W=1000.0

F=sqrt(30.0*W)
T=sprintf('%d Watt',W)
ym=F/28.0+2.0

set y2range [0:ym]
set xrange  [.1:10000]
set yrange  [0:100]
set logscale x
set xlabel  'f/MHz'
set ylabel  'E / V/m' tc rgb 'blue'
set y2label 'r/m'     tc rgb 'green'
set y2tics 2
set ytics nomirror

plot 0 title T

replot [   .1 :    1] 87.0               title ''  lt rgb 'blue' axis x1y1
replot [   1  :   10] 87.0/sqrt(x)       title ''  lt rgb 'blue' axis x1y1
replot [  10  :  400] 28.0               title ''  lt rgb 'blue' axis x1y1
replot [ 400  : 2000] 1.375*sqrt(x)      title ''  lt rgb 'blue' axis x1y1
replot [2000  :10000] 61.0               title ''  lt rgb 'blue' axis x1y1

replot [   .1 :    1] F/87.0             title ''  lt rgb 'green' axis x1y2
replot [   1  :   10] F*sqrt(x)/(87.0)   title ''  lt rgb 'green' axis x1y2
replot [  10  :  400] F/28.0             title ''  lt rgb 'green' axis x1y2
replot [ 400  : 2000] F/(1.375*sqrt(x))  title ''  lt rgb 'green' axis x1y2
replot [2000  :10000] F/61.0             title ''  lt rgb 'green' axis x1y2