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 <[email protected]>
To: Bob Stewart <[email protected]>; Discussion of precise time and frequency
measurement <[email protected]>
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 <[email protected]> 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 <[email protected]>
> To: Bob Stewart <[email protected]>; Discussion of precise time and frequency
> measurement <[email protected]>
> 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 <[email protected]> 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 <[email protected]>
>> To: Discussion of precise time and frequency measurement
>> <[email protected]>
>> 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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