Re: ZED-F9P and PPP processing

[John Ackermann N8UR]

Gerry, I'd love to learn more about this.  I'm not sure if from what
you're saying there is/was a better approach, or if what we got wasn't
what it could have been.

Thanks!
John
----

On 5/5/20 6:04 PM, Gerry Creager - NOAA Affiliate wrote:
> We might need to talk about the geodetic mode of the Z-12 and NetRS. I
> used Trimble and Ashtech a lot (and I still have a Z-12, as well). L1
> code was better-resolved in position and timing using L2 carrier phase.
> The correlation between L1C/A and L2P(Y) wasn't ever good enough to
> allow high precision resolution involving simple code-phase solutions.
> Had an L2C been implemented in the clear, with the higher chipping rate,
> that would have been a good thing. Even if you'd had access to P(Y),
> there was no benefit in looking at L1C/A after it initialized the
> position for L2P(Y).
> 
> gerry
> 
> On Tue, May 5, 2020 at 7:59 PM John Ackermann N8UR <address@hidden
> <mailto:address@hidden>> wrote:
> 
>     On 5/5/20 3:37 PM, Gary E. Miller wrote:
> 
>     >> See, those ancient Z-12s and (slightly less ancient) NetRS units have
>     >> their value.  I still have a couple of working Z12s but mainly
>     use the
>     >> NetRS as my "real" reference these days.
>     >
>     > The security clearance you need for P(Y) also helps.
> 
>     No, Ashtech and then others figured out how to correlate to the
>     encrypted military code and extract code phase without decrypting it, so
>     no key needed.  The results probably aren't quite as good as working
>     with the raw code, but it gets down into the single-mm range for RTK and
>     PPP.
> 
>     That's what Ashtech called its "Z" technology that gave the Z-12 its
>     name.  Trimble and I'm sure others have their own variation on that
>     theme.
> 
>     The Trimble NetRS can be a nice eBay catch for a few hundred bucks if
>     you're lucky.  It's fairly small and has ethernet (in addition to four
>     RS-232 ports).  It runs Linux so is hackable.  The primary interface is
>     via web browser so it's easy to remote.  The downside is that it's GPS
>     only and does not support L2C, so when the old L2 P code goes away as it
>     may do someday, it could be out of luck.
> 
>     Another big advantage, for me, of the Ashtech and NetRS is that they
>     support an external 10 MHz reference signal input.  With that, your PPP
>     results give you a timing record you can use to compare your local clock
>     stability and accuracy to the GPS constellation.  So I feed my local
>     cesium standard into it and get a running record of local vs GPS
>     frequency.
> 
>     [ But conversely, for a time-nut the "PPS" output on both the Ashtech
>     and the Trimble are horrible; they're intended for time-tagging photos
>     and not precise time interval.  They are worse than the PPS output on a
>     plain GPS. ]
> 
>     > I hope you write this up nicely for others to learn with less pain.
> 
>     There are a number of things in the works to document what I've been
>     learning.  Part is in conjunction with the "HamSci" citizen science
>     project to build a "Personal Space Weather Station" that will include
>     GPS (probably F9T) both for timing and to allow the scientists to gather
>     ionospheric data like Total Electron Count.
> 
>     John
> 
> 
> 
> 
> 
> -- 
> Gerry Creager
> NSSL/CIMMS
> 405.325.6371
> ++++++++++++++++++++++
> /The way to get started is to quit talking and begin doing./
> /   Walt Disney/