[time-nuts] ADEV query Timelab and TICc

ed briggs edbriggs at outlook.com
Mon Mar 20 12:18:10 EDT 2017

The 1 PPS signal is derived from an 81 MHz clock (12 ns) on the GPS chip according to the  Skytraq manual.  So that would mean n * 12ns.
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Today's Topics:

   1. Re: ADEV query Timelab and TICC (Orin Eman)
   2. ADEV query Timelab and TICC (Mark Sims)
   3. Re: ADEV query Timelab and TICC (GandalfG8 at aol.com)
   4. Re: ADEV query Timelab and TICC (Dave Martindale)


Message: 1
Date: Sun, 19 Mar 2017 22:09:57 -0700
From: Orin Eman <orin.eman at gmail.com>
To: Tom Van Baak <tvb at leapsecond.com>,  Discussion of precise time and
        frequency measurement <time-nuts at febo.com>
Subject: Re: [time-nuts] ADEV query Timelab and TICC
        <CAPjY7U9JrUkbfZ=Qy-Wtna9S+=kruW0xyjj8+4LaeGb_B6uOeA at mail.gmail.com>
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On Sun, Mar 19, 2017 at 8:03 PM, Tom Van Baak <tvb at leapsecond.com> wrote:

> Thanks for the raw data. It's very nice (2 hours 16 minutes = 8219
> points). Everything looks fine with the exception of 8 glitches. These are
> sometimes obvious jumps in phase, which cause massive spikes in frequency.
> Two plots attached.

First, thanks to Tom for taking a look at these files.

> Almost every data point is within a few ns of each other. This is good.
> The standard deviation is a fraction of 1 ns. But once in a while there is
> a relatively massive phase jump. This is bad. Interestingly these 8 phase
> jumps all appear to be about 25 ns or a multiple of 25 ns in magnitude. The
> full list is (ns units):
> 24.575
> 24.724
> 24.831
> 25.047
> 25.087
> 25.549
> 25.589
> 49.623
> 25 * N ns is not random. So I think this is not a Windows problem, not a
> USB problem, not a TimeLab problem, not a TICC problem either.

Personally, I didn't think it was any of the the above either.  The PicDiv
trace showed no such glitches, so I was fairly confident that the TICC was
working well.  But just to verify that, I connected the LTE-Lite PPS to the
5370A and let it run for a few hours.  The 5370A captures similar
glitches.  I have sent the file on to Tom.

For entertainment value, I have attached the current Lady Heather
screenshot for the LTE-Lite.  It has little relationship to the .tim files
I sent to Tom since I generated those a few weeks ago.  FWIW, it shows an
off by two error writing some text, for example: "PDTDT".  This seems to
happen if you go to some other screen (I think it was help in this case)
then returning.


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Message: 2
Date: Mon, 20 Mar 2017 06:35:35 +0000
From: Mark Sims <holrum at hotmail.com>
To: "time-nuts at febo.com" <time-nuts at febo.com>
Subject: [time-nuts] ADEV query Timelab and TICC
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Yes,  programs like Timelab and Stable32 are definitely the way to go for post-processing and analyzing your data in depth.   Lady Heather is more of a real-time monitoring and data acquisition program.

The sensitivity of ADEV to data hiccups can be a good thing.  If your ADEV data goes to crap you know you have a problem and need to examine the data in more depth to find out why.   You can go in and remove / fixup the outliers to get a better understanding of the typical device performance  but leaving in the "zingers" tells you what the device is truly doing.


> And without preaching too much, this is why I recommend no one does statistical work (e.g., ADEV) without first looking at the raw phase and frequency data. A doubting Thomas attitude and the human eye are valuable tools in science. Both Stable32 and TimeLab make it easy to display phase and frequency, not just ADEV. This is not by accident.

Maybe we have hyped ADEV too much on this list. This rant is especially addressed at several LH and NTP authors who think analyzing clock data and making ADEV plots is just something you blindly code or script or automate, as if working with clock measurement data was as pure as mathematics.


Message: 3
Date: Mon, 20 Mar 2017 04:23:44 -0400
From: GandalfG8 at aol.com
To: time-nuts at febo.com
Subject: Re: [time-nuts] ADEV query Timelab and TICC
Message-ID: <77065e.182eb885.4600eb90 at aol.com>
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Many thanks for the replies on this, what was initially intended as a quick
 "Hello World" test seems to have become far more interesting:-)

I'll forward my results to Tom as requested and see where we go from  there.



Message: 4
Date: Mon, 20 Mar 2017 09:18:58 -0400
From: Dave Martindale <dave.martindale at gmail.com>
To: Discussion of precise time and frequency measurement
        <time-nuts at febo.com>
Subject: Re: [time-nuts] ADEV query Timelab and TICC
        <CAJU10StpMEDa_a+cmOydDWkBGOyWJYQKObo52HuR=VSCDkuHBQ at mail.gmail.com>
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The LTE-Lite User Manual (version 1.3) says:

2.3.7 1 PPS Module outputs
The LTE-Lite SMT Module provides GPS raw 1 PPS CMOS pulse on pin 15 with
sawtooth present, and a clean TCXO-generated, sawtooth-removed, UTC(GPS)
phase-locked 1PPS output on pin 4.

It is the pin 4 output that connects to the 1PPS-OUT jack on the eval
board.  So it is supposed to be cleanly divided down from the TCXO.  (But I
don't think Jackson Labs has published any of the circuitry on the LTE-Lite
module itself).

- Dave

On Mon, Mar 20, 2017 at 2:07 AM, Mark Sims <holrum at hotmail.com> wrote:

> It is also interesting that the LTE GPSDO 1PPS has such a wide range of
> TIE.   A Tbolt / Z38xx GPSDO typically has a TIE in the 1PPS signal of
> around 1 nsec.   The LTE TIE spans over 40 nanoseconds (not including the
> spikes).  It seems like the LTE 1PPS may be from the GPS and not derived
> from dividing down the disciplined oscillator output.
> _______________________________________________


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