Re: gpsrinex and Trimble

[John Ackermann N8UR]

The high-gain thing is interesting and I've wondered whether I could
have overload/IMD problems.  From what I've seen, I don't think so.

And regarding interaction, the second antenna is not powered on right
now, so I doubt that's it.

My results aren't uniformly horrible -- NRCan did my 24 hours of NetRS
data (taken simultaneously with the F9P data that is the subject of
these messages) with 0.07% rejected epochs and sigma(95%) of
0.006/0.011/0.020m for LLH (using the Rapid data set).


73,
John
----
On 5/5/20 6:37 PM, Gerry Creager - NOAA Affiliate wrote:
> Since you've got a reasonable antenna, the other elements in this, from
> a history of post-processing geodetic measurements, are proximity to the
> tower and height above ground. The zephyr appears to be an enclosed
> calibrated ground plane reflector, with a similarly calibrated
> preamplified patch antenna. Reasonable design, been in use for decades.
> A choke ring might mitigate multipath a little better (I used to
> question some of that contention with Gerry Mader, antenna geek
> extraordinaire at the National Geodetic Survey).
> 
> Trimble has always claimed to have advanced multipath mitigation but
> urban canyon geodesy taught me they had better marketing than factual
> content until you got to the choke ring antenna (Mader was right) but it
> was better for incident multipath from above and sides than from below.
> Your position above the roof suggests it's likely to see
> reflections from whatever is nearby and below. Ground planes also are
> prone to some knife-edge diffraction. Nearby trees will almost certainly
> be in the far field and likely not contributing to multipath so much as
> absorbing signal when they can. Of course, the tower is likely a
> multipath contributor. Still, getting sufficient data to derive
> cross-arm azimuth shouldn't be a big deal for dual-frequency resolved data.
> 
> The coax is likely not contributing to much beyond lower signal levels. 
> 
> One thing I recall is that Trimble liked high power preamps, They were
> working, back in the bad old days, with 45 dB preamps, and testing with
> 2 Trimble receivers and preamplified antennas side by side tended to
> cause ringing between the antennas! Based on published specs, I suspect
> they're still doing that. I doubt that's an issue here with a completely
> different manufacturer's antenna; Ashtech antennas didn't cause ringing
> when used in tests close to Trimble hardware.
> 
> For what it's worth, we did have a pair of antennas on a secure mount on
> the roof of the building where the geodesy lab was and collected L1 data
> for differential corrections, and L1/L2 RINEX to support CORS, and for
> local campaigns where we'd process against its long-term derived
> position (which was pretty bad vertically, and changed with each heavy
> rain). 
> 
> The work I did that led to the rewrite of NGS-58 was done with both
> Trimble and Ashtech receivers, and Trimble ground planes and Ashtech
> choke rings. 
> 
> gc
> 
> 
> On Tue, May 5, 2020 at 9:54 PM John Ackermann N8UR <address@hidden
> <mailto:address@hidden>> wrote:
> 
>     Hi Gerry --
> 
>     Good question.
> 
>     The antenna is engineered, I hope, to make the best of a mediocre
>     situation.  Unfortunately for this purpose (and UHF contesting), my
>     house is on a quite wooded lo with nearby tall trees in just about every
>     direction.
> 
>     The antenna is a Trimble Zephyr Geodetic.  To get a better sky view,
>     it's mounted on a very stiff (1/4 inch thick aluminum channel) side arm
>     that extends about 30 inches out from both sides of a Rohn 45G tower at
>     about 10 feet above the roof of the house.  There's only another 20 feet
>     of tower above that, and the antennas are pretty small, so while there
>     may be some twist in strong winds, I don't think it's very substantial.
> 
> 
>     The feedline is about 60 feet of LMR-400 going to a couple of HP
>     8-channel distribution amp/splitters, one with filters removed so it's
>     not limited to L1.
> 
>     The worst tree cover is to the north, where thankfully it does the least
>     harm.  The trees in other directions are a bit more distant.
> 
>     There's a Chinese L1/L2/L5 antenna on the other end of the side-arm so I
>     can do base and rover tests without leaving home. :-)  And actually
>     doing that gave me a *very* accurate bearing for the sidearm which means
>     sooner or later I'll get the Zephyr fiducial mark aligned more
>     accurately to north (it could well be 15 or 20 degrees off now).
> 
>     I need to do some experiments now that the leaves are coming out, but I
>     suspect I should be running with an elevation mask quite a bit higher
>     than the default 7.5 degrees.
> 
>     John
>     ----
> 
>     On 5/5/20 5:29 PM, Gerry Creager - NOAA Affiliate wrote:
>     > Yo, I believe is the appropriate salutation; it's been a long COVID...
>     > First, a question for John: What was the antenna and where was it
>     > (indoors, outdoors, sitting on a pvc pole waving in the wind?
>     >
>     > On Tue, May 5, 2020 at 8:23 PM Gary E. Miller <address@hidden
>     <mailto:address@hidden>
>     > <mailto:address@hidden <mailto:address@hidden>>> wrote:
>     >
>     >     Yo John!
>     >
>     >     On Tue, 5 May 2020 16:15:06 -0400
>     >     John Ackermann N8UR <address@hidden <mailto:address@hidden>
>     <mailto:address@hidden <mailto:address@hidden>>> wrote:
>     >
>     >     > Well, I was actually able to get TrimbleRTX to accept my F9P
>     RINEX
>     >     > file created by gpsrinex.
>     >
>     >
>     >     Good.  Someone reported otherwise this week.
>     >
>     >     > It would *not* accept the one created by
>     >     > rtklib's convbin tool -- no useful explanation what was
>     wrong, just
>     >     > unrecognized file format.
>     >
>     >     Those are called "Lassie Errors".  Content free.
>     >
>     >     Does anyone here have Timb;e contacts?
>     >
>     >  
>     > Not anymore, thankfully but let me reach out to someone who might. 
>     >
>     >
>     >     > The bad news is that the results were pretty awful.  Since
>     the results
>     >     > are just a single-page PDF, I've attached it here.  But in
>     summary:
>     >     >
>     >     > Out of 2873 total observations, 100% were usable, but only
>     207 (7%)
>     >     > were used.  That raises a lot more questions than it answers...
>     >
>     >
>     > A couple thoughts
>     >
>     >   * Antenna wasn't stable
>     >   * Multipath due to an inadequate antenna
>     >   * Misrepresented as static which tightens the error criteria
>     >   * Trimble is sometimes obnoxious in its interpretations 
>     >
>     >     No thanks.  We already have enough unanswetred questions
>     here.  :-)
>     >
>     >     > The sigmas (not clear if 1 or 2 stdevs) are 0.185m, 0.131m,
>     and 0.066m
>     >     > for XYZ, and 0.062m, 0.195m, and 0.130m for lat/lon/height.  The
>     >     > report came with this warning:
>     >
>     >  
>     > 1 sigma; Top of the column...
>     >  
>     >
>     >     Which are about 10x worse than NRCan.
>     >
>     >     > Of course, those numbers don't actually appear in the report
>     itself.
>     >
>     >     Typical Trimble.
>     >
>     >
>     > What he said
>     >
>     > gerry
>     >  
>     >
>     >     RGDS
>     >     GARY
>     >   
>      
> ---------------------------------------------------------------------------
>     >     Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend,
>     OR 97703
>     >             address@hidden <mailto:address@hidden>
>     <mailto:address@hidden <mailto:address@hidden>>  Tel:+1 541 382 8588
>     >
>     >                 Veritas liberabit vos. -- Quid est veritas?
>     >         "If you can't measure it, you can't improve it." - Lord Kelvin
>     >
>     >
>     >
>     > --
>     > Gerry Creager
>     > NSSL/CIMMS
>     > 405.325.6371
>     > ++++++++++++++++++++++
>     > /The way to get started is to quit talking and begin doing./
>     > /   Walt Disney/
> 
> 
> 
> 
> -- 
> Gerry Creager
> NSSL/CIMMS
> 405.325.6371
> ++++++++++++++++++++++
> /The way to get started is to quit talking and begin doing./
> /   Walt Disney/