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

Graham / KE9H timenut at austin.rr.com
Tue Nov 19 12:31:22 EST 2013


Stephan:

This sounds like some kind of antenna placement issue.

What is your Latitude?

Can you describe your antenna systems?

Best case: Antennas above all nearby reflecting objects/buildings/trees, 
clear
view of the sky for 360 degrees,

Worst case: Indoors, patch antenna on the window edge of a North facing 
window, so that
100 percent of all signals received are via reflections and multi-path, 
bouncing from
tall buildings in the area.

When there are signals received via reflection, and the receiver changes the
set of satellites it is using for the solution, you will see a time jump 
equal to
the apparent change in location of the receiver, for the different solution.

With heavy multi-path/reflections, antennas just a few cm apart will be 
looking
at different solutions, and will jump time/location at different times.

--- Graham / KE9H

==

On 11/19/2013 10:45 AM, Chris Albertson wrote:
> Two antennas near each other?   Could they interact under some conditions?
>
> Could you be seeing multi path in some satellite geometries?
>
>   Try spacing them apart or BETTER get a splitter and use only one antenna
> but take the second antenna an far away, I wonder if it is acting like a
> reflector or if the amplifier is radiating EMI.
>
>
> On Tue, Nov 19, 2013 at 6:01 AM, Azelio Boriani <azelio.boriani at screen.it>wrote:
>
>> One M12+ is the reference and the others are DUTs? Three times but in
>> one direction only for a 300ns total or what? The offset returned to
>> 0? Please, detail better what happened.
>>
>> On Tue, Nov 19, 2013 at 12:17 PM, Stephan Sandenbergh
>> <ssandenbergh at gmail.com> wrote:
>>> Hi,
>>>
>>> I've recently measured the 1PPS outputs of three Motorola M12+T GPS
>>> receivers using two HP53131A TICs. Antennas are located next to one
>> another.
>>> Now I notice the one M12+T has changed its time offset by 100ns three
>> times
>>> over the period of 48hrs. The jitter remains the same, only the offset
>> that
>>> changes.
>>>
>>> I'm currently having a re-run of the measurement. But, in meanwhile, has
>>> anyone seen this kind of behaviour? A firmware issue perhaps?
>>>
>>> Regards,
>>>
>>> Stephan.
>>> _______________________________________________
>>>



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