Re: [time-nuts] Building a mains frequency monitor

[Chris Albertson]

It works the same on PC hardware

The PPS causes an interrupt and the handler captures the value of a counter
that is driven by the system clock.  It is typically a nanosecond level
clock that just free runs.  It saves the captured value were a user level
process can read it.  The user level process can do whatever it likes it
typically load the captured counter value.  I would not use the syslog time
stamp as that has more lag but for this purpose maybe it is close enough.

The source for Linux PPS has a test program that does exactly the above.

On Fri, Apr 8, 2016 at 10:32 AM, Ben Hall  wrote:

> On 4/6/2016 11:34 PM, Nick Sayer via time-nuts wrote:
>
>> fed into a Raspberry Pi serial port that was running a simple daemon
>> that logged every line it got to syslog. Syslog is handy because it
>> timestamps everything for you and keeps rotating log files and the
>> like.
>>
>
> Would you be so kind as to elaborate how to do this?  Been looking for
> such a solution off and on for a while...and I'm not having a lot of luck
> with Google search at the moment.
>
> thanks much and 73,
> ben
>
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-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] Building a mains frequency monitor

[Nick Sayer via time-nuts]

The instructable I wrote about it is at 
http://www.instructables.com/id/Science-fair-How-accurate-is-the-AC-line-frequency/

There’s code for the Arduino and the Linux side as well as schematics.

> On Apr 8, 2016, at 10:32 AM, Ben Hall  wrote:
> 
> On 4/6/2016 11:34 PM, Nick Sayer via time-nuts wrote:
>> fed into a Raspberry Pi serial port that was running a simple daemon
>> that logged every line it got to syslog. Syslog is handy because it
>> timestamps everything for you and keeps rotating log files and the
>> like.
> 
> Would you be so kind as to elaborate how to do this?  Been looking for such a 
> solution off and on for a while...and I'm not having a lot of luck with 
> Google search at the moment.
> 
> thanks much and 73,
> ben
> 
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Re: [time-nuts] Advise on building a DIY GPSDO?

[Bob Camp]

Hi

If you start from a 24 MHz TCXO (different modules use different TCXO’s):

On an 8 MHz output, most of the time you divide by three. 

On a 10 MHz output, you need to divide by 2.4. The net result is that you 
divide by 2 sometimes and 3 other times. 

In the 10 MHz case, there is a *lot* of energy at 12 MHz and 8 MHz, along with 
the 10 MHz output. 

In the 8 MHz case, most of the RF energy is at 8 MHz.



To correct the output by 1 ppm on the 8 MHz output, you need to either drop or
add one pulse out of every million pulses. Effectively you divide the 24 MHz by
2 or by 4 when you do that. You get a bit of 12 MHz or a bit of 6 MHz as a 
result. 
That can be filtered out with a RF filter. The same is true with a (somewhat 
more 
complex) filter on the 10 MHz output.

In addition to the “big” RF spurs, you get a low frequency component to the 
output 
modulation. You are “phase hitting” the output eight times a second. That gives 
you
an 8 Hz sideband along with the further removed stuff. Since it’s not simple / 
clean
phase modulation, there are more sidebands than just the few mentioned above. 

What messes things up even more is that you never are quite doing one ppm. You 
are doing 
corrections like 0.12356 ppm this second and 0.120201 ppm the next second. 
The pattern of pulse drop and add is not as simple as you might hope. The low 
frequency part of the jitter (and it will be there) is no different than the 
noise on 
a 1 pps output. You still need to do very long time constant (or very narrow 
band)
filtering to take it out. 

Bob

> On Apr 8, 2016, at 7:06 AM, Herbert Poetzl  wrote:
> 
> On Mon, Apr 04, 2016 at 06:07:54PM -0700, Alexander Pummer wrote:
>> and it is relative easy to make 10MHz from 8MHz with analog
>> frequency manipulation, which generates less jitter
> 
> Could you elaborate on this a little if time permits? 
> I'm more a 'digital person' but it sounds interesting.
> 
> Thanks in advance,
> Herbert
> 
>> 73
> 
>> On 4/4/2016 4:27 PM, Attila Kinali wrote:
>>> On Mon, 4 Apr 2016 17:56:29 -0400
>>> Bob Camp  wrote:
> 
 The variable frequency output on the uBlox (and other) GPS
 receivers has come up many times in the past.
> 
 If you dig into the archives you can find quite a bit of
 data on the (lack of) performance of the high(er) frequency
 outputs from the various GPS modules. They all depend on
 cycle add / drop at the frequency of their free running TCXO.
 Regardless of the output frequency, that will put a *lot* of
 jitter into the output.
>>> That's why you should put the output frequency of the ublox modules
>>> to an integer divisor of 24MHz. Ie 8MHz works but not 10MHz.
> 
>>> Attila Kinali
> 
> 
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Re: [time-nuts] FTS1050A performance

[jimlux]

It's NASA property and not likely to be excessed.   You'll wait in vain 



Sent via the Samsung Galaxy S®6 active, an AT 4G LTE smartphone 
Original message From: Tom Knox  Date: 4/8/2016  
11:34 AM  (GMT-08:00) To: Discussion of precise time and frequency measurement 
 Subject: Re: [time-nuts] FTS1050A performance 
Actually they are really nice, especially if it has the external 5MHz reference 
input.
For many aspects of Time and Freq related work I do close in Phase Noise is a 
primary concern.
If you ever decide it is not needed let me know I and I am sure many other 
"Time Nuts" would be interested.
Cheers;

Thomas Knox
1-303-554-0307
act...@hotmail.com


From: time-nuts  on behalf of jimlux 

Sent: Friday, April 8, 2016 9:12 AM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] FTS1050A performance

I just ran across an unused FTS1050A at work, and before spending any
significant time seeing if it still works (like finding a power source..
there's no AC inlet, so I think it runs off DC), I decided to look up
the data sheet performance.  Interestingly, it seems it's not that
wonderful, compared to a $200 Wenzel streamline, except for "real close in"

    FTS1050 Wenzel
1   -116    -105? (est from 1/f^3 and 10 Hz offset)
10  -140    -135
100 -150    -155
1k  -157    -165
10k -160    -165



I note that John Ackerman reports on
https://www.febo.com/pages/oscillators/fts1050a/old/
  a similar observation

I suppose that you use these things for "close in" and ADEV performance,
not for phase noise at 10 kHz out.


Some of these units were modified at the lab to replace the original
oscillator with a better one (a BVA, it's rumored).  And who knows what
else was done..
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[time-nuts] Korean Peninsula GPS Jamming Notice

[Tom Van Baak]

Not that any of us are in the affected area, but it's an interesting notice 
nonetheless.
No replies necessary.
/tvb

___
All CGSIC:

On 7 April 2016 the U.S. Department of State released the following notice. 

START NOTICE

Korean Peninsula GPS Jamming Notice
A continuing series of incidents have been reported in the general location of 
Incheon, Republic of Korea and the surrounding Gyeonggi and Gangwon provinces 
out to approximately 100 nautical miles beginning on or about Z31March16. 
The nature of the events appear to be Global Positioning System (GPS) jamming 
emanating from the Democratic People's Republic of Korea causing signal 
disruptions to airplanes, ships, and buoys in the area. Exercise caution when 
transiting this area. If appropriate, further information may be forthcoming. 
Vessels experiencing disruptions in the area are urged to report them to the 
point of contact (POC) below.

POC: 
CIVILIAN - NAVCEN AT 703-313-5900, http://www.navcen.uscg.gov
MILITARY - GPS OPERATIONS CENTER at https://gps.afspc.af.mil/gpsoc,
DSN 560-2541, COMM 719-567-2541, gpsoperationscen...@us.af.mil, 
https://gps.afspc.af.mil 
MILITARY ALTERNATE - JOINT SPACE OPERATIONS CENTER, DSN 276-3514, 
COMM 805-606-3514, jspoccombat...@vandenberg.af.mil

END NOTICE

V/R
CGSIC Executive Secretariat
U.S. Coast Guard Navigation Center
703-313-5900
___

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Re: [time-nuts] FTS1050A performance

[Tom Knox]

Actually they are really nice, especially if it has the external 5MHz reference 
input.
For many aspects of Time and Freq related work I do close in Phase Noise is a 
primary concern.
If you ever decide it is not needed let me know I and I am sure many other 
"Time Nuts" would be interested.
Cheers;

Thomas Knox
1-303-554-0307
act...@hotmail.com


From: time-nuts  on behalf of jimlux 

Sent: Friday, April 8, 2016 9:12 AM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] FTS1050A performance

I just ran across an unused FTS1050A at work, and before spending any
significant time seeing if it still works (like finding a power source..
there's no AC inlet, so I think it runs off DC), I decided to look up
the data sheet performance.  Interestingly, it seems it's not that
wonderful, compared to a $200 Wenzel streamline, except for "real close in"

FTS1050 Wenzel
1   -116-105? (est from 1/f^3 and 10 Hz offset)
10  -140-135
100 -150-155
1k  -157-165
10k -160-165



I note that John Ackerman reports on
https://www.febo.com/pages/oscillators/fts1050a/old/
  a similar observation

I suppose that you use these things for "close in" and ADEV performance,
not for phase noise at 10 kHz out.


Some of these units were modified at the lab to replace the original
oscillator with a better one (a BVA, it's rumored).  And who knows what
else was done..
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Re: [time-nuts] Building a mains frequency monitor

[Ben Hall]

On 4/6/2016 11:34 PM, Nick Sayer via time-nuts wrote:

fed into a Raspberry Pi serial port that was running a simple daemon
that logged every line it got to syslog. Syslog is handy because it
timestamps everything for you and keeps rotating log files and the
like.


Would you be so kind as to elaborate how to do this?  Been looking for 
such a solution off and on for a while...and I'm not having a lot of 
luck with Google search at the moment.


thanks much and 73,
ben

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[time-nuts] FTS1050A performance

[jimlux]

I just ran across an unused FTS1050A at work, and before spending any 
significant time seeing if it still works (like finding a power source.. 
there's no AC inlet, so I think it runs off DC), I decided to look up 
the data sheet performance.  Interestingly, it seems it's not that 
wonderful, compared to a $200 Wenzel streamline, except for "real close in"


FTS1050 Wenzel
1   -116-105? (est from 1/f^3 and 10 Hz offset)
10  -140-135
100 -150-155
1k  -157-165
10k -160-165



I note that John Ackerman reports on
https://www.febo.com/pages/oscillators/fts1050a/old/
 a similar observation

I suppose that you use these things for "close in" and ADEV performance, 
not for phase noise at 10 kHz out.



Some of these units were modified at the lab to replace the original 
oscillator with a better one (a BVA, it's rumored).  And who knows what 
else was done..

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Re: [time-nuts] LEA-M8T

[Tom Van Baak]

> The runs I did used a number of modules, not just uBlox products. Some modules
> did worse than others on position. I dropped them out of the group before I 
> moved
> on to timing. 

Hi Bob,

I had access to a pre-release ublox combined GNSS receiver a few years ago and 
found the same thing. My conclusion was that for GPSDO timing use, a plain 
GPS-only receiver was superior.

Like I said yesterday, at some point in the evolution of GNSS integration and 
cooperation, the situation will improve. AFAIK there's no intrinsic, technical 
reason that multiple proprietary PNT systems can't perform better as a whole 
than one alone. But for a GPSDO it seems we're not there yet. Who knows how 
much receiver firmware or OOB internet access it will take to solve this. But 
it can be solved.

Note that these multi-GNSS problems are likely much less if you post-process or 
use common-view. But a cheap GNSS receiver in a GPSDO is in the awkward 
position that it only works with live signals.

Again if someone has links to technical papers on this topic, that would be 
welcome. 

/tvb

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Re: [time-nuts] Advise on building a DIY GPSDO?

[Herbert Poetzl]

On Mon, Apr 04, 2016 at 06:07:54PM -0700, Alexander Pummer wrote:
> and it is relative easy to make 10MHz from 8MHz with analog
> frequency manipulation, which generates less jitter

Could you elaborate on this a little if time permits? 
I'm more a 'digital person' but it sounds interesting.

Thanks in advance,
Herbert

> 73

> On 4/4/2016 4:27 PM, Attila Kinali wrote:
>> On Mon, 4 Apr 2016 17:56:29 -0400
>> Bob Camp  wrote:

>>> The variable frequency output on the uBlox (and other) GPS
>>> receivers has come up many times in the past.

>>> If you dig into the archives you can find quite a bit of
>>> data on the (lack of) performance of the high(er) frequency
>>> outputs from the various GPS modules. They all depend on
>>> cycle add / drop at the frequency of their free running TCXO.
>>> Regardless of the output frequency, that will put a *lot* of
>>> jitter into the output.
>> That's why you should put the output frequency of the ublox modules
>> to an integer divisor of 24MHz. Ie 8MHz works but not 10MHz.

>>  Attila Kinali


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Re: [time-nuts] LEA-M8T

[Bob Camp]

Hi

In my case, the antennas were nice brand new NovaTel L/L2/L5 Glonass rated 
survey antennas. The were up far enough to have a 360 degree view of the sky
down to 10 degrees of the horizon. 

The runs I did used a number of modules, not just uBlox products. Some modules
did worse than others on position. I dropped them out of the group before I 
moved
on to timing. 

No attempt was made to compare the self survey location to any sort of 
“correct” survey 
data. The main goals were:

1) Can multiple systems give better self survey? 
2) Can multiple systems give better timing? 

There also was no real attempt to turn the project into a full blown “paper” 
level 
experiment. The only reason for doing the work was to be able to answer the very
basic questions of multi system timing as it applies right now. 

One important note - If you are in an antenna challenged location, the answers 
may be different. If you are in a < 4 sats situation 80% of the time, the added 
systems will likely improve things. 

In any case, a “perfect” solution would use an independent self survey location 
for each system. It also would use a separate sawtooth output for each system. 
So far, I have not seen a small module that does this. 

Bob

> On Apr 7, 2016, at 11:14 PM, Gregory Maxwell  wrote:
> 
> On Fri, Apr 8, 2016 at 12:06 AM, Tom Van Baak  wrote:
>> Meanwhile it would not surprise me if each GNSS system gives a slightly 
>> different position and a slightly different time than GPS does.
> 
> One could easily imagine a system that when signals from both
> constellations were strong it fit a model matching a secondary system
> to a primary.  Then when the primary was degraded/unavailable used the
> secondary data with the model-- which would hopefully fix any bias
> between the systems-- assuming that it's fairly stable. But that would
> be a fairly specialized mode of operation.
> 
> If the solutions were pooled with weighing and knowledge of their
> process errors adding more shouldn't make it worse... but might not
> add anything: the ideal weight might be zero.
> 
> I wonder how much of these negative experience with glonass are due to
> non-calibrated antenna: Glonass does frequency division multiplexing,
> and so the antenna's angle/frequency dependent phase can harm
> performance... many GPS antenna greatly attenuate the glonass signal
> too.
> 
> For time-nuts operation where the GPS is conditioning one (or more)
> nice OCXO or atomic clocks in a world where tens of gigaflops of CPU
> are among the least expensive toys we can buy, I imagine that fairly
> different signal processing approaches would be ideal: e.g. instead of
> just computing second by second solutions and putting the error into a
> PLL, one could collect hours of observation data and produce after the
> fact correction data that uses prior assumptions about the stability
> of the local oscillator.  Such a processing mode could be more robust
> against disturbance from multipath and SV failure, as that data could
> be excluded as hopelessly inconsistent compared to modes that didn't
> assume a stable local clock and didn't use potentially hours of
> observation that watched the SV move across the whole sky.
> 
> It's somewhat annoying that this kind of experimentation first would
> require something like getting a software GPS implementation working
> well; when you just want to try changing around secondary processing
> after all the coorelators and such.
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