[time-nuts] General questions about making measurements with time interval counter.

Bob Camp kb8tq at n1k.org
Thu Jan 12 09:27:10 EST 2017


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.  


> On Jan 12, 2017, at 4:36 AM, Dr. David Kirkby (Kirkby Microwave Ltd) <drkirkby at kirkbymicrowave.co.uk> wrote:
> On 12 January 2017 at 02:31, Bob Camp <kb8tq at n1k.org> wrote:
>> Hi
> Hi Bob
>> The most basic issue you are going to run into is that your counter is not
>> high enough
>> resolution / accuracy to give you meaningful data for time intervals under
>> a few hundred
>> seconds.
> Is that true if I'm not testing very high quality sources? There are
> significant differences observed between these two setups
> 1) START and STOP from distribution amplifier.
> 2) START from distribution amplifier. STOP from Stanford Research SR345 30
> MHz function generator set to produce 10 MHz.
> 1) ADEV plot at http://www.kirkbymicrowave.co.uk/time-stuff/ADEV.PNG
> where ADEV is about 5x poorer on the function generator at 100 seconds
> 2) MDEV plot at http://www.kirkbymicrowave.co.uk/time-stuff/MDEV.PNG
> where MDEV is about 5 x poorer on the function generator at 10 seconds.
> The raw data is in the same directory
> http://www.kirkbymicrowave.co.uk/time-stuff/ . I should have zipped that,
> as it is quite large
> I'm pretty sure the HP 83623A 20 GHz sweep generator will be a lot worst
> than either of those, as a simple check of the standard deviation on the
> display of the HP 5370B (no data collected from GPIB), showed much higher
> SD on the microwave sweeper than the function generator.
> I can see if I were testing masers, Cs source, and decent GPS receivers,
> what you say would be true. But is it true for lesser quality sources?
> Maybe testing lesser quality sources is not such a stupid idea, as the
> instrumentation is less of a limiting factor.
> I admit I did say in my original post SHORT/MEDIUM time scales, and I guess
> 10/100s is not short.
>> I would focus on improving on that part of things before I went off on a
>> major
>> “test everything” adventure.
> But is there any way without spending lots of cash? The following
> instruments are out of the question due to price
> * Keysight 53230A 350 MHz Universal Frequency Counter/Timer, 12 digits/s,
> 20 ps
> * John's Timepod
> A Stanford Research SR620 is not out of the question. I did have one
> before, but swapped it, along with a 4.2 GHz signal generator for an
> HP4391B impedance/material analyzer. The 5370B came along fairly cheap
> ($300), but I don't mind spending more on  a SR620. But will that gain me
> much? I know the single shot resolution is a bit better than the 5370B, but
> it does not appear to be a massive improvement, given they are 3~4 x the
> cost.on the used market.
> I also have many other contraiints, which limit what I can realistically
> achieve
> * Small lab in my garmage- opening door on lab will change temperature.
> * Single glazed window
> * Air con that is a standard unit designed for offices - not metrology
> labs.
> Simply collecting a lot of data that is resolution limited is
>> not a lot of fun …..
> Agreed. But am I doing that at > 10 seconds? Is the counter my limit on
> those two sets of data? I will collect some from the HP 83623A 20 GHz sweep
> generator later today, but that generates a lot of heat, and I'd rather let
> that warm up for a couple of hours before doing anything with that.
>> Bob
> You clearly have a lot of knowledge Bob. Can I learn anything useful with
> what I have, or am I wasting my time?
> Dave
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