It turns out that some of the newer Android phones support an API which
returns raw GNSS data and that can be logged to a file in RINEX format.
There's a few apps out there that do this although I've not tried it (my
Samsung S6 doesn't have the right hardware).
In any case, it might be interesting, if you have one of these devices,
to let it log for a while, with the phone in a fixed place, and then
post process the data.
I ran across this when looking for software to generate RINEX files from
data from NEO-7 GPS modules (which I'm still looking for)
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