I couldn't find any documentation for those but the official
> public one provided by u-blox. I would guess, that the pin out is very
> similar if not the same, but without guarante.
> 
> (I know that least the UBX-M8030-KT datasheet UBX-13001634 is floating
> around, but So far i was not able to get hold of it, due to insufficient
> chinese language skills)
> 
> As for the UBX-G7020, you can find the following documents:
> 
> 
> UBX-G7020-KT/KA u-blox 7 GPS/GNSS chips Data Sheet GPS.G7-HW-12001
> https://raw.githubusercontent.com/ArdentHeavyIndustries/straightedge-gps-firmware/master/Datasheets/UBX-G7020-Kx_DataSheet_(GPS%20G7-HW-12001)_Confidential.pdf.pdf
> 
> u-blox 7 GPS/GNSS chips Hardware Integration Manual GPS.G7-HW-10003
> https://www.olimex.com/Products/Modules/GPS/MOD-GPS/resources/UBX-G7020_HardwareIntegrationManual_-GPS.G7-HW-10003-_Confidential.pdf
> 
> 
> So, if anyone would want to give those a try, let us know.
> I'm sure many here would be interested.
> 
> 
>   Attila Kinali
> 
> -- 
> Malek's Law:
>Any simple idea will be worded in the most complicated way.
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

"The power of accurate observation is commonly called cynicism by those who 
have not got it. »
George Bernard Shaw

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[time-nuts] u-blox "naked" chips - anyone brave enough to try them?

[Attila Kinali]

Moin,

Some of you might know that the u-blox chips are available in small
quantities and for quite cheap too. Just go to aliexpress or taobao
and type in "UBX-G7020" or "UBX-M8030" and you will get plenty of
results. My guess is, that these chips are leftovers from cellphone
production that get sold off close at wholesale price (I've seen
that with other chips as well). So it is likely that these are 
actually genuine chips.

Now, the documentation for those chips is not that readily available.
But fret not! Some of it can be found if you look hard enough. At least
for the G7020. I think, this information should be enough for anyone
who wants to build his own GPSDO with Trimble like oscillator control
(ie that the reference oscillator of the GPS module is steered directly).

The UBX-M8030-KT, which would be a timing chip and thus for sure
support the RAW data commandos, is unfortunately quite google proof.
At least I couldn't find any documentation for those but the official
public one provided by u-blox. I would guess, that the pin out is very
similar if not the same, but without guarante.

(I know that least the UBX-M8030-KT datasheet UBX-13001634 is floating
around, but So far i was not able to get hold of it, due to insufficient
chinese language skills)

As for the UBX-G7020, you can find the following documents:


UBX-G7020-KT/KA u-blox 7 GPS/GNSS chips Data Sheet GPS.G7-HW-12001
https://raw.githubusercontent.com/ArdentHeavyIndustries/straightedge-gps-firmware/master/Datasheets/UBX-G7020-Kx_DataSheet_(GPS%20G7-HW-12001)_Confidential.pdf.pdf

u-blox 7 GPS/GNSS chips Hardware Integration Manual GPS.G7-HW-10003
https://www.olimex.com/Products/Modules/GPS/MOD-GPS/resources/UBX-G7020_HardwareIntegrationManual_-GPS.G7-HW-10003-_Confidential.pdf


So, if anyone would want to give those a try, let us know.
I'm sure many here would be interested.


Attila Kinali

-- 
Malek's Law:
Any simple idea will be worded in the most complicated way.
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