Hi Bob,
OK, like Bugs Bunny, I'll venture out on the limb, cut the limb, and see
whether I fall or the tree falls:
Wouldn't it take 1801 samples to get 18 seconds at 100S tau? Maybe I didn't
state that properly, but I think you get my meaning. Also, I've never actually
taken the time to look at the formula or the code to see how the ADEV is
calculated. But doesn't it use a sliding boxcar type of calculation? Or is
that some other *DEV? My point is that for 1801 seconds, aren't there a lot
more than 18 samples put in the 100S bin? And I've probably stated that
incorrectly, too.
Bob
From: Bob Camp <kb...@n1k.org>
To: Bob Stewart <b...@evoria.net>; Discussion of precise time and frequency
measurement <time-nuts@febo.com>
Sent: Thursday, January 12, 2017 2:38 PM
Subject: Re: [time-nuts] General questions about making measurements with time
interval counter.
Hi
Keep in mind that when you do 1800 samples at 1 second, that data will only
meet the
100 sample requirement out to tau = 18 seconds. Past that you are in the “under
100 samples
region”.
Bob
> On Jan 12, 2017, at 2:32 PM, Bob Stewart <b...@evoria.net> wrote:
>
> Hi Bob,
> OK, thanks for explaining. When you and others use highly technical terms
> like "small number of samples" it's not always clear to me what you mean. =)
> Ten samples? That's not enough for anything. Normally I run at least 1800
> samples; at least if I plan to share them with someone.
>
> Bob -----------------------------------------------------------------
> AE6RV.com
>
> GFS GPSDO list:
> groups.yahoo.com/neo/groups/GFS-GPSDOs/info
>
> From: Bob Camp <kb...@n1k.org>
> To: Bob Stewart <b...@evoria.net>; Discussion of precise time and frequency
> measurement <time-nuts@febo.com>
> Sent: Thursday, January 12, 2017 1:03 PM
> Subject: Re: [time-nuts] General questions about making measurements with
> time interval counter.
>
> Hi
>
> It varies from 5370 to 5370. You see a lot of plots that run out to 10
> samples or less. Anything below 100 samples
> is risky in some senses.
>
> Bob
>
>> On Jan 12, 2017, at 12:25 PM, Bob Stewart <b...@evoria.net> wrote:
>>
>> Hi Bob,
>> OK, what's a small number of data points? Attached is a screencap of
>> captures for 25, 50, 75, 100, and 150 seconds. Yeah, at 25 seconds, the 1S
>> tau is up at 4.56E-11, but it falls pretty quickly. I will mention that
>> this particular 5370 is much better than my other one. So, maybe this one
>> is an exceptional example?
>>
>> Just for grins, I also included a screencap of the phase points.
>>
>> Bob -----------------------------------------------------------------
>> AE6RV.com
>>
>> GFS GPSDO list:
>> groups.yahoo.com/neo/groups/GFS-GPSDOs/info
>>
>> From: Bob Camp <kb...@n1k.org>
>> To: Bob Stewart <b...@evoria.net>; Discussion of precise time and frequency
>> measurement <time-nuts@febo.com>
>> Sent: Thursday, January 12, 2017 11:04 AM
>> Subject: Re: [time-nuts] General questions about making measurements with
>> time interval counter.
>>
>> Hi
>>
>> There is a big difference between RMS and single shot. Single shot, the 5370
>> is a very different beast.
>> That’s not a big deal when you have a few thousand readings and it all
>> averages down. Unfortunately
>> we all love to do runs with a very small number of points and then draw
>> conclusions from them. As the
>> sample size goes down, you no longer have a 2 to 4 x 10^-11 beast, it’s more
>> like 5X that.
>>
>> Bob
>>
>>
>>> On Jan 12, 2017, at 11:31 AM, Bob Stewart <b...@evoria.net> wrote:
>>>
>>> Hi Bob,
>>> Normally I see somewhere between 2E-11 and 4E-11 at 1S tau on my 5370A, as
>>> in the blue trace on the attached plot. Am I misunderstanding your
>>> meaning? Granted, I am clocking the 5370A with a GPSDO, but I believe I
>>> see about the same thing with the HP10811. This test was 1PPS vs 1PPS on
>>> two different units.
>>> The plot also has a test run by Tom, in orange, using his H Maser and a
>>> Timepod to show how poor the 5370 is compared to the Timepod below about
>>> 60S tau. These are essentially apples vs apples tests.
>>>
>>> Bob
>>>
>>>
>>>
>>>
>>> From: Bob Camp <kb...@n1k.org>
>>> To: Discussion of precise time and frequency measurement
>>> <time-nuts@febo.com>
>>> Sent: Thursday, January 12, 2017 8:27 AM
>>> Subject: Re: [time-nuts] General questions about making measurements with
>>> time interval counter.
>>>
>>> Hi
>>>
>>> There are a number of ways to improve the resolution (and accuracy) of your
>>> data without spending
>>> big piles of cash. They have been discussed here on the list many times
>>> over the last few years.
>>> What I’m suggesting is that you dig into that ahead of taking data. You
>>> will dive into it eventually as you
>>> look more and more at devices that are locked to some sort of stable
>>> reference internally.
>>>
>>> Ideally you would like a device with a floor 5X to 10X better than what you
>>> are measuring. For ADEV style
>>> data, the 5370 is a 1x10^-10 sort of device single shot (so 1x10^-9 is the
>>> limit at 10:1). With a lot of averaging
>>> (which is not something you do with ADEV) you can get about 5X better than
>>> that as a floor. In either case, it is getting in the way of any
>>> readings that are much below 1x10^-9 at one second. A low cost XO can hit
>>> that level of performance.
>>>
>>> Bob
>>>
>>>
>>> <ADEV.png>_______________________________________________
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>>
>>
>> <ADEVs.png><Phase.png>_______________________________________________
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>
>
>
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