# Hilbert transform of a bandpass signal [closed]

I have a bandpass signal x. I am taking hilbert transform of it. I want to reconstruct amplitude and phase of the signal.Therefore, i am using Hilbert transform.

hil = hilbert(x);

f = ?

amp = abs(hil);

figure, plot(f,abs(hil);

phase = angle(hil);

figure, plot(f,angle(hil)


Here how to define the frequency axis, so i can get the amplitude graph 's length equal to my bandwidth. Moreover, is this the correct way for amplitude and phase reconstruction? My bandwidth is here 40 KHz. Thank you everyone in advance

## closed as unclear what you're asking by A_A, Peter K.♦Oct 31 '17 at 19:07

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

• The result of hilbert(x) is not a function of frequency. Note that its real part is simply the original signal. – Matt L. Jul 9 '15 at 9:53
• Hi Matt L. Thanks for your reply. But what if i want to see the amplitude and phase at different frequencies. I am doing simulation of radar. I have some data and want to add this amplitude and phase information in my ideal simulation. – Urban_Yogi Jul 9 '15 at 10:46
• Fourier transform? – Matt L. Jul 9 '15 at 10:47
• ahh. ya mabe be i shoud apply fourier transform. – Urban_Yogi Jul 9 '15 at 10:51

## 2 Answers

You need to use a bank of bandpass filters before applying the Hilbert transform to get per frequency band amplitude and phase change over time.

Hilbert transform is usually used to analyze the instantaneous frequency.

You can do this by making sure that your signal is monotonic first. The instantaneous frequency as a function of time will be given by the derivative of the phase (angle of the output of the transform).

Make sure you know more about your application before trying to implement certain techniques. They might be time-consuming and end up not being useful (talking through experience here).