Re: [time-nuts] Ublox 6T receiver, noisy PPS.

[Bob Camp]

Hi

It sounds like you are not doing sawtooth correction. If that is correct, then 
you may have been watching hanging bridges. 

Bob

> On Jan 16, 2015, at 7:03 PM, d...@irtelemetrics.com wrote:
> 
>Hi All,
>  
> I've been playing a Ublox 6T receivers on a synergy SSR-6Tru module. The unit 
> has been running as part of a GPSDO. In logging the phase between GPS PPS and 
> OXCO, a few days ago the normally small amplitude short term (10s to ~500s) 
> phase wander became rather erratic. For the previous several months the short 
> term wander was around +/- 3nS to 5nS. All of a sudden this jumped up to 
> about +/- 25nS.   
> Anyway, the guess was that it was GPS related. So the first step was to 
> verify GPS was still using the last survey-in points, which it was. The 
> modules was seeing 14 or 15 good birds at a signal strength of 35 to 50. For 
> kicks another survey in (48 hour) was started, which just finished up today. 
> As soon as the survey in completed the phase wander dropped back down to 
> about +/-3nS. The change was immediate, like a switch was thrown.  The 
> antenna hasn't moved, but the corresponding survey coordinates from September 
> and January show a phase center position change of about 1.8m. This seems 
> like a pretty small number, and wouldn't have expected it to make that big of 
> a difference. At this point I'm not sure what to think.   
>  
> Has anyone seen any of the Ulbox 6T modules PPS suddenly get 'noisy'. Is 
> there anything else I should be looking at?
>  
> Any recommendations on what I should be setting for NAV5 and NAVX5 settings 
> that could improve things? Elevation angles, or C/N thresholds? 
>  
> I'm quite puzzled by this sudden degradation of the system. 
>  
> Thanks,
> Dan
>  
> 
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Re: [time-nuts] Ublox 6T receiver, noisy PPS.

[Azelio Boriani]

I have noticed the sudden improvement of the PPS wander after the
survey on a LEA-5T but the RMS wander is 30ns (see the timing appnote
GPS.G6-X-11007 from uBlox) uncorrected and 15ns if sawtooth corrected.
Your 3ns is strange, not the 30ns.

On Sat, Jan 17, 2015 at 1:03 AM,   wrote:
> Hi All,
>
>  I've been playing a Ublox 6T receivers on a synergy SSR-6Tru module. The
> unit has been running as part of a GPSDO. In logging the phase between GPS
> PPS and OXCO, a few days ago the normally small amplitude short term (10s to
> ~500s) phase wander became rather erratic. For the previous several months
> the short term wander was around +/- 3nS to 5nS. All of a sudden this jumped
> up to about +/- 25nS.
>  Anyway, the guess was that it was GPS related. So the first step was to
> verify GPS was still using the last survey-in points, which it was. The
> modules was seeing 14 or 15 good birds at a signal strength of 35 to 50. For
> kicks another survey in (48 hour) was started, which just finished up today.
> As soon as the survey in completed the phase wander dropped back down to
> about +/-3nS. The change was immediate, like a switch was thrown.  The
> antenna hasn't moved, but the corresponding survey coordinates from
> September and January show a phase center position change of about 1.8m.
> This seems like a pretty small number, and wouldn't have expected it to make
> that big of a difference. At this point I'm not sure what to think.
>
>  Has anyone seen any of the Ulbox 6T modules PPS suddenly get 'noisy'. Is
> there anything else I should be looking at?
>
>  Any recommendations on what I should be setting for NAV5 and NAVX5 settings
> that could improve things? Elevation angles, or C/N thresholds?
>
>  I'm quite puzzled by this sudden degradation of the system.
>
>  Thanks,
>  Dan
>
>
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Re: [time-nuts] Ublox 6T receiver, noisy PPS.

[John C. Westmoreland, P.E.]

Hello Dan,

I have a LEA-6T running; have a nice external antenna, etc - it's been
running for several days - I will check the 1PPS and report if I find
anything like what you've discussed.

Regards,
John


On Fri, Jan 16, 2015 at 4:03 PM,  wrote:

> Hi All,
>
>  I've been playing a Ublox 6T receivers on a synergy SSR-6Tru module. The
> unit has been running as part of a GPSDO. In logging the phase between GPS
> PPS and OXCO, a few days ago the normally small amplitude short term (10s
> to ~500s) phase wander became rather erratic. For the previous several
> months the short term wander was around +/- 3nS to 5nS. All of a sudden
> this jumped up to about +/- 25nS.
>  Anyway, the guess was that it was GPS related. So the first step was to
> verify GPS was still using the last survey-in points, which it was. The
> modules was seeing 14 or 15 good birds at a signal strength of 35 to 50.
> For kicks another survey in (48 hour) was started, which just finished up
> today. As soon as the survey in completed the phase wander dropped back
> down to about +/-3nS. The change was immediate, like a switch was thrown.
> The antenna hasn't moved, but the corresponding survey coordinates from
> September and January show a phase center position change of about 1.8m.
> This seems like a pretty small number, and wouldn't have expected it to
> make that big of a difference. At this point I'm not sure what to think.
>
>  Has anyone seen any of the Ulbox 6T modules PPS suddenly get 'noisy'. Is
> there anything else I should be looking at?
>
>  Any recommendations on what I should be setting for NAV5 and NAVX5
> settings that could improve things? Elevation angles, or C/N thresholds?
>
>  I'm quite puzzled by this sudden degradation of the system.
>
>  Thanks,
>  Dan
>
>
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> mailman/listinfo/time-nuts
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[time-nuts] Ublox 6T receiver, noisy PPS.

[dan]

Hi All,
  
 I've been playing a Ublox 6T receivers on a synergy SSR-6Tru module. 
The unit has been running as part of a GPSDO. In logging the phase 
between GPS PPS and OXCO, a few days ago the normally small amplitude 
short term (10s to ~500s) phase wander became rather erratic. For the 
previous several months the short term wander was around +/- 3nS to 
5nS. All of a sudden this jumped up to about +/- 25nS. 
  
 Anyway, the guess was that it was GPS related. So the first step was 
to verify GPS was still using the last survey-in points, which it was. 
The modules was seeing 14 or 15 good birds at a signal strength of 35 
to 50. For kicks another survey in (48 hour) was started, which just 
finished up today. As soon as the survey in completed the phase wander 
dropped back down to about +/-3nS. The change was immediate, like a 
switch was thrown.  The antenna hasn't moved, but the corresponding 
survey coordinates from September and January show a phase center 
position change of about 1.8m. This seems like a pretty small number, 
and wouldn't have expected it to make that big of a difference. At this 
point I'm not sure what to think. 
  

  
 Has anyone seen any of the Ulbox 6T modules PPS suddenly get 'noisy'. 
Is there anything else I should be looking at?

  
 Any recommendations on what I should be setting for NAV5 and NAVX5 
settings that could improve things? Elevation angles, or C/N 
thresholds? 

  
 I'm quite puzzled by this sudden degradation of the system. 
  
 Thanks,
 Dan
  

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Re: [time-nuts] Current state of optical clocks and the definition of the second

[Stéphane Rey]

Hi,

 

I've took the time to read carefully your long and detailed message Magnus and 
this was very interesting. I've learned many things that have enabled me to 
investigate further. Ah yes, you're right saying that the more you fall into 
these things, the more you discover that you have to learn. Recently I've 
worked a lot on PLLs and I've actually learned a lot on special care to ensure 
low noise Very interesting. By the way I'm still working on this topic to 
improve again the noise (currently on a 3 GHz LO)

 

 

Here are some experiment results : 
http://www.ptp-images.com/affiche-directement-l-image-kccsz71c9a.html

 

1.   Setup #1 (blue plot)

HP5370A

standard input from HP GPSDO

EXT input not connected, internal Arming 0.4s rate

START input from 10 MHz distribution unit RacalDana 9478 Rubidium 

 

2.   Setup #2 (pink plot)

HP5370A 

standard input from HP GPSDO

EXT input not connected, internal Arming 0.4s rate

START input from DUT (10 MHz homemade GPSDO)

 

I'm not sure this is the proper way to connect everything... but this is the 
setup providing the lowest ADEV... which is between 1E-10 and 1E-13. But is the 
truth ?

I feel strange the two plots having the same decreasing path along a linear 
slope (I mean linear on the log-log plot) ... I'm not sure of what I'm 
measuring ? Could this be the system measurement floor ? By the way how to 
measure the ADEV floor of a system other than having a source greater than the 
measurement system ?

What could be these oscillations on the homemade (not by me) GPSDO  ?

 

 

I've tried to downmix the DUT 10 MHz to few kHz using a SR DDS generator and a 
double balanced mixer from minicircuit via a low pass filter tuned at 100 kHz, 
but the level wasn't high enough for the counter (which I found strange as it 
was already nearly 200mV). I hadn't anything in hands to make a squarer quickly 
so I've just added a Minicircuits RF amplifier. The level was good but the ADEV 
has jumped to 1E-6. The signal was noisy already on the oscilloscope which I 
know is for sure the cause. 

I need to make a squarer. I was hesitating between several methods : using a 
CMOS gate, but this will increase the flicker noise from what I've read, using 
an amplifier and clamping diodes or a fast comparator which might create some 
noise around the trigger point... Any recommendation there ? 

I'll try to make this squarer next week to continue my investigations

 

Cheers 

Stephane

 

 

 

-Message d'origine-
De : time-nuts [mailto:time-nuts-boun...@febo.com] De la part de Magnus 
Danielson
Envoyé : mercredi 14 janvier 2015 06:05
À : time-nuts@febo.com
Cc : mag...@rubidium.se
Objet : Re: [time-nuts] Current state of optical clocks and the definition of 
the second

 

 

 

On 01/13/2015 11:41 AM, Attila Kinali wrote:

> On Mon, 12 Jan 2015 20:09:45 +

> Gregory Maxwell <  gmaxw...@gmail.com> wrote:

> 

>> On Mon, Jan 12, 2015 at 12:34 PM, Attila Kinali <  
>> att...@kinali.ch> wrote:

>> Seems that the state of the art in stabilized lasers has improved a 

>> lot lately, e.g. there are commercial available 1550nm devices which 

>> have a <=3Hz line-width:   
>> http://stablelasers.com/products.html (well 

>> on a short term basis, the medium term performance is not so

>> impressive)

> 

> Laser stabilization, especially for quantum metrology is still an 

> actively researched field. Current state of the art is IIRC 0.3Hz 

> linewidth (sorry, cannot find the reference at the moment).

> Mid- and long term stability depends highly on the reference used. 

> Current research is fucused mainly on special, low vibration 

> structures made out of low expansion glass or silicon. And these 

> cavities are usually put into a temperature controlled chamber in 

> vacuum.

 

Well, guess what I found standing around in a lab with an optical comb? :)

 

With optical line-widths in sub-Hz range and optical combs you have a nice way 
of comparing the frequency of that free-running and un-steerable but stable 
oscillator. However, as you mix it down the noise of the optical comb will 
dominate, but you can know which multiple of the optical comb and offset it is.

 

>> Considering the rarity and extreme cost of H-masers, or just really 

>> exceptional quarts oscillators; might it be the case that optical LOs 

>> start looking interesting for applications which just need stability 

>> (or being steered by other sources; e.g. GPSDL)?

> 

> Well, an 8607 costs more than a Rb-standard. Yes, the 8607 has lower 

> close in phase noise and up to several 1000s it rivals the Rb, but 

> handling it is much more difficult than handling an Rb.

> Also, if you want to buy one of those exceptionally low noise/high 

> stable 8607's (those that go down into the 10^-14 range) you'd have to sell 
> your car.

> 

> But, if you buy a H-maser from SpectraTime, yo

[time-nuts] Shera VXCO Controller and PCM61P

[Jerry Pixton]

Hello all.

I am a Freq-nut recently joining the Time-nut list.

I am putting together the parts for the Shera VXCO controller using the 
A&A PCB.


What are folks using now a days for the Burr-Brown PCM-61P DAC?

I can not find the Analog Devices AD1861N chip anywhere either. I do see 
the PCM-61P from Asia via eBay. But if there is another solution i might 
prefer that.




Jerry, W6IHG

--
--
Dr. Jerry R. Pixton, PIXOS Designs
http://www.shentel.net/pixosdesigns/RadioTuner
jpix...@shentel.net
--

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Re: [time-nuts] Advantest U3641 problem

[Magnus Danielson]

Hi,

Well, there can be steerable "pots", DACs, DDSes and other similar 
settings, but it may need the control which has not been left for either 
users or service stations. This is sufficient to make enough boards go 
through factor testing and out as sold products.


We didn't use to have requirements on this service degree on 
instruments, since we used to have it anyway, but maybe there needs to 
be such requirements about service-ability over time. If enough 
govrement and industry adopt such rules, the market motivator may be 
there. However, I see no such force today.


It's hard to show what the bottom line cost of different approaches is.
So... WAS.

Cheers,
Magnus

On 01/16/2015 04:48 PM, paul swed wrote:

Chuck if its not a totally integrated PLL board then you might reverse
engineer it and go from there.
As Bob says thats harder and harder to do because adjustments are done in
software and theres a big black chip with no clue these days. Technically
speaking WAS (we are screwed). :-) Or in a sentence it WAS working.
Regards
Paul
WB8TSL

On Fri, Jan 16, 2015 at 7:05 AM, Bob Camp  wrote:


Hi

Usually (but not always) these are VCO drift issues. If you can spot a
tuning adjust on that board you are lucky. A lot of this stuff is now done
“no adjust” boards. They just swap out the board …

Bob


On Jan 16, 2015, at 12:27 AM, Chuck Forsberg WA7KGX 

wrote:


My Advantest spectrum analyzer now comes up with an
error 900 complaining about no PLL lock.

This would appear to be a fault on the PLL board but the
brain damaged Advantest service manual has no schematics
for the boards.

Any suggestions other than don't buy anything from Advantest?


--
 Chuck Forsberg WA7KGX   c...@omen.com   www.omen.com
Developer of Industrial ZMODEM(Tm) for Embedded Applications
  Omen Technology Inc  "The High Reliability Software"
10255 NW Old Cornelius Pass Portland OR 97231   503-614-0430

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Re: [time-nuts] L1 and L2 frequencies

[Magnus Danielson]

Hi,

Well, if you can avoid reception from ground you avoid both handling 
reflexes as well as the thermal noise (300K vs. 3K).


You can't have higher antenna gain, since you want to receive fairly 
omni-directional above the horizon, with maybe the first 5-10 degrees 
nulled out.


What however is important is the noise-figure and gain of the LNA in the 
antenna. You want sufficient gain to make sure that antenna cable 
damping is handled and that the GPS signal is sufficiently above the 
internal noise of the actual receiver. I have installed low-loss cable 
to make sure the damping in manageable.


Cheers,
Magnus

On 01/16/2015 01:58 PM, Li Ang wrote:

Hi
   I have a question about the GPS antenna. Since the GPS signal strength on
the ground is about 20db lower than the thermal noise, does the gain of
antenna matter?

2015-01-16 7:01 GMT+08:00 "Björn Gabrielsson" :


Magnus,


If civilian receivers where to implement L2C and L5 which now is
becoming common, they would gain quite a bit of precision in a similar
fashion. For car navigation, the GPS would know which lane you are in.


There ARE civilian receivers doing this, and has been for quite some
years. And its not from only a few vendors - all the big ones have it -
Trimble, Novatel, Topcon, Javad, Leica, Septentrio and a few more. There
are now receivers tracking "GPS L1/L2/L2C/L5, Galileo
E1/E5A/E5B/AltBoc/E6, GLONASS L1/L2/L3, BeiDou B1/B2/B3, QZSS L1/L2/L5"

The price exceeds my home hobby budget, but so does a replacement
CS-tube
a factory new OCXO based GPSDO and many other things you can sometime
find
at reasonable cost used/recycled.


I naturally meant with a reasonable price-tag, sorry for being sloppy on
that detail, and I do know that there is vendors for those signals.

If we had dual or triple frequency receivers below 500 USD things would
start to be interesting. If high-volume kits would be just twice as
expensive, it would be possible to consider for more luxury models.


Receiver with 24 universal channels each of GPS L1/L2/L2C/L5 is cheaper
than a entry level TCXO-based 19" GPSDO (M300GPS @ Dustin). And about the
same price as a modern Loran receiver. What is a reasonable commercial
price?

  But yes, multi frequency GNSS is much more expensive than the Oncore,
Ublox traditionally used in a GPSDO. Is the performance gain worth the
cost? Certainly not for all but a few.

On the oscillator side, we consider everything from XO, TCXO, OCXO, DOCXO,
to devar based designs - BVAs and others, and rubidiums, cesiums and
Masers. What are reasonable price-tags for oscillators compared to various
time transfer capable receiver?

--

  Björn

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Re: [time-nuts] Advantest U3641 problem

[paul swed]

Chuck if its not a totally integrated PLL board then you might reverse
engineer it and go from there.
As Bob says thats harder and harder to do because adjustments are done in
software and theres a big black chip with no clue these days. Technically
speaking WAS (we are screwed). :-) Or in a sentence it WAS working.
Regards
Paul
WB8TSL

On Fri, Jan 16, 2015 at 7:05 AM, Bob Camp  wrote:

> Hi
>
> Usually (but not always) these are VCO drift issues. If you can spot a
> tuning adjust on that board you are lucky. A lot of this stuff is now done
> “no adjust” boards. They just swap out the board …
>
> Bob
>
> > On Jan 16, 2015, at 12:27 AM, Chuck Forsberg WA7KGX 
> wrote:
> >
> > My Advantest spectrum analyzer now comes up with an
> > error 900 complaining about no PLL lock.
> >
> > This would appear to be a fault on the PLL board but the
> > brain damaged Advantest service manual has no schematics
> > for the boards.
> >
> > Any suggestions other than don't buy anything from Advantest?
> >
> >
> > --
> > Chuck Forsberg WA7KGX   c...@omen.com   www.omen.com
> > Developer of Industrial ZMODEM(Tm) for Embedded Applications
> >  Omen Technology Inc  "The High Reliability Software"
> > 10255 NW Old Cornelius Pass Portland OR 97231   503-614-0430
> >
> > ___
> > time-nuts mailing list -- time-nuts@febo.com
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Re: [time-nuts] L1 and L2 frequencies

[Jim Lux]

On 1/16/15 4:58 AM, Li Ang wrote:

Hi
   I have a question about the GPS antenna. Since the GPS signal strength on
the ground is about 20db lower than the thermal noise, does the gain of
antenna matter?


Not a whole lot.. Obviously, you don't want something -10dBi, and there 
is a direct effect of SNR and timing uncertainty (which turns into 
position uncertainty).  If the SNR is too bad, you won't be able to 
acquire the signal.
The PN code runs at 1 Mchip/sec, so you can look at the SNR in 1 Hz 
bandwidth as being 60dB higher than the received SNR.


Typically with GPS you worry more about side/back lobe performance so 
that you don't pick up multipath reflections.



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Re: [time-nuts] L1 and L2 frequencies

[Li Ang]

Hi
  I have a question about the GPS antenna. Since the GPS signal strength on
the ground is about 20db lower than the thermal noise, does the gain of
antenna matter?

2015-01-16 7:01 GMT+08:00 "Björn Gabrielsson" :

> Magnus,
>
> >>> If civilian receivers where to implement L2C and L5 which now is
> >>> becoming common, they would gain quite a bit of precision in a similar
> >>> fashion. For car navigation, the GPS would know which lane you are in.
> >>
> >> There ARE civilian receivers doing this, and has been for quite some
> >> years. And its not from only a few vendors - all the big ones have it -
> >> Trimble, Novatel, Topcon, Javad, Leica, Septentrio and a few more. There
> >> are now receivers tracking "GPS L1/L2/L2C/L5, Galileo
> >> E1/E5A/E5B/AltBoc/E6, GLONASS L1/L2/L3, BeiDou B1/B2/B3, QZSS L1/L2/L5"
> >>
> >> The price exceeds my home hobby budget, but so does a replacement
> >> CS-tube
> >> a factory new OCXO based GPSDO and many other things you can sometime
> >> find
> >> at reasonable cost used/recycled.
> >
> > I naturally meant with a reasonable price-tag, sorry for being sloppy on
> > that detail, and I do know that there is vendors for those signals.
> >
> > If we had dual or triple frequency receivers below 500 USD things would
> > start to be interesting. If high-volume kits would be just twice as
> > expensive, it would be possible to consider for more luxury models.
>
> Receiver with 24 universal channels each of GPS L1/L2/L2C/L5 is cheaper
> than a entry level TCXO-based 19" GPSDO (M300GPS @ Dustin). And about the
> same price as a modern Loran receiver. What is a reasonable commercial
> price?
>
>  But yes, multi frequency GNSS is much more expensive than the Oncore,
> Ublox traditionally used in a GPSDO. Is the performance gain worth the
> cost? Certainly not for all but a few.
>
> On the oscillator side, we consider everything from XO, TCXO, OCXO, DOCXO,
> to devar based designs - BVAs and others, and rubidiums, cesiums and
> Masers. What are reasonable price-tags for oscillators compared to various
> time transfer capable receiver?
>
> --
>
>  Björn
>
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Re: [time-nuts] Advantest U3641 problem

[Bob Camp]

Hi

Usually (but not always) these are VCO drift issues. If you can spot a tuning 
adjust on that board you are lucky. A lot of this stuff is now done “no adjust” 
boards. They just swap out the board …

Bob
 
> On Jan 16, 2015, at 12:27 AM, Chuck Forsberg WA7KGX  wrote:
> 
> My Advantest spectrum analyzer now comes up with an
> error 900 complaining about no PLL lock.
> 
> This would appear to be a fault on the PLL board but the
> brain damaged Advantest service manual has no schematics
> for the boards.
> 
> Any suggestions other than don't buy anything from Advantest?
> 
> 
> -- 
> Chuck Forsberg WA7KGX   c...@omen.com   www.omen.com
> Developer of Industrial ZMODEM(Tm) for Embedded Applications
>  Omen Technology Inc  "The High Reliability Software"
> 10255 NW Old Cornelius Pass Portland OR 97231   503-614-0430
> 
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Re: [time-nuts] L1 and L2 frequencies

[Magnus Danielson]

Björn,

On 01/16/2015 12:01 AM, "Björn Gabrielsson" wrote:

Magnus,


I naturally meant with a reasonable price-tag, sorry for being sloppy on
that detail, and I do know that there is vendors for those signals.

If we had dual or triple frequency receivers below 500 USD things would
start to be interesting. If high-volume kits would be just twice as
expensive, it would be possible to consider for more luxury models.


Receiver with 24 universal channels each of GPS L1/L2/L2C/L5 is cheaper
than a entry level TCXO-based 19" GPSDO (M300GPS @ Dustin). And about the
same price as a modern Loran receiver. What is a reasonable commercial
price?

  But yes, multi frequency GNSS is much more expensive than the Oncore,
Ublox traditionally used in a GPSDO. Is the performance gain worth the
cost? Certainly not for all but a few.

On the oscillator side, we consider everything from XO, TCXO, OCXO, DOCXO,
to devar based designs - BVAs and others, and rubidiums, cesiums and
Masers. What are reasonable price-tags for oscillators compared to various
time transfer capable receiver?


Well, I think you missed my point. My point being that when 
multifrequency receivers would become more commodity, they could be more 
commodity for time-nuts, time-equipment in general as well as other 
uses. For advanced hobby-ist use, they are reachable, but they are still 
expensive for many commercial uses, especially when considering the 
price upscale you have as you integrate an OEM board into a product.


But beside that, what boards should one look at today?

Cheers,
Magnus
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[time-nuts] Advantest U3641 problem

[Chuck Forsberg WA7KGX]

My Advantest spectrum analyzer now comes up with an
error 900 complaining about no PLL lock.

This would appear to be a fault on the PLL board but the
brain damaged Advantest service manual has no schematics
for the boards.

Any suggestions other than don't buy anything from Advantest?


--
 Chuck Forsberg WA7KGX   c...@omen.com   www.omen.com
Developer of Industrial ZMODEM(Tm) for Embedded Applications
  Omen Technology Inc  "The High Reliability Software"
10255 NW Old Cornelius Pass Portland OR 97231   503-614-0430

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