[time-nuts] Re: 100 MHz Low Phase Noise Mobile GPSDO/GNSSDO?

[Lux, Jim]

On 4/19/22 2:53 AM, Markus Kleinhenz via time-nuts wrote:
> Hello Carsten,
>
> thats quite the set of requirements you got there.
>
> I believe you will have a hard time finding a COTS solution that fits
> most of your requirements.
>
> You will likely have to split your signal chain into multiple devices:
>
> 1. UBlox ZED-F9T based GPS-Receiver with 1PPS out
> 2. Something like a JacksonLabs RCM (a ULN Oscillator that locks to a
> externally provided 1PPS)
> 3. Distribution Unit
>
> So you can spread your requirements.
>
> Another big challenge will be the 1ns relative accuracy between multiple
> (moving!) devices. Without communication between devices this should not
> be possible.


I think that 1 ns might be achievable, if the receivers are in the same 
general area, so they see the same propagation, but perhaps not as an 
"off the shelf" device.

We are getting <1ns with post processing using GIPSYx in a weak signal 
environment with generally poor geometry from GNSS standpoint (we're 
going to be in GEO, above the constellation, so the signals we see are 
on the other side of Earth).

Yes, that's post processed so you can "fit" a kinematic model over a 
larger span of time that's on both sides of your observation.

Can you do that in real time, only looking backwards?  I suspect it 
depends on the motion dynamics and their predictability (whether by a 
priori knowledge, or constrained by laws of physics, and estimated by 
some filter).


This is sort of the boundary between knowledge (post process) and 
control (real-time).


I would venture that there are people doing precision UAV work that are 
either doing what you need, or working towards it.