Following myself up:
>> <
https://www.ardusimple.de/product/simplertk2blite-bt-case-kit/>
[...]
> I'll have to dig a bit deeper. But especially the triple band Septentrio
> Mosaic-X5 receiver seems worth testing even from a semi-professional basis.
During the last couple of weeks I did some tests comparing the ArduSimple
RTK2B receiver (GNSS chipset: ublox F9P) against the ArduSimple RTK3B
receiver (GNSS chipset: Septentrio Mosaic X5).
As is expected, connecting these receivers to an external survey grade
antenna provides significantly better reception than attaching a small
helical one (= average "sub 3 to 5 m" vs. "submeter" for the RTK2B under
typical forest conditions with moderate canopy). All following information
refers to a combination of the GNSS device with this antenna:
https://www.ardusimple.com/product/calibrated-survey-gnss-quadband-antenna-ip67
I tested the devices concurrently attached to the same antenna using a
GNSS antenna splitter and confirmed the results by connecting both
devices (independently) one after another without splitter.
NTRIP Correction data was applied from SAPOS Brandenburg VRS_3_4G_BB.
With optimal signal reception both devices reach status RTK fixed with
maximum deviation of the (known) real position of less than 10 cm in
seconds, when the devices were "warmed up" and had full almanach data.
In situations with only a small area of clear sky (about 90° horizontally
west and 20° to 60° degree vertically) and a complete block of GNSS
reception in all other directions, the RTK3B performed better. It was
able to reach RTK fixed after a couple of minutes and deviated less
than 2 m from known real position during RTK float state. The RTK2B
did not reach RTK fixed and deviated around 5 m on average from real
position. Because both devices used the same antenna signals, the
differences will result mostly from the higher number of GNSS signal
bands of the RTK3B. Chipset sensitivity and differences in firmware
algorithm may also play a role. Multipath signals from "invisible"
satellites have been +/- static in this setup. Therefore, both GNSS
chipsets should have been able to easily identify and filter them out.
Under heavy tree canopy the positioning quality of both receivers was
reversed. The RTK2B reached RTK fixed in few minutes. Starting from
DGNSS, followed by RTK float the position shown deviated only a few
meters from the (known) real position and fluctuated mostly in very
smalls steps. RTK fixed position was "submeter" in every single test.
(10 different forest points with different tree coverage, terrain,
and sometimes nearby bulky tree stems to block part of the reception
hemisphere. Repetitions on different days and weather conditions.)
Gusts of wind resulted in a bit higher position fluctuation during
RTK float state and sometimes loss of RTK fixed.
The RTK3B device failed to reach RTK fixed on several points with
moderate to heavy tree coverage, especially when wind was not fully
calm. RTK float was jumpy on the merest change of wind and showed
rapid positional changes around 5 to 10 meters on average and more
than 15 meters quite often. Wait time for RTK fixed was half an hour.
(If not acquired earlier.)
I contacted Septentrio to get configuration advice for using their
Mosaic X5 chipset in forest conditions. Unfortunately, they declined.
To eliminate unsuited NTRIP correction data for the frequencies not
supported by the ublox F9P I configured the Mosaic X5 to use only the
frequencies used by the F9P. This had no effect on the bad performance
of the RTK3B in forests. I also tried to enable "Smoothing". This did
not improve positioning, either. (I did hope, smoothing would result
in less extreme positioning jumps. But it did not.)
;--------------
To sum up:
The RTK2B receiver using the ublox F9P chipset showed excellent performance
under forest conditions, when connected to a good GNSS multiband antenna.
(As did other F9P based devices I tested during the last years.)
The RTK3B receiver using the Septentrio Mosaic X5 excels in clear sky
environments (construction sites and the like), especially when part of
the sky is completely blocked.
If I should guess, the differences result mostly from multipath handling.
The ublox F9P seems to have superior handling of very dynamic multipath
situations, like wind-moved leaves and branches under moderate to heavy
tree canopy. The Septentrio Mosaic X5 profits from the higher number of
supported GNSS frequency bands during bad (used) satellite geometries,
as long as any multipath is more or less static.
Maybe, this information is useful to other GNSS users.
Bernd