4FSK+ the raised-cosine filter has worked for me on both the 868
and the 878 from the beginning, although I have flashed the 868
to become a 878 since. See:
https://en.wikipedia.org/wiki/Raised-cosine_filter
and
https://forum.sharkrf.com/viewtopic.php?t=1371&start=20
73, Alex DH2ID