Power spectrum of a signal

Hello,

I laready posted this here and got some replies but was confused with the implementation

Could someone please explain me how to plot the power spectrum of the signal attached

If the sampling frequency used was 64Hz and data is of 10 seconds duration

a1=load('a1.mat');
plot(a1.a1);
a2_fft = abs(fft(a2));
a2_fft = a2_fft(1:length(a2)/2);
for x=1:1:length(a2_fft)
t(x)=x/64;
end
plot(t, a2_fft);
xlabel('Frequency(Hz)');
ylabel('Magintude(dB)');

Now, I only see the first peak frequency as 0.015 and second as 0.17Hz but the origianl signal should contain 1Hz as first peak freuqnecy.

I don't what is wrong with my implemenataion.Can somoeone please help me out in plotting FFT of 'a1' signal to show the Single-Sided Amplitude Spectrum of a1 over the scale of 10Hz. Thanks

Can someone explain why the other frequency components are also in larger magnitude.