Bit Error Rate of Digital Modulation

Hello all,

I tried to use this grc file to test the bit error rate for the
digital modulation method, but it doesn’t work so well.

When **I set Gray Code(No), Diff Encoding(No), the BER of QAM Mod and
Demod is 0.

In the other case, the BER is not 0.

Do I need any block else to make it work better?