Powerspektrum of BFSK

How can I calculate the amplitudes of the power spectrum of a BFSK-signal?

I calculated u(f) via A*0.5*si(pi*f/(2*fm) fm=Frequenz=15kHz of the rectangular signal |||||____
and placed than my spectrum on f0(180kHz) and f1(420kHz) and calculated U(f)=|U1(f)+U2(f)| (super position) but the values that I received for P(f) are different from the values I calculated. (P=-10dBm)
I would really appreciate every kind of ideas.

close all
clear all
f=-12*15:15:28*15;
u=sqrt(10^-1*(10^-3)*50);
uu=u*0.5*sinc(f/(2*15))
P=10*log10(uu.^2/50)+30
f=0:15length(P)-1)*15;
stem(f,uu)
%stem(f,uu,'BaseValue', -80)
%ylim([-60 0])
hold on
stem(f,fliplr(uu),'*r')
grid on
u1=uu;
u2=fliplr(uu);
P=10*log10((u1+u2).^2/50)+30;
figure(2)
stem(f,P,'BaseValue', -80)
ylim([-80 0])
grid on
disp([f' P'])