In that case, have you taken the time to look at the math of the sawtooth vs
measured phase? If you like, you can send me 20 or 30 sequential data samples
that contains what appears to be good as well as the bad to look at? And which
receiver are you using for this?
Bob -----------------------------------------------------------------
AE6RV.com
GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info
From: Nick Sayer via time-nuts <[email protected]>
To:
Cc: Discussion of precise time and frequency measurement <[email protected]>
Sent: Wednesday, October 5, 2016 6:57 PM
Subject: Re: [time-nuts] ADC sample voting algorithm?
> On Oct 5, 2016, at 4:52 PM, Bob Stewart <[email protected]> wrote:
>
> Hi Nick,
>
> Are you applying sawtooth correction to your phase measurement?
Yes, these are post-correction observations. I have some confidence that my
corrections are scaled appropriately for the ADC values because of their
stability “most” of the time (meanwhile, the uncorrected values are bouncing
around inside a 12 ns corridor).
> If not, are you merely seeing a hanging bridge that dissolves into at a
> normal sort of tick-tock movement?
>
> Bob
>
> From: Nick Sayer via time-nuts <[email protected]>
> To: Discussion of precise time and frequency measurement <[email protected]>
> Sent: Wednesday, October 5, 2016 6:45 PM
> Subject: [time-nuts] ADC sample voting algorithm?
>
> This is tangentially on topic, I suppose. It’s for my GPSDO.
>
> I notice periodically that the phase measurements seem “noisy.” You can see
> that over the course of several seconds the value doesn’t change, then it
> jumps a bunch and then comes right back.
>
> My theory at the moment is that sampling the ADC multiple times in a row
> might help, but then what’s the best way to (quickly) pick which sample to
> use?
>
> The mean would allow a bad sample undue influence.
>
> At the moment, I’ve coded taking 3 samples, averaging them and picking the
> sample that is closest to the mean. If I’m right, and two of the samples
> happen to be very close to each other and a third is an outlier, then that
> seems like it would eliminate it.
>
> I guess what I want is the mode, but with 3 samples, that’s going to be
> poorly defined (if at all).
>
> Anyone have any suggestions (besides a larger sample size)?
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