set xlabel "Frequency (Hz)"
set ylabel "Zd (ohms)"
set logscale x
plot "Zd.dat" u 1:2 title "Re{Zdfilter}" w l,\
     "Zd.dat" u 1:4 title "Re{ZdFH2}" w l
pause -1
pause -1

plot "Zd.dat" u 1:3 title "Im{Zdfilter}" w l,\
     "Zd.dat" u 1:5 title "Im{ZdFH2}" w l
pause -1