[time-nuts] Mentorship needed in learning about Allan Deviation and variation.

[Jim Harman]

Rather than using the hardware delay line, I suggest you add or subtract
(as appropriate) the sawtooth correction data directly to/from your time to
digital converter data. In the Ublox devices, the sawtooth should be
applied to the following pps pulse.

Also you might consider using the TI TDC7200 TDC chip. It has a resolution
of 55 psec and reads out directly in psec. I have built an Arduino-based
GPSDO using this, with good results.

On Tue, Nov 10, 2020 at 12:56 PM Bob kb8tq <kb8tq at n1k.org> wrote:

> Hi
>
> If you are handling the sawtooth correctly, you should see no hanging
> bridges
> at all. My guess is that the spikes are coming from a problem in the
> sawtooth
> correction “stuff”. With no correction, you *will* see a spike as is rolls
> over. With
> a correction error, you would also see a spike.
>
> Bob
>
> > On Nov 10, 2020, at 11:37 AM, Joe & Gisela Noci <jgnoci at gmail.com>
> wrote:
> >
> > Hi Bob,
> > Yes, I am - I use a Dallus digital delay line in series with the GPS 1pps
> > and program the delay line each second with the GPS delay estimate in the
> > GPS NAV message.
> > It works really well, jitter on the 1pps pulse is hugely reduced, but one
> > side effect is that those 'hanging bridges' can become severely extended
> in
> > time.
> > I can by pushbutton selection bypass the delay line, ie, no sawtooth
> > correction - since I do not have a reference frequency source, I cannot
> say
> > if it is better or worse.
> > However, the logged values output from the time-digital convertor still
> > shows the spikes either way- I still suspect the spikes are conversion
> > artifacts from digital noise in the box..
> > Being green on the science of this I packed to much 'stuff' into the
> > enclosure and there are DC-DC converters for power, Nucleo processor
> > running at 140MHz, a NEXTION touch screen LCD, which
> > I am discovering is very noisy, etc....It is difficult to target any
> > solution at the moment as I believe there are too many areas that are
> > marginal - I need to clean it up!
> > Joe
> >
> > On Tue, Nov 10, 2020 at 6:24 PM Bob kb8tq <kb8tq at n1k.org> wrote:
> >
> >> Hi
> >>
> >> Are you using sawtooth correction?
> >>
> >> Bob
> >>
> >>> On Nov 10, 2020, at 8:55 AM, Joe & Gisela Noci <jgnoci at gmail.com>
> wrote:
> >>>
> >>> Hi everyone,
> >>> Still playing with my GPSDO..The Rubidium source I was hoping to have
> the
> >>> loan off did not work out, so still in the dark. I have sort of
> convinced
> >>> myself to procure a reasonable 'proven' source, Rubidium or whatever,
> but
> >>> that
> >>> seems to be more easily decided than done..Or at least so if the money
> >>> available is not astronomical... Also complicated by the difficulties
> >>> getting the goods here to Namibia!
> >>>
> >>> Anyway, I am still unhappy with my analogue time-to-digital conversion
> -
> >> I
> >>> do see the odd spike in the logged data and have been unable to find
> why
> >> -
> >>> have applied lots of filtering of supplies, used a separate A/D
> >> convertor (
> >>> as opposed to the convertor internal to the STM Processor) with own dc
> >>> regulated supply, own clean A/D Reference voltage ( 1ppm device).
> etc...
> >>>
> >>> Does not mean implementing a digital method will get rid of the spikes,
> >> so
> >>> I am still chasing that till I understand, but to that end:
> >>> I found this device and am keen to get the dev kit and try it out :
> >>>
> >>
> https://www.sciosense.com/products/time-to-digital-converters/development-kit-for-as6500/
> >>>
> >>> Has anyone perhaps played with it? Would be interested to know more
> about
> >>> it if so..
> >>> Regards
> >>> Joe
> >>> V51JN / ZS6JGN
> >>>
> >>> On Wed, Oct 28, 2020 at 7:08 PM Alberto di Bene <dibene at usa.net>
> wrote:
> >>>
> >>>> On 2020-10-28 2:29, jimlux wrote:
> >>>>> I'm still agitating for alien deviation - Microsoft offers it as a
> >>>>> suggestion, but not Allan, so it must be true.
> >>>>
> >>>> :-):-):-)
> >>>>
> >>>> Thanks Tom and Jim for the explanations. All clear now.
> >>>>
> >>>> 73  Alberto  I2PHD
> >>>>
> >>>>
> >>>>
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-- 

--Jim Harman