[time-nuts] Moving GPSDO

[Magnus Danielson]

Joe,

In T-mode, the location in X, Y and Z is assumed known so those values 
is used as constants in producing the T difference between a satellite 
and the GPSDO. As you now move your receiver from the original X, Y and 
Z those location errors will translate into time errors. The worst of 
this will the T-RAIM hopefully clip out, but for the remaining the 
errors might drive the receiver all over the place, and as it shifts 
around so will the frequency. It won't be a pretty picture.

What you should do, if you can, is to go out of T-mode into normal 
tracking. Choosing the speed-grade of your movement can be worth some 
effort. Far from all GPSDOs can do this, since they typically is 
intended for fixed locations.

Potentially can aiding by IMU help some, but very few GPSDOs come close 
to support it. When moving you have to consider other factors of a 
dynamic environment.

I know of only a handful of GPSDOs for dynamic platforms.

Cheers,
Magnus

On 10/17/2016 08:02 AM, Joseph Gray wrote:
> Bill,
>
> My question was more generally about any GPSDO, but it's good to know
> about the Motorola/Lucent.
>
> What about this scenario - the GPSDO has a fixed position on initial
> powerup, but then it is moved periodically or even continuously,
> without updating the GPS coordinates. The distance from the original
> coordinates could be anywhere from close by, to across the state.
> Periodically, a new survey could be run to keep things from getting
> too far out in left field.
>
> At some point, I'll have to do some field testing, but I wanted to get
> the list wisdom first.
>
> Joe Gray
> W5JG
>
>
> On Sun, Oct 16, 2016 at 11:08 PM, Bill Hawkins <bill.iaxs at pobox.com> wrote:
>> The Motorola receivers in Lucent gear won't output a time signal if they
>> don't have an initial survey.
>>
>> I make this assertion because the RFTG I had would not lock. The
>> Motorola bag of bits decodes to say there's no position fix because
>> enough satellites have not been acquired. Too bad I lived in a valley.
>>
>> Let us know how this turns out, starting from an initial survey.
>>
>> Bill Hawkins
>>
>> -----Original Message-----
>> From: Joseph Gray
>> Sent: Sunday, October 16, 2016 11:20 PM
>>
>> I'm curious to know how accurately a GPSDO will keep its 10 MHz output
>> while moving. No initial survey to set a position would be done. I don't
>> care about the UTC time.
>>
>> Joe Gray
>> W5JG
>>
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