didac, thanks for append.
You are correct.
In most actual vector signal analyzer, different demodulation algorithms are used for generating the reference signals for MSK and QPSK.
So I can't use QPSK mode for measuring EVM of MSK signal even if their constellation points are completely same.
See attached figure first is MSK's Constellation as MSK, and second is MSK's Constellation as QPSK.
Note : EVM value in "Signal Quality Window" is not correct.
In IEEE802.15.4, MSK signal is generated as OQPSK with Halfsine pulse shaping.
See pp.47-48 of the following.
http://standards.ieee.org/getieee802/download/802.15.4-2003.pdfSo appropriate measurement method of EVM is (3)
But I don't have this measurement setup condition in my instruments.
What is different between (1) and (3)
(1) EVM measured as MSK with Tsymb=Tbit, reference_filter=none
and measurement_filter=none.
(3) EVM measured as OQPSK with Tsymb=2*Tbit, reference_filter=halfsine
and measurement_filter=none.
Here Tbit mean bit period and Tsymb mean symbol period.