I am finding some strange stuff in the way SBAS is being reported by this GPS.
The standard GGA sentence shows no SBAS
The proprietary PUBX00 sentence shows a differential fix
The proprietary PUBX03 sentence shows three SBAS vehicles (EGNOS actually) but none of them show as being Used (with a “U” e.g. the 5,U at the start)
I am wondering whether this behaviour is caused by the WAAS satellites providing position, in addition to the corrections, whereas EGNOS ones provide the corrections only.
If the software was written and tested in the US, it would not be surprising to see this behaviour.
Peter wrote:
If the software was written and tested in the US, it would not be surprising to see this behaviour.
Possible. The geo satellites did not always provide a usable ranging signal, so it may also matter when the software was developed.
I actually received my M9N GPs receiver, and although it gets and acquire satellites much faster it takes time to lock on the waas.
It takes 2 minutes in my cave to get a 3D position with 4 sats, but another 2 minutes to have sbas and 7m precision.
Here is the received sat list (from stratux sw)
It is strange that only E13 is received and help to get waas precision. Actually E13 is very far from this map:
Indeed M9N is far better than M8 generation, 5 to 6m precision is achieved although I am only seeing half of the sky where I am doing my test, it is seeing from 20 to 35 sats, including beidus.
I am getting amazing accuracy (~1m claimed) from this little unit, but there does appear to be a, ahem, strange thing in the way they report SBAS satellites.
Both the GGA (“2”) and the PUBX03 (“D3”) report a differential 3D fix, which implies SBAS is “used” (whatever that means).
Practically everybody will be using the GGA sentence as the default, so I would think a bug there would be noticed. Well, outside of aviation, maybe not, because as someone in the US told me, nobody there cares about SBAS anymore since even without it the system is so accurate now – within a metre or so, with the latest satellites.
And it is then quite likely that nobody has tested it with EGNOS because, ahem, you can’t if you are in the US 
And even if they did test it with EGNOS they would likely not have noticed the lack of the “U” since that appears in the PUBX03 sentence only, and you won’t be using that one unless you want HDOP VDOP HACC VACC all in one packet.
And you have to explicitly enable PUBX03 to come out. And the commands to enable these are obscure as hell, needing checksums. Of course U-BLOX have a piece of bloatware for calculating these…
The only thing I haven’t yet tested is whether this thing does the initial acquisition successfully if powered up at 150kt. Some consumer GPSs can’t, although I haven’t come across one lately. I think the Thuraya phones could not. They had to be powered up on the ground. But this unit has different modes which you can select, to solve this sort of issue. I am using the default one.
Tonight I will test with a King rooftop antenna; I have several kicking around. These are the $2000 ones.
Someone in the U-BLOX forum has now tested the unit in the US and posted this
Magnified portion of above:
which shows the WAAS PRNs with a “U” next to them, so it looks like my conclusion is probably right.
I am now running with an old KA91 antenna and getting 21 satellites indoors!
H accuracy now showing as 2m, V accuracy 2.5m.
With the latest Ublox chip and ANM-MB-00-00 GNSS antenna I can confirm a 1.5m H and 2.5m V accuracy.
And I am somewhat at the edge of the WAAS coverage in Europe.
There does seem to be quite a difference between different antennae… The King one picks up ~5 more sats than some cheap one, although both contain the usual preamp.
Having said that, I have just found a no-name active antenna, probably £5, SMA connector, which picks up the same sats as the King one. So probably half the stuff in “aviation” is snake oil
I would also like to test my GPS with a passive one but – apart from the one I have on the plane, used for the ADL150, they are hard to find used.
