function Hd = filter_notch
Fs=500; Fnotch=50; BW=1; Apass=1;
[b, a] = iirnotch(Fnotch/(Fs/2), BW/(Fs/2), Apass);
Hd     = dfilt.df2(b, a);

filter_block=filter_notch;
out_signal=filter(filter_block,in_signal);