Re: [time-nuts] Leap second to be introduced at midnight UTC December 31 this year

[Gary E. Miller]

Yo Tom!

> > IERS is free to schedule a leap second at the end of any month. And
> > it may be an insert or a delete. Assume nothing more or less in your
> > code. Code and test and document for positive and negative leap
> > seconds equally.  
> 
> Got a reference for that?  I know many people that will insist
> otherwise.

Never mind, I think I found a reference that is commonly quoted:

CCIR Recommendation 460-4 (1986).

http://www.itu.int/rec/R-REC-TF.460-4-198607-S/en

2.  Leap-seconds
2.1 A positive or negative leap-second should be the last second
of a UTC month, but first preference should be given to the end of
December and June, and second preference to the end of March and
September.

But it is marked Superceded.  I'm guessing that is replaced by 460-6?

http://www.itu.int/rec/R-REC-TF.460-6-200202-I/en

It says the same thing in section 2.1

Nothing says it has to be those 4 months...

I have some code comments in gpsd to fix...

RGDS
GARY
---
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
g...@rellim.com  Tel:+1 541 382 8588


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Re: [time-nuts] Leap second to be introduced at midnight UTC December 31 this year

[Gary E. Miller]

Yo Tom!

Here we go again.  Leap seconds always cause stress...

On Tue, 19 Jul 2016 22:08:48 -0700
"Tom Van Baak"  wrote:

> In general there's a common belief that a leap second can only occur
> at the end of June or December. This is false. Don't ever hardcode
> this assumption.

NTP Classic thinks otherwise:
http://bugs.ntp.org/show_bug.cgi?id=1090

gpsd follows the lead of NTP folks.

> IERS is free to schedule a leap second at the end of any month. And
> it may be an insert or a delete. Assume nothing more or less in your
> code. Code and test and document for positive and negative leap
> seconds equally.

Got a reference for that?  I know many people that will insist otherwise.

RGDS
GARY
---
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
g...@rellim.com  Tel:+1 541 382 8588


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Re: [time-nuts] Leap second to be introduced at midnight UTC December 31 this year

[Tom Van Baak]

Hi Mark,

Three comments:

1)
I recall this is a known problem in the Z3801A status reporting, and possibly 
other GPS receivers of that era as well. It stems indirectly from a change 
years ago in how far in advance IERS and DoD were able to update the leap 
second info into the GPS constellation. Nowadays it's common to get 6 months 
notice; it wasn't always that much.

We typically reserve the word leap second "pending" for the month in which the 
leap second will actually occur. So just because we now know a leap second will 
occur in December we don't say, here in July, that a leap second is pending. 
Instead we say a leap second has been scheduled, or has been announced, or 
something like that.

There's more info on all of this back in the time-nuts and LEAPSECS archives if 
you want to dig deeper.

2)
Note this is not a problem for LF time services like WWVB which reserve two 
bits; one that tells you if a leap second is pending (this month) and one that 
tells you if it's an insert (positive) or delete (negative) leap second. For 
WWVB it's either this month or it's not at all.

It's a minor problem for NTP because it AFAIK it can only tell you one day in 
advance if a leap second is going to happen at midnight.

It's a mess for NMEA; there are no standard messages that give leap second 
announcements. The time just jumps or stutters, whether you or your boating 
equipment expects it or not.

It's not a problem for GPS because internally a leap second is not indicated by 
flag bits at all. Instead they use two fields for the pre- and the post- 
UTC-GPS offset, as well as the GPS week/day number when the change takes/took 
effect. So there's the potential for years of advance notice of a leap second.

So GPS is robust, WWVB is fine, avoid NMEA, and NTP is kind of fragile with 
respect to leap second announcements. I assume Galileo does it right. GLONASS, 
on the other hand, is known to have problems every time there's a leap second.

Just to be clear, this Z3801 anomaly is not a GPS problem. IIRC, it's not even 
an Oncore VP GPS board problem either; instead the hp CPU firmware is overly 
enthusiastic about how to transform a GPS leap second *announcement* into a 
Z3801A leap second *pending*. But it all works out fine in the end; this has 
happened on other recent leap second announcements, so not to worry.

3)
Some things to know, as a writer of software that involves users, GPS 
receivers, and leap seconds...

If you're writing embedded software try to never hardcode any leap second 
tables.

In general there's a common belief that a leap second can only occur at the end 
of June or December. This is false. Don't ever hardcode this assumption.

There's also a less common belief that a leap second may occur at the end of 
March, June, September, or December. This is also false. Don't hardcode this 
either.

IERS is free to schedule a leap second at the end of any month. And it may be 
an insert or a delete. Assume nothing more or less in your code. Code and test 
and document for positive and negative leap seconds equally.

I say this because with the gradual warming / melting of the planet since the 
last major ice age we may soon enter a decade where the earth returns to a 
"normal" 86400.000 seconds per day or even a bit less. In that case we'll 
switch from positive leap seconds for a while, to no leap seconds for a while, 
to negative leap seconds for a while. We got very close to this during the 
years 2000 - 2007, when we entered the "no leap seconds for a while" stage.

I don't normally cross-post, but I'll cc the leap second list for comments or 
corrections.

/tvb

- Original Message - 
From: "Mark Sims" 
To: 
Sent: Tuesday, July 19, 2016 4:39 PM
Subject: [time-nuts] Leap second to be introduced at midnight UTCDecember 31 
this year


> The GPS satellites are now reporting the pending leapsecond...
> 
> The Z3801A has it messed up...  it says the leap will occur on 30 Sep 2016 
> (73 days).  The Z3801A has two different messages that report the leap day... 
>  both are wrong.  



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[time-nuts] Leap second to be introduced at midnight UTC December 31 this yea

[Mark Sims]

The Z3801A bug reporting the wrong day for the leap second is has to be in the 
Z3801A firmware and not the GPS receiver...  that receiver does not have a 
message that reports the date of the leapsecond or the almanac data needed to 
calculate it.  It only has the message that says a leapsecond is pending.  I 
bet that when they see the leapsecond pending flag from the receiver they 
assume the day will be on the last day of March,  June,  Sepember, or 
December... whichever comes up next.  I also bet that when October 1st come 
around it will report the correct date.   No telling what time it will report 
at midnight UTC on 31 Sep...   
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Re: [time-nuts] Lucent boxes

[Chris Waldrup]

I sure did. 
Thank you for the follow up. I really appreciate it. 

Chris
KD4PBJ

> On Jul 19, 2016, at 21:16, Douglas Baker  wrote:
> 
> Chris,
> I didn't see that anyone had answered your question about the XO unit
> running by itself.  Yes, the XO unit is or was a hot standby for the
> rubidium unit.  So it had to be able to function if there was a failure of
> the primary unit.
> Have you found the hook-up cable drawings on KO4BB's web site?
>> On Jul 19, 2016 2:56 PM, "Richard W. Solomon"  wrote:
>> 
>> Got it, many thanks. I have a pair of these, NIB,
>> time to hook them up.
>> 
>> 73, Dick, W1KSZ
>> 
>> -Original Message-
>> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Artek
>> Manuals
>> Sent: Tuesday, July 19, 2016 1:11 PM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] Lucent boxes
>> 
>> Ahhh no  ...I have the MANUALS page book marked
>> 
>> try this one
>> 
>> http://www.ko4bb.com/getsimple/index.php?id=manuals
>> 
>> 
>> 
>>> On 7/19/2016 2:49 PM, Richard W. Solomon wrote:
>>> This Home Page ??
>>> 
>>> http://www.ko4bb.com/getsimple/index.php?id=index-1
>>> 
>>> Don't see any search box there ???
>>> 
>>> 73, Dick, w1KSZ
>>> 
>>> -Original Message-
>>> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Artek
>>> Manuals
>>> Sent: Tuesday, July 19, 2016 10:19 AM
>>> To: Discussion of precise time and frequency measurement
>>> Subject: Re: [time-nuts] Lucent boxes
>>> 
>>> Dick
>>> 
>>> Not rocket science ...go to KO4BB main page and enter "RFTGm"
>>> 
>>> In the search box
>>> 
>>> Dave
>>> NR1DX
>>> 
 On 7/19/2016 12:42 PM, Richard W. Solomon wrote:
 KO4BB's site is massive, can you pin down the cable drawing ?
 
 Tnx, Dick, W1KSZ
 
 -Original Message-
 From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of
 Douglas Baker
 Sent: Monday, July 18, 2016 2:39 PM
 To: Discussion of precise time and frequency measurement
 Subject: Re: [time-nuts] Lucent boxes
 
 Chris,
 The RFTGm ("m" for miniature even though still a large box) is a later
>> version of the RFTG line.  The XO unit houses the GPS receiver which is
>> essential for disciplining.  Both boxes operate at 24 VDC and there is an
>> interface cable drawing on line at KO4BB's web site. Never tried to hook
>> them up together, but it might work.  Maybe others here may know.  Good
>> luck with it.
 73's Doug
> On Jul 18, 2016 12:52 PM, "Chris Waldrup"  wrote:
> 
> Hi Everyone,
> 
> I have two Lucent RFTG boxes in my workshop. The XO is a loaner.
> I'm curious if they will interface with each other or (most likely)
> they are a different series as the interface connectors on each have
> a different number of pins.
> One is marked RFTG-u REF 0
> The other is RFTGm-II-XO
> 
> Thanks in advance.
> 
> Chris
> KD4PBJ
> 
> 
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>>> 
>>> 
>>> --
>>> Dave
>>> manu...@artekmanuals.com
>>> www.ArtekManuals.com
>>> 
>>> ---
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>> 
>> 
>> --
>> Dave
>> manu...@artekmanuals.com
>> www.ArtekManuals.com
>> 
>> ---
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Re: [time-nuts] Leap second to be introduced at midnight UTC December 31 this year

[Hal Murray]

hol...@hotmail.com said:
> I get the Z3801A leap pending flag from the #T1 or #T2 time stamp in the
> :PTIM:TCOD? response.

I see it now.  Started a bit after an hour UTC into the new day.

57589 4546.033 127.127.26.1 T22016072001154730+0038  64 0

So either I didn't look carefully enough or it hadn't arrived yet when I was 
looking around to compose my previous message.



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[time-nuts] Leap second to be introduced at midnight UTC December 31 this year

[Mark Sims]

I get the Z3801A leap pending flag from the #T1 or #T2 time stamp in the 
:PTIM:TCOD? response.   For the date, either :PTIM:LEAP:DATE? or 
:PTIM:LEAP:GPST? depending upon the unit type.

And now for some more receiver leapsecond shenanagins:

The Ublox receivers work well.  You can calculate the day of the leapsecond 
from almanac info (gps week and day-of-week) returned in the 0x0B 0x02 
leapsecond message.

The Trimble receivers have a leap pending flag in the primary timing message.  
They also have a message (0x58, subcode 5) that returns the data needed to 
calculate the date of the leapsecond.   However, the GPS week number it returns 
is not compensated for week rollovers.   You need to do that yourself.   Also, 
don't send the original (non-SMT) Resolution-T receiver the 0x38 message to 
request the 0x58 message.  Doing that causes the receiver to get confused for 
at least three seconds.

The Motorola VP/UT/M12 receivers send the leap pending flag in the @@Bj 
message.  It is supposed to work in all Motorola receivers,  but the M12+ 
always reports no leap pending.  The M12's have an @@Gj message that reports 
the date of the leapsecond,  It says 2017/01/01,  not 2016/12/31.

None of the other receivers have messages that report leapsecond related info.
---
> Which messages are you looking at?  
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Re: [time-nuts] Lucent boxes

[Douglas Baker]

Chris,
I didn't see that anyone had answered your question about the XO unit
running by itself.  Yes, the XO unit is or was a hot standby for the
rubidium unit.  So it had to be able to function if there was a failure of
the primary unit.
Have you found the hook-up cable drawings on KO4BB's web site?
On Jul 19, 2016 2:56 PM, "Richard W. Solomon"  wrote:

> Got it, many thanks. I have a pair of these, NIB,
> time to hook them up.
>
> 73, Dick, W1KSZ
>
> -Original Message-
> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Artek
> Manuals
> Sent: Tuesday, July 19, 2016 1:11 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Lucent boxes
>
> Ahhh no  ...I have the MANUALS page book marked
>
> try this one
>
> http://www.ko4bb.com/getsimple/index.php?id=manuals
>
>
>
> On 7/19/2016 2:49 PM, Richard W. Solomon wrote:
> > This Home Page ??
> >
> > http://www.ko4bb.com/getsimple/index.php?id=index-1
> >
> > Don't see any search box there ???
> >
> > 73, Dick, w1KSZ
> >
> > -Original Message-
> > From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Artek
> > Manuals
> > Sent: Tuesday, July 19, 2016 10:19 AM
> > To: Discussion of precise time and frequency measurement
> > Subject: Re: [time-nuts] Lucent boxes
> >
> > Dick
> >
> > Not rocket science ...go to KO4BB main page and enter "RFTGm"
> >
> > In the search box
> >
> > Dave
> > NR1DX
> >
> > On 7/19/2016 12:42 PM, Richard W. Solomon wrote:
> >> KO4BB's site is massive, can you pin down the cable drawing ?
> >>
> >> Tnx, Dick, W1KSZ
> >>
> >> -Original Message-
> >> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of
> >> Douglas Baker
> >> Sent: Monday, July 18, 2016 2:39 PM
> >> To: Discussion of precise time and frequency measurement
> >> Subject: Re: [time-nuts] Lucent boxes
> >>
> >> Chris,
> >> The RFTGm ("m" for miniature even though still a large box) is a later
> version of the RFTG line.  The XO unit houses the GPS receiver which is
> essential for disciplining.  Both boxes operate at 24 VDC and there is an
> interface cable drawing on line at KO4BB's web site. Never tried to hook
> them up together, but it might work.  Maybe others here may know.  Good
> luck with it.
> >> 73's Doug
> >> On Jul 18, 2016 12:52 PM, "Chris Waldrup"  wrote:
> >>
> >>> Hi Everyone,
> >>>
> >>> I have two Lucent RFTG boxes in my workshop. The XO is a loaner.
> >>> I'm curious if they will interface with each other or (most likely)
> >>> they are a different series as the interface connectors on each have
> >>> a different number of pins.
> >>> One is marked RFTG-u REF 0
> >>> The other is RFTGm-II-XO
> >>>
> >>> Thanks in advance.
> >>>
> >>> Chris
> >>> KD4PBJ
> >>>
> >>>
> >>> ___
> >>> 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.
> >>>
> >> ___
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> >>
> >
> >
> > --
> > Dave
> > manu...@artekmanuals.com
> > www.ArtekManuals.com
> >
> > ---
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>
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Re: [time-nuts] Leap second to be introduced at midnight UTC December 31 this year

[Hal Murray]

hol...@hotmail.com said:
> The Z3801A has it messed up...  it says the leap will occur on 30 Sep 2016
> (73 days).  The Z3801A has two different messages that report the leap
> day...  both are wrong.  

Which messages are you looking at?

There is a leap-pending flag in the T2 message.  I don't see it on yet.

ntpd has a hack filter to ignore it unless the month is June or December.  
That's leftover from 2008.  I looked in my old log files.  It didn't come on 
until July 28, late in the day UTC.


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Re: [time-nuts] How does sawtooth compensation work?

[Bob Camp]

Hi



> On Jul 19, 2016, at 7:41 PM, Michael  wrote:
> 
> Thanks Tom, Bob, and Mark (wrote my response to Tom first, but didn't hit 
> send)!
> 
> I've actually been collecting some *ancient* dual-frequency geodetic gear to 
> play with, some of which have external clock inputs (or should be hackable). 
> I've read a lot, but I wasn't sure what people were typically referring to on 
> this list. Thanks for the overview...that helps me connect the dots between 
> the time-nuts and survey/geodetic GPS worlds. 
> 
> For time-nut use, I don't see any harm in using post-processing for 
> evaluation/measurement of clocks. Won't get you something usable in 
> real-time, for sure, but if you're already collecting weeks of data, don't 
> see any harm in waiting for precise orbit and clock solutions to become 
> available for post processing. And it might tell me how far off you are in a 
> 24-hour PPP solution. Which I guess means you'd need to be very stable in the 
> <=24hr region.
> 
> Thinking out loud, I wonder how bad L1-only, post-processed, would be for 
> time-nuts use? Especially with a timing-grade antenna (e.g. the common 
> Trimble Bullet). Dual frequency is great when your receiver has the potential 
> to move, you have to resolve carrier phase ambiguity quickly, or you don't 
> have a reference station (CORS) nearby. (O.T. I was out hiking in Washington 
> state recently, and *accidentally* happened upon my local CORS station, so I 
> guess that's no issue for me :-)). But for many time-nuts, I wonder how badly 
> a timing-grade antenna, something with raw carrier phase output (which you 
> get very cheaply these days), and a stable enough local clock to allow you 
> average out local weather.
> 

The post process “quality” on L1 only depends a *lot* on just how close you are 
to a reference station. The ionospheric data is only just so good. The local 
reference with view of exactly the same sats at exactly the same time is what 
puts the finishing touch on things.

The other issue is “lanes” in carrier phase / code phase. Unless you have a 
very well surveyed location, it can be difficult to determine carrier phase 
directly with L1 only. You fall back to code phase, but that also repeats every 
so often (lanes). 

Bob

> I guess while it's fascinating to me...wonder if it has any use in practice 
> compared to a simple, autonomous, real-time, L1-only receiver? I mean, I'm 
> interested in measuring my local tropospheric and ionospheric delays. But 
> then again, I am an aspiring time-(and maybe GPS)-nut :).
> 
> Michael 
> 
>> Hi Michael,
>> 
>> About #3 below...
>> 
>> There are dozens of technical papers about all this in the PTTI, FCS, UFFC, 
>> EFTF journals. Google for words like: GPS carrier-phase dual-frequency 
>> time-transfer geodetic-receiver IGS precise point positioning PPP
>> 
>> I don't have a link to a handy 1-page summary, but someone else on the list 
>> might. Otherwise skim the first ten papers you find and you'll pick up the 
>> concepts of high-precision time transfer.
>> 
>> The basic idea is that high-end geodetic-grade receivers often have an 
>> external 10 or 20 MHz clock input (and maybe no internal clock at all). You 
>> give it your best lab clock and all then all GPS signal processing and SV 
>> measurements are based on your fancy clock. The output of the receiver is a 
>> stream of these measurements, not necessarily a physical 1PPS or 10 MHz (as 
>> with a GPSDO).
>> 
>> So you can see there's no such thing as sawtooth error here, because you're 
>> not transferring some internal clock to some external clock via a TIC; there 
>> is only the one clock; your clock.
>> 
>> All this measurement data is then post-processed, hours or days later, so 
>> that some of the learned errors in the GPS system can be backed out. This 
>> would include SV clock and orbit errors, as well as tropo/ionospheric 
>> errors. The goal in cases like this are to find out how good your lab clock 
>> is (was), not so much to steer anything in realtime.
>> 
>> These receivers also tend to measure GHz carrier phase instead of (or in 
>> addition to) MHz code phase. And they often capture both L1 (1575.42 MHz) 
>> and L2 (1227.60 MHz) instead of L1, which not only doubles the effective 
>> number of SV received, but also is used to help compensate for 
>> speed-of-light variations through the ionosphere. With all this attention to 
>> precision, you then sometimes enter the realm of fancy temperature 
>> controlled antennas and special RF cables, maybe even temperature controlled 
>> receivers. It's all a very slippery slope.
>> 
>> /tvb
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[time-nuts] Leap second to be introduced at midnight UTC December 31 this year

[Mark Sims]

The GPS satellites are now reporting the pending leapsecond...

The Z3801A has it messed up...  it says the leap will occur on 30 Sep 2016 (73 
days).  The Z3801A has two different messages that report the leap day...  both 
are wrong. 
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Re: [time-nuts] How does sawtooth compensation work?

[Michael]

Thanks Tom, Bob, and Mark (wrote my response to Tom first, but didn't hit send)!

I've actually been collecting some *ancient* dual-frequency geodetic gear to 
play with, some of which have external clock inputs (or should be hackable). 
I've read a lot, but I wasn't sure what people were typically referring to on 
this list. Thanks for the overview...that helps me connect the dots between the 
time-nuts and survey/geodetic GPS worlds. 

For time-nut use, I don't see any harm in using post-processing for 
evaluation/measurement of clocks. Won't get you something usable in real-time, 
for sure, but if you're already collecting weeks of data, don't see any harm in 
waiting for precise orbit and clock solutions to become available for post 
processing. And it might tell me how far off you are in a 24-hour PPP solution. 
Which I guess means you'd need to be very stable in the <=24hr region.

Thinking out loud, I wonder how bad L1-only, post-processed, would be for 
time-nuts use? Especially with a timing-grade antenna (e.g. the common Trimble 
Bullet). Dual frequency is great when your receiver has the potential to move, 
you have to resolve carrier phase ambiguity quickly, or you don't have a 
reference station (CORS) nearby. (O.T. I was out hiking in Washington state 
recently, and *accidentally* happened upon my local CORS station, so I guess 
that's no issue for me :-)). But for many time-nuts, I wonder how badly a 
timing-grade antenna, something with raw carrier phase output (which you get 
very cheaply these days), and a stable enough local clock to allow you average 
out local weather.

I guess while it's fascinating to me...wonder if it has any use in practice 
compared to a simple, autonomous, real-time, L1-only receiver? I mean, I'm 
interested in measuring my local tropospheric and ionospheric delays. But then 
again, I am an aspiring time-(and maybe GPS)-nut :).

Michael 

> Hi Michael,
> 
> About #3 below...
> 
> There are dozens of technical papers about all this in the PTTI, FCS, UFFC, 
> EFTF journals. Google for words like: GPS carrier-phase dual-frequency 
> time-transfer geodetic-receiver IGS precise point positioning PPP
> 
> I don't have a link to a handy 1-page summary, but someone else on the list 
> might. Otherwise skim the first ten papers you find and you'll pick up the 
> concepts of high-precision time transfer.
> 
> The basic idea is that high-end geodetic-grade receivers often have an 
> external 10 or 20 MHz clock input (and maybe no internal clock at all). You 
> give it your best lab clock and all then all GPS signal processing and SV 
> measurements are based on your fancy clock. The output of the receiver is a 
> stream of these measurements, not necessarily a physical 1PPS or 10 MHz (as 
> with a GPSDO).
>
> So you can see there's no such thing as sawtooth error here, because you're 
> not transferring some internal clock to some external clock via a TIC; there 
> is only the one clock; your clock.
> 
> All this measurement data is then post-processed, hours or days later, so 
> that some of the learned errors in the GPS system can be backed out. This 
> would include SV clock and orbit errors, as well as tropo/ionospheric errors. 
> The goal in cases like this are to find out how good your lab clock is (was), 
> not so much to steer anything in realtime.
> 
> These receivers also tend to measure GHz carrier phase instead of (or in 
> addition to) MHz code phase. And they often capture both L1 (1575.42 MHz) and 
> L2 (1227.60 MHz) instead of L1, which not only doubles the effective number 
> of SV received, but also is used to help compensate for speed-of-light 
> variations through the ionosphere. With all this attention to precision, you 
> then sometimes enter the realm of fancy temperature controlled antennas and 
> special RF cables, maybe even temperature controlled receivers. It's all a 
> very slippery slope.
> 
> /tvb
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Re: [time-nuts] Allan Deviation recipe?

[Gary E. Miller]

Yo All!

I know my toys are 1,000x, or worse, then being in time-nut territory, but
you guys have been really helpful so far.  Bear with me just a bit more
as I am almost done.

Here is the part when my head hurst from too much data.

This is the ADEV/TDEV from a SiRF III on an octal Xeon serer:

https://rellim.com/graphs/adev.png

Here is an Adafruit GPS HAT on a Pi3:

https://pi2.rellim.com/adev.png

And now, the weirdest one, an identical Pi3 with an Uputronics GPS HAT.
ADEV and TDEV virtually overlap:

https://pi3.rellim.com/adev.png

The comparision of the last two is baffling to me.  Totally unexpected.

Semi raw data for all three is here:

https://rellim.com/graphs/
https://pi2.rellim.com/
https://pi3.rellim.com/

RGDS
GARY
---
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[time-nuts] How does sawtooth compensation work?

[Mark Sims]

Navspark has some affordable ($80) modules that do "raw" (carrier phase) 
output.Also RTK modules for $50 that can give you real-time centimeter 
accuracy and GPS derived attitude and bearing between two units.Alas, they 
don't seem to do L1/L2 or  accept an external clock.  They claim +/- 10 ns 
timing accuracy and also have a timing receiver that claims 6 ns.   At one time 
not too long ago carrier phase / RTK capabilities would set you back at least a 
couple of grand.

---

So far I have not seen one with the “right options” 
enabled for under $800.   
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Re: [time-nuts] GPS message jitter (was GPS for Nixie Clock)

[Gary E. Miller]

Yo Mark!

On Tue, 19 Jul 2016 21:29:24 +
Mark Sims  wrote:

> The NMEA sentences for sending date and time were very poorly thought
> out.  Several different sentences can contain the time (maybe the
> same time in different sentences with a group,  maybe each sentence
> has a different time).   Only the ZDA and RMC sentences have the
> date.  There is no sentence with unified time/date, position, and
> velocity info.

Yup, when you are talking NMEA.  There are a number of proprietary
binary messages that do.  Most of them are badly thought out in
different ways.

In practice, there is often no advantage to the binary over the NMEA
when gpsd is done with it.

RGDS
GARY
---
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Re: [time-nuts] Allan Deviation recipe?

[Gary E. Miller]

Yo Hal!

On Tue, 19 Jul 2016 14:28:32 -0700
Hal Murray  wrote:

> [You sent that to 3 lists that I'm on.  I'll reply here.

Yeah, but time-nuts is the one list that knows more about this than
I do.  So good choice.

> I think your X axis is off.  Your left edge is 1 second and you don't
> have data for that.  peerstats is every 64 seconds. (unless you
> mucked with maxpoll)  I'm guessing the software you used is assuming
> they are every second.  There may be a command line parameter.

I'm taking the time and offset from the /var/log/ntpstats/peerstats
file.  So the data is collected every minpoll (16 seconds), timestamped
in seconds with millisecond precision.  The offsets are also in seconds.

Should I set the left edge to 16 seconds?

> The normal ADEV is V shaped.  The left slope is noise in the
> readings.  The right slope is drift in the clock.  That assumes you
> have a good reference clock, where good means much better than the
> DUT.

Well, the data is the data.  I used Tom Van Baak's adev5 program
to do the calculations.  Given that the system is GPS stabilized
on PPS I can't see why the accuracy should not get better over long
durations.

> In this case, there is no long term drift since ntpd is tracking
> GPS.  You will probably get a traditional V if you disable ntpd.

Well, I'm trying to measure ntpd, so chicken and egg here.

> There is a slight step in the NMEA data at 1000 seconds and maybe a
> similar step in the PPS data at the right edge of the graph.  I don't
> know what that means.

At Tom's suggestion, I upped the sampling from Octaves to 50/decade.
I also added TDEV.  Now there is some structure in there.

https://rellim.com/graphs/adev.png

Some weird things in there...

RGDS
GARY
---
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[time-nuts] Motorla Oldie

[Pete Lancashire]

Saw this guy at GoodWill, but they wanted $25 for it so didn't get it.

Model: A11121Z115

http://petelancashire.com/gallery/main.php?g2_itemId=7196

http://petelancashire.com/gallery/main.php?g2_itemId=7200

-pete
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Re: [time-nuts] How does sawtooth compensation work?

[Bob Camp]

Hi

The only way to be sure on either the sawtooth or the cable delay is to 
try it and see. I have observed it being put in backwards (in both cases) 
more often than I have seen it put in the right way around. 

Bob

> On Jul 19, 2016, at 12:47 PM, Mark Sims  wrote:
> 
> While on the subject of antenna cable delay and sawtooth values,  I have only 
> seen Trimble document the sign of the value that you enter to compensate for 
> cable delays (for Trimble devices you enter a negative value).   Other 
> receivers may require a positive or negative value.  Also, some receivers 
> will not accept will not accept negative cable delay values and can only move 
> the PPS in one direction from nominal using their cable delay feature.
> 
> Also, I have never seen anybody document how the sign of their reported 
> sawtooth compensation value relates to the PPS edge.   For some receivers it 
> is the offset of the PPS edge from true time.  For others it is the delay you 
> need to apply to the edge to get it to true time.  
> 
> Asking the manufacturer about either value may or may not give the correct 
> answer.   The only way to know for sure is to test it...  and that requires 
> comparison to a known to be correct and very accurate PPS source...  
> 
> 
> 
> 
>> The systems that use 1PPS delay chips solve your worry with an at-power-on 
>> adjustment to the receiver's antenna delay parameter.
>>
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Re: [time-nuts] Allan Deviation recipe?

[Gary E. Miller]

Yo Tom!

On Tue, 19 Jul 2016 12:47:12 -0700
"Tom Van Baak"  wrote:

> > Check it out:
> > https://rellim.com/graphs/adev.png
> >
> > That is for a SiRF III (MR-350P) with a bad sky view.
> > How does that look?  Totally wrong?  Somewhat wrong?
> > Once I get this packaged up I'll have lots more similar graphs.  
> 
> Hi Gary,
> 
> Looking good. Not sure how artistically picky you are, but:

I'm picky enough to annoy others.  :-)

For the moment, I'm happy if the data is technically correct.
 
> - consider changing 'PPS' to '1PPS'

In NTP land they are synonymous.  I appreciate the vendors now talk
of 5PPS, but my audience is NTP.

> - consider changing 'GPS' to 'NMEA' (at least I think that's what you
> mean)

Well, in this case, it is actually SiRF Binary.  So maybe 'Serial', 
or 'GPS Serial'.

> - the y-axis title is partially cropped off the chart; center the
> plot to get the same amount of border as top, bottom, and right sides

I'm gonna make them the same sie as the other chrony-graphs.

> - for mobile or printed usage, the axis titles (powers of ten) font
> size is too small by maybe 2 or 3 points

Ditto, they'll be chrony-graph style.  Once they look that way I'll
see about getting the project style changed.

> - consider using a greater depth of adev5 points (e.g., 10 or 20 or
> 50 per decade) and skip the solid line; or just try both ways to see
> if one looks better

The lines are so straight, is there any data hiding in there?  Well,
surprise, there is!  

> Also try plotting TDEV instead.

That was next on my list.  Just done.  Those curves are more interesting,
just not sure what that means...

I gotta figure it out to explain it to the NTP folks.

> In a case like this an ADEV plot is
> somewhat boring or even misleading -- it's just a -1 slope going down
> forever. It's not quite what ADEV was meant for. The slope suggests
> you have a bounded amount of white phase noise and that's that.

Which pretty much what I expected.

> So,
> for example, the entire PPS red trace can thought of as 6e-4/tau. In
> other words, you can represent the performance of the receiver with a
> single rms number, instead of a featureless ADEV plot. Similarly the
> blue trace is essentially 0.6/tau.

That is what I love about plots, now it seems to obvious.  Execpt the new
bumps...

> The weird jump in the NMEA blue trace between tau 1000 and 2000
> should be investigated. Increasing the point density (using adev5) or
> eliminating the false line interpolation or using TDEV may help you
> look into this.

More points added.  Yeah, weird...

> The other thing, that Bob just alluded to, is that while your NMEA
> measurements are probably legit, your PPS measurements may be totally
> skewed by the fact that you're using a plain PC and its operating
> system (and NTP, and drivers, interrupts, BIOS, caches, etc.) as a
> measuring instrument. The actual 1PPS out of a typical GPS receiver
> is orders of magnitude more precise than the "tool" you're using to
> measure it.

Yeah, sorta backwards, but that is the data I got.  How to plot it
to show interesting things is what I'm working on.

> Therefore it's possible that the red trace is more a measurement of
> how bad your PC/NTP measurement setup is rather than a measurement of
> how good the 1PPS is. In other words, you have accidentally used 1PPS
> to measure the limits of your measurement system, rather than use
> your measurement system to measure the 1PPS. Does that make sense?

Yup, exactly, and sorta what I am trying to get to.  Given a good PPS,
how well is the ntpd working?  The point of PPS is to discipline the
NTP, and that is sorta what this shows.

It gets more interesting when using the PPS to be sure the system clock
is good, then using the system clock to measure other refclocks.  Like a
USB GPS compared to the PPS.  That will come in time.

The USB GPS results have surprised a lot of people, and solid proof
required to overcome disbelief.

NTP has some long standing questions on how to really model NTP time
served over real networks.  So using the system clock, disciplined by PPS,
will be a good place to measure that.

If I could get a real good PCI clock (that I could afford) then that
could be the reference for the PPS, ntpd, and/or system clock.

RGDS
GARY
---
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g...@rellim.com  Tel:+1 541 382 8588


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Re: [time-nuts] How does sawtooth compensation work?

[Bob Camp]

Hi

The reason people do not routinely jump to number 3 on the list is cost. The 
only 
new GPS modules that I am aware of in category 3 are well over $2K each. That 
is in comparison to Mark’s favorite $5 modules. You can buy eBay surplus older
versions of the fancy boards. So far I have not seen one with the “right 
options” 
enabled for under $800. 

There is another tangent and that is ionospheric correction. It is normally done
before you get to option 3. You run some combination of L1/L2/L5 to let the 
delta frequency enable a real time guesstimate of the ionospheric delay. The
cost for that part of it can be in the ~$300 for an older receiver. You also 
need
an L1/L2 antenna. Getting an accurate PPS in or out of a $300 receiver may 
range from
“exciting” to “impossible”. 

Lots of choices.

Bob


> On Jul 19, 2016, at 12:32 PM, Michael Gray  wrote:
> 
> Alright, may I vote for tangent #3? I've heard this mentioned in passing
> a few times on this list, but never seen it described in detail...so
> much so that I have no idea what it means.
> 
> Are we talking an external, steerable LO/clock (similar to #2, except
> for the location of the oscillator itself)? An external oscillator
> triggering a timestamp against the GPS's internal clock (seems identical
> to PPS error-wise, except you can introduce your own dither)? Something
> else? Why does carrier phase tracking matter, as long as the GPS is
> deriving a time solution through some mechanism that exceeds the
> granularity of its CPU clock?
> 
> Forgive my ignorance here, but I'd love to see more of this tangent,
> since I've never seen anyone jump into it in detail.
> 
> Michael
> 
>> There are some tangents we could go down:
>> 1) There are cases where the inherent dithering you get from sawtooth error 
>> is actually hugely beneficial to the design of a GPSDO.
>> 2) One GPSDO design (Trimble Thunderbolt) is unique in that is has no 
>> sawtooth problem or TIC or XO or TCXO at all. Instead it directly uses the 
>> high-quality OCXO as the receiver's LO. They get away with this clean 
>> solution because they are a company that makes their own receiver h/w.
>> 3) Carrier phase receivers with external clock input.
>> 
>> /tvb
> 
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[time-nuts] GPS message jitter (was GPS for Nixie Clock)

[Mark Sims]

A lot of GPS receivers either don't support the ZDA message, or turn it off by 
default.  And many (most?)  that do send it send the time with  millisecond 
resolution.

The NMEA sentences for sending date and time were very poorly thought out.  
Several different sentences can contain the time (maybe the same time in 
different sentences with a group,  maybe each sentence has a different time).   
Only the ZDA and RMC sentences have the date.  There is no sentence with 
unified time/date, position, and velocity info.

---

> So for a GPS or a timing unit on a NMEA-0183 bus, do they report their best
estimate of time to the nearest 10ms when the packet is sent? (since a PPS
line isn't shared)
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Re: [time-nuts] Allan Deviation recipe?

[Hal Murray]

[You sent that to 3 lists that I'm on.  I'll reply here.

I think your X axis is off.  Your left edge is 1 second and you don't have 
data for that.  peerstats is every 64 seconds. (unless you mucked with 
maxpoll)  I'm guessing the software you used is assuming they are every 
second.  There may be a command line parameter.

The normal ADEV is V shaped.  The left slope is noise in the readings.  The 
right slope is drift in the clock.  That assumes you have a good reference 
clock, where good means much better than the DUT.

In this case, there is no long term drift since ntpd is tracking GPS.  You 
will probably get a traditional V if you disable ntpd.  That will turn things 
inside out.  Your DUT will be good (GPS) and your reference clock (PC) will 
drift.

There is probably a simple way to do that but I can't think of it.  I would 
try adding noselect to all the servers and refclocks, and add a localclock if 
you want to monitor that box from other systems.

There is a slight step in the NMEA data at 1000 seconds and maybe a similar 
step in the PPS data at the right edge of the graph.  I don't know what that 
means.



-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Lucent boxes

[Richard W. Solomon]

Got it, many thanks. I have a pair of these, NIB, 
time to hook them up.

73, Dick, W1KSZ

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Artek Manuals
Sent: Tuesday, July 19, 2016 1:11 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Lucent boxes

Ahhh no  ...I have the MANUALS page book marked

try this one

http://www.ko4bb.com/getsimple/index.php?id=manuals



On 7/19/2016 2:49 PM, Richard W. Solomon wrote:
> This Home Page ??
>
> http://www.ko4bb.com/getsimple/index.php?id=index-1
>
> Don't see any search box there ???
>
> 73, Dick, w1KSZ
>
> -Original Message-
> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Artek 
> Manuals
> Sent: Tuesday, July 19, 2016 10:19 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Lucent boxes
>
> Dick
>
> Not rocket science ...go to KO4BB main page and enter "RFTGm"
>
> In the search box
>
> Dave
> NR1DX
>
> On 7/19/2016 12:42 PM, Richard W. Solomon wrote:
>> KO4BB's site is massive, can you pin down the cable drawing ?
>>
>> Tnx, Dick, W1KSZ
>>
>> -Original Message-
>> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of 
>> Douglas Baker
>> Sent: Monday, July 18, 2016 2:39 PM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] Lucent boxes
>>
>> Chris,
>> The RFTGm ("m" for miniature even though still a large box) is a later 
>> version of the RFTG line.  The XO unit houses the GPS receiver which is 
>> essential for disciplining.  Both boxes operate at 24 VDC and there is an 
>> interface cable drawing on line at KO4BB's web site. Never tried to hook 
>> them up together, but it might work.  Maybe others here may know.  Good luck 
>> with it.
>> 73's Doug
>> On Jul 18, 2016 12:52 PM, "Chris Waldrup"  wrote:
>>
>>> Hi Everyone,
>>>
>>> I have two Lucent RFTG boxes in my workshop. The XO is a loaner.
>>> I'm curious if they will interface with each other or (most likely) 
>>> they are a different series as the interface connectors on each have 
>>> a different number of pins.
>>> One is marked RFTG-u REF 0
>>> The other is RFTGm-II-XO
>>>
>>> Thanks in advance.
>>>
>>> Chris
>>> KD4PBJ
>>>
>>>
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>
>
> --
> Dave
> manu...@artekmanuals.com
> www.ArtekManuals.com
>
> ---
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www.ArtekManuals.com

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Re: [time-nuts] Lucent boxes

[Dave M]

It's under the MANUALS tab.

Dave M

Richard W. Solomon wrote:

This Home Page ??

http://www.ko4bb.com/getsimple/index.php?id=index-1

Don't see any search box there ???

73, Dick, w1KSZ

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of
Artek Manuals Sent: Tuesday, July 19, 2016 10:19 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Lucent boxes

Dick

Not rocket science ...go to KO4BB main page and enter "RFTGm"

In the search box

Dave
NR1DX

On 7/19/2016 12:42 PM, Richard W. Solomon wrote:

KO4BB's site is massive, can you pin down the cable drawing ?

Tnx, Dick, W1KSZ

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of
Douglas Baker
Sent: Monday, July 18, 2016 2:39 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Lucent boxes

Chris,
The RFTGm ("m" for miniature even though still a large box) is a
later version of the RFTG line.  The XO unit houses the GPS receiver
which is essential for disciplining.  Both boxes operate at 24 VDC
and there is an interface cable drawing on line at KO4BB's web site.
Never tried to hook them up together, but it might work.  Maybe
others here may know.  Good luck with it. 73's Doug
On Jul 18, 2016 12:52 PM, "Chris Waldrup"  wrote:



Hi Everyone,

I have two Lucent RFTG boxes in my workshop. The XO is a loaner.
I'm curious if they will interface with each other or (most likely)
they are a different series as the interface connectors on each have
a different number of pins.
One is marked RFTG-u REF 0
The other is RFTGm-II-XO

Thanks in advance.

Chris
KD4PBJ


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Dave M

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Re: [time-nuts] Lucent boxes

[Artek Manuals]

Ahhh no  ...I have the MANUALS page book marked

try this one

http://www.ko4bb.com/getsimple/index.php?id=manuals



On 7/19/2016 2:49 PM, Richard W. Solomon wrote:

This Home Page ??

http://www.ko4bb.com/getsimple/index.php?id=index-1

Don't see any search box there ???

73, Dick, w1KSZ

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Artek Manuals
Sent: Tuesday, July 19, 2016 10:19 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Lucent boxes

Dick

Not rocket science ...go to KO4BB main page and enter "RFTGm"

In the search box

Dave
NR1DX

On 7/19/2016 12:42 PM, Richard W. Solomon wrote:

KO4BB's site is massive, can you pin down the cable drawing ?

Tnx, Dick, W1KSZ

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of
Douglas Baker
Sent: Monday, July 18, 2016 2:39 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Lucent boxes

Chris,
The RFTGm ("m" for miniature even though still a large box) is a later version 
of the RFTG line.  The XO unit houses the GPS receiver which is essential for 
disciplining.  Both boxes operate at 24 VDC and there is an interface cable drawing on 
line at KO4BB's web site. Never tried to hook them up together, but it might work.  Maybe 
others here may know.  Good luck with it.
73's Doug
On Jul 18, 2016 12:52 PM, "Chris Waldrup"  wrote:


Hi Everyone,

I have two Lucent RFTG boxes in my workshop. The XO is a loaner.
I'm curious if they will interface with each other or (most likely)
they are a different series as the interface connectors on each have
a different number of pins.
One is marked RFTG-u REF 0
The other is RFTGm-II-XO

Thanks in advance.

Chris
KD4PBJ


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manu...@artekmanuals.com
www.ArtekManuals.com

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Re: [time-nuts] Allan Deviation recipe?

[Tom Van Baak]

> Check it out:
> https://rellim.com/graphs/adev.png
>
> That is for a SiRF III (MR-350P) with a bad sky view.
> How does that look?  Totally wrong?  Somewhat wrong?
> Once I get this packaged up I'll have lots more similar graphs.

Hi Gary,

Looking good. Not sure how artistically picky you are, but:

- consider changing 'PPS' to '1PPS'
- consider changing 'GPS' to 'NMEA' (at least I think that's what you mean)
- the y-axis title is partially cropped off the chart; center the plot to get 
the same amount of border as top, bottom, and right sides
- for mobile or printed usage, the axis titles (powers of ten) font size is too 
small by maybe 2 or 3 points
- consider using a greater depth of adev5 points (e.g., 10 or 20 or 50 per 
decade) and skip the solid line; or just try both ways to see if one looks 
better

Also try plotting TDEV instead. In a case like this an ADEV plot is somewhat 
boring or even misleading -- it's just a -1 slope going down forever. It's not 
quite what ADEV was meant for. The slope suggests you have a bounded amount of 
white phase noise and that's that. So, for example, the entire PPS red trace 
can thought of as 6e-4/tau. In other words, you can represent the performance 
of the receiver with a single rms number, instead of a featureless ADEV plot. 
Similarly the blue trace is essentially 0.6/tau.

The weird jump in the NMEA blue trace between tau 1000 and 2000 should be 
investigated. Increasing the point density (using adev5) or eliminating the 
false line interpolation or using TDEV may help you look into this.

The other thing, that Bob just alluded to, is that while your NMEA measurements 
are probably legit, your PPS measurements may be totally skewed by the fact 
that you're using a plain PC and its operating system (and NTP, and drivers, 
interrupts, BIOS, caches, etc.) as a measuring instrument. The actual 1PPS out 
of a typical GPS receiver is orders of magnitude more precise than the "tool" 
you're using to measure it.

Therefore it's possible that the red trace is more a measurement of how bad 
your PC/NTP measurement setup is rather than a measurement of how good the 1PPS 
is. In other words, you have accidentally used 1PPS to measure the limits of 
your measurement system, rather than use your measurement system to measure the 
1PPS. Does that make sense?

Thanks,
/tvb

- Original Message - 
From: "Gary E. Miller" 
To: "Tom Van Baak" 
Cc: "Discussion of precise time and frequency measurement" 
Sent: Tuesday, July 19, 2016 11:42 AM
Subject: Re: [time-nuts] Allan Deviation recipe?

Yo All!

With help from Tom Van Baak and Bob Stewart, I have 6 weeks worth of
GPS Serial and PPS timing data in a nice ADEV chart.  I think.

Check it out:
 https://rellim.com/graphs/adev.png

That is for a SiRF III (MR-350P) with a bad sky view.

How does that look?  Totally wrong?  Somewhat wrong?

Once I get this packaged up I'll have lots more similar graphs.

RGDS
GARY
---
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
 g...@rellim.com  Tel:+1 541 382 8588

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Re: [time-nuts] Allan Deviation recipe?

[Bob Stewart]

I don't know what your data looks like of course, but to me it looks like you 
have a scaling problem.  At the very least, I would think you should be in the 
xE-9 at tau = 1 second.  Are you feeding it whole numbers of nanoseconds, but 
it's interpreting them as milliseconds or something like that?

Bob
 -
AE6RV.com

GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info

  From: Gary E. Miller 
 To: Tom Van Baak  
Cc: Discussion of precise time and frequency measurement 
 Sent: Tuesday, July 19, 2016 1:42 PM
 Subject: Re: [time-nuts] Allan Deviation recipe?
   
Yo All!

With help from Tom Van Baak and Bob Stewart, I have 6 weeks worth of
GPS Serial and PPS timing data in a nice ADEV chart.  I think.

Check it out:
    https://rellim.com/graphs/adev.png

That is for a SiRF III (MR-350P) with a bad sky view.

How does that look?  Totally wrong?  Somewhat wrong?

Once I get this packaged up I'll have lots more similar graphs.

RGDS
GARY
---
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
    g...@rellim.com  Tel:+1 541 382 8588
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Re: [time-nuts] Lucent boxes

[Richard W. Solomon]

This Home Page ??

http://www.ko4bb.com/getsimple/index.php?id=index-1

Don't see any search box there ???

73, Dick, w1KSZ

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Artek Manuals
Sent: Tuesday, July 19, 2016 10:19 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Lucent boxes

Dick

Not rocket science ...go to KO4BB main page and enter "RFTGm"

In the search box

Dave
NR1DX

On 7/19/2016 12:42 PM, Richard W. Solomon wrote:
> KO4BB's site is massive, can you pin down the cable drawing ?
>
> Tnx, Dick, W1KSZ
>
> -Original Message-
> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of 
> Douglas Baker
> Sent: Monday, July 18, 2016 2:39 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Lucent boxes
>
> Chris,
> The RFTGm ("m" for miniature even though still a large box) is a later 
> version of the RFTG line.  The XO unit houses the GPS receiver which is 
> essential for disciplining.  Both boxes operate at 24 VDC and there is an 
> interface cable drawing on line at KO4BB's web site. Never tried to hook them 
> up together, but it might work.  Maybe others here may know.  Good luck with 
> it.
> 73's Doug
> On Jul 18, 2016 12:52 PM, "Chris Waldrup"  wrote:
>
>> Hi Everyone,
>>
>> I have two Lucent RFTG boxes in my workshop. The XO is a loaner.
>> I'm curious if they will interface with each other or (most likely) 
>> they are a different series as the interface connectors on each have 
>> a different number of pins.
>> One is marked RFTG-u REF 0
>> The other is RFTGm-II-XO
>>
>> Thanks in advance.
>>
>> Chris
>> KD4PBJ
>>
>>
>> ___
>> 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.
>>
> ___
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> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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--
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manu...@artekmanuals.com
www.ArtekManuals.com

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Re: [time-nuts] GPS message jitter (was GPS for Nixie Clock)

[Scott Stobbe]

Very true. If your exchanging data for loose timing purposes (wall clock)
over a UART whether it is binary coded or ASCII coded is immaterial. You
will always introduce at least 1/16 of a bit time of jitter, if not one
full bit time, allowing the uart to sync to start bit edge.

In full honesty I have never read the official NMEA-0183 specification.
Just a sample from an unoffical NMEA0183.pdf

*ZDA Time & Date – UTC, Day, Month, Year and Local Time Zone*
*$--ZDA,hhmmss.ss,xx,xx,,xx,xx*hh*

So for a GPS or a timing unit on a NMEA-0183 bus, do they report their best
estimate of time to the nearest 10ms when the packet is sent? (since a PPS
line isn't shared)

On Tue, Jul 19, 2016 at 1:17 PM, Chris Albertson 
wrote:

> On Mon, Jul 18, 2016 at 10:44 AM, Scott Stobbe 
> wrote:
> > I am happy to hear you issue was resolved. What I meant to say is the
> > problem could also be mitigated using the UART's flow control, this could
> > be done by the original GPS designers or by an end user if the CTS line
> is
> > pined out.
>
> The original GPS designers where sending NMEA-0183 data out to devices
> that accept and use NMEA data.   GPS was not the first to work with
> NMEA.  Lots of other instruments also output NMEA.   I doubt they ever
> would have envisioned people using NMEA data for precision timing.
> Typically if you want to do precision timing you's use a GPS that
> outputs some binary data format.  NMEA-0183 does not have flow control
>
> --
>
> Chris Albertson
> Redondo Beach, California
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Re: [time-nuts] Allan Deviation recipe?

[Gary E. Miller]

Yo All!

With help from Tom Van Baak and Bob Stewart, I have 6 weeks worth of
GPS Serial and PPS timing data in a nice ADEV chart.  I think.

Check it out:
https://rellim.com/graphs/adev.png

That is for a SiRF III (MR-350P) with a bad sky view.

How does that look?  Totally wrong?  Somewhat wrong?

Once I get this packaged up I'll have lots more similar graphs.

RGDS
GARY
---
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
g...@rellim.com  Tel:+1 541 382 8588


pgpJW1ithaaXi.pgp
Description: OpenPGP digital signature
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Re: [time-nuts] How does sawtooth compensation work?

[Tom Van Baak]

Hi Michael,

About #3 below...

There are dozens of technical papers about all this in the PTTI, FCS, UFFC, 
EFTF journals. Google for words like: GPS carrier-phase dual-frequency 
time-transfer geodetic-receiver IGS precise point positioning PPP

I don't have a link to a handy 1-page summary, but someone else on the list 
might. Otherwise skim the first ten papers you find and you'll pick up the 
concepts of high-precision time transfer.

The basic idea is that high-end geodetic-grade receivers often have an external 
10 or 20 MHz clock input (and maybe no internal clock at all). You give it your 
best lab clock and all then all GPS signal processing and SV measurements are 
based on your fancy clock. The output of the receiver is a stream of these 
measurements, not necessarily a physical 1PPS or 10 MHz (as with a GPSDO).

So you can see there's no such thing as sawtooth error here, because you're not 
transferring some internal clock to some external clock via a TIC; there is 
only the one clock; your clock.

All this measurement data is then post-processed, hours or days later, so that 
some of the learned errors in the GPS system can be backed out. This would 
include SV clock and orbit errors, as well as tropo/ionospheric errors. The 
goal in cases like this are to find out how good your lab clock is (was), not 
so much to steer anything in realtime.

These receivers also tend to measure GHz carrier phase instead of (or in 
addition to) MHz code phase. And they often capture both L1 (1575.42 MHz) and 
L2 (1227.60 MHz) instead of L1, which not only doubles the effective number of 
SV received, but also is used to help compensate for speed-of-light variations 
through the ionosphere. With all this attention to precision, you then 
sometimes enter the realm of fancy temperature controlled antennas and special 
RF cables, maybe even temperature controlled receivers. It's all a very 
slippery slope.

/tvb

- Original Message - 
From: "Michael Gray" 
To: 
Sent: Tuesday, July 19, 2016 9:32 AM
Subject: Re: [time-nuts] How does sawtooth compensation work?


> Alright, may I vote for tangent #3? I've heard this mentioned in passing
> a few times on this list, but never seen it described in detail...so
> much so that I have no idea what it means.
> 
> Are we talking an external, steerable LO/clock (similar to #2, except
> for the location of the oscillator itself)? An external oscillator
> triggering a timestamp against the GPS's internal clock (seems identical
> to PPS error-wise, except you can introduce your own dither)? Something
> else? Why does carrier phase tracking matter, as long as the GPS is
> deriving a time solution through some mechanism that exceeds the
> granularity of its CPU clock?
> 
> Forgive my ignorance here, but I'd love to see more of this tangent,
> since I've never seen anyone jump into it in detail.
> 
> Michael
> 
>> There are some tangents we could go down:
>> 1) There are cases where the inherent dithering you get from sawtooth error 
>> is actually hugely beneficial to the design of a GPSDO.
>> 2) One GPSDO design (Trimble Thunderbolt) is unique in that is has no 
>> sawtooth problem or TIC or XO or TCXO at all. Instead it directly uses the 
>> high-quality OCXO as the receiver's LO. They get away with this clean 
>> solution because they are a company that makes their own receiver h/w.
>> 3) Carrier phase receivers with external clock input.
>>
>> /tvb
> 
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[time-nuts] GPS message jitter (preliminary results)

[Mark Sims]

I ran some tests on the message timing of some V.KEL gps receivers in both NMEA 
and binary mode.  These receivers are the cheapest ones I have (3 for $15 - 
$20, shipped).   They use a SIRF III chip and have an on-board ceramic patch 
antenna.  They performed amazingly well.  No problems tracking sats indoors in 
a very poor location.   Message jitter was less than 20 msecs peak-peak,  
standard deviation less than 2 milliseconds.   ADEVs at tau 1 after an 
overnight run in NMEA mode (hardware serial port) were in the 1E-7 range!
They also have a 1PPS signal on the connector so no need to go digging for a 
place to bodge on a wire like with some of the other cheap GPS modules out 
there.   

V.KEL also makes a Ublox based version of the module (around $22 for one)... 
mine reports that it has a Ublox 7 chip, though V.KEL's part number implies 
that it a Ublox 6.
  
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Re: [time-nuts] Lucent boxes

[Artek Manuals]

Dick

Not rocket science ...go to KO4BB main page and enter "RFTGm"

In the search box

Dave
NR1DX

On 7/19/2016 12:42 PM, Richard W. Solomon wrote:

KO4BB's site is massive, can you pin down the cable drawing ?

Tnx, Dick, W1KSZ

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Douglas Baker
Sent: Monday, July 18, 2016 2:39 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Lucent boxes

Chris,
The RFTGm ("m" for miniature even though still a large box) is a later version 
of the RFTG line.  The XO unit houses the GPS receiver which is essential for 
disciplining.  Both boxes operate at 24 VDC and there is an interface cable drawing on 
line at KO4BB's web site. Never tried to hook them up together, but it might work.  Maybe 
others here may know.  Good luck with it.
73's Doug
On Jul 18, 2016 12:52 PM, "Chris Waldrup"  wrote:


Hi Everyone,

I have two Lucent RFTG boxes in my workshop. The XO is a loaner.
I'm curious if they will interface with each other or (most likely)
they are a different series as the interface connectors on each have a
different number of pins.
One is marked RFTG-u REF 0
The other is RFTGm-II-XO

Thanks in advance.

Chris
KD4PBJ


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www.ArtekManuals.com

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Re: [time-nuts] GPS message jitter (was GPS for Nixie Clock)

[Chris Albertson]

On Mon, Jul 18, 2016 at 10:44 AM, Scott Stobbe  wrote:
> I am happy to hear you issue was resolved. What I meant to say is the
> problem could also be mitigated using the UART's flow control, this could
> be done by the original GPS designers or by an end user if the CTS line is
> pined out.

The original GPS designers where sending NMEA-0183 data out to devices
that accept and use NMEA data.   GPS was not the first to work with
NMEA.  Lots of other instruments also output NMEA.   I doubt they ever
would have envisioned people using NMEA data for precision timing.
Typically if you want to do precision timing you's use a GPS that
outputs some binary data format.  NMEA-0183 does not have flow control

-- 

Chris Albertson
Redondo Beach, California
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Re: [time-nuts] How does sawtooth compensation work?

[Michael Gray]

Alright, may I vote for tangent #3? I've heard this mentioned in passing
a few times on this list, but never seen it described in detail...so
much so that I have no idea what it means.

Are we talking an external, steerable LO/clock (similar to #2, except
for the location of the oscillator itself)? An external oscillator
triggering a timestamp against the GPS's internal clock (seems identical
to PPS error-wise, except you can introduce your own dither)? Something
else? Why does carrier phase tracking matter, as long as the GPS is
deriving a time solution through some mechanism that exceeds the
granularity of its CPU clock?

Forgive my ignorance here, but I'd love to see more of this tangent,
since I've never seen anyone jump into it in detail.

Michael

> There are some tangents we could go down:
> 1) There are cases where the inherent dithering you get from sawtooth error 
> is actually hugely beneficial to the design of a GPSDO.
> 2) One GPSDO design (Trimble Thunderbolt) is unique in that is has no 
> sawtooth problem or TIC or XO or TCXO at all. Instead it directly uses the 
> high-quality OCXO as the receiver's LO. They get away with this clean 
> solution because they are a company that makes their own receiver h/w.
> 3) Carrier phase receivers with external clock input.
>
> /tvb

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[time-nuts] How does sawtooth compensation work?

[Mark Sims]

While on the subject of antenna cable delay and sawtooth values,  I have only 
seen Trimble document the sign of the value that you enter to compensate for 
cable delays (for Trimble devices you enter a negative value).   Other 
receivers may require a positive or negative value.  Also, some receivers will 
not accept will not accept negative cable delay values and can only move the 
PPS in one direction from nominal using their cable delay feature.

Also, I have never seen anybody document how the sign of their reported 
sawtooth compensation value relates to the PPS edge.   For some receivers it is 
the offset of the PPS edge from true time.  For others it is the delay you need 
to apply to the edge to get it to true time.  

Asking the manufacturer about either value may or may not give the correct 
answer.   The only way to know for sure is to test it...  and that requires 
comparison to a known to be correct and very accurate PPS source...  




> The systems that use 1PPS delay chips solve your worry with an at-power-on 
> adjustment to the receiver's antenna delay parameter. 
>
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Re: [time-nuts] Lucent boxes

[Richard W. Solomon]

KO4BB's site is massive, can you pin down the cable drawing ?

Tnx, Dick, W1KSZ

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Douglas Baker
Sent: Monday, July 18, 2016 2:39 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Lucent boxes

Chris,
The RFTGm ("m" for miniature even though still a large box) is a later version 
of the RFTG line.  The XO unit houses the GPS receiver which is essential for 
disciplining.  Both boxes operate at 24 VDC and there is an interface cable 
drawing on line at KO4BB's web site. Never tried to hook them up together, but 
it might work.  Maybe others here may know.  Good luck with it.
73's Doug
On Jul 18, 2016 12:52 PM, "Chris Waldrup"  wrote:

> Hi Everyone,
>
> I have two Lucent RFTG boxes in my workshop. The XO is a loaner.
> I'm curious if they will interface with each other or (most likely) 
> they are a different series as the interface connectors on each have a 
> different number of pins.
> One is marked RFTG-u REF 0
> The other is RFTGm-II-XO
>
> Thanks in advance.
>
> Chris
> KD4PBJ
>
>
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Re: [time-nuts] How does sawtooth compensation work?

[Nick Sayer via time-nuts]

So now that I’ve said that out loud, I’ve gone back and taken a thousand points 
from log and plotted them in excel.



PastedGraphic-1.pdf
Description: Adobe PDF document



Looks a *lot* more like sawtooth than noise. Hmm. I might have to reconsider.


> On Jul 18, 2016, at 8:06 PM, Nick Sayer via time-nuts  
> wrote:
> 
> 
>> On Jul 18, 2016, at 3:55 PM, Hal Murray  wrote:
>> 
>>> The systems gravitate towards PLL time constants that average it all away. 
>> 
>> You are overlooking hanging bridges.
> 
> Yes, that’s true. Given the facilities I have available with the present 
> hardware, I don’t believe I have much choice. I am not confident that I could 
> tell the difference between noise in the phase detection system and PPS 
> jitter variations that small. If the PA6H receiver gave sawtooth corrections, 
> I’d be able to do better.
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Re: [time-nuts] GPS message jitter (was GPS for Nixie Clock)

[David]

On Tue, 19 Jul 2016 06:16:16 -0700, you wrote:

>On 7/18/16 9:44 PM, David wrote:
>> The aged 16550 has various timeouts so an interrupt is triggered with
>> a partially full buffer even if it is below the interrupt threshold.
>> For implementations which do not do that, I assume they intend for the
>> UART to be polled regularly.
>>
>exactly... you have some sort of blocking read that waits either for an 
>interrupt or for time to expire

Oh, from the application program interface?  Ya, that would be a
problem if it lacks a non-blocking read.  The UART itself has a status
flag which says if there is data available to be read but if you
cannot access that, then you have to wait for the UART's interrupt
timeout assuming it has one.

I seem to recall this issue coming up long ago in connection with
dodgy 16550 implementations where data was getting stuck below the
interrupt threshold but I never encountered it myself.  For the lower
level programming I have done, it was never an issue since I had
direct access to the hardware and could check the flags anytime I
wanted.
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Re: [time-nuts] GPS message jitter (was GPS for Nixie Clock)

[Martin Burnicki]

John Ackermann N8UR wrote:
> Long ago I measured the impact of the linux low_latency flag on a 16550 UART. 
>  I don't know where that data is sitting now, but I remember that it made a 
> significant difference.
>
>> On Jul 18, 2016, at 9:59 PM, Hal Murray  wrote:
>>
>>
>> jim...@earthlink.net said:
>>> except that virtually every UART in use today has some sort of buffering
>>> (whether a FIFO or double buffering) between the CPU interface and the  bits
>>> on the wire, which completely desynchronizes the bits on the wire  from the
>>> CPU interface.
>>
>> The idea was to reduce the CPU load processing interrupts by batching things 
>> up.
>>
>> Some of those chips generate an interrupt when the see a return or line-feed 
>> character.
>>
>> Most of them have an option to disable that batching.  On Linux the 
>> setserial 
>> command has a low_latency option.  I haven't measured the difference.  It 
>> would be a fun experiment.

AFAIK the low_latency flag just sets the UART's FIFO threshold to 1,
i.e. the UART generates an IRQ when the 1st character came in. If you
don't set this flag then the FIFO threshold is set to something different.

A *very* quick search on the Linux source code seems to indicate the
default threshold is 16 in current kernels, but if I remember correctly
then it was 4 or 8 in earlier kernel versions.

If you need to timestamp the 1st character of the serial time string
then things are easy. For example, for Meinberg time strings the
on-rtime character is the 1st character, STX (0x02), and subsequent
characters are sent without gap. So it doesn't matter much if you get an
IRQ after the 1st character, and compensate for 1 character only, or the
IRQ occurs after the 8th character, and you compensate for 8 characters.
But of course you need to know the current FIFO threshold.

I think if you need to timestamp e.g. the CR of LF at the end of a
string which eventually has even variable length then the timing may
vary depending on the actual string length.

E.g., with a FIFO threshold of 16 the first IRQ is generated when 16
characters have been received, but if the whole string is e.g. only 30
characters then only 14 characters follow after the first part, and the
FIFO threshold (16) is never reached by that single string. I'm not sure
if the UART then generates an IRQ anyway after some kind of timeout, but
this seems to make exact timing quite a bit more tricky.

Martin

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Re: [time-nuts] GPS message jitter (was GPS for Nixie Clock)

[jimlux]

On 7/18/16 9:44 PM, David wrote:

The aged 16550 has various timeouts so an interrupt is triggered with
a partially full buffer even if it is below the interrupt threshold.
For implementations which do not do that, I assume they intend for the
UART to be polled regularly.

exactly... you have some sort of blocking read that waits either for an 
interrupt or for time to expire



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Re: [time-nuts] Leap second to be introduced at midnight UTC December 31 this year

[Martin Burnicki]

Hal Murray wrote:
> 
> michael.c...@sfr.fr said:
>> The relevant NTP leap-seconds-list file can be downloaded with anonymous ftp
>> from the pub directory at time.nist.gov.  (The leap-seconds-list file is a
>> symbolic link to the data file leap-seconds.3676924800 in the same
>> directory. ) 
> 
> The NIST servers at that "host" don't work very well for FTP.  That host name 
> rotates across their NTP servers and a lot of those sites don't have a FTP 
> server on that machine.
> 
> Some of the sites work.
>   ftp://utcnist.colorado.edu/pub/
> 
> The IETF has a copy, but it hasn't been updated yet.
>   http://www.ietf.org/timezones/data/

No, because it's extracted from the TZ database. The leap second file in
the TZ DB is only updated when the next TZ DB version is released after
a new leap second file has been released.

Just recently a patch has been submitted for the TZ DB to update the
leap second file.

> USNO has a similar version:
>   ftp://tycho.usno.navy.mil/pub/ntp/
> Sometimes it doesn't work.  ??
> 
> Meinberg has a version:
>   http://www.meinberg.de/download/ntp/leap-seconds.list

which is a copy of the IERS file available at
https://hpiers.obspm.fr/iers/bul/bulc/ntp/

I've put some information on leap second files together in a PDF:
https://www.meinberg.de/download/burnicki/the_ntp_leap_second_file.pdf

BTW, some GPS satellites began recently to broadcast the leap second
information. The "mbgstatus" program for Meinberg PCI cards reports:

---
t0t: 1906|405504.000, A0: 0 A1: -1.77636e-15
WNlsf: 1929, DN: 7, offs: 17/18
UTC offset transition from 17s to 18s due to leap second
insertion at UTC midnight at the end of 2016-12-31.
---

Martin

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Re: [time-nuts] How does sawtooth compensation work?

[Tom Van Baak]

Bob,

> On the sub-set of receivers that send you the sawtooth correction *after* (as 
> in 200 ms after) the PPS

Right. The 1PPS delay line method is not compatible with these chips.

> If the sawtooth says the edge was late, you can never get it back to correct 
> (accurate). 

The systems that use 1PPS delay chips solve your worry with an at-power-on 
adjustment to the receiver's antenna delay parameter. 

So if you have a 256 ns 8-bit programmable silicon delay line, instead of 
telling your receiver that your antenna delay is X you tell it X - 128 ns. Then 
the delay chip acts like a -128 ns to +127 ns phase stepper instead of a 0 to 
255 ns phase stepper.

/tvb

- Original Message - 
From: "Bob Camp" 
To: "Discussion of precise time and frequency measurement" 
Sent: Tuesday, July 19, 2016 4:06 AM
Subject: Re: [time-nuts] How does sawtooth compensation work?


Hi

On the sub-set of receivers that send you the sawtooth correction *after* (as 
in 200 ms after) the PPS …. the delay 
line correction thing does not work very well. Also in a “strict time nuts” 
sense, you can only delay the edge. If the 
sawtooth says the edge was late, you can never get it back to correct 
(accurate). Not at all a big deal for a GPSDO. 
It is a big deal if you are looking for a “perfect tick” time wise.

Bob

> On Jul 18, 2016, at 11:28 PM, Mark Sims  wrote:
> 
> Or use the sawtooth compensation value  to control an external variable delay 
> line circuit to move around the PPS signal from the receiver.  This can get 
> interesting to implement if the receiver can output negative values for the 
> sawtooth compensation (hint: add a bias to  the sawtooth value to make the 
> compensation values always positive and adjust the antenna cable delay 
> command to remove the bias value that you add.  Oh, and for some receivers 
> you have to reverse the meaning of positive and negative sawtooth corrections 
> and/or cable delay values).  It is even more interesting if the receiver 
> outputs the sawtooth correction after the pulse it just generated... hint: 
> get a different GPS receiver).
> 
> 
>> A device that uses the sawtooth data shoves it into the control loop along 
>> with the measured early / late information on the PPS. 
> 
>  
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Re: [time-nuts] GPS message jitter (was GPS for Nixie Clock)

[John Ackermann N8UR]

Long ago I measured the impact of the linux low_latency flag on a 16550 UART.  
I don't know where that data is sitting now, but I remember that it made a 
significant difference.

> On Jul 18, 2016, at 9:59 PM, Hal Murray  wrote:
> 
> 
> jim...@earthlink.net said:
>> except that virtually every UART in use today has some sort of buffering
>> (whether a FIFO or double buffering) between the CPU interface and the  bits
>> on the wire, which completely desynchronizes the bits on the wire  from the
>> CPU interface.
> 
> The idea was to reduce the CPU load processing interrupts by batching things 
> up.
> 
> Some of those chips generate an interrupt when the see a return or line-feed 
> character.
> 
> Most of them have an option to disable that batching.  On Linux the setserial 
> command has a low_latency option.  I haven't measured the difference.  It 
> would be a fun experiment.
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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Re: [time-nuts] How does sawtooth compensation work?

[Bob Camp]

Hi

On the sub-set of receivers that send you the sawtooth correction *after* (as 
in 200 ms after) the PPS …. the delay 
line correction thing does not work very well. Also in a “strict time nuts” 
sense, you can only delay the edge. If the 
sawtooth says the edge was late, you can never get it back to correct 
(accurate). Not at all a big deal for a GPSDO. 
It is a big deal if you are looking for a “perfect tick” time wise.

Bob

> On Jul 18, 2016, at 11:28 PM, Mark Sims  wrote:
> 
> Or use the sawtooth compensation value  to control an external variable delay 
> line circuit to move around the PPS signal from the receiver.  This can get 
> interesting to implement if the receiver can output negative values for the 
> sawtooth compensation (hint: add a bias to  the sawtooth value to make the 
> compensation values always positive and adjust the antenna cable delay 
> command to remove the bias value that you add.  Oh, and for some receivers 
> you have to reverse the meaning of positive and negative sawtooth corrections 
> and/or cable delay values).  It is even more interesting if the receiver 
> outputs the sawtooth correction after the pulse it just generated... hint: 
> get a different GPS receiver).
> 
> 
>> A device that uses the sawtooth data shoves it into the control loop along 
>> with the measured early / late information on the PPS. 
> 
> 
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Re: [time-nuts] How does sawtooth compensation work?

[Tom Van Baak]

Mark,

I forgot to add -- see pages 12 to 19 of 
http://www.gpstime.com/files/PTTI/PTTI_2006.pdf where Rick uses a DS1020, 
especially page 16 where he compares both the traditional TIC-based sawtooth 
correction method with the [new] delay line method. The agreement is about 1 ns 
rms.

/tvb

- Original Message - 
From: "Tom Van Baak" 
To: "Discussion of precise time and frequency measurement" 
Sent: Monday, July 18, 2016 9:41 PM
Subject: Re: [time-nuts] How does sawtooth compensation work?


>> Or use the sawtooth compensation value  to control an external variable 
>> delay line circuit
> 
> Hi Mark,
> 
> Right, one example is https://datasheets.maximintegrated.com/en/ds/DS1020.pdf 
> or google for silicon delay line. Not sure they're in production still but 
> you can find them at the reseller sites.
> 
> This delay line idea came up in the early Oncore-VP era gps mailing list (pre 
> time-nuts) by someone who first explored sawtooth correction and "hanging 
> bridges"; and it's the method that Rick then chose for his CNS Clock product 
> line. See: http://cnssys.com and http://gpstime.com for details.
> 
> The advantage of the delay line method is that you don't need a nanosecond 
> TIC in the box; you correct for the sawtooth error live on the 1PPS. Very 
> simple and effective. The main GPS feed in my lab is a CNS Clock.
> 
> This disadvantage is that if you already have a TIC connected to your 
> GPS/1PPS, there's not much point in pre-sawtooth correcting with a delay 
> line. The error is something that you're going to correct with arithmetic 
> anyway so there's no need to correct it in pulse phase. Rick's TAC32 software 
> (that many time nuts use) handles integration of serial TIC data (such as hp 
> 53132) along with GPS binary data to provide sawtooth corrected measurements. 
> Several of Rick's papers at the above sites explain this in fine detail.
> 
> /tvb
> 
> 
> - Original Message - 
> From: "Mark Sims" 
> To: 
> Sent: Monday, July 18, 2016 8:28 PM
> Subject: [time-nuts] How does sawtooth compensation work?
> 
> 
>> Or use the sawtooth compensation value  to control an external variable 
>> delay line circuit to move around the PPS signal from the receiver.  This 
>> can get interesting to implement if the receiver can output negative values 
>> for the sawtooth compensation (hint: add a bias to  the sawtooth value to 
>> make the compensation values always positive and adjust the antenna cable 
>> delay command to remove the bias value that you add.  Oh, and for some 
>> receivers you have to reverse the meaning of positive and negative sawtooth 
>> corrections and/or cable delay values).  It is even more interesting if the 
>> receiver outputs the sawtooth correction after the pulse it just 
>> generated... hint: get a different GPS receiver).
>> 
>> 
>>> A device that uses the sawtooth data shoves it into the control loop along 
>>> with the measured early / late information on the PPS. 
>> 
> 

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Re: [time-nuts] GPS message jitter (was GPS for Nixie Clock)

[David J Taylor]

From: Scott Stobbe

I am happy to hear you issue was resolved. What I meant to say is the
problem could also be mitigated using the UART's flow control, this could
be done by the original GPS designers or by an end user if the CTS line is
pined out. Gating the UART with a conservative delay, say 500 ms from the
time mark or PPS signal. The serial string would just sit in the transmit
buffer until the fixed delay expires and the UART starts transmitting.
==

It was a Garmin problem, and they released updated firmware after some 
badgering.


Again, it's nothing to do with serial communication, but CPU loading.

Many GPS devices can only just send the default information at default speed 
(typically 4800/9600), so the UART would need quite a lot of buffering for 
such a scheme to work.  For any serious use, the PPS line is the way to go.


Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk
Twitter: @gm8arv 


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[time-nuts] Trimble 63090/73090/65256

[Mark Sims]

I think they are all pretty much the same unit.   I don't know if any of the 
oscillator models is any better.  I assume they are all equivalent and actual 
performance (like any OCXO) is luck of the draw.  

Those boards run on 6VDC.  The Trimble units use a 5V oscillator (which lots of 
places that remove and re-sell them say are 12VDC devices...  surprise, 
surprise, surprise.   The equivalent Symmetricom boards use a 12V oscillator 
and a DC-DC converter to run them off of 6V.



  
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[time-nuts] How does sawtooth compensation work?

[Mark Sims]

The Tektronix TM509/5009 (and I think the 5010) counter modules have a National 
Semiconductor noise generator chip in them.  It injects noise into the counter 
to get around counter oscillator/input frequency synchronization.  I was once 
given a TM509 with a bad noise generator chip...   Some Very Smart People spent 
ages thinking the problem was in the device they were working on until they 
tried a different counter.  The Very Smart People (too smart to RTFM)  could 
never figure out why the counter was flakey and finally tossed it.  A little 
dumpster diving a few minutes with a scope yielded a very nice little counter.


> Universal timer/counters and equivalent time sampling DSOs can have
this problem when their timebase ends up synchronized with the signal
they are measuring.   
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