[time-nuts] Digital Mixing with a BeagleBone Black and D Flip Flop

Simon Marsh subscriptions at burble.com
Wed Oct 15 03:40:40 EDT 2014


Thanks Tom, though I'm less sure about competence and persistence as 
opposed to ignorance and naivity

This started as an exercise to see if the approach could be done (more 
or less) in software. It can, and the results are promising enough to 
continue working on it. Even with my hacked together breadboard, I get 
sub-ns resolution and can easily measure the lengths of wire that I'm 
using in under a second. Whilst 'sub-ns' isn't perhaps quite time nut 
standard yet and doesn't sound great against the theoretical ps/fs 
resolution, it is significantly better than can be achieved using, say, 
just the BBB counters on their own. It's not a bad improvement for the 
simple addition of an external flip flop.

As a taster, attached is a current ADEV plot for a TCXO, neatly showing 
that I still have work to do for tau < 1s.

Cheers


Simon


On 15/10/2014 00:52, Magnus Danielson wrote:
> Tom,
>
> I think I wrote some VHDL code for a project like this... if I should 
> dig it out again?
>
> Cheers,
> Magnus
>
> On 10/14/2014 11:19 PM, Tom Van Baak wrote:
>> Hi Simon,
>>
>> Some additional info. I first heard about the D-FF method of 
>> frequency comparison in the late 90's (from Rick Hambly, I think) on 
>> the old gps mailing list. It sounded really interesting. Since then, 
>> the subject has turned up every few years on this list. But each 
>> time, the topic seems to go away quietly with little or no data, 
>> plots or explanation. In addition, none of the commercial products 
>> I've taken apart appear to use this approach. Hmm. So that begs the 
>> question -- what's really going on, and why.
>>
>> I'm enjoying this thread because you've shown both technical 
>> competence and optimistic persistence. Perhaps once and for all, with 
>> your efforts, we can settle this matter. You will either find a 
>> working combination with excellent performance, or you will uncover 
>> enough uncontrolled variables that you never want to try it again. 
>> Either way, we all learn a lot. Keep the photos, data, and plots coming.
>>
>> Thanks,
>> /tvb
>>
>> ----- Original Message -----
>> From: "Simon Marsh" <subscriptions at burble.com>
>> To: <time-nuts at febo.com>
>> Sent: Tuesday, October 14, 2014 9:34 AM
>> Subject: Re: [time-nuts] Digital Mixing with a BeagleBone Black and D 
>> Flip Flop
>>
>>
>>> Yes, I do understand I'm asking for trouble, though I kinda expected to
>>> see more noise rather than less.
>>> I guess its time to break out the soldering iron.
>>>
>>> Cheers
>>>
>>>
>>> Simon
>>
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