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Re: [time-nuts] ADC sample voting algorithm?

Nick Sayer

Wed, Oct 5, 2016 11:57 PM

On Oct 5, 2016, at 4:52 PM, Bob Stewart bob@evoria.net 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 time-nuts@febo.com
To: Discussion of precise time and frequency measurement time-nuts@febo.com
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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> On Oct 5, 2016, at 4:52 PM, Bob Stewart <bob@evoria.net> 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 <time-nuts@febo.com> > To: Discussion of precise time and frequency measurement <time-nuts@febo.com> > 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)? > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com <mailto:time-nuts@febo.com> > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts <https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> > and follow the instructions there. > >

Bob Stewart

Thu, Oct 6, 2016 12:05 AM

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

  From: Nick Sayer via time-nuts <time-nuts@febo.com>

To:
Cc: Discussion of precise time and frequency measurement time-nuts@febo.com
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 bob@evoria.net wrote:

Hi Nick,

Are you applying sawtooth correction to your phase measurement?

If not, are you merely seeing a hanging bridge that dissolves into at a normal sort of tick-tock movement?

Bob

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.

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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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 <time-nuts@febo.com> To: Cc: Discussion of precise time and frequency measurement <time-nuts@febo.com> 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 <bob@evoria.net> 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 <time-nuts@febo.com> > To: Discussion of precise time and frequency measurement <time-nuts@febo.com> > 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)? > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com <mailto:time-nuts@febo.com> > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts <https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> > and follow the instructions there. > > _______________________________________________ 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.