[time-nuts] Re: 20210423: Introduction and Request for Spirent GSS4200 User Manual / Help

[Bob kb8tq]

Hi


> On Apr 25, 2021, at 9:31 AM, Lux, Jim <jim at luxfamily.com> wrote:
> 
> On 4/25/21 6:02 AM, Bob kb8tq wrote:
>> Hi
>> 
>> The thing that I find useful about a GPS simulator is it’s ability to calibrate the
>> time delay through a GPS based system. In the case of a GPSDO, there may be
>> things beyond the simple receiver delay that get into the mix. Getting the entire
>> offset “picture” all at once is nice thing. Yes, that’s a Time Nutty way to look at it…..
>> 
>> So far, I have not seen anybody extending this sort of calibration to the low cost
>> SDR based devices. Without digging into the specific device, I’m not sure how
>> well a “generic” calibration would do. Indeed, it might work quite well. Without
>> actually doing it … no way to tell.
>> 
>> So if anybody knows of the results of such an effort, I suspect it would be of
>> interest to folks here on the list.
>> 
>> Bob
> 
> 
> A double difference kind of relative measurement might be useful - compare two (or three) GNSS receivers.  Then the absolute timing of the test source isn't as important.

Well …. it is and it isn’t. If you are trying to get “UTC in the basement” (or even 
GPS time)  to a couple nanoseconds, then you do need to know absolute delays 
of a number of things. Is this a bit crazy? Of course it is :) 

Bob

> 
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