how to find the phase difference between two signals of different freqencies

[weak.element]

i have  two signals of "A" and "B" of 1 kHz. "A" signal is at base band that is at 1KHz while "B" is modulated on 10kHz carrier. Thus "B" is shifted in frequency domain and lie on 11KHz and 9kHz. We can not demodulate the "B" signal as it is very noisy and by demodulating we will loose its phase information. The signal at base band i.e. "A" is the reference signal whose phase is taken as reference and we want to find out the difference of phase that occured in signal "B".

can anyone help me out in this regard. can anyone knows if this problem can be solved by some method.

thanks in advance.

[pawel]

Hi

The fact that the signal is noisy should not stop you from mixing it up and down in frequency with the noiselss heterodyne.

Besides, if you really want to compare phases you better have you singal denoised so you can get any useful information out of it.

I would suggest to do the basebanding  both signals and obtain their complex envelope to compare phases. LabVIEW has useful easy to use Hilbert transform and some examples how to use it. 

Depending on what you want to do, you may want to try using complex FFT and see if there is any useful information in the phase, but I am not sure if will get you anywhere. 

good luck

[johnsold]

I do not know of any way to get that information while the signal is modulated.

Is the modulating signal noisy but on a clean carrier or is the carrier and the modulation corrupted with noise? What kind of modulation is this?  From your spectral description, it appears to be amplitude modulation. What is the modulation depth? Where does the noise get into the system?  How stable is the carrier frequency? Is it frequency or phase locked to the modulation frequency?

Do you have any knowledge about the phase of B, such as the range or the rate of change?

Lynn