[time-nuts] Strange 100ns jumps on Motorola M12+T

Bob Camp lists at rtty.us
Fri Nov 22 00:25:34 UTC 2013


Hi

To be clear - the idea of going to a non-100 ns multiple is a good one. You probably should avoid multiples of 1/10.24 MHz as well.

Bob

On Nov 21, 2013, at 8:00 AM, Azelio Boriani <azelio.boriani at screen.it> wrote:

> Yes, do not use tiny offsets, go to 1us: I use microseconds offsets to
> take PPSes measurements .
> 
> On Thu, Nov 21, 2013 at 1:34 PM, Bob Camp <lists at rtty.us> wrote:
>> Hi
>> 
>> The counter and offset generator both should be quite accurate at a 1 us offset. That’s large enough that you are outside the range of most GPS jumps. If you are going to move things around, you might as well move out to that vicinity.
>> 
>> Bob
>> 
>> On Nov 21, 2013, at 6:20 AM, Tom Van Baak <tvb at LeapSecond.com> wrote:
>> 
>>>> Below is a plot so you could see exactly what I measured. What is peculiar
>>>> is that the time jumps by exactly 100ns to 200ns. Almost as if the GPS
>>>> receiver decides to offset the time by twice the amount I set it to. Which
>>>> is why I initially thought it might be a firmware thing. I suppose
>>>> multipath is a good explanation, it is just odd that the time error is
>>>> exactly 100ns.
>>> 
>>> Hi Stephan,
>>> 
>>> A quick test you could perform is set the offset to 125 ns instead of 100 ns and see if the jumps still occur, still occur at 100 ns, or now occur at 125 ns.
>>> 
>>> Since you have three M12's offset the third one by 150 ns and see if it experiences jumps too.
>>> 
>>> Question -- are you using the external 10 MHz reference input or output for any of your 53131A counters?
>>> 
>>> /tvb
>>> 
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